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Shorter lesions at high radiofrequencies are most effective in ablation for atrial fibrillation

The findings from PiLOT-AF study (radiofrequency Power, target LSI and Oesophageal Temperature alerts during Atrial Fibrillation ablation), which was presented yesterday at EHRA EUROPACE - CARDIOSTIM 2017, indicate that shorter lesions at higher radiofrequency (RF) power result in fewer oesophageal temperature alerts, higher rates of first-pass pulmonary vein isolation (PVI), and lower rates of acute pulmonary vein reconnection (PVR) than longer lesions at lower power during catheter ablation for atrial fibrillation (AF).  

Invasive Electrophysiology and Ablation
Atrial Fibrillation


Doctor Milena Leo (Oxford University Hospitals NHS Foundation Trust, Oxford, UK) and colleagues report that further large randomised controlled trials are required to formally assess differences in freedom from AF and the incidence of severe complications.

Oesophageal heating is a collateral effect of RF catheter ablation for AF on the left atrial (LA) posterior wall. It is attributed to conductive heat transfer from the ablation site, a time-dependent process. Lower powers are routinely used to prevent this damage, requiring a longer duration of RF applications to reach the target lesion size index (LSI). LSI is a recently introduced parameter to predict the RF lesion size and depth, and thus permanence of effect, and it is automatically and continuously calculated during AF ablation by a non-linear function that combines power, contact force, and ablation duration. An LSI of 5 on the LA posterior wall is currently suggested as a measure of lesion transmurality to maximise the chance of durable PVI. The impact of different target LSI values on oesophageal heating is currently unknown.

Dr. Leo said: “Oesophageal temperature alerts are very common during ablation on the LA posterior wall and, regardless of the chosen power, they tend to occur before achieving the suggested LSI of 5. Whether it is safer to use higher powers for shorter times, or lower powers for longer times, and whether a lower target LSI value represents a better compromise between safety from oesophageal heating and lesion transmurality and durability, it is not known. This study tested the impact of different combinations of RF power and target LSI during AF ablation on the LA posterior wall in terms of the incidence of oesophageal temperature alerts and acute procedural success.” 

There were 80 patients in the randomised prospective trial (59 males, mean age 59 ± 9.57 years), elected to catheter ablation for symptomatic paroxysmal/persistent AF. They were split into four groups using different powers (20W and 40W) and different target LSI (4 or 5). The primary endpoint was the rate and characteristics of oesophageal temperature alerts (defined as oesophageal temperature rise >39oC) during the ablation, with secondary endpoints the rate of first pass PVI, acute PVR, and total RF time.

Leo et al found that the occurrence of oesophageal temperature alerts was similar in each group. However, the rate of oesophageal temperature alerts per patient was significantly higher in group 4 (the group where a low power was used for the longest time). This was also the study arm with the lowest occurrence of first pass PVI, requiring a longer total RF time, and the highest occurrence of acute PVR. A target LSI of 4 was associated with a similar acute procedural success rate as an LSI of 5.

“These results suggest a high efficacy and safety profile of short RF applications at high powers for AF ablation on the LA posterior wall. Larger randomised controlled trials with follow-up data are needed to confirm the results of our study. It is important to expand the sample size in order to confirm the differences in acute procedural success and to directly assess the incidence of complications, rather than surrogate safety endpoints such as oesophageal temperature alerts in our study. Follow-up data are fundamental to assess differences in freedom from AF,” Dr. Leo commented.

Late Breaking Trial Session: Atrial fibrillation ablation

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