Review Question - QID 100517

This clinical picture is consistent with hypertrophic cardiomyopathy (HCM) and autopsy would reveal a hypertrophic intraventricular septum.

HCM is the most common cause of sudden cardiac death in otherwise healthy, young athletes. The disorder can be autosomal dominant (>50% cases) or idiopathic. Muscle hypertrophy is asymmetric, and is due to increased synthesis of actin and myosin. On microscopic examination, the cardiac muscle fibers will appear hypertrophied and in disarray. On echocardiography, HCM patients exhibit a septum:left ventricular wall ratio > 1.3:1 and may have systolic anterior motion of the mitral valve with diastolic dysfunction.

As discussed by Wexler et al., the genetic cause of HCM can be attributed to 11 mutant genes with more than 500 individual transmutations. The most frequent genes identified involve the beta-myosin heavy chain and myosin-binding protein C. However, not everyone with a HCM genetic defect is symptomatic, likely due to the high phenotypic diversity of HCM.

Echocardiography is used to diagnose HCM and 24-Holter monitors are often employed to detect the presence of dangerous arrhythmias. However, a randomized cross-over trial by Kinlay et al., found that transtelephonic event monitors may be more likely than ambulatory (Holter) monitoring to detect clinically important arrhythmias. In their study of 43 patients, diagnostic rhythm strips were obtained in 67% with event monitors vs. 35% with Holters.

Illustration A depicts a cut section of a normal heart contrasted with hypertrophic cardiomyopathy. Note the enlarged myocardium and muscular disarray.
Illustration B is a histologic depiction of HCM. Note the myocyte disarray and increased connective tissue (as compared to normal parallel arrangement of myocytes).

Incorrect Answers:
Answer 1: Atheromatous plaque rupture and resulting intracoronary thrombosis are thought to account for most acute coronary syndromes. This clinical picture, particularly a young, healthy athlete, is not consistent with ACS.
Answer 2: Coagulation necrosis with loss of nuclei and striations is characteristic of MI. This clinical picture, particularly a young, healthy athlete, is not consistent with MI.
Answer 4: Postductal coarctation of the aorta is a congenital condition in which the aorta narrows at the level of the ductus arteriosus. Patients usually present at birth or in infancy with difficulty breathing, difficulty feeding, or failure to thrive. Later on, children may experience intermittent claudication with exercise due to insufficient blood flow.
Answer 5: Cardiac myxomas are typically pedunculated tumors attached to the interatrial septum. While they may present with syncope or sudden death, they generally occur in older adults.