Effectiveness of first versus subsequentes ATP attemps: predictors and clinical consequences

Abstract Introduction Antitachycardia pacing (ATP) terminates the majority (but not all) of slow VTs (S-VT) with a cycle length (CL) >320 ms. Purpose To analyze the efficacy, safety and predictors of ATP, comparing the first (ATP-1) to the second (ATP-2) and third (ATP-3) attempts. Methods We studied 556 S-VT (CL=354±18 ms; range: 321–415 ms; 1.6% syncopes) occurring in 67 patients. ATP programming was standardized, including three consecutive bursts of 15 pulses at 91% of VT CL. Results ATP effectiveness declined significantly from ATP-1 (436/556: 78%) compared to ATP-2 (24/103: 23%) and ATP-3 (10/79: 13%), p<0.01 for all comparisons. The percentage of variation of RR intervals (P-RR, %) was significantly higher prior to effective ATP-1 (2.73±1.45 vs 1.23±0.9; p<0.001). After an ineffective ATP-1, the P-RR decreased dramatically, with no differences between episodes terminated or not at ATP-2 (0.6±0.14 vs 0.44±0.16; p=0.6) or ATP-3 (0.54±0.15 vs. 0.52±0.14; p=0.7). The postpacing interval – CL difference (PPI-CLd) after an unsuccessful ATP-1 was shorter in episodes terminating at ATP-2 or ATP-3 (180±24 vs 211±15 ms; p<0.001) being 200 ms the cut-off point with the best sensitivity and specificity for non-effective ATP-2 and ATP-3 (93% and 74%, respectively). By multivariate analysis, the duration of native QRS complex (dQRS) (ms) was found the only independent predictor of a PPI-CLd ≥200 ms (OR=1.04; p=0.003). The best cutoff point of dQRS for PP-CLd ≥200 ms was 120 ms (sensitivity and specificity of 66% and 79%, respectively). Several predictors of ATP efficacy were found by logistic regression: a) ATP-1: P-RR (OR=7.3; p<0.001), beta-blockers (OR=4.1; p<0.001) and dQRS (OR=0.95; p<0.001); b) ATP-2: PPI-CLd (OR=0.94; p=0.001) and dQRS (OR=0.96; p=0.04); c) ATP-3: PPI-CLd (OR=0.93; p=0.009). Patients with a dQRS≥120 ms had a lower adjusted effectiveness of ATP and a higher proportion of S-VT causing syncope. Table. Table 1 Patients with QRS <120 ms Patients with QRS ≥120 ms p value Adjusted effectiveness of ATP-1 89% (82–96) 70% (59–80) 0.008 Adjusted effectiveness of ATP-2 47% (32–63) 23% (11–35) 0.036 Adjusted effectiveness of ATP-3 18% (3–33) 3% (0–6) 0.003 Adjusted incidence of syncope due to S-VT 0.18% (0–0.6) 4.1% (2.1–6.1) 0.025 Values are expressed as mean (95% CI). Generalized Estimating Equations Method. Conclusions The efficacy of ATP in terminating S-VT is mainly due to the ATP-1. The regularization of RR intervals after ineffective ATP-1 underlies the lower efficacy of ATP-2 and ATP-3. Since the dQRS correlated significantly with the PPI-CLd, patients with a dQRS≥120 ms had a lower ATP-1, ATP-2 and ATP-3 effectiveness, leading to a higher incidence of syncope.