Angiogenesis: a possible mechanism underlying the clinical benefits of transmyocardial laser revascularization

Ten-year follow-up after combined coronary artery bypass grafting and transmyocardial laser revascularization in patients with disseminated coronary atherosclerosis

Coronary artery disease involving heavily calcified lesions has been associated with worse short- and long-term outcomes including increased mortality. This paper aims to evaluate long-term survival benefit when CABG + transmyocardial laser revascularization (TMLR) are performed on the hearts of patients with disseminated coronary atherosclerosis (DCA). This novel retrospective study was conducted between 1997 and 2002 and followed 86 patients with ischemic heart disease and severe DCA who underwent TMLR using a Holmium:YAG laser and/or CABG. There were 46 patients who had CABG plus TMLR on at least one heart wall ("combined therapy group") and 40 patients who had CABG or TMLR separately on at least one heart wall ("single therapy group"). For the whole group, actuarial survival at 10 years was 78.3% in the combined group compared to 72.5% in the single therapy group (p = 0.535). Ten-year survival in the combined vs. single therapy group for the anterior heart walls was 100 vs. 72.2% (p = 0.027). For the lateral and posterior heart walls were 73.7 vs. 73.3% (p = 0.97) and 84.2 vs. 72% (p = 0.27), respectively. Kaplan-Meier survival analysis showed benefit only for the anterior heart wall (F Cox test, p = 0.103). Single therapy procedures on all heart walls (odds ratio 1.736, p = 0.264) or on the anterior heart wall only (odds ratio 3.286, p = 0.279) were found to be predictors of 10-year late mortality. Combined therapy (TMLR + CABG) provides benefit for perioperative mortality and long-term survival only when provided on the anterior heart wall. For patients with disseminated coronary atherosclerosis, cardiac mortality was found to be increased when followed up 6 years later, regardless of the therapy applied.

Transmyocardial revascularization devices: technology update

Transmyocardial laser revascularization (TMR) emerged as treatment modality for patients with diffuse coronary artery disease not amendable to percutaneous or surgical revascularization. The procedure entails the creation of laser channels within ischemic myocardium in an effort to better perfuse these areas. Currently, two laser devices are approved by the US Food and Drug Administration for TMR – holmium:yttrium–aluminum–garnet and CO₂. The two devices differ in regard to energy outputs, wavelengths, ability to synchronize with the heart cycle, and laser–tissue interactions. These differences have led to studies showing different efficacies between the two laser devices. Over 50,000 procedures have been performed worldwide using TMR. Improvements in angina stages, quality of life, and perfusion of the myocardium have been demonstrated with TMR. Although several mechanisms for these improvements have been suggested, evidence points to new blood vessel formation, or angiogenesis, within the treated myocardium, as the major contributory factor. TMR has been used as sole therapy and in combination with coronary artery bypass grafting. Clinical studies have demonstrated that TMR is both safe and effective in angina relief long term. The objective of this review is to present the two approved laser devices and evidence for the safety and efficacy of TMR, along with future directions with this technology.

Transmyocardial laser revascularization

It has been almost a decade since transmyocardial laser revascularization (TMR) was approved for clinical use in the United States. The safety of TMR was demonstrated initially with nonrandomized studies in which TMR was used as the only treatment for patients with severe angina. TMR efficacy was proven after multiple randomized controlled trials. These revealed significant angina relief compared to maximum medical therapy in patients with diffuse coronary disease not amenable to conventional revascularization. In light of these results, TMR has been used as an adjunct to coronary artery bypass grafting (CABG). By definition, patients treated with this combined therapy have more severe coronary disease and comorbidities that are associated with end-stage atherosclerosis. Combination CABG + TMR has resulted in symptomatic improvement without additional risk. The likely mechanism whereby TMR has provided benefit is the angiogenesis engendered by the laser-tissue interaction. Improved perfusion and concomitant improvement in myocardial function have been observed post-TMR. Additional therapies to enhance the angiogenic response include combining TMR with stem cell-based treatments, which appear to be promising future endeavors.

Use of human VEGF(165) gene for therapeutic angiogenesis in coronary patients: first results

The paper presents the first results of therapeutic angiogenesis in clinical cardiosurgery: human VEGF(165) gene transplantation to coronary patients. The use of this therapeutic method is particularly effective in patients with inoperable cardiovascular injuries, i.e. patients with the most severe condition, in whom treatment remains little effective at the modern level of cardiosurgery development.

The vascular response induced by transmyocardial laser revascularization is determined by the size of the channel scar: Results of CO2, holmium and excimer lasers

BACKGROUND AND OBJECTIVES

To investigate the angiogenic effect of CO2, Ho:YSGG, and XeCl excimer TMLR in a rat model with morphologic characteristics of chronic myocardial ischemia.

STUDY DESIGN/MATERIALS AND METHODS

Two channels (200-320 microm) were created per rat heart. After 14 days, vessel numbers and densities in and around laser scars were assessed.

RESULTS

Capillary densities in the laser scars were equal between the three lasers ( approximately 130 vessels/mm2) but much lower than in control areas ( approximately 2,100 vessels/mm2). Vessel densities excluding capillaries were significantly higher in Ho:YSGG and CO2 scars compared to excimer scars, while only Ho:YSGG scars contained significantly more large vessels (diameter > or = 20 microm) than control areas. Only rarely, extension of vascular growth into adjacent myocardium was observed in any of the three groups.

CONCLUSIONS

These results indicate that the angiogenic response following TMLR is limited to the channel scar and related to the scar size rather than the specific laser type.

Improvement of myocardial contractility in a porcine model of chronic ischemia using a combined transmyocardial revascularization and gene therapy approach

OBJECTIVES

The purpose of this study was to investigate whether a novel fibroblast growth factor-2 gene formulation, providing a localized and sustained availability of the adenoviral vector from a collagen-based matrix, in combination with CO 2 transmyocardial laser revascularization would lead to an enhanced angiogenic response and improved myocardial function.

METHODS

Fibroblast growth factor-2 gene was delivered by means of an adenoviral vector (adenoviral fibroblast growth factor-2) formulated in a collagen-based matrix. The ischemic areas of 33 animals were then treated. Group 1 was treated with CO 2 transmyocardial laser revascularization; group 2 was treated with intramyocardial injections of adenoviral fibroblast growth factor-2 in a collagen-based matrix; group 3 had a combination treatment of matrix adenoviral fibroblast growth factor-2 and CO 2 transmyocardial laser revascularization; and group 4 received injections with saline-formulated adenoviral fibroblast growth factor-2. Baseline left ventricular function was assessed by echocardiography and cine magnetic resonance imaging. Studies were repeated 6 weeks after treatment. Vascular development was assessed using anti-alpha-actin immunohistochemistry.

RESULTS

Matrix adenoviral fibroblast growth factor-2 + transmyocardial laser revascularization-treated areas had a 105% increase in arteriolar development versus either treatment alone ( P < .05) and a 390% increase compared with saline-formulated adenoviral fibroblast growth factor-2 treatment alone ( P < .05). Contractility was significantly improved in matrix adenoviral fibroblast growth factor-2 + transmyocardial laser revascularization-treated areas as measured by myocardial wall thickening. This functional improvement was confirmed by cine magnetic resonance imaging, in which a 90% increase in the contractility of the treated segments was demonstrated after matrix adenoviral fibroblast growth factor-2 + transmyocardial laser revascularation. The other treatments provided significantly less restoration of myocardial function.

CONCLUSIONS

The increase in angiogenesis as a result of matrix adenoviral fibroblast growth factor-2 gene therapy in combination with CO 2 transmyocardial laser revascularization is greater than that seen in either therapy alone. A concomitant improvement in myocardial function was seen as a result of this angiogenic response.

Cardiac denervation after clinical transmyocardial laser revascularization: short-term and long-term iodine 123–labeled meta-iodobenzylguanide scintigraphic evidence

OBJECTIVES

This study was designed to investigate whether transmyocardial laser revascularization induces myocardial denervation and to correlate this with myocardial perfusion and clinical status.

METHODS

Transmyocardial laser revascularization was performed with a Holmium:YAG (n = 3) or xenon chloride excimer laser (n = 5). Preoperative and postoperative iodine 123-labeled meta-iodobenzylguanide SPECT scintigraphy to assess cardiac innervation and perfusion scintigraphy were also performed. Furthermore, New York Heart Association functional angina class and quality of life were assessed.

RESULTS

In all patients postoperative iodine 123-labeled meta-iodobenzylguanide SPECT showed significantly decreased uptake and therefore sympathetic myocardial denervation at up to 16 months' follow-up (average preoperative and postoperative summed defect scores of 14.8 +/- 5.3 and 24.5 +/- 4.2, respectively; P =.00005). In 86% of segments, the decreased meta-iodobenzylguanide uptake could be correlated to the treated area. In all patients angina was reduced by 2 or more classes at 12 months' follow-up, and quality of life improved significantly.

CONCLUSIONS

Transmyocardial laser revascularization-induced improvement of angina and quality of life can be explained by destruction of nociceptors or cardiac neural pathways, changing the perception of anginal pain.

Laser revascularization of ischemic skeletal muscle

BACKGROUND

Clinical trials have shown that transmyocardial laser revascularization is an effective secondary treatment for ischemic heart disease patients. Laser revascularization may also provide an alternative method for treating peripheral vascular disease.

METHODS

The purpose of this study was to investigate the potential for laser revascularization in ischemic skeletal muscle. Eighteen rabbits (3-4 kg) were instrumented chronically with transit time ultrasound flowprobes on both common iliac arteries. All rabbits performed graded exercise tests on a treadmill where maximal blood flow was recorded. Unilateral hindlimb ischemia was produced by ligation of one femoral artery. At week 3 postligation, 10 rabbits received laser therapy and 8 underwent a sham surgery. In each of four muscles (gracilius, medialis, sartorius, and biceps femoris) 5 to 22 laser channels were created (average = 52 channels per leg).

RESULTS

At week 3 postligation the maximal blood flow of the ischemic limb for the treated group was 64 +/- 3 ml/min (mean +/- SEM) and at 6 weeks postlaser therapy maximal blood flow increased to 75 +/- 5 ml/min. The sham surgery group had a maximal blood flow of 58 +/- 4 ml/min at week 3 postligation and 66 +/- 3 ml/min at week 6 postsham surgery.

CONCLUSION

These results indicate that laser therapy does not induce angiogenesis and vascular remodeling in the ischemic hindlimb of a rabbit which exceeds that seen with a sham surgery.

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.

Magnetic resonance imaging demonstrates improved regional systolic wall motion and thickening and myocardial perfusion of myocardial territories treated by laser myocardial revascularization

OBJECTIVES

This study was designed to investigate the use of magnetic resonance (MR) functional and perfusion imaging to evaluate laser myocardial revascularization (LMR).

BACKGROUND

Most clinical studies of LMR have shown improvements in angina class and exercise capacity, with minimal or absent improvements in myocardial perfusion and function.

METHODS

Fifteen patients who underwent percutaneous Biosense-guided holmium:yttrium aluminum garnet LMR to areas of viable but ischemic myocardium were followed clinically and underwent functional and perfusion MRI at baseline, 30 days and 6 months.

RESULTS

The mean age was 64 +/- 11 years; four patients were women. The ejection fraction was 47.4 +/- 14.0%. Angina class at baseline was 3.4 +/- 0.6 and improved to 2.5 +/- 1.4 at six months (p = 0.054). Exercise time at baseline was 298 +/- 97 s and increased to 350 +/- 95 s at 30 days and 365 +/- 79 s at six months, p = 0.04. There were no significant changes in nuclear perfusion scans. Although MR determined that resting radial motion and thickening of the target wall were significantly less than normal at baseline (p < 0.001), they improved significantly during follow-up (wall thickening: baseline, 30.6 +/- 11.7%; day 30, 41.2 +/- 13.3% and day 180, 44.2 +/- 11.9%, p = 0.01). The size of the underperfused myocardial area was 14.5 +/- 5.4% at baseline and was reduced to 6.3 +/- 2.8% at 30 days and 7.7 +/- 3.7% at 6 months (p < 0.001).

CONCLUSIONS

This small phase I, open-label, uncontrolled study of MR functional and perfusion imaging in patients undergoing Biosense-guided LMR suggests a beneficial effect of this treatment strategy on myocardial function and perfusion. The efficacy of Biosense-guided LMR is being evaluated in a large phase II, randomized, blinded placebo-controlled trial with an MRI substudy (DIRECT).

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.

Combined percutaneous biosense-guided laser myocardial revascularization and coronary intervention

Laser myocardial revascularization is a promising new treatment strategy for patients with severe ischemic heart disease who are not candidates for conventional percutaneous or surgical revascularization. The open chest surgical approach to transmyocardial revascularization has been approved by the FDA for the treatment of angina in inoperable patients, but has had limited use as a stand-alone procedure. More recently, use of fiber-optic catheters has made it possible to use a holmium:yttrium aluminum garnet laser to perform percutaneous catheter-based transmyocardial revascularization. To the extent that many patients have a combination of ischemic sources, some amenable to conventional revascularization and some not, combination or hybrid approaches have been considered. We report herein two patients with class IV angina who underwent laser myocardial revascularization using the Biosense system and complex percutaneous coronary intervention during the same procedure. Areas amenable to conventional percutaneous coronary intervention (PCI) were so treated, and viable but ischemic areas were supplied by totally occluded native vessels and bypass grafts underwent Biosense-guided laser myocardial revascularization (LMR). As the results of more controlled and blinded studies of laser myocardial revascularization become available (if results continue to be promising) and a better understanding of the mechanism of action of this treatment modality is achieved, LMR-PTCA hybrid will be performed in increasing frequency. However, even after establishing LMR efficacy, studies of LMR-PTCA hybrid should be conducted to determine the efficacy of this approach.

Activation of myocardial angiogenesis and upregulation of fibroblast growth factor-2 in transmyocardial-revascularization-treated mice

OBJECTIVE

To evaluate the growth factor responses associated with myocardial angiogenesis.

DESIGN

Mice were treated with transmyocardial revascularization (TMR) and evaluated for angiogenic and growth factor responses.

METHODS

TMR was performed via thoractomy with a 27 g needle. At 2, 5, and 7 days post-treatment, hearts were removed from the TMR treated and control groups, then assayed for angiogenesis, fibroblast growth factor (FGF)-2 expression and vascular endothelial cell growth factor (VEGF) expression.

RESULTS

TMR caused an angiogenic reaction in the myocardial blood vessels at 7 days post-TMR treatment. Elevated FGF-2 corresponded with increased TMR related angiogenesis. VEGF levels only increased in hearts that were prewounded then TMR treated.

CONCLUSIONS

The data show that TMR stimulates myocardial angiogenesis. The angiogenic reaction is mediated by FGF-2 which increased in most experimental treatment groups. The VEGF response was more specific, requiring prewounding then TMR treatment for a VEGF increase.

Ultrastructural and immunohistochemical analysis of early myocardial changes following transmyocardial laser revascularization

BACKGROUND AND AIM OF THE STUDY

Transmyocardial laser revascularization (TMR) has demonstrated significant relief in patients presenting with refractory angina. However, the mechanism by which TMR improves clinical symptoms is unclear. This study analyzes the early immunohistochemical and ultrastructural features of the human myocardium following TMR.

METHODS

Specimens of myocardium that contained laser channels were removed in toto at autopsy from three male patients, ages 41, 57, and 65 (mean age 55.8) who had died 1 to 11 days (mean 6.8) following laser revascularization. Consecutive parallel sections of specimens were stained with cell-type specific antibodies to CD3 (to identify T-lymphocytes), CD68 (macrophages), Factor VIII (endothelial cells), and myosin (myocytes). Additionally, adjacent areas of myocardium that contained laser channels were processed and analyzed by transmission electron microscopy.

RESULTS

The internal lining surface of laser channels was composed of vacuolized and condensed myocardial debris. No obvious connections were noted between laser channels and the ventricular cavity. No endothelialization of channels was observed, whereas the adjacent noninjured myocardium demonstrated microvessels lined by well-preserved endothelial cells. The laser channels were surrounded by zones of necrotic cardiomyocytes.

CONCLUSIONS

Our observations suggest that laser channels are not lined by endothelial cells during the early stages following TMR. Mechanisms other than direct myocardial perfusion from the ventricular cavity by patent endothelialized channels may explain the immediate relief from angina provided by TMR.

Perioperative cardiac function and predictors for adverse events after transmyocardial laser treatment

BACKGROUND

Previous studies have reported that mortality and morbidity after transmyocardial laser treatment (TML) mainly occur perioperatively. The present study was designed to evaluate left-ventricular function and identify risk factors for cardiac-related adverse events in this phase.

METHODS

Forty-nine patients were studied. The inclusion criteria were angina pectoris Canadian Cardiovascular Society Angina Score (CCSAS) class III and IV refractory to medical therapy and untreatable by coronary artery bypass graft or percutaneous transluminal coronary angioplasty, age less than 75 years, left ventricular ejection fraction greater than or equal to 30%, and myocardial regions with reversible ischemia. Hemodynamic data and cardiac adverse events were registered. The follow-up time was 30 days.

RESULTS

A transient decrease in mean cardiac index (CI) was observed, reaching its minimum immediately after end of the surgical procedure (1.8+/-0.4, p<0.01 vs. baseline). Two patients (4%) died during the postoperative period (30 days). Seventeen patients (35%) experienced adverse cardiac-related events, where CCSAS class IV, unprotected left main stem stenosis, and diabetes mellitus were identified as risk factors in a multivariate analysis.

CONCLUSIONS

A transient impairment of left ventricular function was observed after TML. The morbidity and mortality after TML were almost exclusively cardiac-related, identifying CCSAS class IV, unprotected left main stem stenosis, and diabetes as risk factors.

Comparison of transmyocardial revascularization with medical therapy in patients with refractory angina

BACKGROUND

Transmyocardial revascularization involves the creation of channels in the myocardium with a laser to relieve angina. We compared the safety and efficacy of transmyocardial revascularization performed with a holmium laser with those of medical therapy in patients with refractory class IV angina (according to the criteria of the Canadian Cardiovascular Society).

METHODS

In a prospective study conducted between March 1996 and July 1998 at 18 centers, 275 patients with medically refractory class IV angina and coronary disease that could not be treated with percutaneous or surgical revascularization were randomly assigned to receive transmyocardial revascularization followed by continued medical therapy (132 patients) or medical therapy alone (143 patients).

RESULTS

After one year of follow-up, 76 percent of the patients who had undergone transmyocardial revascularization had improvement in angina (a reduction of two or more classes), as compared with 32 percent of the patients who received medical therapy alone (P<0.001). Kaplan-Meier survival estimates at one year (based on an intention-to-treat analysis) were similar for the patients assigned to undergo transmyocardial revascularization and those assigned to receive medical therapy alone (84 percent and 89 percent, respectively; P=0.23). At one year, the patients in the transmyocardial-revascularization group had a significantly higher rate of survival free of cardiac events (54 percent, vs. 31 percent in the medical-therapy group; P<0.001), a significantly higher rate of freedom from treatment failure (73 percent vs. 47 percent, P<0.001), and a significantly higher rate of freedom from cardiac-related rehospitalization (61 percent vs. 33 percent, P<0.001). Exercise tolerance and quality-of-life scores were also significantly higher in the transmyocardial-revascularization group than in the medical-therapy group (exercise tolerance, 5.0 MET [metabolic equivalent] vs. 3.9 MET; P=0.05); quality-of-life score, 21 vs. 12; P=0.003). However, there were no differences in myocardial perfusion between the two groups, as assessed by thallium scanning.

CONCLUSIONS

Patients with refractory angina who underwent transmyocardial revascularization and received continued medical therapy, as compared with similar patients who received medical therapy alone, had a significantly better outcome with respect to improvement in angina, survival free of cardiac events, freedom from treatment failure, and freedom from cardiac-related rehospitalization.

Percutaneous revascularization modalities in heart transplant recipients

Accelerated allograft vasculopathy significantly limits the survival of heart transplant recipients. The prevalence of allograft coronary artery disease is as high as 18% by 1 year and 50% by 5 years following heart transplant. Heart failure and sudden cardiac death are the two most common clinical presentations. In heart transplant recipients with severe, discrete focal allograft vascular disease, percutaneous balloon angioplasty is a viable palliative option. However, its application is limited by a significant restenosis rate and progression of allograft disease in nontreated segments. Diffuse disease with tapering of vessels may be approached by debulking devices. Emerging revascularization modalities for focal stenoses and some of the diffuse tapering vessels include coronary stents, rotational atherectomy, various wavelength lasers, and, to a lesser extent, directional atherectomy. Conceivably, stents will reduce restenosis rates related to focal, discrete plaques; yet it is unknown whether they will be efficacious in short- and long-term treatment of diffusely diseased segments affected by allograft disease. Accurate assessment of clinical outcomes and long-term evaluation is imperative prior to acceptance of these devices as fundamental interventional tools for treatment of allograft coronary artery disease.

An examination of potential mechanisms underlying transmyocardial laser revascularization induced increases in myocardial blood flow

Within the past few years, transmyocardial laser revascularization (TMR) has attracted the attention of cardiologists and cardiac surgeons as a therapy for patients suffering from otherwise treatable coronary artery disease. Clinical studies have consistently shown symptomatic improvement that lasts at least 1 year in a majority of patients. The original hypothesis that prompted development of the technique was that direct myocardial perfusion from the chamber could be achieved through chronically patent channels, as is the case in reptilian hearts. Results of our early studies failed to support this hypothesis and we turned to investigations aimed at testing other possible explanations. The experiments, which are reviewed in this article, showed that TMR enhances vascular growth in ischemic myocardium.