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(Circulation. 1996;94:253-257.)
© 1996 American Heart Association, Inc.

Articles

Low-Temperature Mapping Predicts Site of Successful Ablation While Minimizing Myocardial Damage

Jean-Marc Cote, MD; Michael R. Epstein, MD; John K. Triedman, MD; Edward P. Walsh, MD; J. Philip Saul, MD

Children's Hospital, Department of Cardiology, Department of Pediatrics, Harvard Medical School, Boston, Mass.

Correspondence to J. Philip Saul, MD, Children's Hospital, Department of Cardiology, 300 Longwood Ave, Boston, MA 02115. E-mail psaul@cardio.tch.harvard.edu.

Background Temperatures near 50°C can cause reversible loss of excitability in myocardial cells.

Methods and Results Low-temperature, short-duration applications of radiofrequency energy were used to determine the adequacy of electrophysiological mapping of accessory pathway (AP) locations in 15 patients at 27 target sites using a closed-loop, temperature-controlled generator set to 50°C. Energy was delivered until evidence of conduction block, or for a maximum of 10 seconds. If AP block occurred, a full 70°C set point radiofrequency application was delivered to the same site. In the absence of AP block, tests with higher temperature settings (60°C and 70°C) were delivered to determine if inadequate temperature or catheter position led to failure of the initial 50°C test. At 15 successful target sites where permanent AP block was achieved, the 50°C test resulted in AP block in 14 (93%). Conduction returned in 13 of 14 APs after radiofrequency power was turned off. The time to block for the 70°C applications was significantly shorter than for the 50°C tests, and the peak temperature achieved was significantly higher. At unsuccessful sites where permanent AP block was not achieved, no block was induced with 11 of 12 tests at 50°C, 6 of 6 tests at 60°C, and 1 of 2 tests at 70°C, suggesting that failure was due to incorrect catheter position. The sensitivity and positive predictive values of a 50°C test identifying a successful site were >90%.

Conclusions Low-temperature radiofrequency applications that cause transient AP block predict permanent success when a higher-temperature application is delivered at the same site. The time to achieve conduction block is a function of the temperature set point, and low-temperature tests produce reversible conduction block, suggesting minimal permanent injury.

Key Words: ablation • mapping • electrophysiology

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