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Eur J Cardiothorac Surg 2001;20:956-960
© 2001 Elsevier Science NL

Effectiveness of two radiofrequency ablation systems in atrial tissue

^a Department of Cardiothoracic Surgery, University of Cape Town, Cape Town 7925, South Africa
^b Herzzentrum, University of Leipzig, Leipzig, Germany

Received 11 June 2001; received in revised form 6 August 2001; accepted 7 August 2001.

Corresponding author. Current address: Cardiac Directorate, University Hospital of Wales, Heath Park, Cardiff, CF14 4XW, UK. Tel.: +27-21-406-6181; fax: +27-21-448-1145
e-mail: uvonopp{at}thoracic.cts.uct.ac.za

Objective: The efficacy of the left atrial radiofrequency ablation procedure, for the curative treatment of atrial fibrillation, is dependent upon obtaining a confluent transmural line of hyperthermic cellular death. We compare the in vitro effectiveness of obtaining transmural hyperthermic cellular death (>55°C) of both the Osypka single electrode and Boston Scientific Thermaline multi-electrode radiofrequency systems. Methods: Isolated cadaver porcine hearts were used to measure epicardial temperatures either ‘central’ or at the ‘edge’ in relation to an endocardial applied radiofrequency electrode. Reference set point was 70°C, and 4–6-mm thick atrial tissue was used for all applications. ‘Edge’ temperatures with the Boston Scientific unit were measured whilst activating both adjacent electrodes. Results: Boston Scientific: Probe temperature closely approximated the set point. ‘Central’ epicardial temperature was lower than probe temperature until after 40 s application (P<0.05), 55°C was reached at 50 s, maximal mean temperature 63.0±8.9°C was reached at 100 s. Epicardial ‘edge’ temperature remained lower than probe temperature for the entire 120 s (P<0.05). Osypka: Probe temperature tended to overshoot the set point. ‘Central’ epicardial temperature paralleled and occasionally exceeded probe temperature reaching 55°C within 10 s, maximal mean temperature 76.3±12.7°C was reached at 10 s and exceeded the set point thereafter. ‘Edge’ temperature was no different to probe temperature or ‘central’ epicardial temperature. The mean epicardial temperatures produced with a 65°C set point was no different to that with the 70°C set point, except for a lower final temperature at 60 s. Conclusions: The Boston Scientific system (70°C set point) requires a minimum in vitro application of 40 s to transmurally increase 4–6 mm atrial tissue temperature above 55°C, and 120-s duration per application would appear to be a reasonable clinical recommendation. The Osypka system transfers thermal energy more effectively, requiring less than 10 s in vitro to achieve a similar transmural temperature, and a 30-s application can be recommended. However, a tendency to overshoot both probe and set point temperature, suggests that a lower set point of 65°C might be safer and as effective.

Key Words: Heart • Atrium • Atrial fibrillation • Treatment • Radiofrequency • Hyperthermia

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