Reliability of luminal oesophageal temperature monitoring during pulmonary veins isolation

The paper by Knecht et al.1 has the merit of addressing an important issue concerning monitoring of the luminal oesophageal temperature (LET) during radiofrequency ablation procedures for the treatment of atrial fibrillation. The authors point out that LET value measured by an oesophageal thermal probe not necessarily corresponds to the actual maximum oesophageal temperature, since the lumen width offers the possibility that a flexible probe takes a path avoiding the hottest spot. Certainly, a useful information to clinicians. I only wish to add some comments. In the section ‘Anatomical relationship’ the authors suggest that ‘The S-shaped 12-pole LET [Circa] probe is wider and may potentially … cover the area of interest better. An alternative option to address this problem is an oesophageal infra-red thermography catheter.’ The key word in the first statement is ‘may’: will the ‘S’ actually take the optimal position? If the S orientation is random, not only the electrodes may miss their target as well but also the oesophagus may undergo a displacement, and if it gets closer to the ablator, then the risk of lesions is increased. In their 2013 comparative study between LET monitoring with the Circa probe vs. a single sensor probe, Carroll et al.2 wrote: ‘… despite an increased rate of temperature rise detection, there was a significantly increased incidence of esophageal injury with the multi-sensor probe’ (temperature beyond 39 °C were reached in 75% of cases vs. 39%, with esophageal injuries in 46% vs. 29% of cases)’. This suggests that the S-shape (rather than the electrode numbers) may have been responsible for the worse outcome. Concerning the infra-red thermography catheter, it usually measures abnormally high-luminal temperatures (order ∼60 °C: see Crozier et al3 ref. 14 in the paper). At the ablation site (typical temperature 70–80 °C) infrared waves are emitted with ∼20 μm wavelength for which the expected penetration depth is order 1 cm (see e.g. Jacques4). Thus, in my opinion the infrared sensor can actually ‘see’ the heat source through the oesophageal wall. Conflict of interest: Antonio Fasano declares to be R&D manager and Scientific Director at FIAB, Italy, manufacturing oesophageal thermal probes.