Thermal effects of laser and electrical discharge on cardiovascular tissue: Implications for coronary artery recanalization and endocardial ablation

To determine the thermal responses of cardiovascular tissues to laser and electrical ablation, and to characterize the effects of different supervising media and temperatures on target tissue temperatures and resulting extent of tissue injury, 184 laser and 15 electrical discharges were delivered to segments of human and canine aorta and canine ventricular endocardium. Tissue temperatures were measured 2 mm from the point of contact of laser fiber tip and tissue.When superfusing media consisted of whole blood or plasma at room temperature, a standard 40 J laser discharge caused peak arterial temperatures to rise 29.2 ± 1.6°C and 30 ± 1.4°C, respectively; however, tissue cooling was significantly slower in blood than in plasma. When saline solution was superfused, tissue temperatures rose by 11.4 ± 2.2°C, and tissue cooling occurred significantly faster than with either plasma or blood. The dimensions of the resulting aortic lesions were larger when blood (1.69 ± 0.26 mm) was superfused than when plasma (1.39 ± 0.04 mm) or saline (0.77 ± 0.13 mm) was superfused (p < 0.0001). Similar findings were observed with ventricular endocardium using blood or saline as the superfusing medium. In arterial tissue, superfusion with cold blood or saline solution resulted in lower peak temperature elevations (22 ± 3.8°C and 13.5 ± 1.3°C, respectively) and faster tissue cooling after laser discharge. Corresponding aortic lesion sizes were significantly smaller (1.4 ± 0.03 and 0.5 ± 0.02 mm, respectively) than when blood or saline medium was superfused at room temperature (p < 0.05). When 200 J of cathodal shock was delivered to ventricular endocardium, tissue temperatures rose approximately 15°C regardless of whether they were superfused with blood or saline.In conclusion, thermal mechanisms play an important role in both laser and electrical ablation of cardiac tissues; however, the composition of surrounding fluid medium affects the response of the tissue to laser to a greater degree than to electrical shock. Blood appears to enhance laser-induced tissue injury by allowing for higher peak tissue temperatures and slower tissue cooling. In contrast, superfusion of cold saline during laser discharge results in lower peak temperatures, faster tissue cooling and, consequently, less tissue injury. This may have important implications for preventing perforations during laser recanalization of obstructed arteries