Irrigated Microwave Catheter Ablation Can Create Deep Ventricular Lesions Through Epicardial Fat with Relative Sparing of Adjacent Coronary Arteries.

Background: Radiofrequency ablation depth can be inadequate to reach intramural or epicardial substrate, and energy delivery in the pericardium is limited by penetration through epicardial fat and coronary anatomy. We hypothesized that open irrigated microwave catheter ablation can create deep myocardial lesions endocardially and epicardially though fat while acutely sparing nearby the coronary arteries. Methods: In-house designed and constructed irrigated microwave catheters were tested in in vitro phantom models and in 15 sheep. Endocardial ablations were performed at 140 to 180 W for 4 minutes; epicardial ablations via subxiphoid access were performed at 90 to 100 W for 4 minutes at sites near coronary arteries. Results: Epicardial ablations at 90 to 100 W produced mean lesion depth of 10 +/- 4 mm, width 18 +/- 10 mm, and length 29 +/- 8 mm through median epicardial fat thickness of 1.2 mm. Endocardial ablations at 180 W reached depths of 10.7 +/- 3.3 mm, width of 16.6 +/- 5 mm, and length of 20 +/- 5 mm. Acute coronary occlusion or spasm was not observed at a median separation distance of 2.7 mm (IQR, 1.2-3.4 mm). Saline electrodes recorded unipolar and bipolar electrograms; microwave ablation caused reductions in voltage and changes in electrogram morphology with loss of pace-capture. In vitro models demonstrated the heat sink effect of coronary flow, as well as preferential microwave coupling to myocardium and blood as opposed to lung and epicardial fat phantoms. Conclusions: Irrigated microwave catheter ablation may be an effective ablation modality for deep ventricular lesion creation with capacity for fat penetration and sparing of nearby coronary arteries because of cooling endoluminal flow. Clinical translation could improve the treatment of ventricular tachycardia arising from mid myocardial or epicardial substrates.