Effect of inter-electrode distance on bipolar intramural radiofrequency ablation.

Objectives: We aimed at evaluating bipolar radiofrequency ablation by correlating inter-electrode distance (ILD) with lesion dimensions and continuity.

Background: Previous reports indicated that bipolar radiofrequency (RF) current applied to two adjacent sites in vitro, synergistically increased lesion sizes greater than that observed for unipolar RF current delivery using the same electrodes.

Methods: Ablations were performed intramurally to ensure that each electrode surface (radius = 0.4 mm, area = 3.52 mm(2)) provided consistent contact with the myocardium. Ninety-six ablations were performed in four greyhounds using bipolar ablation needles with ILDs of 1, 2, 3, and 4 mm. An epicardial approach was used to ensure accurate positioning of the needles within the myocardium. Lesions were created using temperature-controlled RF delivery for a duration of 60 seconds to achieve 90 degrees C at the electrode proximal to the needle base. Lesion dimensions were determined histologically.

Results: Increasing the ILD, decreased lesion width (P = 0.003) but increased lesion depth (P = 0.001). Lesions remained continuous with ILDs of 1-3 mm but became discontinuous at 4 mm. Energy requirements during ablation increased with increasing ILDs.

Conclusion: Using the above parameters (electrode radius, RF power delivery, time) during bipolar ablation, lesion continuity was critically dependent on the ILD. The maximum ILD threshold to create contiguous overlapping lesions was 3 mm. Lesions of greater width were created using shorter ILDs. Clinically, greater control over lesion dimensions can be obtained by manipulating the ILD distance.