Modulating the Baseline Impedance

Abstract

Background-Radiofrequency ablation (RFA) 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 (VT) or frequent ventricular premature complexes (VPCs) refractory to ablation with irrigated catheters. Following a failed response to RFA, impedance was modulated by adding or repositioning return patches in attempt to decrease the circuit impedance. Ablation was repeated at similar location and power settings, and the effect on arrhythmia suppression and adverse effects were evaluated. Results-Six patients with idiopathic VPCs originating from the left ventricular summit (n=4) or papillary muscles (n=2), 6 patients with non-infarct related VT and 4 patients with infarct related VT had unsuccessful response to RFA at critical sites (number of applications: 10.4±3.1, power: 42.3±2.9W, duration: 55.3±25.5sec, impedance reduction: 14.6±3.5Ohms, low ionic solution was used in 81.25%). Modulating the return patches resulted in reduced baseline impedance (111.7 ± 8.2 vs. 134.7±6.6 Ohms, p<0.0001), increased current output (0.6±0.02 vs. 0.56±0.02Amp; p<0.0001) and greater impedance drop (16.8±3.0Ohms, 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 vs. 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 RFA. However, its combination with low-ionic solutions may increase the risk for steam-pops and neurological events.

Anterior vs. posterior position of dispersive patch during radiofrequency catheter ablation: insights fromin silicomodelling

“… 12 Prior clinical studies have suggested reducing baseline impedance can improve current delivery during RFCA by changing the location or number of dispersive electrodes, which may facilitate successful ablation in intramural ventricular substrates. 17 While most electrophysiology laboratories place the DP on the patient’s back, flanks, or thigh, some groups have advocated placing the DP anteriorly on the chest. A recent pilot study compared the anterior and posterior positions of the DP during AF ablation.…”

“…Remote factors, such as the amount of SAT underneath the DP, may affect the baseline impedance and hence the lesion size. 12 , 17 There are no conclusive data about differences of subcutaneous fat in anterior and posterior side. For instance, Störchle et al 18 found a difference of 3 mm greater thickness of anterior fat compared to posterior fat above fibrous septae.…”

Novel case of linear ultra-low cryoablation catheter for treatment of ventricular tachycardia

“…When using novel forms of energy delivery for achieving the increased tissue depth required for VT ablation, there is a balance between efficacy and risk. 8 Use of low-ionic irrigants may increase tissue depth but has been associated with steam pops. 4 Bipolar ablation between 2 catheters has been used but is also reported to be associated with steam pop, perforation, and clot formation.…”

“…7 However, more recent preclinical data have demonstrated that depths approaching 15 mm can be achieved with ULTC in ventricular tissue. 8 The first-in-human cavotricuspid isthmus ablation using ULTC demonstrated its capability as an effective energy source for typical flutter ablation. 7 Data from Cryocure-2 reported 85% freedom from atrial fibrillation at 12 months in patients with persistent atrial fibrillation after a single ULTC procedure.…”

“… 7 However, more recent preclinical data have demonstrated that depths approaching 15 mm can be achieved with ULTC in ventricular tissue. 8 …”