MECHANISM OF BENEFIT OF NEGATIVE INOTROPES IN OBSTRUCTIVE HYPERTROPHIC CARDIOMYOPATHY

Background-Drugs with negative inotropic effect are widely used to dec rease obstruction in hypertrophic cardiomyopathy (HCM). However, the m echanism of therapeutic benefit has not been studied. Methods and Resu lts-We used M-mode, two-dimensional, and pulsed Doppler echocardiograp hy to study 11 patients with obstructive HCM before and after medical elimination of left ventricular-outflow tract obstruction, We measured 148 digitized pulsed Doppler tracings recorded in the: left ventricul ar cavity 2.5 cm apical of the mitral valve. Successful treatment slow ed average acceleration of left ventricular ejection by 34% (P=.001). Mean time to peak velocity in the left ventricle was prolonged 31% (P= .001). Mean time to an ejection velocity of 60 cm/s was prolonged 91% (P=.001). Before treatment, left ventricular ejection velocity peaked in the first half of systole; after successful treatment, it peaked il l the second half(P=.001). In contrast, after treatment, we found no c hange in peak left ventricular-ejection velocity. We also found Ilo ch ange in the distance between the mitral coaptation point and the septu m, as measured in two planes, indicating no treatment-induced alterati on of this anatomic relationship. Conclusions-Medical treatment elimin ates mitral-septal contact and obstruction by decreasing left ventricu lar ejection acceleration. By slowing acceleration, treatment reduces the hydrodynamic force on the protruding mitral leaner and delays mitr al-septal contact. This, in turn, results in a lower final pressure gr adient.