Comparison of ablation channels created by the ultrapulsed CO2 laser, holmium laser, and 308-nm excimer laser in view of transmyocardial revascularization

The perfusion of hibernating myocardium by oxygenated blood coming from transmyocardial channels to the left ventricular cavity has been considered as an alternative for patients unsuitable for bypass surgery. Channels created by lasers are believed to assure patency in the long term. At this moment, several laser systems have become available to create these channels with minimal thermal effects. The systems should be ECG triggered and the exposure should preferably be within the relaxation phase of the cardiac cycle (0.1 - 0.2 s). The lasers examined were an ultrapulsed carbon-dioxide laser with long focus delivery optics, a Holmium laser coupled to a 1 mm spot fiber and an Excimer laser coupled to a 950 fiber. Pieces of bovine myocardium (10 - 20 mm thickness) were exposed while the displacement during penetration was monitored. Pulse trains were delivered within 0.05 - 0.2 s with a repetition rate of 1 - 3 Hz. The fiber delivery devices were loaded with weights between 10 - 80 gram to study the influence of exerted force. For the carbon dioxide laser the creation of the channels was also recorded on high speed video and with a thermal imaging method in a model tissue to visualize explosive and thermal effects. With the Holmium laser immediate penetration of the fiber was obtained while with the Excimer laser the penetration of the fiber started only after several pulses within the train depending on force and energy. The carbon-dioxide laser beam created a channel instantly, up to 30 mm/pulse depending on spotsize and energy. We conclude that all three lasers are capable of creating a channel of 20 mm long on the heart within a few cardiac cycles. Histologic analysis showed that in contrast to the smooth channels of the carbon-dioxide laser, the Holmium and Excimer laser create irregular channels with ruptures to the sides with some thermal damage. It is not clear which kind of channels will have the best potentials to provide maximum perfusion of the myocardium.