Modulating the Baseline Impedance: An Adjunctive Technique for Maximizing Radiofrequency Lesion Dimensions in Deep and Intramural Ventricular Substrate

Background: Radiofrequency ablation of intramural ventricular substrate is often limited by insufficient tissue penetration despite high energy settings. As lesion dimensions have a direct and negative relationship to impedance, reducing the baseline impedance may increase the ablation effect on deep ventricular tissue. Methods: This study included 16 patients with ventricular tachycardia or frequent ventricular premature complexes refractory to ablation with irrigated catheters. After a failed response to radiofrequency ablation, impedance was modulated by adding or repositioning return patches in an attempt to decrease the circuit impedance. Ablation was repeated at a similar location and power settings, and the effect on arrhythmia suppression and adverse effects were evaluated. Results: Six patients with idiopathic ventricular premature complexes originating from the left ventricular summit (n=4) or papillary muscles (n=2), 6 patients with noninfarct related ventricular tachycardia and 4 patients with infarct-related ventricular tachycardia had unsuccessful response to radiofrequency ablation at critical sites (number of applications: 10.4±3.1, power: 42.3±2.9 W, duration: 55.3±25.5 seconds, impedance reduction: 14.6±3.5 Ω, low-ionic solution was used in 81.25%). Modulating the return patches resulted in reduced baseline impedance (111.7±8.2 versus 134.7±6.6 Ω, P<0.0001), increased current output (0.6±0.02 versus 0.56±0.02 Amp; P<0.0001) and greater impedance drop (16.8±3.0 Ω, P<0.001). Repeat ablation at similar locations had a successful effect in 12 out of 16 (75.0%) patients. During a follow-up duration of 13±5 months, 10 out of 12 (83.3%) patients remained free of arrhythmia recurrence. The frequency of steam pops was similar between the higher and lower baseline impedance settings (7.1 versus 8.2%; P=0.74). Conclusions: In patients with deep ventricular substrate, reducing the baseline impedance is a simple, safe, and effective technique for increasing the effect of radiofrequency ablation. However, its combination with low-ionic solutions may increase the risk for steam pops and neurological events.