Cardiac Muscle and Cardiomyopathy

by Robert Tallitsch, PhD | November 16, 2022

Video introduction of Cardiac Muscle and Cardiomyopathy with a patient case example!

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Written by: Robert Tallitsch, PhD

The term cardiomyopathy refers to a group of diseases that affect heart muscle (cardiac muscle.) Often cardiomyopathy goes undiagnosed, so the true numbers of those diagnosed with or possessing this disease are unknown. In this Brain Builder we will only discuss the cellular anatomy of cardiac muscle, as the gross anatomy of the heart and the cardiovascular system is discussed in our Cardiovascular System and Pacemaker Brain Builder. Then we will discuss the different types of cardiomyopathies, the cellular changes seen in cardiomyopathy, the symptoms, and treatment of the disease.

Cellular Anatomy of Cardiac Muscle

Like skeletal muscle (Skeletal Muscle and Muscular Dystrophy Brain Builder), cardiac muscle exhibits the same A bands and I bands. Cardiac muscle also contains the same contractile proteins as skeletal muscle. Even though cardiac muscle exhibits the above similarities to skeletal muscle, there are significant cellular differences between these two types of muscle.

Cardiac muscle is composed of individual cells that are joined by complex cellular junctions termed intercalated discs. These specialized junctions cause cardiac muscle to function as one functional unit, in that the stimulation of one cardiac muscle cell results in the contraction of all of the cardiac muscle cells. Because of this characteristic cardiac muscle is referred to as a functional syncytium. In contrast, skeletal muscle cells do not function in this way, in that individual cells of skeletal muscle are not joined by intercalated discs and, therefore, function more independently than cardiac muscle cells. In addition to this difference, other differences include:

• Cardiac muscle cells are branched rather than being spindle shaped, like skeletal muscle cells.

• Unlike the skeletal muscle cells, which are multi-nucleated, cardiac muscle cells possess only one nucleus.

• The nuclei of skeletal muscle cells are peripherally located, while cardiac muscle cells possess one centrally located nucleus. 

• The sarcoplasmic reticulum and t-tubules of cardiac muscle are significantly less prominent when compared to skeletal muscle cells.

• There is considerably less connective tissue between cardiac muscle cells when compared to skeletal muscle.

Cardiomyopathy

Cardiomyopathy represents a diverse collection of pathologies of the heart and its muscular walls. In cardiomyopathy, the muscle of the heart may either (1) fill with substances produced by the body that are not normally present within cardiac muscle, (2) thicken, or (3) become thinner than normal. In all forms of cardiomyopathy the heart’s ability to contract and pump blood becomes significantly reduced, and may result in heart failure. 

Different Types of Cardiomyopathy 

The main types of cardiomyopathy include:

• Hypertrophic cardiomyopathy: With this form, the cardiac muscle thickens considerably. This form of the disease may occur anytime in an individual’s lifetime. If it occurs in adolescents or young athletes it is often an inherited condition, and the person typically does not present any symptoms. It is not uncommon for this form of cardiomyopathy to result in sudden death of the young individual. In adults this is the most common form of cardiomyopathy, and its causes are unknown.

• Restrictive cardiomyopathy: Here the cardiac muscle becomes very rigid and stiff. Scarring of the heart is often seen in patients with this form of cardiomyopathy.

• Dilated cardiomyopathy: In this form the chambers of the heart are significantly enlarged in size. This form of cardiomyopathy is more common in males, and can occur at any age. This is the most common pediatric form of cardiomyopathy.

• Arrhythmogenic cardiomyopathy. This is an inherited form of cardiomyopathy that is most common in males. This form leads to irregular cardiac rhythms and may lead to the formation of clots and, as a result, strokes in the patient.

Cellular Changes Seen in Hypertrophic Cardiomyopathy (HCM)

Numerous cellular changes are seen in patients with hypertrophic cardiomyopathy. The arrangement of the cells of the heart is considerably different in individuals with HCM. Rather than being arranged in straight, parallel bundles of cells, cardiac cells are often seen perpendicular to each other, or are described as being in a basket-weave pattern. In addition, the intercalated discs between individual cardiac cells are significantly different from those seen between normal cardiac muscle. Such intercalated discs are believed to conduct electrical impulses between cardiac muscle cells differently and possibly less effectively than the intercalated discs found within a normal heart.

Patients with HCM also have a significant infiltration of connective tissue between the cells of the heart, resulting in a reduction in the force of contraction and a reduction in the heart’s ability to pump blood.

Symptoms

If a patient with HCM presents symptoms they might include any combination of the following:

• Frequent fainting (termed syncope)

• Fatigue

• Shortness of breath

• Swelling in the ankles and legs

• Irregular heartbeat

Treatment and Prevention

Treatment of HCM is dependent on how far the disease has progressed. Treatments utilized are intended to slow the progress of the disease and, hopefully, reduce the chances of sudden cardiac death. There is no cure for hypertrophic cardiomyopathy.

Any medications prescribed will reduce heart rate and/or the strength of contraction of the patient’s heart. These physiological changes will help the heart pump blood more efficiently, and reduce the strain on the patient’s heart. If medications do not improve the patient’s symptoms, one of several surgical procedures may be recommended. In addition, patients will be recommended to make significant changes in their lifestyle, including the introduction of moderate-intensity physical activity (or the reduction of physical activity from intense to moderate levels in younger patients), avoid the consumption of alcohol and the use of tobacco products, obtain and maintain a healthy weight, and eat a healthy diet.

Because there is no cure the physical and mental health of HCM patients need to be monitored regularly.