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Introduction: High-rate pacing may have an inhibitory effect on the initiation of Torsade de Pointes arrhythmias (TdP). However, permanent pacing is only indicated in high-risk patients. We performed a proof of concept study into automatic overdrive pacing for prevention of drug-induced TdP, using short-term variability of repolarization (STV) as a feedback parameter of arrhythmic risk. Methods and Results: The minimal signal sampling frequency required for measuring STV was determined through computer simulation. Arrhythmogenic response to dofetilide (25 μg/kg/5minutes) was tested at two different paced heart rates (60-65 bpm vs 100-110 bpm) in 7 dogs with chronic atrioventricular block, while recording right and left ventricular (LV) monophasic action potential (MAP) and LV electrogram (EGM). Simulations showed a sampling frequency of 500 Hz is sufficient to capture relevant STV values. High-rate pacing prevented dofetilide-induced TdP seen at the low rate (low: 6/7 vs high: 1/7). At the low rate, STV from LV MAP duration increased before occurrence of spontaneous, ectopic activity and TdP (1.7 ± 0.6-3.0 ± 1.8 ms, P < 0.05), but at the high-rate STV did not change significantly (0.9 ± 0.2-1.5 ± 1.4 ms, NS). Regression analysis showed a close relation between STV calculated from LV MAP and from LV EGM (R= 0.71). Conclusions: High-rate pacing increases repolarization reserve in dogs with chronic atrioventricular block, preventing dofetilide-induced TdP. Changes in repolarization reserve are reflected in values of STV. (J Cardiovasc Electrophysiol, Vol. 21, pp. 1384-1391, December 2010) [ABSTRACT FROM AUTHOR]

Introduction: The aim of this study is to characterize ablation lesions using varying ratios of bipolar:unipolar energy and to show the feasibility of a circular decapolar pulmonary vein ablation catheter (PVAC™) to create transmural lesions in an in vivo porcine superior vena cava (SVC) model. Methods and Results: Ablations were performed on (1) isolated blocks of bovine myocardium, (2) thigh muscle preparations (4 pigs), and (3) the junction between SVC and right atrium (6 pigs). Radiofrequency (RF) energy was delivered simultaneously to all electrodes (target temperature 60°C, maximum power 10 W/electrode) with various ratios of bipolar:unipolar energy. (1) In vitro PVAC™ resulted in circumscript lesions. Changing RF energy mode from unipolar only to bipolar:unipolar 1:1, 2:1 and 4:1 and bipolar only decreased lesion depth significantly (6.7 ± 0.2 vs. 5.0 ± 0.2, 4.1 ± 0.3, 3.6 ± 0.1 and 3.1 ± 0.1 mm, P < 0.001). (2) Similar results were obtained in vivo (thigh muscle) showing less deep lesions with more bipolar energy modes (e.g., 5.4 ± 1.3 for unipolar only vs. 4.1 ± 0.8 mm for bipolar only, P < 0.05). (3) Ablation at the SVC did not result in device-related complications. All animals survived and were sacrificed after 7 ± 1 days except for one pig, which died immediately postoperatively from an unknown cause. Macroscopy and microscopy showed circumferential transmural SVC lesions. Conclusions: Temperature-controlled, power-limited RF energy with the PVAC™ is feasible for creating circumferential transmural lesions (SVC) that sometimes extended to neighboring structures. Lesion depth can be titrated by varying the bipolar:unipolar energy ratio. This novel ablation system paves the way for single-catheter ablation of AF. [ABSTRACT FROM AUTHOR]