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.