A comparison of mechanical and laser transmyocardial revascularization for induction of angiogenesis and arteriogenesis in chronically ischemic myocardium

Objectives The purpose of the present study was to compare the use of a mechanical transmyocardial implant (TMI) device with transmyocardial laser revascularization (TMR) for induction of therapeutic angiogenesis and arteriogenesis in the chronically ischemic heart. Background Prior experimental studies have demonstrated evidence for neovascularization after both mechanical and laser transmyocardial revascularization, although a long-term comparison of the two techniques has not been performed. Methods Using an established model of chronic hibernating myocardium, mini-swine underwent 90% proximal left circumflex (LCx) coronary artery stenosis. One month later, baseline positron emission tomography (PET) and dobutamine stress echocardiography (DSE) were performed to quantitate regional myocardial blood flow (MBF) and function. Animals then underwent TMR with a holmium:yttrium-aluminum-garnet (holmium:YAG) laser (n = 5), TMI (n = 5), or sham redo-thoracotomy (n = 5). In the TMR group, the entire LCx region was treated with transmural laser channels at a density of 1/cm2. Transmyocardial implants were placed transmurally at a similar density in the LCx region of the TMI group. Six months later, the PET and DSE studies were repeated, and the animals were euthanized. Results Six months after TMR, there was a significant increase over baseline in resting MBF to the lased LCx region (68.9 ± 4.6% vs. 89.3 ± 3.0% reference non-ischemic septal segments; p < 0.001). This increased MBF was accompanied by a significant improvement in LCx regional wall motion during peak dobutamine stress (p = 0.04). Compared with baseline, there was no change in LCx region MBF six months after either TMI (72.9 ± 4.8% vs. 85.7 ± 3.4%; P = 0.10) or sham redo-thoracotomy (75.6 ± 4.6% vs. 80.1 ± 5.0%; p > 0.2). Likewise, there was no significant change in rest or stress wall motion by DSE six months postoperatively in either group. Overall vascular density was increased only in the TMR-treated regions six months postoperatively. The difference between groups was most notable for a twofold increase in the number of small arterioles seen in the lased (4.4 ± 0.3 arterioles per high power field; p < 0.001 vs. both TMI and sham) compared with TMI (2.2 ± 0.2) and sham (1.9 ± 0.2)-treated regions. Conclusions Mechanical transmyocardial revascularization with a TMI device does not appear to promote physiologically significant angiogenesis or arteriogenesis in the chronically ischemic porcine heart and cannot be recommended for clinical trials at this time. Infrared laser-mediated injury mechanisms may be important for inducing therapeutic neovascularization with direct myocardial revascularization techniques.