Myocardial laser revascularization: the controversy and the data

Tissue Engineering of the Microvasculature

The ability to generate new microvessels in desired numbers and at desired locations has been a long-sought goal in vascular medicine, engineering, and biology. Historically, the need to revascularize ischemic tissues nonsurgically (so-called therapeutic vascularization) served as the main driving force for the development of new methods of vascular growth. More recently, vascularization of engineered tissues and the generation of vascularized microphysiological systems have provided additional targets for these methods, and have required adaptation of therapeutic vascularization to biomaterial scaffolds and to microscale devices. Three complementary strategies have been investigated to engineer microvasculature: angiogenesis (the sprouting of existing vessels), vasculogenesis (the coalescence of adult or progenitor cells into vessels), and microfluidics (the vascularization of scaffolds that possess the open geometry of microvascular networks). Over the past several decades, vascularization techniques have grown tremendously in sophistication, from the crude implantation of arteries into myocardial tunnels by Vineberg in the 1940s, to the current use of micropatterning techniques to control the exact shape and placement of vessels within a scaffold. This review provides a broad historical view of methods to engineer the microvasculature, and offers a common framework for organizing and analyzing the numerous studies in this area of tissue engineering and regenerative medicine. © 2019 American Physiological Society. Compr Physiol 9:1155-1212, 2019.

Transmyocardial Revascularization

Low-powered lasers were first used in the 1980s to produce transventricular channels as an adjunct to coronary artery bypass surgery. High-powered lasers, which were introduced in the 1990s, are powerful enough to create transmyocardial channels with minimal damage to surrounding tissues. Clinical studies were first carried out in patients with inoperable coronary artery disease and angina pectoris refractory to medical therapy. Based on these studies, the Food and Drug Administration granted approval of transmyocardial revascularization (TMR) as a sole therapy. Recently, TMR has been combined with coronary artery bypass surgery and 2 types of laser systems are currently available which have not been compared. The results of clinical trials provide contrasting findings regarding benefit, and the procedure is associated with potential morbidity and mortality risk. Furthermore, the mechanism of action of TMR remains undefined. Additional studies need to be done with TMR to assess whether it is a useful treatment or an addition to the list of placebo therapies initially thought to have been of benefit in the therapy for angina pectoris.

Influence of transmyocardial laser revascularization (TMLR) on regional cardiac function and metabolism in an isolated hemoperfused working pig heart

The mechanism of an indirect revascularization in ischemic myocardium by transmyocardial laser revascularization (TMLR) is not yet fully understood. An improvement of clinical symptoms caused by TMLR is reported in many clinical trials with patients in which a direct revascularization is not possible. An increase of myocardial perfusion through laser channels is doubtful, because the myocardial pressure in the wall is higher than in the cavum. Therefore we measured the local cardiac function (intramyocardial pressure, wall thickness, pressure-length curves) and acute metabolic changes (tissue lactate content, tissue pO2) in ischemic and nonischemic regions before and after TMLR in isolated hemoperfused pig hearts. An isolated heart was chosen because it enabled us to separate coronary flow from flow through ventricular channels. The ischemia was induced by coronary occlusion or microembolization (eight hearts each). It should be noted that microembolization leads to conditions which are more comparable with those found in patients selected for TMLR. In the isolated working heart, the coronary perfusion can be controlled independently from perfusion through the ventricular cavum. Under the ischemic conditions mentioned above, we observed that the intramyocardial pressure in the ischemic region decreased below the left ventricular pressure, so one premise for indirect perfusion was met. TMLR after microembolization led to a significant improvement of regional cardiac work and the tissue oxygen pressure. These acute effects demonstrate the possibility of functional and metabolic amelioration by TMLR after ischemia induced by microembolization in an isolated hemoperfused pig heart.

One-year outcome after combined coronary artery bypass grafting and transmyocardial laser revascularization for refractory angina pectoris

Long-term outcomes after coronary artery bypass graft surgery (CABG) plus transmyocardial revascularization (TMR) are largely unknown. We report the results of 30-day and 3-, 6-, and 12-month clinical follow-up after CABG plus TMR in a consecutive series of patients with refractory angina pectoris and > or = 1 myocardial ischemic area not amenable to CABG. All patients who underwent CABG plus TMR (n = 169) (mean age 63 +/- 10 years, 70% men, 51% with previous CABG, 82% were deemed inoperable at other heart surgery centers due to small vessels or diffuse disease) between March 1996 and February 2000 were clinically followed and end points of interest (survival, stroke, acute myocardial infarction, and revascularization) and angina class were recorded at 30 days and 3, 6, and 12 months after CABG. At 1 year, actuarial survival and event-free survival were 85% and 81%, respectively. At the end of the first year after the procedure, 7 patients (4%) had angina class III/IV versus 152 patients (90%) at baseline (p <0.001). Predictors of major adverse cardiac events were advanced age (odds ratio [OR] 3.4, 95% confidence intervals [CI] 1.2 to 9.4, p = 0.01), prolonged intensive care unit stay (OR 3.3, CI 1.1 to 9.7, p <0.001), new-onset atrial fibrillation (OR 2.8, CI 1.1 to 7.0, p = 0.02), and in-hospital myocardial infarction (OR 1.5, CI 1.3 to 1.7, p <0.001). Thus, procedural success at 30 days and overall event-free and actuarial survival in a high-risk population setting shows that CABG plus TMR is a safe revascularization option for patients with intractable angina pectoris.

Intramyocardial delivery of FGF2 in combination with radio frequency transmyocardial revascularization

Therapeutic angiogenesis and percutaneous transmyocardial revascularization (PMR) are potentially synergistic modalities to improve myocardial perfusion. To evaluate the efficiency of FGF2 delivery into an area that has been radio frequency (RF) ablated, we studied two catheter-based delivery methods, a direct injection system (Stiletto) and a combined RF ablation-delivery system (RF-PMR). Four groups (n = 3/group) of pigs received six transendocardial injections of (125)I-FGF2/fluorescent microspheres with either the Stiletto or the RF-PMR catheter. RF-PMR injections were preceded by a 0.6 sec RF ablation step. After either 1 or 24 hr, hearts and other tissues were harvested. Intramyocardial deposition sites were located with UV light and isolated. Specific activity per site was expressed as a percentage of total activity injected per site corrected for quenching. Injection site recovery was high for both catheter systems (average = 88%) and systemic uptake was low (< 6% in the liver). FGF2 retention was significantly higher with the Stiletto than the RF-PMR catheter (Stiletto 1 hr 41% +/- 17%, 24 hr 26% +/- 10%, RF-PMR 1 hr 21% +/- 14%, 24 hr 13% +/- 8%; P < 0.001), principally explained by the differences in catheter design. The Stiletto has a retractable needle and is optimized for intramyocardial delivery, whereas infusion from the RF-PMR device occurs at the endocardial surface and relies on channels created during RF ablation. Overall, FGF2 retention after transendocardial intramyocardial delivery by the Stiletto or the RF-PMR system is significantly higher than previously observed for intracoronary, intravenous and intrapericardial delivery. In conclusion, the combination of RF ablation and growth factor delivery using the RF-PMR system is feasible and efficient. Cathet Cardiovasc Intervent 2001;53:429-434.

Transmyocardial laser revascularization in ischemic cardiomyopathy

BACKGROUND

In ischemic cardiomyopathy (left ventricular ejection fraction [LVEF] < or = 30%), myocardial revascularization by coronary artery surgery has better results than heart transplantation, provided there is sufficient ischemic but viable myocardium. The mode of action of transmyocardial laser revascularization (TMR) is still being debated, but if the procedure induces improved myocardial perfusion it could be a "bridge," or alternative, to heart transplantation.

METHODS

We retrospectively analyzed 194 patients, who underwent TMR between July 1997 and October 1999. Patients with TMR as an adjunct to coronary artery surgery (n = 30) and those who did not provide written consent to the procedure (n = 8) were excluded; 126 patients had normal or moderately reduced left ventricular function, and 30 patients with ischemic cardiomyopathy (LVEF < or = 30%) were included.

RESULTS

After 12 months, the Canadian Cardiovascular Society (CCS) score dropped significantly from 3.6 (3 to 4) to 2.4 (1 to 4) and maximum work load increased significantly from 58 W (25 to 100 W) to 73 W (25 to 120 W). However, thallium score and LVEF did not improve significantly (27% [15% to 30%] to 32% [15% to 45%]). Prior to the TMR procedure, all 30 patients had a "low risk" or "medium risk" of death according to the Aaronson classification. The 30-day, 1-year, and 2-year survival rates were 83%, 50%, and 47%, respectively.

CONCLUSIONS

We conclude that TMR in ischemic cardiomyopathy (LVEF < or = 30%) has a perioperative risk comparable to that for heart transplantation, but there is no improvement of myocardial performance or life expectancy. Therefore, TMR cannot be regarded as a "bridge," or alternative, to transplantation. However, in individual cases with contraindications for transplantation the anti-anginal effect may justify use of the procedure.