presentation on cardiac muscle

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StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-.

StatPearls [Internet].

Physiology, cardiac muscle.

Rashelle Ripa ; Tom George ; Karlie R. Shumway ; Yasar Sattar .

Affiliations

Last Update: July 30, 2023 .

• Introduction

Cardiac muscle also called the myocardium, is one of three major categories of muscles found within the human body, along with smooth muscle and skeletal muscle. Cardiac muscle, like skeletal muscle, is made up of sarcomeres that allow for contractility. However, unlike skeletal muscle, cardiac muscle is under involuntary control.

The heart is made up of three layers—pericardium, myocardium, and endocardium. The endocardium is not cardiac muscle and is comprised of simple squamous epithelial cells and forms the inner lining of the heart chambers and valves. The pericardium is a fibrous sac surrounding the heart, consisting of the epicardium, pericardial space, parietal pericardium, and fibrous pericardium. [1]

The cardiac muscle is responsible for the contractility of the heart and, therefore, the pumping action. The cardiac muscle must contract with enough force and enough blood to supply the metabolic demands of the entire body. This concept is termed cardiac output and is defined as heart rate x stroke volume, which is determined by the contractile forces of the cardiac muscle and the frequency at which they are activated. With a change in metabolic demand comes a change in the contractility of the heart.

• Cellular Level

Cardiac muscle cells (cardiomyocytes) are striated, branched, contain many mitochondria, and are under involuntary control. Each myocyte contains a single, centrally located nucleus surrounded by a cell membrane known as the sarcolemma. The sarcolemma of cardiac muscle cells contains voltage-gated calcium channels, specialized ion channels that skeletal muscle does not possess.

Cardiac muscle cells contain branched fibers connected via intercalated discs that contain gap junctions and desmosomes. These interconnections allow the cardiomyocytes to contract together synchronously to enable the heart to work as a pump. [2]  

Gap junctions between adjacent cardiomyocytes allow for the propagation of coordinated action potentials from one cell to the next in a phenomenon known as electrical coupling. [3]  Cardiac desmosomes are intercellular structures that anchor cardiac muscle fibers together and are vital in maintaining the structural integrity of the heart. [4]

The functional unit of cardiomyocyte contraction is the sarcomere, which consists of thick (myosin) and thin (actin) filaments, the interactions between which form the basis of the sliding filament theory. [5]  

The sarcolemma is the cardiomyocyte plasma membrane containing transverse tubules (t-tubules). These t-tubules are highly branched invaginations of the cardiomyocyte sarcolemma that function in excitation-contraction coupling (ECC), action potential initiation and regulation, maintaining the resting membrane potential, and signal transduction. T-tubules regulate the cardiac ECC by concentrating voltage-gated L-type calcium channels and positioning them in close proximity to calcium sense and release channels, ryanodine receptors (RyRs), at the junctional membrane of the sarcoplasmic reticulum. [6]

• Development

The development of the heart occurs in various stages. During embryogenesis, the formation of the primitive streak follows the invagination of epiblast cells, indicating the start of gastrulation. Gastrulation divides the embryonic plate, which originally contained two layers between the yolk sac and amniotic cavity, into three germ layers; ecto-, meso-, and endoderm. The mesoderm is situated between the ectoderm and endoderm layers and, during development, spreads laterally and cranially, forming different structures, particularly the heart. [7]

The myocardium begins developing during the second week of gestation in the dorsal mesocardium. After three weeks post-fertilization, the primitive heart begins to develop as a straight tube changing its configuration as time proceeds. This entails folding of the tube, giving rise to bulges that become analogous to the adult heart; truncus arteriosus develops into the aorta and pulmonary artery, bulbus cordis develops into smooth left and right ventricles, primitive ventricle into trabeculated LV/RV, primitive atrium into trabeculated atria and the sinus venosus which develops into the right atrium (sinus venarum) and coronary sinus. [8]

Around the fourth week of development, the heart undergoes a cardiac looping process that establishes the heart's left-sided orientation. This is performed with the help of cilia, a motile structure, and dynein, a protein. [9]  If these factors fail to function correctly, dextrocardia will occur, which places the heart on the right side of the chest. This cardiac anomaly is typically seen in Kartagener Syndrome and primary ciliary dyskinesia (PCD). [10]

Further developmental changes occur as the heart is shaped into its proper configuration. The heart begins as a single chamber, but four separate chambers are created through the growth of various septa. The muscular ventricular septum originates from the bottom of the ventricle, with a membranous septum forming shortly after, joining with the aortic-pulmonary septum as its twists down and fuses. The endocardial cushions also appear at this time and separate the left and right atria and ventricles. Any structural changes or defects in these processes can lead to congenital heart disorders.

The primary function of cardiac muscle is to pump blood into circulation by generating sufficient force. The mechanism behind each coordinated contraction involves the cardiac muscle and electrical impulses. These contractile functions of the heart require ATP,  which can be obtained through various substrates, including fatty acids, carbohydrates, proteins, and ketones. Aerobic production is the core utilization process; however, the heart may use anaerobic processes in a limited capacity. [11]

The cardiac action potential lasts approximately 200 ms and is divided into 5 phases: (4) resting, (0) upstroke, (1) early repolarization, (2) plateau, and (3) final repolarization.

Approximate resting membrane potential (RMP): -90 mV

• Phase 4 - RMP due to activity of the Na/K ATPase pump. The exchange of three sodium ions out for two potassium ions in maintains the negative intracellular potential.
• Phase 0 - depolarization to approximately +52 mv due to sodium influx via fast sodium channels
• Phase 1 - partial repolarization due to the closure of fast sodium channels and efflux of potassium and chloride
• Phase 2 - plateau phase maintained by the influx of calcium. Potassium efflux also occurs.
• Phase 3 - repolarization back to RMP due to potassium efflux and closure of sodium and calcium channels

The generation of a cardiac action potential is involuntary and proceeds via a process known as excitation-contraction coupling (ECC). Action potentials travel along the sarcolemma and into the t-tubules to depolarize the membrane. Voltage-sensitive dihydropyridine (DHP) receptors on t-tubules allow calcium influx into the cell via L-type (long-lasting) calcium channels during the plateau phase (phase 2) of the action potential. This increased intracellular calcium concentration triggers the sarcoplasmic reticulum to release more calcium through the ryanodine receptor, known as calcium-induced calcium-released. [12]  

The released calcium attaches to troponin C, causing tropomyosin to detach from the myosin-binding sites on actin. Actin and myosin then form a cross-bridge, and contraction occurs. Cross bridges last as long as calcium is attached to troponin. [13]  

Lusitropy is the term used to define the relaxation of the myocardium following ECC. Lusitropy is mediated by the SERCA (sarco-endoplasmic reticulum calcium-ATPase) pump, which sequesters calcium into the sarcoplasmic reticulum, allowing calcium to be removed from troponin-C and returning the myocardium to its relaxed state. [14]

Unlike the cardiac muscle cells, the pacemaker cells' action potential is divided into 3 phases instead of 5, as phases 1 and 2 are absent. Pacemaker cells are comprised of sinoatrial (SA) and atrioventricular (AV) nodes, which are known to fire spontaneously, sending electrical activity throughout the heart, and do not require stimulation to initiate their action.

This autorhythmicity transpires because of funny current channels, which allow sodium ions to leak continuously into the cell (Phase 4), slowly raising the membrane potential until a certain threshold is reached, causing depolarization of the cell. This subsequently opens calcium channels causing calcium ions to enter the cell, further raising the membrane potential (Phase 0). After a positive membrane potential is sensed, potassium channels open, causing an outward flow of ions, returning the membrane potential to its resting potential (Phase 3). [15]

• Related Testing

Many clinical tests are utilized to evaluate the function of cardiac muscle. This list discusses high-yield clinical testing and is not meant to be exhaustive.

Echocardiogram:  an ultrasound of the heart routinely used to identify cardiac abnormalities. An echocardiogram can assess valvular abnormalities, masses, pericardial disease, congenital abnormalities, and pulmonary hypertension. An echo is also routinely utilized to assess cardiac muscle function and is useful in diagnosing congestive heart failure and cardiomyopathies. An echocardiogram can be performed as a transthoracic echocardiogram (TTE) or a transesophageal echocardiogram (TEE). 

• TTE: a non-invasive test that utilizes an echocardiography probe placed on the chest wall.
• TEE: a specialized probe with an ultrasound transducer at the tip passed into the patient's esophagus, allowing for a posterior view of the heart.

Echocardiogram reports are detailed and offer essential information regarding the heart's function. Echo reports typically include:

• Rate and rhythm
• Chamber size
• Indications of hypertrophy
• Right ventricular function
• Left ventricular systolic function and ejection fraction
• Left ventricular diastolic function
• Valvular pathology (if any)
• Evidence of mass or thrombus
• Congenital abnormalities
• Pericardial anomalies
• Incidental findings [16]

Electrocardiogram (ECG or EKG): an EKG is a non-invasive test that utilizes electrodes placed on the body's surface to record the heart's electrical rhythms. These electrical rhythms cause depolarization of the heart, which, in turn, leads to the contraction of the myocardium. With this knowledge, one can understand that the EKG indirectly indicates the heart's contraction. [17]

Cardiac biomarkers : blood tests may be performed to identify enzymes and proteins that can indicate heart disease or cardiac damage. 

• Troponin: measures the levels of cardiac proteins troponin T and troponin I. These proteins are found in cardiac muscle and are released upon damage to cardiac muscle, with troponin I being the more sensitive and specific marker of cardiac injury. [18]
• Creatine kinase (CK):  This enzyme is released from cardiac and skeletal muscle following damage. The isozyme CK-MB is more sensitive in diagnosing heart damage after a heart attack, with CK-MB levels rising 4 to 6 hours after a heart attack, peaking at 24 hours, and returning to baseline in 48 to 72 hours. [19]
• Brain natriuretic peptide (BNP):  a hormone secreted by the ventricular myocardium in response to ventricular wall stress (ie, pressure overload or volume expansion). The gold standard in diagnosing heart failure is the measurement of BNP levels, with an elevated level indicating heart failure. [20]
• Pathophysiology

The pathophysiology of cardiac muscle is based on damage to cardiac muscle cells, leading to inappropriate contractility. 

Cardiomyopathy:  A cardiomyopathy is a genetic or acquired disorder of the myocardium associated with cardiac dysfunction. According to the World Health Organization, there exist five main categories of non-ischemic cardiomyopathy: dilated cardiomyopathy (DCM), hypertrophic cardiomyopathy (HCM), restrictive cardiomyopathy (RCM), arrhythmogenic right ventricular cardiomyopathy (ARVC), and unclassified cardiomyopathies.

• Dilated cardiomyopathy (DCM):  This condition is dilation and impaired contraction of one or both ventricles that cannot be explained by coronary artery disease, valvular disease, or hypertension. Patients with DCM present with decreased systolic contraction and symptoms of heart failure. Inherited forms of DCM have shown mutations in at least 40 individual genes, many of which encode structural components of the sarcomere and desmosome. [21]  Nongenetic causes of DCM occur, most often from viral infections leading to inflammation of the myocardium. In addition, certain medications, toxins or allergens, or systemic autoimmune diseases may lead to DCM. [22]
• Hypertrophic cardiomyopathy (HCM):  This condition is an autosomal dominant disease leading to a thickened (hypertrophied) left ventricle and abnormal heart contraction caused by a mutation in the sarcomere protein genes. This hypertrophied left ventricle leads to outflow obstruction, diastolic dysfunction, mitral regurgitation, and myocardial ischemia. In severe cases, sudden cardiac death may occur. [23]
• Restrictive cardiomyopathy (RCM):  This condition results in impaired ventricular filling in the setting of nondilated ventricles. RCM is typically characterized by nondilated nonhypertrophied ventricles, with biatrial enlargement secondary to increased atrial pressures. Diseases in which RCM may be seen include sarcoidosis, amyloidosis, and hemochromatosis. [24]
• Arrhythmogenic right ventricular cardiomyopathy (ARVC):  This is the replacement of the myocardium with fibrofatty tissue leading to an increased predisposition to ventricular tachycardia and sudden cardiac death, especially in young adults and athletes. The release of exercise-induced catecholamines provokes ventricular arrhythmias in predisposed individuals. ARVM typically affects the right ventricle. [25]
• Unclassified cardiomyopathies:  
• Stress-induced cardiomyopathy (Takotsubo cardiomyopathy):  A condition known as "broken heart syndrome" presents as a reversible transient ballooning of the apex of the left ventricle leading to wall motion abnormalities brought on by severe emotional or physical stress. [26]
• Cirrhotic cardiomyopathy:  This is a condition of diastolic and systolic dysfunction, impaired cardiac response to stress, and ECG abnormalities (QT prolongation) in patients with cirrhosis. Cardiac function is typically altered only under stressful conditions. [27]  
• Ischemic cardiomyopathy (ICM) is  a form of dilated cardiomyopathy related to coronary artery disease (CAD). ICM is the decreased ability of the heart to properly pump blood throughout the body due to myocardial damage from cardiac ischemia. The lack of blood supply to the cardiomyocytes leads to cell death, cardiac fibrosis, and left ventricular enlargement and dilation. [28]  Globally, ischemic heart disease (IHD) is the leading cause of death, with approximately 7.2 million deaths yearly. [29]

Heart Failure:  impairment of ventricular filling and systolic ejection of blood due to structural and functional defects of the myocardium. The left ventricular ejection fraction (LVEF) is crucial in the specific assessment of heart failure. A heart failure patient with an ejection fraction (EF) greater than or equal to 50% is diagnosed as having heart failure with preserved ejection fraction (HFpEF).

An ejection fraction less than or equal to 40% is termed heart failure with reduced ejection fraction (HFrEF), and an ejection fraction of 41 to 49% is diagnosed as heart failure with mid-range ejection fraction (HFmrEF). Distinguishing between these three types of heart failure is of clinical importance, as each has specific treatments and medications. [30]

Myocarditis:  an inflammatory disease of the myocardium most commonly caused by acute rheumatic fever or viral infections (Coxsackie virus, parvovirus B19). The long-term outcome of untreated myocarditis is dilated cardiomyopathy with heart failure. [31]

• Clinical Significance

Heart disease is the leading cause of death in both men and women in the United States and worldwide. [29]  The clinical care of patients with heart disease is based on assessing myocardial function and using interventions to improve cardiac muscle performance and prevent myocardial maladaptations. Based on the pathophysiology previously mentioned, treatment modalities will vary from patient to patient. 

As heart failure is seen worldwide, clinicians must understand the physiology and management of this disease. Symptomatic heart failure is typically managed with vasodilators, diuretics, positive inotropes, or digoxin. The ideal therapy would include a diuretic and a vasodilator, such as an angiotensin-converting enzyme (ACE) inhibitor or hydralazine plus isosorbide dinitrate. Depending on the patient's presentation, this therapy would occur with or without digoxin. [32]

Clinicians must talk with each patient about the importance of cardiovascular health. Simply put, the stronger the heart muscles are, the more efficient they become. Regular aerobic exercise is of great importance in the overall health of cardiac muscles and helps strengthen muscle tissue, lowering the risk of stroke and heart attack. Aerobic exercise includes running or walking, swimming, cycling, dancing, and climbing stairs. 

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Cardiac Myocyte Action Potential Contributed By Action_potential2.svg: *Action_potential.png: User:Quasarderivative work: Mnokel (talk)derivative work: Silvia3 (Action_potential2.svg) [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/) or GFDL (more...)

Disclosure: Rashelle Ripa declares no relevant financial relationships with ineligible companies.

Disclosure: Tom George declares no relevant financial relationships with ineligible companies.

Disclosure: Karlie Shumway declares no relevant financial relationships with ineligible companies.

Disclosure: Yasar Sattar declares no relevant financial relationships with ineligible companies.

This book is distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ), which permits others to distribute the work, provided that the article is not altered or used commercially. You are not required to obtain permission to distribute this article, provided that you credit the author and journal.

• Cite this Page Ripa R, George T, Shumway KR, et al. Physiology, Cardiac Muscle. [Updated 2023 Jul 30]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-.

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Muscle Tissue

Cardiac Muscle Tissue

OpenStaxCollege

Learning Objectives

By the end of this section, you will be able to:

• Describe intercalated discs and gap junctions
• Describe a desmosome

Cardiac muscle tissue is only found in the heart. Highly coordinated contractions of cardiac muscle pump blood into the vessels of the circulatory system. Similar to skeletal muscle, cardiac muscle is striated and organized into sarcomeres, possessing the same banding organization as skeletal muscle ( [link] ). However, cardiac muscle fibers are shorter than skeletal muscle fibers and usually contain only one nucleus, which is located in the central region of the cell. Cardiac muscle fibers also possess many mitochondria and myoglobin, as ATP is produced primarily through aerobic metabolism. Cardiac muscle fibers cells also are extensively branched and are connected to one another at their ends by intercalated discs. An intercalated disc allows the cardiac muscle cells to contract in a wave-like pattern so that the heart can work as a pump.

View the University of Michigan WebScope to explore the tissue sample in greater detail.

Intercalated discs are part of the sarcolemma and contain two structures important in cardiac muscle contraction: gap junctions and desmosomes. A gap junction forms channels between adjacent cardiac muscle fibers that allow the depolarizing current produced by cations to flow from one cardiac muscle cell to the next. This joining is called electric coupling, and in cardiac muscle it allows the quick transmission of action potentials and the coordinated contraction of the entire heart. This network of electrically connected cardiac muscle cells creates a functional unit of contraction called a syncytium. The remainder of the intercalated disc is composed of desmosomes. A desmosome is a cell structure that anchors the ends of cardiac muscle fibers together so the cells do not pull apart during the stress of individual fibers contracting ( [link] ).

Contractions of the heart (heartbeats) are controlled by specialized cardiac muscle cells called pacemaker cells that directly control heart rate. Although cardiac muscle cannot be consciously controlled, the pacemaker cells respond to signals from the autonomic nervous system (ANS) to speed up or slow down the heart rate. The pacemaker cells can also respond to various hormones that modulate heart rate to control blood pressure.

The wave of contraction that allows the heart to work as a unit, called a functional syncytium, begins with the pacemaker cells. This group of cells is self-excitable and able to depolarize to threshold and fire action potentials on their own, a feature called autorhythmicity ; they do this at set intervals which determine heart rate. Because they are connected with gap junctions to surrounding muscle fibers and the specialized fibers of the heart’s conduction system, the pacemaker cells are able to transfer the depolarization to the other cardiac muscle fibers in a manner that allows the heart to contract in a coordinated manner.

Another feature of cardiac muscle is its relatively long action potentials in its fibers, having a sustained depolarization “plateau.” The plateau is produced by Ca ++ entry though voltage-gated calcium channels in the sarcolemma of cardiac muscle fibers. This sustained depolarization (and Ca ++ entry) provides for a longer contraction than is produced by an action potential in skeletal muscle. Unlike skeletal muscle, a large percentage of the Ca ++ that initiates contraction in cardiac muscles comes from outside the cell rather than from the SR.

Chapter Review

Cardiac muscle is striated muscle that is present only in the heart. Cardiac muscle fibers have a single nucleus, are branched, and joined to one another by intercalated discs that contain gap junctions for depolarization between cells and desmosomes to hold the fibers together when the heart contracts. Contraction in each cardiac muscle fiber is triggered by Ca ++ ions in a similar manner as skeletal muscle, but here the Ca ++ ions come from SR and through voltage-gated calcium channels in the sarcolemma. Pacemaker cells stimulate the spontaneous contraction of cardiac muscle as a functional unit, called a syncytium.

Review Questions

Cardiac muscles differ from skeletal muscles in that they ________.

• are striated
• utilize aerobic metabolism
• contain myofibrils
• contain intercalated discs

If cardiac muscle cells were prevented from undergoing aerobic metabolism, they ultimately would ________.

• undergo glycolysis
• synthesize ATP
• stop contracting
• start contracting

Critical Thinking Questions

What would be the drawback of cardiac contractions being the same duration as skeletal muscle contractions?

An action potential could reach a cardiac muscle cell before it has entered the relaxation phase, resulting in the sustained contractions of tetanus. If this happened, the heart would not beat regularly.

How are cardiac muscle cells similar to and different from skeletal muscle cells?

Cardiac and skeletal muscle cells both contain ordered myofibrils and are striated. Cardiac muscle cells are branched and contain intercalated discs, which skeletal muscles do not have.

Cardiac Muscle Tissue Copyright © 2013 by OpenStaxCollege is licensed under a Creative Commons Attribution 4.0 International License , except where otherwise noted.

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Everything to Know About Cardiac Muscle Tissue

• Maintenance

Frequently Asked Questions

Cardiac muscle is found in the walls of the heart . It helps the heart perform its function of pumping blood throughout the body. Cardiac muscle tissue is located in the middle of three layers of the heart, called the myocardium . Problems in the myocardium can cause heart failure and arrhythmias or contribute to sudden cardiac death.

This article discusses the role of muscle tissue in the heart and ways to keep your heart's muscle tissue healthy.

manusapon kasosod / Getty Images

Heart Tissue Layers

The heart has three layers of tissue:

• Epicardium : The outermost layer of tissue
• Myocardium : The middle layer of tissue, made of muscle
• Endocardium : The tissue lining the inside of the heart and valves

The pericardium is the sac in which the heart sits.

Cardiac Muscle Tissue Function

The heart can be thought of as a pump. It is responsible for pumping blood throughout the body to provide oxygen and nutrients.

The heart's muscle is stimulated by the electrical system of the heart. Specialized pacemaker cells create an electrical signal that causes contraction, or shortening, of the muscle fibers. This muscle contraction is what causes the heart to squeeze and pump out blood.

At a cellular level, heart muscle tissue is made up of bundles or fibers of interconnected muscle cells, called cardiomyocytes . These cells are packed with units called sarcomeres that are made of proteins called actin and myosin . When stimulated, these two proteins slide against each other to result in contraction of the heart.

Types of Muscle Tissue

The body has three types of muscle tissue. All of them share the ability to contract and have important functions. The tissue types are:

• Skeletal muscle tissue provides the function of body movement. It is under voluntary control.
• Smooth muscle is found in the digestive tract and in the arteries. It is not under voluntary control.
• Cardiac muscle is only found in the heart. It is responsible for pumping blood out of the heart.

Conditions That Affect Cardiac Muscle Tissue

Heart muscle problems have many causes.

Cardiomyopathy , or heart muscle weakness, is a general term for problems with the heart muscle. It can be caused by:

• Genetic mutations
• Lack of blood flow
• Autoimmune or inflammatory conditions
• Vitamin deficiency
• Damage from toxins

Sometimes the cause is not determined, which is known as idiopathic cardiomyopathy.

Other conditions can affect cardiac muscle tissue. These can cause varying problems, from thickening of the heart muscle to heart failure, arrhythmias, and sudden cardiac death.

Most common causes:

• Ischemic heart disease from blocked coronary arteries
• Heart attack
• High blood pressure
• Valvular heart disease, such as aortic stenosis

High Blood Pressure and the Heart

Blood pressure is the force that the heart must pump against to eject blood. When blood pressure is high, the heart must work harder. Just like any other muscle, the heart muscle thickens in response to this increased work. This thickened (hypertrophied) heart muscle can lead to problems with heart filling and heart failure. High blood pressure is one of the more common causes of heart failure.

Other possible issues that could affect heart muscle include:

• Myocarditis (inflammation of the heart muscle)
• Toxins like alcohol, cocaine, amphetamines
• Medications, including certain cancer therapies
• Infiltrative disorders (accumulation of abnormal proteins or particles in the heart muscle), including cardiac amyloidosis , cardiac sarcoidosis , or hemochromatosis (iron overload)
• Genetic conditions, including left ventricular noncompaction , hypertrophic cardiomyopathy , arrhythmogenic right ventricular cardiomyopathy , glycogen storage disease, or muscular dystrophy
• Heart rhythm problems
• Congenital heart disease (heart defects present from birth)
• Endocrine disorders such as thyroid problems
• Extreme stress
• Vitamin B1 ( thiamine ) deficiency

When to See a Healthcare Provider

If you are concerned about cardiomyopathy, you should see a healthcare provider for evaluation. Seek medical attention for symptoms like shortness of breath, exercise intolerance, leg swelling, and fatigue, which are signs of heart failure. Even if you don't have any symptoms, if heart failure runs in your family, you should discuss this with your healthcare provider to determine whether screening or genetic testing is needed.

How to Keep Cardiac Muscle Tissue Healthy

While not all types of cardiomyopathy can be prevented, there are things you can do to help keep your heart muscle as healthy as possible.

Living a healthy lifestyle can help keep the heart's muscle tissue healthy by preventing coronary artery disease, high blood pressure, and diabetes. This includes eating a healthy diet , getting regular physical exercise, maintaining a healthy weight, and avoiding tobacco use.

In addition to living a healthy lifestyle, the following can be done to prevent cardiomyopathy:

• Controlling blood pressure
• Controlling cholesterol levels
• Treating coronary artery disease
• Avoiding toxins such as drugs and excess alcohol
• Controlling blood sugar (recent guidelines recommend sodium-glucose cotransporter-2 (SGLT2) inhibitors for those with diabetes and elevated risk of heart disease)

For those diagnosed with cardiomyopathy, several medications have been proven to prevent or reverse the abnormal remodeling that occurs due to heart disease. These include:

• Certain beta-blockers
• ACE ( angiotensin-converting enzyme ) inhibitors
• Angiotensin receptor blocker/ neprilysin inhibitor
• Aldosterone antagonists
• SGLT2 inhibitors

Cardiologists (doctors who specialize in heart disease) can prescribe and adjust these medications and provide an individualized treatment plan.

Cardiac muscle tissue is found in the middle of three layers of heart tissue. It enables the heart to pump blood and provide nutrients and oxygen throughout the body. Several things can cause problems with the heart muscle, including ischemic heart disease, heart attack, high blood pressure, and valvular heart disease.

The best ways to prevent cardiomyopathy are to live a healthy lifestyle, control blood pressure, cholesterol, and diabetes, and avoid substances that are known to be toxic to the heart. Those with cardiomyopathy can benefit from effective medications.

A Word From Verywell

The heart is arguably the most important muscle in the body. Keeping cardiac tissue healthy helps the heart function properly and decreases the risk of complications. Knowing your risk and controlling modifiable risk factors such as blood pressure, cholesterol, blood sugar, and smoking are important ways to lower your risk and protect your heart muscle.

Cardiac muscle tissue is a type of muscle tissue found only in the heart. It appears striated (striped) under a microscope due to the presence of sarcomere units that are responsible for its ability to contract. Heart muscle contracts in response to signals from specialized pacemaker cells located in the heart.

Cardiac muscle tissue is located in the middle of three layers of the heart, called the myocardium. It is the thickest of the three layers. On its outer surface, the myocardium is surrounded by a thin, protective layer called the pericardium. On its inner surface, it is lined by the endocardium.

The heart is made up of three layers of tissue. The epicardium is the outer, fibrous layer that lines and protects the heart. The myocardium is the thick muscular layer of tissue. The endocardium lines the inner surface of the heart. The heart also has four valves (aortic, mitral, tricuspid, and pulmonic).

National Heart, Lung, and Blood Institute. How the heart works .

American Heart Association. What is heart failure .

Vikhorev PG, Vikhoreva NN. Cardiomyopathies and related changes in contractility of human heart muscle .  International Journal of Molecular Sciences . 2018; 19(8):2234. doi:10.3390/ijms19082234

MedlinePlus. Types of muscle tissue .

Brieler J, Breeden MA, Tucker J.  Cardiomyopathy: an overview .  AFP . 2017;96(10):640-646.

Heidenreich PA, Bozkurt B, Aguilar D, et al. 2022 AHA/ACC/HFSA guideline for the management of heart failure: a report of the American College of Cardiology/American Heart Association Joint Committee on Clinical Practice Guidelines . Circulation . 2022;145:e895–e1032. doi:10.1161/CIR.0000000000001063

American Heart Association. How to help prevent heart disease at any age .

By Angela Ryan Lee, MD Dr. Lee is an Ohio-based board-certified physician specializing in cardiovascular diseases and internal medicine.

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17.3A: Mechanism and Contraction Events of Cardiac Muscle Fibers

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Cardiac muscle fibers undergo coordinated contraction via calcium-induced calcium release conducted through the intercalated discs.

Learning Objectives

• Describe the mechanism and contraction events of cardiac muscle fibers
• Cardiac muscle fibers contract via excitation-contraction coupling, using a mechanism unique to cardiac muscle called calcium -induced calcium release.
• Excitation-contraction coupling describes the process of converting an electrical stimulus ( action potential ) into a mechanical response (muscle contraction).
• Calcium-induced calcium release involves the conduction of calcium ions into the cardiomyocyte, triggering further release of ions into the cytoplasm.
• Calcium prolongs the duration of muscle cell depolarization before repolarization occurs.Contraction in cardiac muscle occurs due to the the binding of the myosin head to adenosine triphosphate ( ATP ), which then pulls the actin filaments to the center of the sarcomere, the mechanical force of contraction.
• excitation contraction coupling (ECC) : The physiological process of converting an electrical stimulus to a mechanical response.
• calcium-induced calcium release (CICR) : A process whereby calcium can trigger release of further calcium from the muscle sarcoplasmic reticulum.

Cardiomyocytes are capable of coordinated contraction, controlled through the gap junctions of intercalated discs. The gap junctions spread action potentials to support the synchronized contraction of the myocardium. In cardiac, skeletal, and some smooth muscle tissue, contraction occurs through a phenomenon known as excitation contraction coupling (ECC). ECC describes the process of converting an electrical stimulus from the neurons into a mechanical response that facilitates muscle movement. Action potentials are the electrical stimulus that elicits the mechanical response in ECC.

Calcium-Induced Calcium Release

In cardiac muscle, ECC is dependent on a phenomenon called calcium-induced calcium release (CICR), which involves the influx of calcium ions into the cell, triggering further release of ions into the cytoplasm. The mechanism for CIRC is receptors within the cardiomyocyte that bind to calcium ions when calcium ion channels open during depolarization, releasing more calcium ions into the cell.

Similarly to skeletal muscle, the influx of sodium ions causes an initial depolarization; however, in cardiac muscle, the influx of calcium ions sustains the depolarization so that it lasts longer. CICR creates a “plateau phase” in which the cell’s charge stays slightly positive (depolarized) briefly before it becomes more negative as it repolarizes due to potassium ion influx. Skeletal muscle, by contrast, repolarizes immediately.

Pathway of Cardiac Muscle Contraction

The actual mechanical contraction response in cardiac muscle occurs via the sliding filament model of contraction. In the sliding filament model, myosin filaments slide along actin filaments to shorten or lengthen the muscle fiber for contraction and relaxation. The pathway of contraction can be described in five steps:

• An action potential, induced by the pacemaker cells in the sinoatrial (SA) and atrioventricular (AV) nodes, is conducted to contractile cardiomyocytes through gap junctions.
• As the action potential travels between sarcomeres, it activates the calcium channels in the T-tubules, resulting in an influx of calcium ions into the cardiomyocyte.
• Calcium in the cytoplasm then binds to cardiac troponin-C, which moves the troponin complex away from the actin binding site. This removal of the troponin complex frees the actin to be bound by myosin and initiates contraction.
• The myosin head binds to ATP and pulls the actin filaments toward the center of the sarcomere, contracting the muscle.
• Intracellular calcium is then removed by the sarcoplasmic reticulum, dropping intracellular calcium concentration, returning the troponin complex to its inhibiting position on the active site of actin, and effectively ending contraction as the actin filaments return to their initial position, relaxing the muscle.

Sliding Filament Model of Contraction : Muscle fibers in relaxed (above) and contracted (below) positions

Animation of Myosin and Actin : This animation shows myosin filaments (red) sliding along the actin filaments (pink) to contract a muscle cell.

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• Patient Care & Health Information
• Diseases & Conditions
• Cardiomyopathy

Cardiomyopathy (kahr-dee-o-my-OP-uh-thee) is a disease of the heart muscle. It causes the heart to have a harder time pumping blood to the rest of the body, which can lead to symptoms of heart failure. Cardiomyopathy also can lead to some other serious heart conditions.

There are various types of cardiomyopathy. The main types include dilated, hypertrophic and restrictive cardiomyopathy. Treatment includes medicines and sometimes surgically implanted devices and heart surgery. Some people with severe cardiomyopathy need a heart transplant. Treatment depends on the type of cardiomyopathy and how serious it is.

Dilated cardiomyopathy

• Hypertrophic cardiomyopathy

Some people with cardiomyopathy don't ever get symptoms. For others, symptoms appear as the condition becomes worse. Cardiomyopathy symptoms can include:

• Shortness of breath or trouble breathing with activity or even at rest.
• Chest pain, especially after physical activity or heavy meals.
• Heartbeats that feel rapid, pounding or fluttering.
• Swelling of the legs, ankles, feet, stomach area and neck veins.
• Bloating of the stomach area due to fluid buildup.
• Cough while lying down.
• Trouble lying flat to sleep.
• Fatigue, even after getting rest.

Symptoms tend to get worse unless they are treated. In some people, the condition becomes worse quickly. In others, it might not become worse for a long time.

When to see a doctor

See your healthcare professional if you have any symptoms of cardiomyopathy. Call 911 or your local emergency number if you faint, have trouble breathing or have chest pain that lasts for more than a few minutes.

Some types of cardiomyopathy can be passed down through families. If you have the condition, your healthcare professional might recommend that your family members be checked.

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Dilated cardiomyopathy causes the chambers of the heart to grow larger. Untreated, dilated cardiomyopathy can lead to heart failure.

Illustrations of a typical heart, as shown on the left, and a heart with hypertrophic cardiomyopathy. Note that the heart walls are much thicker in the heart with hypertrophic cardiomyopathy.

Often, the cause of the cardiomyopathy isn't known. But some people get it due to another condition. This is known as acquired cardiomyopathy. Other people are born with cardiomyopathy because of a gene passed on from a parent. This is called inherited cardiomyopathy.

Certain health conditions or behaviors that can lead to acquired cardiomyopathy include:

• Long-term high blood pressure.
• Heart tissue damage from a heart attack.
• Long-term rapid heart rate.
• Heart valve problems.
• COVID-19 infection.
• Certain infections, especially those that cause inflammation of the heart.
• Metabolic disorders, such as obesity, thyroid disease or diabetes.
• Lack of essential vitamins or minerals in the diet, such as thiamin (vitamin B-1).
• Pregnancy complications.
• Iron buildup in the heart muscle, called hemochromatosis.
• The growth of tiny lumps of inflammatory cells called granulomas in any part of the body. When this happens in the heart or lungs, it's called sarcoidosis.
• The buildup of irregular proteins in the organs, called amyloidosis.
• Connective tissue disorders.
• Drinking too much alcohol over many years.
• Use of cocaine, amphetamines or anabolic steroids.
• Use of some chemotherapy medicines and radiation to treat cancer.

Types of cardiomyopathy include:

Dilated cardiomyopathy. In this type of cardiomyopathy, the heart's chambers thin and stretch, growing larger. The condition tends to start in the heart's main pumping chamber, called the left ventricle. As a result, the heart has trouble pumping blood to the rest of the body.

This type can affect people of all ages. But it happens most often in people younger than 50 and is more likely to affect men. Conditions that can lead to a dilated heart include coronary artery disease and heart attack. But for some people, gene changes play a role in the disease.

Hypertrophic cardiomyopathy. In this type, the heart muscle becomes thickened. This makes it harder for the heart to work. The condition mostly affects the muscle of the heart's main pumping chamber.

Hypertrophic cardiomyopathy can start at any age. But it tends to be worse if it happens during childhood. Most people with this type of cardiomyopathy have a family history of the disease. Some gene changes have been linked to hypertrophic cardiomyopathy. The condition doesn't happen due to a heart problem.

Restrictive cardiomyopathy. In this type, the heart muscle becomes stiff and less flexible. As a result, it can't expand and fill with blood between heartbeats. This least common type of cardiomyopathy can happen at any age. But it most often affects older people.

Restrictive cardiomyopathy can occur for no known reason, also called an idiopathic cause. Or it can by caused by a disease elsewhere in the body that affects the heart, such as amyloidosis.

• Arrhythmogenic right ventricular cardiomyopathy (ARVC). This is a rare type of cardiomyopathy that tends to happen between the ages of 10 and 50. It mainly affects the muscle in the lower right heart chamber, called the right ventricle. The muscle is replaced by fat that can become scarred. This can lead to heart rhythm problems. Sometimes, the condition involves the left ventricle as well. ARVC often is caused by gene changes.
• Unclassified cardiomyopathy. Other types of cardiomyopathy fall into this group.

Risk factors

Many things can raise the risk of cardiomyopathy, including:

• Family history of cardiomyopathy, heart failure and sudden cardiac arrest.
• Conditions that affect the heart. These include a past heart attack, coronary artery disease or an infection in the heart.
• Obesity, which makes the heart work harder.
• Long-term alcohol misuse.
• Illicit drug use, such as cocaine, amphetamines and anabolic steroids.
• Treatment with certain chemotherapy medicines and radiation for cancer.

Many diseases also raise the risk of cardiomyopathy, including:

• Thyroid disease.
• Storage of excess iron in the body, called hemochromatosis.
• Buildup of a certain protein in organs, called amyloidosis.
• The growth of small patches of inflamed tissue in organs, called sarcoidosis.

Complications

Enlarged heart, in heart failure

If the heart weakens, as it can with heart failure, it begins to enlarge. This forces the heart to work harder to pump blood to the rest of the body.

Cardiomyopathy can lead to serious medical conditions, including:

• Heart failure. The heart can't pump enough blood to meet the body's needs. Without treatment, heart failure can be life-threatening.
• Blood clots. Because the heart can't pump well, blood clots might form in the heart. If clots enter the bloodstream, they can block the blood flow to other organs, including the heart and brain.
• Heart valve problems. Because cardiomyopathy can cause the heart to become larger, the heart valves might not close properly. This can cause blood to flow backward in the valve.
• Cardiac arrest and sudden death. Cardiomyopathy can trigger irregular heart rhythms that cause fainting. Sometimes, irregular heartbeats can cause sudden death if the heart stops beating effectively.

Inherited types of cardiomyopathy can't be prevented. Let your healthcare professional know if you have a family history of the condition.

You can help lower the risk of acquired types of cardiomyopathy, which are caused by other conditions. Take steps to lead a heart-healthy lifestyle, including:

• Stay away from alcohol or illegal drugs such as cocaine.
• Control any other conditions you have, such as high blood pressure, high cholesterol or diabetes.
• Eat a healthy diet.
• Get regular exercise.
• Get enough sleep.
• Lower your stress.

These healthy habits also can help people with inherited cardiomyopathy control their symptoms.

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Celebrating 10-years with a new heart - just like her big sister

Linsey Rippy was 16 weeks pregnant with her second child when she learned her daughter, Madi, had dilated cardiomyopathy. She was just two-and-a-half years old. “Our hospital in the Twin Cities ran every genetic test on Madi, but nothing came up,” Linsey said. “She’d had a virus a few weeks before, so they figured that’s what caused her to develop the condition.” Doctors also figured that meant there was little risk of the baby Linsey…

• Cooper LT. Definition and classification of the cardiomyopathies. https://www.uptodate.com/contents/search. Accessed Oct. 27, 2023.
• Cardiomyopathy. American Heart Association. https://www.heart.org/en/health-topics/cardiomyopathy/. Accessed Oct. 27, 2023.
• Cardiomyopathy. National Heart, Lung, and Blood Institute. https://www.nhlbi.nih.gov/health/cardiomyopathy. Accessed Oct. 27, 2023.
• Arrhythmias: Treatment. National Heart, Lung, and Blood Institute. https://www.nhlbi.nih.gov/health/arrhythmias/treatment. Accessed Oct. 27, 2023.
• Loscalzo J, et al., eds. Cardiomyopathy and myocarditis. In: Harrison's Principles of Internal Medicine. 21st ed. McGraw Hill; 2022. https://accessmedicine.mhmedical.com. Accessed Oct. 27, 2023.
• Caforio ALP. COVID-19: Cardiac manifestations in adults. https://www.uptodate.com/contents/search. Accessed Oct. 27, 2023.
• Giustino G, et al. Takotsubo cardiomyopathy in COVID-19. Journal of the American College of Cardiology. 2020; doi:10.1016/j.jacc.2020.05.068.
• Mankad R (expert opinion). Mayo Clinic; Nov. 6, 2023.
• Cardiomyopathy. Centers for Disease Control and Prevention. https://www.cdc.gov/heartdisease/cardiomyopathy.htm. Accessed Oct. 27, 2023.
• Jordan E, et al. Evidence-based assessment of genes in dilated cardiomyopathy. Circulation. 2021; doi:10.1161/CIRCULATIONAHA.120.053033.
• Ommen SR, et al. 2020 AHA/ACC guideline for the diagnosis and treatment of patients with hypertrophic cardiomyopathy: A report of the American College of Cardiology/American Heart Association Joint Committee on Clinical Practice Guidelines. Journal of the American College of Cardiology. 2020; doi: 10.1016/j.jacc.2020.08.045.
• Colucci WS, et al. Natriuretic peptide measurement in heart failure. https://www.uptodate.com/contents/search. Accessed Oct. 30, 2023.
• McKenna WJ. Arrhythmogenic right ventricular cardiomyopathy: Anatomy, histology, and clinical manifestations. https://www.uptodate.com/contents/search. Accessed Nov. 7, 2023.

Associated Procedures

• Cardiac catheterization
• Chest X-rays
• Echocardiogram
• Electrocardiogram (ECG or EKG)
• Extracorporeal membrane oxygenation (ECMO)
• Heart transplant
• Implantable cardioverter-defibrillators (ICDs)
• Needle biopsy
• Ventricular assist device
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13.15: Smooth, Skeletal, and Cardiac Muscles

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What exactly are muscles?

Does the word "muscle" make you think of the biceps of a weightlifter, like the man in pictured above? Muscles such as biceps that move the body are easy to feel and see, but they aren’t the only muscles in the human body. Many muscles are deep within the body. They form the walls of internal organs such as the heart and stomach. You can flex your biceps like a body builder, but you cannot control the muscles inside you. It’s a good thing that they work on their own without any conscious effort on your part, because movement of these muscles is essential for survival.

What Are Muscles?

The muscular system consists of all the muscles of the body. Muscles are organs composed mainly of muscle cells, which are also called muscle fibers . Each muscle fiber is a very long, thin cell that can do something no other cell can do. It can contract, or shorten. Muscle contractions are responsible for virtually all the movements of the body, both inside and out. There are three types of muscle tissues in the human body: cardiac, smooth, and skeletal muscle tissues. They are shown in Figure below and described below.

Types of Muscle Tissue. Both skeletal and cardiac muscles appear striated, or striped, because their cells are arranged in bundles. Smooth muscles are not striated because their cells are arranged in sheets instead of bundles.

Smooth Muscle

Muscle tissue in the walls of internal organs such as the stomach and intestines is smooth muscle . When smooth muscle contracts, it helps the organs carry out their functions. For example, when smooth muscle in the stomach contracts, it squeezes the food inside the stomach, which helps break the food into smaller pieces. Contractions of smooth muscle are involuntary. This means they are not under conscious control.

Skeletal Muscle

Muscle tissue that is attached to bone is skeletal muscle . Whether you are blinking your eyes or running a marathon, you are using skeletal muscle. Contractions of skeletal muscle are voluntary, or under conscious control. When skeletal muscle contracts, bones move. Skeletal muscle is the most common type of muscle in the human body.

Cardiac Muscle

Cardiac muscle is found only in the walls of the heart. When cardiac muscle contracts, the heart beats and pumps blood. Cardiac muscle contains a great many mitochondria, which produce ATP for energy. This helps the heart resist fatigue. Contractions of cardiac muscle are involuntary, like those of smooth muscle. Cardiac muscle, like skeletal muscle, is arranged in bundles, so it appears striated , or striped.

• There are three types of human muscle tissue: smooth muscle (in internal organs), skeletal muscle, and cardiac muscle (only in the heart).
• Compare and contrast the three types of muscle tissue.
• What can muscle cells do that other cells cannot?
• Why are skeletal and cardiac muscles striated?
• Where is smooth muscle tissue found?
• What is the function of skeletal muscle? Give an example.

CARDIAC MUSCLE

Jul 21, 2014

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بسم الله الرحمن الرحيم. CARDIAC MUSCLE. Prepared by Dr.Mohammed Sharique Ahmed Quadri Assistant Professor Department Basic Medical Sciences Division of Physiology Faculty of Medicine Almaarefa Colleges. CARDIAC MUSCLE. ATRIAL MUSCLE VENTRICULAR MUSCLE

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بسم الله الرحمن الرحيم CARDIAC MUSCLE Prepared by Dr.MohammedSharique Ahmed Quadri Assistant Professor Department Basic Medical Sciences Division of Physiology Faculty of Medicine Almaarefa Colleges

CARDIAC MUSCLE • ATRIAL MUSCLE • VENTRICULAR MUSCLE • SPECIALISES EXCITATORY &CONDUCTIVE MUSCLE FIBERS

Cardiac Muscle Fibers • Interconnected by intercalated discs and form functional syncytia • Within intercalated discs – two kinds of membrane junctions • Desmosomes • Gap junctions

Electrical Activity of Heart • Heart beats rhythmically as result of action potentials it generates by itself (Autorhythmicity) • Two specialized types of cardiac muscle cells • Contractile cells • 99% of cardiac muscle cells • Do mechanical work of pumping • Normally do not initiate own action potentials • Autorhythmic cells • Do not contract • Specialized for initiating and conducting action potentials responsible for contraction of working cells

Electrical Activity of Heart • Ca2+ entry through L-type channels in T tubules triggers larger release of Ca2+ from sarcoplasmic reticulum • Ca2+ induced Ca2+ release leads to cross-bridge cycling and contraction

Excitation-Contraction Coupling in Cardiac Contractile Cells

Ventricular action potential

Electrical Activity of Heart • Because long refractory period occurs in conjunction with prolonged plateau phase, summation and tetanus of cardiac muscle is impossible • Ensures alternate periods of contraction and relaxation which are essential for pumping blood

Relationship of an Action Potential and the Refractory Period to the Duration of the Contractile Response in Cardiac Muscle

AUTORHYTHMICITY( PACE MAKER POTENTIAL)

Length tension relationship

References • Human physiology by Lauralee Sherwood, 7th edition • Text book physiology by Guyton &Hall,12th edition • Text book of physiology by Linda .s contanzo,third edition

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the Heart Muscle Cell ( Cardiac striated muscle )

the Heart Muscle Cell ( Cardiac striated muscle ). Juan Andrés Díaz Luciana Gonzales del Valle Brunella Limonchi 9 A Teacher : Gerardo Lazaro. Part of the heart muscle cell. What are inside this cell ?.

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Cardiac Muscle. Found only in heart Striated Each cell usually has one nucleus Has intercalated disks and gap junctions Autorhythmic cells Action potentials of longer duration and longer refractory period Ca 2+ regulates contraction. Cardiac Muscle.

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Cardiac Muscle Physiology

Cardiac Muscle Physiology. Faisal Mohammed, MD, PhD. Objectives :. By The end of this lecture students should be able to: Distinguish the cardiac muscle cell microstructure Describe cardiac muscle action potential Point out the functional importance of the action potential

612 views • 44 slides