Different effects of abnormal activation and myocardial disease on left ventricular ejection and filling times

Background-Ventricular activation is often abnormal in patients with dilate d cardiomyopathy, but its specific effects on timing remain undetermined. Objective-To investigate the use of the ratio of the sum of left ventricula r ejection and filling times to the total RR interval (Z ratio) to dissocia te the effects of abnormal activation from those of cavity dilatation. Methods-Subjects were 20 normal individuals, 11 patients with isolated left bundle branch block (LBBB, QRS duration > 120 ms), 17 with dilated cardiom yopathy and normal activation, and 23 with dilated cardiomyopathy and LBBB. An additional 30 patients (nine with normal ventricular systolic function and 21 with dilated cardiomyopathy) were studied before and after right ven tricular pacing. Left ventricular ejection and filling times mere measured by pulsed wave Doppler and cavity size by hi mode echocardiography. Results-Z ratio was independent of RR interval in all groups. Mean (SD) Z r atio was 82 (10)% for normal subjects,66 (10)% for isolated LBBB (p < 0.01 v normal), 77 (7)% for dilated cardiomyopathy without LBBB (NS v normal), a nd 61 (7)% for dilated cardiomyopathy with LBBB (p < 0.01 v normal). In the nine patients with normal left ventricular size and QRS duration, Z ratio fell from 88 (6)% in sinus rhythm to 77 (10)% with right ventricular pacing (p = 0.26). In the 21 patients with dilated cardiomyopathy and LBBB, Z rat io rose from 59 (10)% in sinus rhythm to 74 (9)% with right ventricular DDD pacing (p < 0.001). Conclusions-Z ratio dissociates the effects of abnormal ventricular activat ion and systolic disease. It also clearly differentiates right ventricular Facing from LBBB. It may thus be useful in comparing the haemodynamic effec ts of different pacing modes in patients with or without left ventricular d isease.