Submyocardial Pacing Threshold Distribution During Cold Saline Application; Exploring Reversible Arrhythmia Inhibition.

Introduction: Cold saline application through an irrigation catheter may induce reversible inhibition of submyocardial excitation, which may be used to identify in advance an ideal site for radiofrequency (RF) energy delivery around delicate areas.

Methods: An open irrigation catheter was positioned vertically or parallel with 10-g contact on coronary perfusing porcine hearts and the contacted myocardium was cooled by cold saline at 4°C (20 mL/min). A temperature electrode was inserted 2 mm below the myocardial surface (intra-myocardial temperature at approximately 2 mm below the surface [Temp-BS]). Pacing threshold inside the ventricular wall was measured using an eight-pole electrode plunge needle inserted 5-8 mm close to the ablation catheter, and percent increase of the pacing threshold by the cold saline application (%increase-PT) was calculated.

Results: During cooling, pacing at 10 V from the myocardial surface interrupted constant capture in 7/10 experiments in vertical and in 9/10 experiments in parallel ablation catheter contact. Minimum Temp-BS was not different in both catheter contact positions (25.9 ± 4.0°C in vertical vs. 25.4 ± 2.6°C in parallel). Large % increase-PT on the surface myocardium decreased as the myocardial depth became deeper, and > 150% increase was at a depth approximately 2-3 mm from the surface and > 120% increase around 6-7 mm from the surface. After cessation of cold saline application, the increased %increase-PT recovered to the pre-cooling values.

Conclusions: Cold saline application through an irrigation catheter reversibly inhibited submyocardial excitation. This simple method may have the potential to pre-determine the ideal ablation site in sensitive areas of the heart, although further studies and technological adjustments are required before clinical use.