Laser ablation of normal and diseased human ventricle

The feasibility and safety of laser photoablation in patients with ventricular tachycardia (VT) and accessory pathways are currently being examined. We studied the qualitative and quantitative effects of argon laser radiation on normal and diseased human ventricle to determine the relationship between the size of tissue lesion and delivered energy. Twenty-nine human ventricle segments (normal ventricle = 10; diseased ventricle = 19) were excised from patients during mapping-guided subendocardial resection for VT (seven patients), mitral valve replacement (five patients), or immediately at autopsy (three patients). Lasing was performed with a 15 W argon laser coupled to a 300 μm optical fiber. Incremental laser discharges from 10 to 1000 J were delivered in air and saline with the optical fiber 5 mm from the endocardial surface. Gross and microscopic damage was quantified and correlated with laser discharges at low (10 to 100 J), intermediate (101 to 300 J), and high (> 300 J) energies. Histologic examination of laser-induced lesions in both normal and diseased human ventricle in either medium showed focal thermal injury with crater formation, vacuolization, and coagulation necrosis of endocardium and myocardium. In normal ventricle, mean lesion diameter and depth in air increased with increasing energies up to 300 J. Over 300 J, tissue perforation was frequently observed. In saline, the mean lesion depth was significantly reduced ( p < 0.02) at comparable energies. In diseased ventricle, mean lesion diameter and depth in air and saline also increased with increasing laser discharge energies up to 300 J. Higher energy laser discharges did not increase mean lesion dimensions or result in tissue perforation. Lesion dimensions were usually comparable in air and saline media except for increased lesion diameter in saline at moderate energies ( p < 0.03). Comparison of lesion dimensions at the same energy level in normal and diseased human ventricle in air showed markedly reduced diameter and depth in diseased tissues ( p < 0.04), but comparable dimensions in saline medium ( p > 0.2). We conclude that argon laser irradiation of normal and diseased human ventricle results in focal lesions. The dimensions of these lesions are defined by the total energy dose, the medium used, and tissue characteristics. Higher laser discharge energies are required to produce comparable lesions in diseased human ventricle than in other cardiac or vascular tissues.