Myocardial scarring after transmyocardial laser revascularization: A potential mechanism of clinical improvement?

35 years of experimental research in transmyocardial revascularization: what have we learned?

In the past 35 years many experimental studies have been performed to investigate the revascularization potential of transmyocardial revascularization and the possible working mechanisms underlying the observed clinical improvement in angina pectoris after this treatment. In this review of the experimental literature, the various methods that have been used to create transmyocardial channels and the most supported hypotheses on the working mechanism (channel patency, angiogenesis and myocardial denervation) are discussed and evaluated.

Angiogenesis three months after clinical transmyocardial laser revascularization using an excimer laser

BACKGROUND AND OBJECTIVE

We present for the first time histologic findings 3 months after clinical transmyocardial laser revascularization using a XeCl excimer laser.

STUDY DESIGN/MATERIALS AND METHODS

Histology was performed on a patient who died from a noncardiac cause 3 months post-excimer TMLR.

RESULTS

In the treated myocardium, no patent channels were found but scars were seen with a linear distribution and in continuity with circumscribed small fibrotic endocardial and epicardial scars. The scars were highly vascularized by new vessels, ranging from small capillaries to large thin walled, and sometimes branching ectatic vessels. Sprouting of vessels into the adjacent myocardium was also observed.

CONCLUSION

These results suggest that angiogenesis might play a role in the clinical improvement after TMLR.

[Coronary artery bypass graft combined with transmyocardial laser revascularization. Survival and functional class at one-year follow-up]

INTRODUCTION AND OBJECTIVES

The use of Transmyocardial Laser Revascularization (TMLR) as a strategy to treat unstable angina has been reported in many studies. We analyze its safety and effectiveness in combined procedures (CABG + TMLR).

METHODS

A non-randomized, retrospective cohort study was performed from May 4, 1999 to May 25, 2000 in 21 TMLR patients (18 combined CABG + TMLR) and 118 CABG only procedures. Mortality and NYHA analyses were determined by telephone at follow-up.

RESULTS

Three hospital deaths were observed: one isolated TMLR patient, one valvular + CABG + TMLR patient, and one CABG + TMLR patient. A significantly higher incidence of preoperative angina was found in the group of patients with TMLR + CABG, than in the group with only CABG (83 vs 25%; p < 0.001). There were no differences in age, gender, ejection fraction, Parsonnet and EuroSCORE risk estimation, or mortality (5.1% isolated CABG, 5.6% combined). No episode of angina was detected during follow-up in the CABG + TMLR group: 88% patients were NYHA I, and 21% NYHA II.

CONCLUSION

Incomplete coronary revascularization may be complemented with TMLR in the areas in which CABG is not possible without increased mortality. This technique may avoid postoperative unstable angina due to residual ischemic areas.

Is an endocardial connection necessary for growth factor induced angiogenesis in transmyocardial laser revascularization?

Transmyocardial laser revascularization (TMLR) and therapeutic angiogenesis had emerged as potential tools in the treatment of angina refractory to conventional therapies. This combination might potentiate their effects, because angiogenesis is believed to be a basic mechanism in TMLR. The influence of channel connection with endocardial blood flow on angiogenesis is unclear. Twenty-five pigs (mean weight, 72.3 +/- 5 kg) were randomly assigned into five groups. In the transmural laser group, five transmyocardial channels were drilled. In the transmural mixed group, the same protocol was used followed by the injection of 100 microg of bovine bone derived growth factor mixture within each channel. The nontransmural laser group and the nontransmural mixed group underwent the same procedures, respectively, but the laser channels were drilled through the outer two-thirds of the myocardial wall. The control group had sham operations. Animals were allowed to survive for 1 month. Vascular densities were determined by computed morphometric analysis of histologic sections. Vascular counts of areas adjacent to the channels in the non- and transmural laser groups did not differ significantly from control groups (arteriolar counts: 0.27 +/- 0.16 and 0.26 +/- 0.16 vs. 0.29 +/- 0.11/mm2, respectively). When bovine bone protein growth factor mixture is added, neovascularization is increased significantly in non- and transmural mixed groups (1.04 +/- 0.79 and 0.69 +/- 0.37/mm2, respectively, p < 0.001 for both comparisons with corresponding laser groups), and there was no significant difference between mixed groups (p = 0.13). In this porcine model, the combination of TMLR with injection of bone protein growth factor mixture induced angiogenesis around the laser channels. Whether the channels did or did not communicate with the endocardial cavity did not influence the neovascular density.