A 27-year-old woman comes to the office due to intermittent episodes of palpitations and dyspnea on exertion. Blood pressure is 130/80 mm Hg and pulse is 78/min. On examination, there is no peripheral edema or jugular venous distension. The lungs are clear to auscultation. A 3/6 ejection-type systolic murmur is heard along the left sternal border and decreases in intensity when the patient moves from a standing to a squatting position. Which of the following additional history is most helpful for establishing a diagnosis?
Effect of maneuvers on hypertrophic cardiomyopathy | |||
Physiologic effect | Left ventricular | Murmur intensity | |
Valsalva | ↓ Preload | ↓ | ↑ |
Abrupt | |||
Nitroglycerin | |||
Sustained | ↑ Afterload | ↑ | ↓ |
Squatting | ↑ Afterload & preload | ||
Passive | ↑ Preload | ||
This patient with palpitations, dyspnea, and a 3/6 systolic murmur that decreases in intensity with maneuvers that increase left ventricular blood volume (eg, squatting) most likely has hypertrophic cardiomyopathy (HCM). HCM typically involves enlargement of the interventricular septum, which can cause dynamic left ventricular outflow tract obstruction that leads to exertional symptoms (eg, dyspnea, angina, light-headedness, syncope).
HCM is the most common inherited cardiomyopathy in the United States. It is inherited in an autosomal dominant fashion, with roughly half of cases resulting from an identifiable mutation in genes encoding for myocardial contractile proteins of the cardiac sarcomere. Cardiac myosin-binding protein C and cardiac beta-myosin heavy chain are most commonly affected, accounting for approximately 40% and 30% of identifiable mutations, respectively. The phenotypic manifestations of the disease (eg, septal enlargement) typically develop around the time of adolescence. Affected patients often have a recognizable family history of HCM but not always because sporadic mutations can occur, not all mutations responsible for the HCM phenotype have been identified, and the phenotypic penetrance of known mutations is not complete (ie, not all patients with an identifiable gene mutation demonstrate the HCM phenotype).
(Choices B, C, D, and E) Chronic use of injectable sympathomimetics (eg, amphetamines, cocaine), receipt of anthracycline chemotherapy (eg, doxorubicin), occupational exposure to cobalt, and infection with Trypanosoma cruzi (ie, Chagas disease, which is endemic to Latin America) can all lead to dilated cardiomyopathy, but are not risk factors for HCM. Dilated cardiomyopathy often causes secondary mitral regurgitation, recognized by a holosystolic murmur at the cardiac apex that increases, rather than decreases, in intensity with maneuvers that increase left ventricular blood volume (eg, squatting).
Educational objective:
Hypertrophic cardiomyopathy (HCM) is an autosomal dominant inherited disorder caused by mutations in genes encoding for myocardial contractile proteins of the cardiac sarcomere. Mutations affecting cardiac myosin-binding protein C gene or cardiac beta-myosin heavy chain gene are responsible for approximately 70% of identifiable mutations in patients with HCM.