Background: Biventricular pacing (cardiac resynchronization therapy) has been shown to improve patients of dilated cardiomyopathy (DCMP), which include largely those with broad QRS complex (LBBB) and a few with normal QRS duration having associated interventricular and/or intraventricular delay. The true prevalence of ventricular asynchrony in a broad subset of patients of DCMP however has not been studied at large and it is unclear if there is association of asynchrony with the LV function. The present study was therefore conducted to assess the prevalence of ventricular asynchrony in a broad set of patients of dilated cardiomyopathy with varying QRS duration and also trying to correlate the same with the LV function.
Method and results: Ninety three consecutive patients of DCMP (EF < 40%) with varying QRS duration and twenty patients with broad QRS complexes (LBBB morphology) with normal LV function (LVEF > 40%) were studied. The patients were then grouped as Group-I, including patients of DCMP with broad QRS (>120 msec, LBBB morphology) (n = 40), Group-II, including patients of DCMP with narrow QRS, (QRS width < or = 120 msec) (n = 53) and Group-III, including patients of LBBB with normal LV function (n = 20). Ventricular asynchrony was diagnosed using standard echocardiography criteria on 2-D, M-mode and pulse wave Doppler including, 1) Interventricular delay:- diagnosed when the difference between aortic (Q-AV) and pulmonary ejection delays (Q-PV) was 340 msec and 2) Intraventricular delay:- diagnosed when posterior left ventricular activation occurred later than onset of diastolic mitral inflow or septal to post wall motion delay of > or = 130 msec. Ventricular asynchrony was present in 97.5% (39/40) in Group-I, 50.9% (27/53) in Group-II and 90% (18/20) in Group-III. Amongst this however interventricular conduction delay was present in 97.5% (39/40) of group-I, 20.7% (11/53) of group-II and 90% )18/20) of group-III, while intraventricular delay was present in 62.5% (25/40) of Group-I, 43.3% (23/53) of Group-II and none of Group-III. Analyzing the contribution of LV dysfunction independent of QRS duration to the occurrence of LV dyssynchrony, patients were further divided in three groups, viz. DCM with LVEF < 20% (group A) (mean LVEF = 16.53 +/- 2.28%), DCM with LVEF > or = 20% (group-B) (mean LVEF = 27.15 +/- 4.29%) and LBBB with normal LV function (group C) (mean LVEF = 53.45 +/- 4.83%). The mean QRS durations were not different between groups A and B (114.3 +/- 32.2 msec vs. 109.1 +/- 13.9 msec, respectively, p = 0.16). However group A had a significantly higher number of patients with ventricular asynchrony compared to group B [37/45 (82.2%) vs. 29/48 (60.4%), p = 0.001)].
Conclusion: We conclude that there is a wide prevalence of, but heterogeneity in occurrence of ventricular asynchrony among patients of dilated cardiomyopathy. The asynchrony possibly relates more to left ventricular function in addition rather than to the QRS duration alone. Criteria for biventricular pacing probably need to relate to ventricular asynchrony than to the QRS duration alone.