Background
Published data showed that high power delivery over a short period of time (HPSD) in radiofrequency-ablation (RFA) is highly efficient and safe while reducing procedure and RF time in pulmonary vein isolation. The QDot catheter (Biosense Webster) is a novel contact force ablation catheter. It allows automated flow and power adjustments depending on the local tissue temperature to maintain a target temperature during 90 watts, 4 seconds lesions. Aim of this study was to analyse intraprocedural and biophysical data as well as periprocedural safety of HPSD ablation using the QDot catheter in patients undergoing PVI for paroxysmal atrial fibrillation (PAF). We especially aimed to analyse steam pops during ablation and potential silent cerebral embolisms detected by cranial MRI. Furthermore, we sought to determine where lesions with 90 watts for 4 seconds were not durable and the ablation mode had to be changed from HPSD to medium power longer duration with 50watts for 15 seconds.

Methods

We included n=38 patients with PAF that were scheduled for PVI. We used the QDot catheter (Biosense Webster) in all patients with a temperature controlled HPSD ablation mode with 90 watts for 4 seconds. All patients underwent point-by-point cirumferential PVI. If focal reconnection occurred besides repeat ablation with 90watts for 4 seconds (QModePlus) the ablation mode was changed to 50watts for 15 seconds (QMode). After PVI all veins were checked with Adenosine for dormant conduction. N=18 patients underwent cerebral MRI to detect silent cerebral lesions. Furthermore, periprocedural complications and biophysical characteristics were analysed.

Results

Mean RF time was 8.1+/-2.8min, procedure duration was 100+/-41min. Average contact force, local temperature and impedance drop, applied current and energy as well as mean applied power are displayed for each segment of the pulmonary veins in Figure 1. The ablation mode had to be changed to QMode with 50watts for 15seconds significantly more often in the area of the Ridge and between the left veins compared to other locations. During Adenosine challenge n=12 (27.9%) patients showed dormant conduction. A total of n=16 steam pops where detected in n=13 patients (30.2%) while no pericardial tamponade occurred. No atrioesophageal fistulas where reported. Furthermore, no periprocedural thromboembolic complications occurred, while n=3 patients (17%) showed silent cerebral lesion in the cMRI scans (Figure 2)(Table 2).

Conclusion

Temperature controlled high power short duration ablation with 90watts for 4 seconds using the QDot catheter appeared to be fast, efficient and safe. Procedure and RF time where short, dormant conduction rate during Adenosin testing was low while no major complications occurred. Nevertheless, especially in areas with thicker tissue like the Ridge the ablation mode had to be changed to lower power for longer duration to achieve transmural lesions. Surprisingly, despite optimized temperature control and power adjustment steam pops occurred in 30% of patients, while none of them lead to tamponade or to clinical or neurological deficits. Clinical relevancy of these steam pops has to be evaluated in larger trials.