For approximately 25 years, ablation of cardiac tissue by radiofrequency energy has been used to halt arrhythmic conduction in the heart. Efficacy of cardiac ablation for the treatment of atrial fibrillation and other arrhythmias depends on the completeness of lesions and their ability to block arrhythmic conduction without disturbing sinus rhythm. A rapid index of lesion quality measured during surgical ablation procedures may improve the probability of long-term success in patients. Trans-lesion stimulus-excitation time delay was evaluated as an intraoperative indicator of lesion completeness. Time delay was shown to be significantly different for complete vs. incomplete lesions. Further, it was shown that activation path length corresponds with time delay, providing an explanation for post-ablation increases in time delay.

Time delay of excitation measured on either side of a lesion having a small gap may increase after ablation, and then recover over time. This recovery would be important since the lesion may then be insufficient to suppress conduction. Although the Langendorff rabbit model used in this project is insufficient to observe long-term cardiac remodeling phenomena, short term recovery over tens of minutes post-ablation is practical with our apparatus. This would be useful for clinicians who may monitor time delay acutely in their patients before withdrawing the ablation probe. Complete recovery following initial trans-lesion block occurred within 5 minutes after ablation, while partial recovery occurred at 14.4 ± 1.0 minutes after ablation. Recovery of the activation complex occurred at 23.7 ± 7.9 minutes after ablation.

Hyperthermia affects the myocardium in a wide variety of ways, including denaturation of myofilaments, disruption of the sarcolemmal membrane and/or denaturation of membrane ion channels, alterations in cellular metabolism, and alterations in intracellular and transmembrane calcium handling. Depending on the extent of the hyperthermic damage sustained during ablation, gaps within lesions may recover following a return to physiological temperature. Conduction recovery may occur following initially successful lesion formation, and it may allow arrhythmic conduction to resume or may result in the formation of one or more new arrhythmias. Further, the temperature of tissue within a small gap of an ablation lesion may correlate with the recovery of myocytes within these gaps. Thus temperature monitoring of ablated tissue may be a useful supplement for monitoring block by measuring time delay.

Temperatures within lesion gaps during complete recovery reached a maximum value of 63.44° C, while temperatures within lesions gaps during partial recovery reached a value of 52.7 ± 3.0° C. In lesions which did not show initial block, supernormal conduction was observed following ablation. Decreases in time delay of 17.8 ± 2.6% were observed, and minima of time delay occurred 28.0 ± 4.0 seconds after ablation. A relationship between temperature and time delay was observed in cases where supernormal conduction occurred, but a relationship was not observed in cases where post-ablation block occurred.