Effects of the Preceding R-R Interval on the Safety of Atrial Defibrillation vi Transvenous Catheter Electrodes in the Sterile Pericarditis Model

Objectives: synchronized shock delivered to the atri through transvenous catheter electrodes will terminate atrial fibrillation (AF). We evaluated the effects of the preceding R-R interval on the relative risk of inducing ventricular arrhythmias ( ) during synchronized atrial defibrillation shocks delivered between implanted transvenous catheter electrodes. Methods: The sterile pericarditis model was created in 15 dogs. Two customized transvenous catheter electrodes with 6 cm coil tip were placed, one in the distal coronary sinus and one in the right atrial appendage, respectively, to deliver atrial defibrillation shocks. Variable preceding R-R intervals were simulated systematically with 3 protocols: 1) single ventricular stimulation (PVC protocol); 2) rapid ventricular stimulation (8 stimuli, S1S1 protocol); and 3) double ventricular stimulation (long-short intervals) following 8 basic stimuli (S1S2S3 protocol). The ventricular coupling interval (VCI) was shortened by 10 ms until refractoriness occurred at the pacing site. After sensing the last paced ventricular beat, an atrial shock was delivered with 2 ms delay at shock intensity of 300 V (maximal intensity of the device). Atrial shocks were delivered 4 times at each VCI in each protocol. VCI was normalized by subtracting the QT interval from the VCI. The relationship between VCI and induction of was compared between protocols. To calculate 99% probability of sinus rhythm (SR) after an atrial shock, logistic regression analysis was used. Results: For all 15 dogs, the mean QT interval was 231 ± 21 ms. The incidence of induction was significantly higher for the S1S2S3 than for the PVC or the S1S1 protocol (p < 0.05). The 99% probability of SR was achieved at significantly longer VCI for the S1S2S3 than for the PVC or the S1S1 protocol (p < 0.05). Conclusions: The long-short R-R interval increases the incidence of induction and shortens the safety zone of the VCI for synchronized atrial shocks. However, large safety zone (VCI > 315 ms) is still present, and is predictable from the QT interval.