Determinants of Lesion Size During Radiofrequency Catheter Ablation: The Role of Electrode‐Tissue Contact Pressure and Duration of Energy Delivery

Determinants of Radiofrequency Lesion Size. Introduction: Radiofrequency (RF) catheter ablation is a promising modality in the management of cardiac arrhythmias, but the optimum protocol for energy delivery has not yet been determined. The purpose of this study was to examine the effects of varying electrode‐tissue contact pressure and varying duration of RF energy delivery on the size of the resultant lesion in an in vitro model of isolated perfused and superfused canine myocardium. Methods and Results: RF power (500 kHz) was delivered through the tip of a specially‐designed thermistor‐tipped 1.6‐mm diameter electrode mounted on an adjustable fulcrum so that contact force could be varied. RF power was adjusted to maintain a constant electrode‐tissue interface temperature of 80°C during lesion production. Seventy‐nine lesions were created with a 90‐second RF energy delivery, and a contact force that was varied between 0 and 400 newtons (N) (0‐41 g). Lesions produced with a small contact force (10 N) were significantly larger than those with a contact force of zero (width 5.5 mm vs 3.8 mm, P <0.0002), but not significantly different from those produced with the maximum contact force of 400 N (width 6.5 mm, P = NS). However, the greater contact force significantly decreased the power required to maintain a constant electrode‐tissue interface temperature. Ninety‐six lesions were then created using a constant contact force, but duration of energy delivery was varied from 10 to 600 seconds. Lesion size grew monoexponentially with time. The t 1/2 of lesion growth was 7.6 and 9.6 seconds for depth and width, respectively. Conclusion: Thus, close electrode‐tissue contact is essential for adequate lesion formation during RF ablation of myocardium, but increasing contact force does not significantly increase lesion size if power is adjusted to maintain a constant electrode‐tissue interface temperature. In order to approach steady‐state and maximize lesion size, duration of RF energy delivery should be at least 40 seconds.