A new use for maximum deflection index: Detection of intraventricular dyssynchrony

CRT has been shown to be very beneficial for patients with reduced LVEF, symptomatic HF and increased QRS width. But many patients do not benefit from CRT. Maximum deflection index (MDI) is a quantitive measure of the rapidity of depolarization of the myocardium. In previous studies, high MDI was found to indicate epicardial origin of ventricular tachycardia. We aimed to detect the relationship between echocardiographic intraventricular dyssynchrony and MDI.

We included 144 patients with HF, QRS≥120ms, LBBB, NYHA II-IV, LVEF<35% and scheduled for CRT (90 male, 54 female; mean age 65.3±9.9years). Septal-lateral >60ms delay for the beginning of systolic velocity in TDI and septum-posterior >130ms delay in M-mode were accepted as intraventricular dyssynchrony. The MDI was calculated by dividing the time from onset of the QRS complex to the earliest point of maximum deflection in V5-V6 by the QRS duration.

Septal-lateral delay was associated with MDI and QRS width in bivariate analysis. In logistic regression analysis, MDI (beta=0,264, p=0.001) and QRS width (beta=0,177, p=0.028) were found to be independent parameters for predicting significant septal-lateral delay. MDI was also associated with significant septum-posterior delay in bivariate correlations and ROC curve (p<0.05 for all). In bivariate analysis MDI was associated with intraventricular dyssynchrony in both non-strict LBBB (r=0.261, p=0.010) and strict LBBB (r=0.305, p=0.035) groups.

MDI is closely associated with all echocardiographic intraventricular dyssynchrony parameters. We suggest that MDI may be used as a marker to detect patients with increased intraventricular dyssynchrony. It may be useful to integrate MDI to CRT patient selection procedure in order to minimize nonresponders.