The creation of linear contiguous lesions in the atri with an expandable loop catheter

OBJECTIVES This article describes catheter system designed to create linear atrial lesions and identifies electrophysiologic markers that are associated with the creation of linear lesions. BACKGROUND Atrial fibrillation (Afib) is the most common arrhythmi in humans and causes significant morbidity. The success of surgical interventions has provided the impetus for the development of catheter-based approach for the ablation of Afib. METHODS We tested catheter system with 24 4-mm ring electrodes that can create loops in the atria. The electrodes can be used to record electrical activity and deliver radiofrequency power for ablation. In 33 dogs, 82 linear lesions were generated using three power titration protocols: fixed levels, manual titration guided by local electrogram activity and temperature control. Bipolar activity was recorded from the 24 electrodes before, during and after lesion generation. Dat were gathered regarding lesion contiguity, transmurality and dimensions; the changes in local electrical activity amplitude; the incidence rate of rapid impedance rises and desiccation or char formation; and rhythm outcomes. RESULTS Catheter deployment usually requires <60 s. Linear lesions (12 to 16 cm in length and 6 ± 2 mm wide) can be generated in 24 to 48 min without moving the catheter. Effective lesion formation can be predicted by decrease of greater than 50% in the amplitude of bipolar recordings. Splitting or fragmentation of the electrogram and increasing pacing threshold (3.1 ± 3.3 mV to 7.1 ± 3.8 mV, p < 0.01) are indicative of effective lesion formation. Impedance rises and char formation occurred at 91 ± 12°C. Linear lesion creation does not result in the initiation of Afib. However, atrial flutter was recorded after the completion of the final lesion in 3/12 hearts. When using temperature control, no char was noted in the left atrium, whereas 8% of the right atrium burns had char. CONCLUSIONS This adjustable loop catheter forces the atrial tissue to conform around the catheter and is capable of producing linear, contiguous lesions up to 16 cm long with minimal effort and radiation exposure. Pacing thresholds and electrogram amplitude and character are markers of effective lesion formation. Although Afib could not be induced after lesion set completion, sustained atrial flutter could be induced in 25% of the hearts.