Maximal electrogram attenuation recorded from mini electrodes embedded on 4.5-mm irrigated and 8-mm nonirrigated catheters signifies lesion maturation.

Background: The electrograms (EGMs) recorded from mini electrodes (ME) placed on the tip of the ablation electrode allow more precise EGM monitoring during lesion formation. Our objective was to define the lesion boundaries and extracardiac injuries resulting from 60-second RF application versus RF application time titrated to maximal attenuation of the ME EGM in the atria and ventricles using 4.5-mm irrigated and 8-mm catheters.

Methods: RF lesions were placed in both atria and ventricles in 13 (30-35 kg) canines; 6 (4.5-mm OI) and 7 (8 mm). The RF application time was fixed at 60 seconds or terminated at maximal ME EGM amplitude attenuation.

Results: Pre/postablation pacing thresholds, EGM amplitudes, and lesion dimensions were not significantly different between maximal EGM attenuation and 60-second RF application using either catheter. Atrial lesion transmurality was also similar for both catheters and groups 91.2% (4.5 mm) and 96% (8 mm) when the RF was titrated to the maximal EGM attenuation and 94.2% (4.5 mm) and 95% (8 mm) with 60-second RF. The 60-second RF ablation, however, presented with significant extracardiac injuries to the lungs and esophagus, along with char formation. Deep ventricular lesions were noted with maximal EGM attenuation that were not different from the 60-second RF ablation.

Conclusion: Titration of the RF application time to the maximal EGM attenuation based on the ME recordings represents atrial lesion maturation and deep ventricular lesions. Prolonging the RF application results in greater extracardiac injury and char formation without increasing lesion size.