Patients with HCM may become symptomatic at any age, but most present between age 30 and 40 years, approximately 10 years earlier than the average of onset of symptomatic valvular aortic stenosis. Symptoms are similar to those of aortic stenosis, except that the patient with HCM may report that symptoms are relieved with squatting.
Signs may be absent in this disease. The classic auscultatory finding is a crescendo-decrescendo harsh systolic murmur heard best at the fifth left intercostal space, mid left thorax, which radiates to the lower left sternal border. The Valsalva maneuver intensifies the murmur by decreasing venous return, which contracts the left ventricle and increases the obstruction. Squatting and passive leg elevation diminish the murmur. Listening at the apex, one can hear an increased murmur as the patient goes from a squatting to a standing postion, due to decreased venous return from pooling. There is no opening snap, as is commonly heard in valvular aortic stenosis. The apical impulse may be double secondary to an abrupt interruption of early systolic ejection by the asymmetrical septum, which blocks outflow, as the ventricle contracts. The pulse has a brisk rise and a double peak, unlike valvular aortic stenosis, in which the pulse has a slow rise and a sustained single peak.
HCM is one cause of sudden death among athletes, and all patients are at significant risk. The mechanism of sudden death is not well understood and is probably due to several mechanisms, including dysrhythmias and massive myocardial infarction. Patients with HCM are at risk for endocarditis, usually involving the thickened mitral valve. Antibiotic prophylaxis is recommended for certain procedures performed in the emergency department ( Table 5,0:1).
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