Cardiomyopathy – Top USMLE Diseases

The heart is a 4-chambered muscular pump made primarily of cardiac muscle tissue. The heart is divided into 4 chambers: 2 upper chambers for receiving blood from the great vessels, known as the right and left atria, and 2 stronger lower chambers, known as the right and left ventricles, which pump blood throughout the body. Blood flows through the heart in 1 direction, moving from the right side of the heart, through the lungs, and then returning to the left side of the heart, where it is pumped out to the rest of the body. As blood moves through the heart, 4 important valves prevent backflow. The heart muscle itself is supplied by the coronary arteries. The heart also has its own conduction system, triggering its own rhythmic contractions.

Heart sounds are brief, transient sounds produced by valve opening and closure and by movement of blood in the heart. They are divided into systolic and diastolic sounds. In most cases, only the first (S1) and second (S2) heart sounds are heard. These are high-frequency sounds and arise from aortic and pulmonary valve closure (S1), as well as mitral and tricuspid valve closure (S2).  The third heart sound (S3) may be physiologic (e.g., athletes) or pathologic (e.g., congestive heart failure), and is related to abnormally rapid deceleration of early diastolic left ventricular inflow. The fourth heart sound (S4) is associated with contraction of the atria into partially-filled and non-compliant (stiff) ventricles. S4 is a pathologic sign in the young, but may be found in older individuals due to an age-related decrease in ventricular compliance. Additional sounds include murmurs (physiologic and pathologic), clicks, and snaps. These sounds are heard in individuals with structural abnormalities of the heart such as septal defects, valvular stenosis, and mitral regurgitation.

Dilated cardiomyopathy (DCM) is the most common type of non-ischemic cardiomyopathy and a common cause of heart failure (HF). The cause may be idiopathic, familial, or secondary to a variety of underlying conditions. The disease is characterized by the enlargement of 1 or both ventricles and reduced systolic function. Patients typically present with symptoms of HF such as shortness of breath, fatigue, weakness, and peripheral edema. Blood tests, ECG, X-rays, echocardiography, and other cardiac studies and procedures are typically done to obtain the diagnosis. Treatment includes medications used to reduce volume overload (e.g., diuretics) and manage HF (e.g., beta-blockers). Devices such as pacemakers and cardioverter-defibrillators may also be needed. In severe cases, a heart transplant is required. Complications include thromboembolic events and sudden cardiac death.

Restrictive cardiomyopathy (RCM) is a fairly uncommon condition characterized by progressive stiffening of the cardiac muscle, which causes impaired relaxation and refilling of the heart during diastole, resulting in diastolic dysfunction and eventual heart failure. It most often occurs secondary to scarring, damage, and/or infiltration of the heart muscle, with amyloidosis being the most common cause. Infrequently, it may be idiopathic or inherited. Signs and symptoms include shortness of breath, low exercise tolerance, fatigue, and peripheral edema. Diagnosis is made through clinical suspicion and confirmed through ECG, X-ray, echocardiography, and cardiac MRI. Treatment includes medications for heart failure, implantable devices such as pacemakers and cardioverter–defibrillators, and heart transplantation in refractory cases.

Examination of the cardiovascular system (CVS) is a critical component of a thorough physical examination. As with all components of a complete physical examination, the CVS examination consists of inspection, palpation, and auscultation. The evaluation of the CVS focuses on the heart, but also includes an assessment of the arterial system throughout the body. A number of cardiovascular conditions can be diagnosed with a physical examination, including valvular heart disease, peripheral artery disease, and arrhythmia.

Cardiomyopathy refers to a group of myocardial diseases associated with structural changes of the heart muscles (myocardium) and impaired systolic and/or diastolic function in the absence of other heart disorders (coronary artery disease, hypertension, valvular disease, and congenital heart disease). The list of causes is extensive, ranging from familial disorders to underlying diseases and infections. Patients often present with chest pain, dyspnea, palpitations, and/or syncope. Some patients may be completely asymptomatic, while others may present with sudden cardiac death as the first sign of an underlying condition. Diagnosis is made through the use of ECG and cardiac imaging such as echocardiography and cardiac MRI. Management involves medications typically used to treat heart failure, as well as implantable devices. In severe cases, heart transplantation may be necessary.

Hypertrophic cardiomyopathy (HCM) is the most commonly inherited cardiomyopathy, which is characterized by an asymmetric increase in thickness (hypertrophy) of the left ventricular wall, diastolic dysfunction, and often left ventricular outflow tract obstruction. Hypertrophic cardiomyopathy is caused by various gene mutations affecting the contractile components of the heart, known as sarcomeres. Inheritance of HCM is typically autosomal dominant, although sporadic mutations also occur. Patients may be asymptomatic, present with dyspnea and chest pain or suffer sudden cardiac death without prior symptoms. Diagnosis is made based on ECG, echocardiography, stress test, and cardiac MRI. Symptomatic HCM is typically treated with beta-blockers as the 1st-line therapy. Additional management depends on the presence of left ventricular outflow tract obstruction.