Demonstration of Blood Flow Through Transmyocardial Laser Channels

Transmyocardial laser revascularization (TMR) is new procedure under investigation for treatment of patients with myocardial ischemi who are unresponsive to other conventional therapies. In theory, TMR channels passing from the LV chamber directly into the myocardium allow oxygenated blood to directly perfuse the myocardium, bypassing the coronary vessels. However, experimental evidence that blood actually flows through the channels has not been available previously. Therefore, the purpose of this study was to test whether blood can reach the myocardium by passing through laser channels. An average of 28 channels/heart were made over the LAD distribution in 5 canine hearts using pulsed holmium/YAG laser (20 pulses, 0.6J/pulse) with energy delivered from the endocardium through 400 μ fiber optic cable introduced vi the left atrial appendage. The heart was then excised while coronary perfusion pressure was maintained constant at 120 mmHg by retrograde aortic blood flow provided by second dog (aortic valve always remains closed). The proximal LAD and epicardial collaterals were ligated. Collateral flow to the ischemic region, measured by colored microspheres injected into the coronary artery, was 20.5% of normal (0.42 ± 0.28 ml/g/min vs. 2.05 ± 0.68 ml/g/min in the non-ischemic region). Colored spheres were then injected into blood placed within the LV chamber to achieve peak LV pressure generation of 20 mmHg (low loading) and then 60 mmHg (high loading) (this blood is not ejected into the aorta). The number of spheres detected per gram of myocardium in the circumflex (LCX) region (control are without TMR channels) and in the LAD region with TMR channels are shown in the table as function of LV loading: The number of spheres in the channel region was significantly higher than in the control region but did not vary with loading conditions. These dat provide direct evidence that blood from the LV can reach the myocardium through TMR channels in the acute setting. Quantification of the flow and whether this can be maintained in the chronic setting are important questions for future research.