The salient phonoechocardiographic features of patients having hypertrophic cardiomyopathy (HCM) with or without left ventricular outflow tract (LVOT) gradients are reviewed. Intracardiac sound and pressure recordings from high fidelity catheter-tipped micromanometers have documented that the precordial murmur is the summation of both the systolic ejection murmur (SEM) arising from the LVOT, as well as the mitral regurgitant murmur recorded from the left atrium. The intensity of the precordial murmur varies directly with the LVOT gradient, which in turn is determined primarily by the contractility and loading conditions of the left ventricle. Reversed splitting of the second heart sound (S2) with paradoxical respiratory movement is a common finding in HCM, and when present, almost always denotes a significant LVOT gradient. It is due to marked lengthening of the left ventricular ejection time secondary to prolongation of the contraction and relaxation phases of left ventricular systole. The presence of a fourth heart sound (S4) is the rule in HCM when normal sinus rhythm is present, and is a reflection of a forceful left atrial contraction into a hypertrophied noncompliant left ventricle. A third heart sound (S3) is also common in HCM, and often the initial vibrations occur before the 0 point of the apexcardiogram (ACG) and continue giving the auscultatory impression of a diastolic rumble. When associated with a loud S1, which is frequently present, the clinical presentation may mimic mitral stenosis. This is particularly true when the patient has chronic atrial fibrillation. Careful attention to evidence of marked left ventricular hypertrophy as well as the typical echocardiographic findings of HCM preclude this diagnosis. In conclusion, phonoechocardiography is a simple non-invasive technique which almost always makes the definitive diagnosis of HCM.
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