Myocardial coagulation by intraoperative Nd:YAG laser ablation and its dependence on blood perfusion

To investigate whether the efficacy of intraoperative laser ablation therapy is affected by myocardial blood perfusion, we irradiated 11 canine hearts through the epicardium with a Nd:YAG laser (10, 20, and 30 J/mm2) using air as the medium. Compared coagulated myocardial depth, width, and volume obtained in the red beating heart was compared with those in the white nonbeating heart infused with 0 degrees C saline (cardioplegic model) via the coronary artery. Histologically, the macro- and microscopical findings were very similar. At each level of energy, the width and volume of red myocardium coagulated were significantly larger than those of white myocardium (P < 0.01). At 30 J/mm2, the depth of coagulation of red myocardium was significantly larger than that of white myocardium (P < 0.01). The coagulated volume of the white myocardium was about 60% of that of the red myocardium. Nd:YAG laser energy was absorbed by blood (red color = hemoglobin), and more energy was transferred in the higher temperature myocardium. During intraoperative Nd:YAG laser ablation, the presence of blood perfusion in cardiac tissue is thought to be an important factor affecting safe irradiation.