9. Angiogenic Response to Transmyocardial Revascularization (TMR): Laser versus Mechanical Punctures

Victor Chu*, Adel Giaid*, Jin-qiang Kuang*, Amy McGinn*, Carlos Li*, Marc Pelletier*, and Ray C-J. Chiu, Montreal, Quebec, Canada

Transmyocardial laser revascularization (TMLR), which has been shown to reduce angina in clinical trials, was originally based on the belief that laser channels are unique and can remain patent. An increasing body of evidence indicates otherwise, and TMLR angiogenesis is currently thought to be induced by non-specific inflammatory response to tissue injury. We therefore tested the hypothesis that mechanical transmyocardial revascularization (TMMR) may induce angiogenic responses similar to that seen with lasers.

Methods: Ameroid constrictors were implanted around proximal circumflex arteries of porcine hearts. Six weeks later, they were randomly assigned (n=5 each) to receive 10 transmural channels in the ischemic zone using a CO₂ laser (TMLR-10) or using a needle (TMMR-10). A third TMMR-30 group had 30 needle channels, while a control group received no transmyocardial revascularization. The hearts were harvested one week later, and using immunohistochemistry, VEGF expression was studied and quantified by computerized morphometric analysis. Vascular densities positively stained for VEGF per high power field (HPF) were also compared.

Results: Virtually no transmyocardial revascularization channels remained patent histologically. Both TMLR and TMMR induced increased VEGF expression and vascular densities compared to the controls. Although each individual laser channel caused greater tissue injury, inflammatory, and angiogenic responses than channels made by a needle, larger number of needle punctures (N=30) fully compensated for such differences.

Conclusions: In view of the significant cost implications, our findings that needle punctures may also induce angiogenic response comparable to that with laser suggest that it is justifiable and desirable to include a TMMR arm for comparison with TMLR in future clinical trials.