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

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Abstract
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.

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