Background: In implantable cardioverter-defibrillators (ICD) patients, the duration of the basal QRS complex (QRSd) is not associated with a greater risk of developing ventricular tachyarrhythmias. QRSd could be inversely related to the effectiveness of antitachycardia pacing (ATP) because it may be associated with longer conduction times of the paced-impulses and hence, with a greater propensity to require shocks to terminate ventricular tachycardias (VTs).
Methods: We followed 216 ICD patients (pacing site: right ventricular apex; QRSd <or= 100: 34%) for 21 +/- 12 months. ICD programming was standardized. QRSd was determined on the electrocardiogram (50 mm/s) at device implantation.
Results: Five hundred and fifty-one VTs (cycle length: 329 +/- 35 ms) occurred in 67 patients (36% had a QRSd <or= 100 ms). ATP terminated 86% of VTs and 11% needed shocks. Mean ATP efficiency per patient was 83%. QRSd was significantly correlated with the probability of successful ATP (C-coefficient: 0.66), the best cut-off point being 100 (sensitivity and specificity of 91% and 49%). Patients with QRSd <or= 100 had a higher ATP effectiveness (98% vs 75%; P = 0.003) and fewer VTs terminated by shocks (1% vs 23%; P = 0.003). By logistic regression, QRSd > 100 remained as an independent predictor of receiving shocks to terminate VTs (P = 0.01). According to Kaplan-Meier analysis, the occurrence of VTs was similar regardless of the QRSd (30% vs 38%; P = 0.2), but the incidence of shock due to VTs was higher in patients with a QRSd > 100 (19% vs 7%; P = 0.01).
Conclusion: Since QRSd is a negative and independent predictor of effective ATP, ICD patients with QRSd > 100 ms require shocks more frequently to terminate VTs.