Abstract 2137: Relationship between Duration of Basal QRS Complex and Effectiveness of Antitachycardia Pacing in Implantable Cardioverter-Defibrillator Patients
In re-entrant Monomorphic Ventricular Tachycardias (MVT), the ability of Antitachycardia Pacing (APT) to terminate the arrhythmia depends on the presence of an excitable gap (EG) and on the capability of the impulses to penetrate this EG. The main limiting factor for penetrating the EG is the distance and the obstacles between pacing site and circuit. Therefore, the duration of basal QRS complex (QRSd), as marker of left ventricle size, fibrosis and/or necrosis, could be related to the efficacy of ATP. Our aim is to determine the relationship between QRSd and the effectiveness of ATP in terminating MVT. In this prospective study we included 200 ICD patients with substrate for presenting MVT (LVEF: 31±11; pacing site: right ventricular apex). Detection and ATP therapies for MVT were programmed as follows: a) Fast-MVT : Cycle Length (CL): 250 –320 ms; 1 burst of 5 pulses at 84 % of CL, and: b) Slow MVT: CL > 320 ms; 3 bursts of 15 pulses at 91%. QRSd was determined on the surface ECG (50 mm/s) inmediatly before the device implant. During a follow-up of 602±368 days, 546 MVT (CL: 329±35 ms; fast MVT: 41 %; QRSd: 111±25 ms) were recorded in 64 patients. Overall success rate of APT was: 87%. MVT terminated with ATP were associated with QRSd values significantly lower: 109±24 vs. 121±29 (p<0.001). After classifying the events into 3 groups according to the QRSd tertiles (≤100, 101–119, ≥120 ms), the frequency of successful ATP (S-ATP) was higher in the first tertile: 96% vs. 80% (Odds Ratio: 5.8; 95% Confidence Interval: 2.9- 11.6; p<0.001). In a multivariate analysis which included LVEF, aetiology, indication, functional class, CL of MVT, beta-blocker therapy (mgs/day) and left ventricle end-diastolic diameter, QRSd (ms) remained as an independent predictor of S-ATP: Odds Ratio: 0.96 (95% Confidence Interval: 0.94 – 0.97; p<0.001). Patients with lower values of QRSd presented higher rates of S-ATP (mean±standard deviation): 98±4 (QRSd≤100) vs. 81±26 (QRSd: 101–120) vs. 72±40 (QRSd>120); p=0.01 (ANOVA). Among ICD patients, the duration of QRS complex is related to the effectiveness of ATP: for each ms of QRSd the adjusted probability of ATP terminating the episode decreases 4 points. Patients with QRSd≤100 ms have significantly higher rates of S-ATP.