QRS prolongation after premature stimulation is associated with polymorphic ventricular tachycardia in nonischemic cardiomyopathy: Results from the Leiden Nonischemic Cardiomyopathy Study

BackgroundProgressive activation delay after premature stimulation has been associated with ventricular fibrillation in nonischemic cardiomyopathy (NICM).ObjectivesThe objectives of this study were (1) to investigate prolongation of the paced QRS duration (QRSd) after premature stimulation as a marker of activation delay in NICM, (2) to assess its relation to induced ventricular arrhythmias, and (3) to analyze its underlying substrate by late gadolinium enhancement cardiac magnetic resonance imaging (LGE-CMR) and endomyocardial biopsy.MethodsPatients with NICM were prospectively enrolled in the Leiden Nonischemic Cardiomyopathy Study and underwent a comprehensive evaluation including LGE-CMR, electrophysiology study, and endomyocardial biopsy. Patients without structural heart disease served as controls for electrophysiology study.ResultsForty patients with NICM were included (mean age 57 ± 14 years; 33 men [83%]; left ventricular ejection fraction 30% ± 13%). After the 400-ms drive train and progressively premature stimulation, the maximum increase in QRSd was larger in patients with NICM than in controls (35 ± 18 ms vs 23 ± 12 ms; P = .005) and the coupling interval window with QRSd prolongation was wider (47 ± 23 ms vs 31 ± 14 ms; P = .005). The maximum paced QRSd exceeded the ventricular effective refractory period, allowing for pacing before the offset of the QRS complex in 20 of 39 patients with NICM vs 1 of 20 controls (P < .001). In patients with NICM, QRSd prolongation was associated with the inducibility of polymorphic ventricular tachycardia (16 of 39 patients) and was related to long, thick strands of fibrosis in biopsies, but not to focal enhancement on LGE-CMR.ConclusionQRSd is a simple parameter used to quantify activation delay after premature stimulation, and its prolongation is associated with the inducibility of polymorphic ventricular tachycardia and with the pattern of myocardial fibrosis in biopsies.