Prevalence of Mechanical Dyssynchrony in Heart Failure Patients with Normal and Wide QRS Complex: An Echocardiography-based Study

Background: Cardiac resynchronization therapy (CRT) has been shown to be an effective treatment for advanced drug refractory heart failure in selected patients. Nevertheless, 20%–30% of patients in multicenter trials did not respond clinically. Moreover, the relationship of QRS duration to mechanical dyssynchrony may not be parallel as documented by several studies. Aim and Objectives: To study the prevalence of inter and intraventricular dyssynchrony by two-dimensional echocardiography in patients of heart failure with either normal or wide QRS. Methods: A total of 105 patients with heart failure (ejection fraction <35%) were included. It was an observational and prospective study. The patients were divided into two categories depending upon QRS duration (<120 ms and >120 ms). Echocardiographic parameters for interventricular and intraventricular dyssynchrony were taken namely aortic and pulmonary preejection time, septoposterior wall delay, septolateral wall delay, and dyssynchrony index. The time-to-peak myocardial sustained systolic velocity (Ts) in six basal and six middle segments of the left ventricular was measured manually using the velocity curves from Tissue Doppler imaging and standard deviation (SD) of the same was taken as dyssynchrony index (cut-off 33 ms). Moreover, cutoff for septal to posterior wall delay was taken as >130 ms, and for septal-to-lateral delay, 65 ms was set as cut-off. Interventricular dyynchrony was defined as interventricular mechanical delay ≥40 ms. Results: Fifty-one patients were included in Group 1 with QRS width <120 ms and 54 patients were enrolled in Group 2 having QRS width >120 ms. 13.7% patients (7) in group 1 had interventricular dyssynchrony with the mean difference of 23.41 (SD 14.51). The interventricular dyssynchrony was present in 55.6% of the patients ( n = 30) in Group 2 with mean time difference of 41.22 (SD 21.63) ms which was significantly more than that in group 1. Intraventricular dyssynchrony was present in 19.6% ( n = 10) in Group 1 and 48.1% (26) in Group 2 patients which was statistically significant. 27.8% with wide QRS did not have any dyssynchrony. There was a weak association between the QRS duration and the dyssynchrony parameters in the study. Conclusion: Intra and interventricular dyssynchrony occurs in a significant proportion of heart failure patients irrespective of QRS duration. Nevertheless, a significant proportion of patients with wide QRS did not exhibit inter-or intraventricular dyssynchrony that could pose a limitation to identify the ideal QRS width for the selection of patients for CRT.