Open-irrigated laser catheter ablation: influence of catheter irrigation and of contact and noncontact mode of laser application on lesion formation in bovine myocardium.

Lesions achieved by radiofrequency application increase with catheter irrigation and with catheter pressure on the endocardial surface. Purpose of this study was to test the influence of catheter irrigation and of contact vs. noncontact mode of laser application on lesion formation in bovine myocardium. By applying continuous wave 1,064 nm laser light via an open-irrigated catheter lesions were produced at 15 W (9.5 W/mm(2))/30 s (285 J/mm(2)), in stagnant blood (activated clotting time > 350 s) at 18 °C, on bovine myocardium. During flow rates of 15, 30, and 50 ml/min radiation was applied with the catheter end hole in contact (n = 10, each) or 2 mm away from the endocardial surface (n = 5, each). Lesions were evaluated morphometrically, and groups of lesions were compared by using the unpaired t test. By augmentation of irrigation flow from 15 to 30 ml/min, contact lesions increased significantly (p = 0.0001). A further increase of flow from 30 to 50 ml/min increased lesions significantly in depth (p = 0.0011) but not in width (p = 0.639) and volume (p = 0.218). Noncontact lesions were significantly smaller than contact lesions (p > 0.05). Lesions of homogenous coagulation necrosis were clear-cut and sharply demarcated from the surrounding normal myocardium. There was no occurrence of steam-pop with intramural cavitation or with tissue vaporization with crater or thrombus formation. It is suggested that by using an open-irrigated laser catheter as described in this study, catheter irrigation at flow rates of 30 to 40 ml/min are optimal for myocardial coagulation, and catheter pressure on the endocardial surface is not needed for lesion formation. Laser lesions can be achieved also without intimate endocardial catheter contact.