Left ventricular diastolic function in hypertrophic cardiomyopathy.
Impaired diastolic function of the hypertrophied and stiffened left ventricle is a characteristic feature of hypertrophic cardiomyopathy (Figure 1). Altered left ventricular filling dynamics and reduced left ventricular distensibility or increased left ventricular diastolic chamber stiffness are associated with reduced left ventricular stroke volume, increased left ventricular filling pressures and compressive effects on the coronary microcirculation. These factors contribute importantly to the clinical presentation of many patients, including symptoms of fatigue, dyspnea and angina pectoris. Reduced distensibility results both from factors determining the passive elastic properties of the ventricular chamber (including severity of hypertrophy, fibrosis and cellular disarray) and from factors influencing the rate and extent of active left ventricular relaxation (Figure 2). The factors contributing to impaired relaxation in hypertrophic cardiomyopathy are mediated via either inactivation dependent or load-dependent mechanisms. In laboratory animals, compromise of myocardial inactivation results in a persistent increase in intracellular calcium concentration and in prolonged interaction of the contractile proteins. Additionally, there is evidence for an increased number of active receptors for calcium antagonists and, lastly, for myocardial ischemia (Figure 3). Load-dependent mechanisms include diminished wall tension at the opening of the mitral valve, changes in afterload, contractility and coronary flow. Other factors are nonuniform and asynchronous regional ventricular function due to differing increases in thickness of the ventricular walls and ischemia (Figure 4). Calcium channel blockers exert a favorable influence on left ventricular relaxation and filling (Figure 5); verapamil and diltiazem are preferable to nifedipine. Verapamil increases left ventricular stroke volume without an increase in the end-diastolic pressure (Figure 6), reduces regional asynchrony if present, and leads to a more homogeneous regional diastolic filling (Figure 4).(ABSTRACT TRUNCATED AT 250 WORDS)
Bonow
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Cardiology Branch, National Heart, Lung, and Blood Institute, Bethesda, Maryland.
D002312:Cardiomyopathy, Hypertrophic / Q000503:physiopathology*; D003971:Diastole / Q000502:physiology*; D006439:Hemodynamics / Q000502:physiology; D006801:Humans; D009200:Myocardial Contraction / Q000502:physiology; D016277:Ventricular Function, Left / Q000502:physiology*