Background
Ablation of atrial fibrillation (AF) using radiofrequency (RF) energy is considered an effective and safe treatment option (1). Due to technical and procedural optimization in RF ablation long-term success rates for pulmonary vein isolation (PVI) in patients with paroxysmal atrial fibrillation (PAF) are satisfying. Nevertheless, the main cause for AF recurrence is related to pulmonary vein (PV) reconnection due to initially non-transmural lesions and tissue edema (2;3).
Recently published data demonstrate 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 PVI (4). Potential reasons for a superiority of HPSD ablation are diverse. A shift of increased resistive heating and decreased conductive heating which is outweighed using standard ablation with 30 to 40 watts leads to a better lesion to lesion contiguity and transmurality. A larger HPSD lesion diameter with less lesion depth compared to standard ablation lesions results in a reduced risk for collateral damage of extra-cardiac structures like esophagus or phrenic nerve (5). Furthermore, as shown by Anter et al, catheter stability is improved due to shorter ablation duration using HPSD. Nevertheless, HPSD has its limitations with reduced effectiveness in areas with thicker atrial tissue like the mitral isthmus (6).
Two HPSD ablation modes are currently available. In a temperature controlled ablation mode novel ablation catheters with very distal temperature probes allow automated flow and power adjustments depending on local tissue temperature. In a power controlled ablation mode using conventional ablation catheters with rather proximal temperature probes, power is ramped up to a fixed power without automated temperature dependent adjustments of flow or power. While in most HPSD publications power controlled standard ablation catheters are used only a few studies are published with specifically designed catheters for the use of temperature controlled HPSD (6;7).
The QDot catheter (Biosense Webster Inc., Irvine, California) is a novel contact force ablation catheter. It allows automated flow and power adjustments depending on the local tissue temperature to maintain a targeted temperature. During ablation using the QMode+ with 90 watts for a maximum of 4 seconds, the QDot catheter only adjusts power depending on local temperature. Additional irrigation adjustment is only possible using the QMode with a maximum of 50watts (figure 1). Aim of this study was to analyse intraprocedural and biophysical data as well as periprocedural safety of very HPSD ablation (QDot catheter with 90watts for 4 seconds) in patients undergoing PVI for paroxysmal atrial fibrillation (PAF). Of special interest was the occurrence of steam pops during ablation and potential silent cerebral embolisms detected by cranial MRI. Furthermore, we sought to determine sites where lesions with 90 watts/4 seconds where not durable and the ablation mode had to be changed from HPSD to medium power and longer duration with 50watts for 15 seconds.