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Pulsed holmium laser ablation of cardiac valves

Ablation efficiency and residual thermal damage produced by pulsed holmium laser radiation were investigated in vitro for bovine mitral valves and human calcified and noncalcified cardiac valves. Low‐OH quartz fibers (200 and 600 μm core diameter) were used in direct contact perpendicular to the specimen under saline or blood. Etch rate was measured with a linear motion transducer. Radiant exposure was varied from 0 to 3 kJ/cm2. For 200‐μm fibers, the energy of ablation was approximately 5 kJ/cm3 in noncalcified and 15 kJ/cm3 in calcified valves. Etch rates were dependent on mechanical tissue properties. Maximum etch rate at 1,000 J/cm2 was 1–2 mm/pulse at 3 Hz repetition rate. Microscopic examination revealed a zone of thermal damage extending 300 μm lateral into adjacent tissue. Thermal damage was independent of radiant exposure beyond twice threshold.