Contact force and ablation assessment of surgical bipolar radiofrequency clamps in the treatment of atrial fibrillation

OBJECTIVES Atrial fibrillation is treated surgically by creating conduction block lesions. Radiofrequency (RF) lesions have reduced efficacy compared to cut-and-sew'. Catheter ablation studies demonstrate a relationship between lesion depth and contact force. We hypothesized that contact force and lesion depth are dependent on design of the bipolar surgical RF clamps. METHODS Hinged and parallel jaw style RF clamps were studied. Muscle samples were clamped with pressure-sensitive film at increasing tissue thicknesses. Films were analysed determining clamp pressure profiles. A sheep model was utilized for ablation testing using each clamp style until the device indicated transmurality. Separate muscle areas had 1, 2 or 3 burns applied. The muscle was excised, sectioned every 1cm and stained for lesion depth and fat thickness analysis. RESULTS Pressure profiling comparing the proximal and distal segments of each clamp style demonstrated only one statistically significant difference in the parallel clamp; the hinged clamp had statistically significant differences (P0.03) for all tissue thicknesses. There was no evidence for differences in the proximal lesion depth of both clamps (P=0.13) but deeper distally in the parallel clamp (10.17mm vs 8.02mm, P=0.003). The logistic regression analysis demonstrated increased odds of transmurality with parallel clamps at 1, 2 or 3 burns (P=0.03, P=0.003 and P=0.002). Every 1mm increase in overlying fat decreased likelihood of transmurality by 11% (P<0.05). CONCLUSIONS The parallel and hinged clamps have different pressure profiles with higher likelihood of transmurality using the parallel clamp. Fat reduces the ability of RF to deliver a transmural lesion. These findings have implications for optimal surgical RF ablation technique.