Antitachycardia pacing (ATP) terminates the majority (but not all) of slow ventricular tachycardias (S-VT) with a cycle length (CL) > 320 ms. Usually, several ATP therapies are programmed in the S-VT zone. Our objective is to analyse the ATP effectiveness, comparing the first ATP attempt (ATP-1) to the second (ATP-2) and third (ATP-3) attempts.

We studied 556 S-VT (CL = 354 ± 18). ATP programming was standardized and included three bursts of 15 pulses at 91% of VT CL.

ATP effectiveness declined 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 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 post-pacing interval—CL difference (PPI-TCLd) 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). Several independent predictors of ATP efficacy were found, as follows: (a) ATP-1: P-RR, % (OR = 7.3; p < 0.001), beta-blockers (OR = 4.1; p < 0.001) and QRS ≥ 120 ms (OR = 0.3; p < 0.001); (b) ATP-2: PPI-TCLd, ms (OR = 0.94; p = 0.001) and QRS ≥ 120 ms (OR = 0.6; p = 0.04); (c) ATP-3: PPI-TCLd, ms (OR = 0.93; p = 0.009).

The effectiveness of ATP is mainly due to ATP-1. The regularization of RR intervals after ineffective ATP-1 underlies the lower efficacy of successive attempts. Shorter PPI-TCLd is associated with higher effectiveness of ATP-2 and ATP-3. Since a duration of QRS ≥ 120 ms predicts a longer PPI-TCLd, patients with wide QRS complexes have less effective ATP-2 and APT-3.