High power short duration ablation for atrial fibrillation: Safety and effectiveness

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As part of a session on novel mapping and ablation technologies of atrial fibrillation (AF) at the recent AF Symposium in Boston, USA (24–26 January), Andrea Natale gave a presentation on high power short duration ablation of AF, focusing on unmet needs and potential solutions. Here, alongside Domenico Giovanni Della Rocca and Luigi Di Biase, he gives a summary of his key points.

Atrial fibrillation (AF) has been described as an emerging epidemic of cardiovascular disease with significant effects on estimated disability and mortality and is rapidly turning into a major public health concern. At the present time, 5% of the over 65 population and up to 8.8% of the population between 80–89 years of age are affected by AF. Catheter ablation is the most effective rhythm control strategy in patients with AF. Since the pivotal study by Haissaguerre et al. documenting pulmonary vein (PV) triggers initiating AF, PV isolation has become the standard catheter-based ablation strategy. Achieving durable lesion formation either to isolate the PVs or to perform other needed ablations is of utmost importance to guarantee higher arrhythmia-free survival rates. Several factors are important to create effective radiofrequency (RF) lesions, such as the RF power, the duration of energy delivered, and the degree and stability of contact between tissue and ablation catheter.

The mechanism involved in lesion formation during higher-power, shorter-duration RF delivery is mostly through local conductive and resistive heating, which occurs early during RF application. On the contrary, distant conductive heating tissue damage is the predominant mechanism during longer RF applications.

To date, many centres prefer performing RF ablation using a power of 25–30W for durations of approximately 20–30 seconds at each point. The main concern of using higher-power RF energy for AF ablation is the potential of increasing the risk of complications. However, the use of higher-power RF energy delivery would result in reduced procedural and fluoroscopy times, as well as decreased total RF energy delivery, which may potentially lead to lower complication rates.

Despite a common clinical apprehension, results from animal and human studies have consistently confirmed that high-power, short-duration AF ablation effectively achieves transmurality with a lower rate of complications.

In 2003 we first reported the incidence of complications and outcomes of PV isolation using a closed-loop ablation catheter and guided by circular mapping (CM) alone (Group 1), CM and intracardiac echocardiography (ICE; Group 2), and CM and ICE with titration of RF energy based on visualisation of microbubbles by ICE (Group 3). In group 3, power was titrated upward (5-watt increments), watching for formation of type 1 bubbles (scattered microbubble reflecting early tissue overheating). When the type 1 microbubble pattern was seen, energy was titrated down by 5-watt decrements until microbubble generation subsided. Energy delivery was terminated when type 2 bubbles (brisk shower of dense microbubbles reflecting impending impedance rise) were seen. Monitoring microbubble generation to guide energy delivery allowed us to optimize lesion formation and adjust power delivery based on objective findings. This was the first study to observe that higher power delivery improves outcomes, as a result of more durable lesions, and significantly reduces the risk of PV stenosis, without increasing the incidence of periprocedural thromboembolic events.

Subsequently, with the introduction of open irrigation catheters, the microbubble power titration technique became no longer feasible.

Therefore, in 2007 we designed a study (2) which randomised AF patients to an ablation strategy using an open irrigation catheter (OIC) with a higher peak power (50 W, Group OIC-1) or OIC with lower peak power (35 W; Group OIC-2).

Although freedom from atrial arrhythmias was significantly higher in Group OIC-1 at 6 months, the main findings of our study were a higher incidence of steam pops, pericardial effusions, and gastrointestinal complaints when using an OIC at 50 W compared to 35 W without shortening the duration of RF energy delivery. These observations first supported the need for a shorter duration and a power of 45-50W, in order to avoid complications.

Similar findings were confirmed in animal models. Goyal V et al. (3) reported that the ablation time required to achieve 4mm-lesion depth decreases with increasing power; therefore, effective lesions can be achieved via high-power and short-duration RF applications, which could effectively reduce procedural time and concentrate the heating to superficial depths potentially reducing collateral injury.

Bjaskaran A et al. (4) observed in an ovine model that steam pops occurred in the settings of 40 W/30 s and 80 W/5 s in 8 and 11% of ablations, respectively; conversely, complications were absent in short-duration ablations of 50 and 60 W.

Achieving effective lesions via high-power RF applications for short duration is not only associated with better outcomes and low complication rates; this strategy also allows for shorter procedures and lower X-ray exposure.

As an example, Nilsson B et al. (5) observed a reduction in PV isolation time, mean fluoroscopy time, radiation dose, and total RF application time among patients undergoing ablations using 45 W/20 s compared to 30 W/120 s, whereas complication rate was similar.

A recent article published on Heart Rhythm Journal (6) analysed the complication rates of 4 experienced centers (including our Institute) performing AF ablations using irrigated-tip RF at power of 45–50 W in the left atrium for 5–15 seconds per lesion. The study included procedural data of 13,974 ablations in 10,284 patients, 99.2% of whom used an esophageal temperature monitoring. On the posterior wall, 11,436 ablations used 45–50 W for 2–10 seconds, and 2538 ablations had power reduced to 35 W applied for 20 seconds.

The average procedural, fluoroscopy and RF times were 116±41 min, 33±6 min and 39±30 min, respectively.

Overall, 33 cases (0.24%) of pericardial tamponade occurred and 7 of them required surgical intervention. Among the 7 patients who required surgery, 2 had left atrial perforations that were likely due to RF energy delivery, 3 did not seem to be related to ablation (1 coronary artery tear, 1 coronary sinus tear from a diagnostic catheter, and 1 right atrial perforation), whereas the site of bleeding could not be determined in the remaining 2 patients since hemostasis was achieved by the time the chest was opened.  The incidence of left atrial steam pops was 0.014%, and catheter char was not observed in any ablations.

Four patients developed atroesophageal fistula: 1 case occurred in 11,436 ablations (0.0087%) performed using 45–50 W power for short durations on the posterior wall, and 3 occurred in the 2538 patients (0.12%) ablated with 35 W on the posterior wall for longer durations (p= 0.021).

Of note, 2 of the 3 patients who developed a fistula in the 35 W group had not undergone esophageal temperature monitoring during a fluoroless procedure.

In conclusion, AF ablations performed at 45–50W for short durations appear effective and are associated with very low complication rates. High-power and short-ablation RF applications allow creating more localized and durable lesions, thereby limiting collateral injury, and may effectively reduce procedural and fluoroscopy times.

References

  1. Marrouche NF, Martin DO, Wazni O, et al. Phased-array intracardiac echocardiography monitoring during pulmonary vein isolation in patients with atrial fibrillation: impact on outcome and complications. Circulation. 2003;107(21):2710-6.
  2. Kanj MH, Wazni O, Fahmy T, et al. Pulmonary vein antral isolation using an open irrigation ablation catheter for the treatment of atrial fibrillation. J Am Coll Cardiol 2007;49:1634–41.
  3. Goyal V, Ali-Ahmed F, Patel M, et al. Low flow, high power, short ablation duration—is this the key to avoid collateral damage? Heart Rhythm 2017;14(Suppl):S464.
  4. Bhaskaran A, Chik W, Pouliopoulos J, et al. Five seconds of 50-60 W radio frequency atrial ablations were transmural and safe: an in vitro mechanistic assessment and force-controlled in vivo validation. Europace. 2017;19(5):874-80.
  5. Nilsson B, Chen X, Pehrson S, Svendsen JH. The effectiveness of a high output/ short duration radiofrequency current application technique in a segmental pulmonary vein isolation of atrial fibrillation. Europace 2006;8:962–5.
  6. Winkle RA, Mohanty S, Patrawala RA, et al. Low complication rates using high power (45-50 W) for short duration for atrial fibrillation ablations. Heart Rhythm. 2019;16(2):165-9.

Andrea Natale is the executive medical director at the Texas Cardiac Arrhythmia Institute at St David’s Medical Center in Austin, USA. One of the pioneers in ablation of atrial fibrillation, Natale is a faculty member at various universities and scientific medical institutions, and is the author, co-author or editor of hundreds of published articles and various books on pacing and electrophysiology.

Domenico Giovanni Della Rocca is an electrophysiology fellow at St David’s Medical Centre.

Luigi Di Biase is the section head of electrophysiology, director of arrhythmia services, and professor of medicine at the Albert Einstein College of Medicine, New York, USA.

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