High-Power Short-Duration Ablation

Turn Up the Heat to Cool Down the Esophagus

Roger A. Winkle MD


J Cardiovasc Electrophysiol. 2019;30(10):1884-1885. 

Since the discovery of the frequent pulmonary vein origin of atrial fibrillation (AF) and the introduction of radiofrequency (RF) ablation therapy, there have been many improvements to make the procedure safer and more effective. These have included introduction of open irrigated tip catheters, more accurate three-dimensional mapping systems, better mapping catheters, and the use of general anesthesia and jet ventilation. There have also been many surrogate endpoints developed to monitor lesion formation including loss of electrogram voltage, impedance drop, noncapture of ablated tissue after ablation and loss of capture during RF energy delivery (pace and ablate), and the proprietary estimators of lesion creation such as the ablation index (AI) and the LSI. A change from the use of low power (25–30 W) and long duration (30–60 seconds) ablation to high power (45–50 W) and short duration (5–15 seconds), termed high-power short-duration (HPSD) ablation, appears to be yet another major improvement. The technique of HPSD ablation is not new but has recently received wide attention and adoption by electrophysiologist doing RF ablation.

The first report of HPSD ablation was published in 2006 by Nilsson et al.[1] They compared 45 patients undergoing ablation at 30 W for 120 seconds to a group of 45 patients undergoing ablation with 45 W for 20 seconds. Both groups had similar long-term freedom from AF and complication rates. HPSD isolated more veins, had shorter fluoroscopy times and had a significant reduction in RF times (19 ± 14 vs 36 ± 17 minutes, P < .001) and procedure times (127 ± 57 vs 94 ± 33, P = .02) defined as time from first to last RF application. In 2008, Bunch and Day[2] reported the use of a "painting" technique where they stayed at each site for 2 to 5 seconds at 50 W power and moved the catheter back and forth until a small area was devoid of electrograms. They had no esophageal injuries and an 85% freedom from AF after one or two ablations with a mean follow-up of almost 1 year. In 2011, we reported our experience[3] with a similar technique termed "perpetual motion" leaving the catheter at each site for 3 to 10 seconds using 40, 45, or 50 W of RF. Increasing the power for a reduced time resulted in shorter fluoroscopy and procedure times, a reduction in RF time to 24.7 minutes with a similar rate of complications and better single procedure outcomes. In 2007, Kanj et al[4] compared patients undergoing open irrigated tip catheter ablation at 35 W and 50 W. Although they increased the power to 50 W, they did not shorten the duration of the energy delivery. The 50 W ablations had shorter fluoroscopy times, atrial instrumentation times, and a better 6-month freedom from AF (82% vs 68%). Unfortunately, they noted a significantly higher rate of complications at 50 W including steam pops, pericardial effusions, moderate edema, and gastrointestinal complaints. They postulated that when using higher power, one should shorten the duration of the energy delivery.

Despite these early promising reports, HPSD ablation did not gain much initial traction. There was widespread concern among the electrophysiologists that it might be too dangerous and result in more complications, especially atrial esophageal fistulas. These concerns have been partially dispelled by a multicenter report on 13 974 ablations done in approximately 10 284 patients including the use of HPSD on the posterior wall.[5] The complications rate was remarkably low, and this has encouraged many to start utilizing HPSD. Baher et al[6] used gadolinium-enhanced magnetic resonance imagings and endoscopy to evaluate 574 patients undergoing ablation at 50 W for 5 seconds and compared them with 113 patients undergoing ablation at less than 35 W for 10 to 30 seconds. Like the earlier studies, with HPSD they found a marked reduction in procedure time from 251 ± 101 to 149 ± 65 (P < .001) and RF ablation time from 55.0 ± 19.2 to 37.9 ± 13.9 (P < .001). The two groups had similar 3-year freedom from AF and there was no difference in esophageal abnormalities, even though the HPSD group had almost twice as many patients undergoing posterior wall isolation.

In this issue of the Journal of Cardiovascular Electrophysiology, Vassallo et al[7] compare ablation data in a small group of 90 patients with AF. In 45 patients, they used 30 W of power for 30 seconds and in another 45 patients they used 45 to 50 W of power for 6 seconds. Like previous reports, they found a reduction in total procedure time from 148 ± 30.6 to 106 ± 23 minutes (P = .00001) and total RF time from 4558 ± 1998 to 1909 ± 675.8 seconds (P < .00001). The number of patients in this study was too small for meaningful long-term freedom from AF comparison. However, there was a nonstatistically significant trend toward a better outcome with HPSD with AF recurrence at 1 year in 31.4% of the patients undergoing standard ablation compared with only 17.1% of the patients in the HPSD group.

One of the theoretical advantages of HPSD ablation is that there may be more local heating of the tissue in the atrial myocardium and less distant collateral damage to structures such as the esophagus. Local resistive heating peaks early during RF energy delivery and the longer duration application of RF energy results in more conductive heating of the distant tissue, which can damage the unwanted structures. With HPSD, the short duration of RF energy application should result in more local resistive heating and local atrial tissue destruction without conductive heating of more distant tissue, such as the esophagus, later in a long duration burn. Using computer models and tissue preparations, Bourier et al[8] showed that HPSD resulted in larger but shallower lesions and that the maximal lesion growth was in the first 10 seconds of RF energy delivery. The current study would seem to confirm this theoretical benefit of HPSD for the first time in patients. In the standard ablation group, they noted an esophageal temperature rise in 74.6% of the patients. However, in the HPSD group the temperature rise was noted in only 51.2% of the patients (P = .0001).

As the authors of the current study point out, it was a relatively small study with retrospective nonrandomized data. Nonetheless, it is consistent with prior observational studies in the literature and provides important new information about the incidence of esophageal heating with conventional vs HPSD RF energy delivery. Even if the outcomes with the two techniques are equivalent, the significant reduction in RF energy time and especially the shortening of procedural time is quite important. Shorter procedure times will allow for more cases to be done in a day in one electrophysiology laboratory. Also, since in any procedure, longer procedure times generally results in more complications, it should lead to a reduction in complications independent of tissue heating. Given the rarity of atrial esophageal fistulas, it may be impossible to ever prove definitively that HPSD results in fewer cases of this dreaded complication compared with the conventional power. However, the observation of less esophageal heating in the current study should reassure electrophysiologists that HPSD is at least as safe as conventional ablation and should help to accelerate the widespread adoption of this technique. Although there are many new technologies in the pipeline, such as one-shot RF ablation and electroporation, they will require substantial time to develop. The beauty of HPSD is that it can be done with currently available catheters and ablation systems. Any electrophysiologist who would like to markedly shorten the procedure time can do so immediately by adopting this technique. There appears to be no worsening of complications and outcomes and there is a suggestion that both might be better with HPSD.