A 24-year-old man is evaluated due to an episode of syncope. He was jogging when he felt light-headed and passed out, but he did not sustain a head injury. The patient has had 2 similar episodes of light-headedness while jogging over the last year, but this was the first time he passed out. He considers himself in good health and has no other medical conditions. The patient does not use tobacco, alcohol, or recreational drugs. His father died suddenly at age 30. Vital signs are within normal limits. On physical examination, the patient has a harsh systolic murmur. The lungs are clear to auscultation. There is no peripheral edema. Transthoracic echocardiography shows asymmetric interventricular septal hypertrophy. This patient's symptoms are most likely explained by left ventricular outflow obstruction created by which of the following structures?
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This patient's presentation suggests hypertrophic cardiomyopathy (HCM), an autosomal dominant disorder resulting from mutations in cardiac sarcomere proteins. HCM is characterized by asymmetric ventricular septal hypertrophy, which often causes left ventricular outflow tract (LVOT) obstruction. Systolic anterior motion of the mitral valve toward the interventricular septum can exacerbate the obstruction, with the anterior leaflet of the mitral valve physically blocking the LVOT.
Many patients with HCM are asymptomatic and may be diagnosed via an abnormal ECG or murmur during routine evaluation. However, patients can also experience exertional dyspnea, chest pain, fatigue, palpitations, lightheadedness, syncope, or sudden cardiac death (due to ventricular arrhythmias). Examination often reveals a harsh crescendo-decrescendo systolic murmur at the apex and left lower sternal border; the murmur is caused by blood flow through the narrowed LVOT. Because the degree of LVOT obstruction is dynamic and changes with left ventricular blood volume, the murmur varies in intensity with physiologic maneuvers.
(Choices A, B, and C) The aortic valve does not contribute to LV obstruction in HCM as the obstruction is subvalvular, resulting from an enlarged intraventricular septum and transient movement of the anterior mitral valve leaflet into the LVOT during ventricular systole. Valvular aortic stenosis often results from age-related leaflet calcification and can present with a murmur and symptoms similar to those of HCM, but it typically affects patients age >40 and does not involve enlargement of the interventricular septum.
(Choice D) Narrowing of the ascending aorta just distal to the aortic valve (ie, supravalvular aortic stenosis) is a characteristic cause of LV obstruction in Williams syndrome, a rare genetic disorder that does not involve enlargement of the interventricular septum. Abnormalities of the ascending aorta do not contribute to LV obstruction in HCM.
Educational objective:
In patients with hypertrophic cardiomyopathy, left ventricular outflow tract (LVOT) obstruction results from a hypertrophied interventricular septum and abnormal systolic anterior motion of the anterior leaflet of the mitral valve. The degree of LVOT obstruction is dynamic and varies with changes in left ventricular blood volume.