butcher
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Tuesday 28th of November 2006 01:11:40 PM (3 years ago)
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Pathophysiology: Since the initial descriptions of HCM, the feature that has attracted the greatest attention is the dynamic pressure gradient across the LV outflow tract. The pressure gradient appears to be related to further narrowing of an already small outflow tract (by the marked asymmetric septal hypertrophy and possibly an abnormal location of the mitral valve) by the systolic anterior motion of the mitral valve against the hypertrophied septum. The likely cause of this is a Venturi effect resulting from increased ejection velocity produced by the abnormal LV outflow tract orientation and geometry.
In addition, most patients have abnormal diastolic function, whether a pressure gradient is present or not. This diastolic dysfunction impairs ventricular filling and increases filling pressure, despite a normal or small ventricular cavity. These patients have abnormal calcium kinetics and subendocardial ischemia, which are related to the profound hypertrophy and myopathic process.
The molecular basis for HCM is defects in several of the genes encoding for the sarcomeric proteins, such as myosin heavy chain, actin, tropomyosin, and titin. Multiple mutations have been identified, with genotype-specific risks of mortality and degree of hypertrophy. Interestingly, the genetic basis of ventricular hypertrophy does not directly correlate with prognostic risk stratification. Patients with some mutations, such as specific tropomyosin substitutions, have only a mild degree of ventricular hypertrophy, with little or no LV outflow tract obstruction, but they still carry a disproportionately high risk of sudden death.
- emedicine
 
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