Impaired Left Atrial Compensation in Hypertrophie Cardiomyopathy

Abstract

To determine to what degree left atrial function contributes to the maintenance of left ventricular function in hypertrophic cardiomyopathy (HCM), we investigated a group of 12 HCM patients as compared to 9 healthy controls using radionuclide (RN) angiography. Cardiac output was calculated by RN angiography using technetium-99m albumin. Next, time-activity curves were constructed by combined forward- and reverse-gating from the R wave. Using the data thus obtained, the left ventricular time-volume curve and its 1 st and 2nd derivative curves were constructed. The ejection fraction was significantly greater in the HCM group than in the control group (p < 0.01). In the rapid filling phase, the filling volume (23 ± 5 vs. 36 ± 6 ml/m^2, p < 0.001), filling fraction (0.58 ± 0.09 vs. 0.76 ± 0.05, p < 0.001) and peak filling rate (153 ± 37 vs. 222 ± 53/s/m2, p < 0.01) all showed lower values in the HCM group, while the time to peak filling rate was significantly prolonged in this group (p < 0.02). In the atrial systolic phase, the filling volume (13 ± 4 vs. 10 ± 3 ml/m^2, p < 0.05), filling fraction (0.33 ± 0.08 vs. 0.20 ± 0.06, p < 0.01) and peak filling rate (132 ± 45 vs. 84 ± 30 ml/s/m^2, p < 0.02) were all significantly increased in the HCM group as compared to the control group. However, the increase in filling volume in the atrial systolic phase was smaller than the decrease in filling volume in the rapid filling phase, and the left ventricular filling volume (= stroke volume) was significantly smaller in the HCM group than in the control group (p < 0.01). The above results suggest that although in the HCM group the contribution of the left atrium is increased and a compensatory mechanism is at work in response to the impairment of left ventricular early diastolic filling, this compensatory response is insufficient to restore normal left ventricular function.