Short- and intermediate-term clinical outcomes from direct myocardial laser revascularization guided by biosense left ventricular electromechanical mapping

Evaluating the importance of sham-controlled trials in the investigation of medical devices in interventional cardiology

Cardiovascular medicine is one of the specialties that has relied most heavily on evidence from randomised clinical trials in determining best practice for the management of common disease conditions. When comparing treatment approaches, trials incorporating random allocation are the most appropriate method for protecting against treatment allocation bias. In order to protect against performance and ascertainment bias, trial designs including placebo control are preferable where feasible. In contrast to testing of medicines, treatments based on procedures or use of medical devices are more challenging to assess, as sham procedures are necessary to facilitate blinding of participants. However, in many cases, ethical concerns exist, as individual patients allocated to sham procedure are exposed only to risk without potential for benefit. Accordingly, the potential benefits to the general patient population must be carefully weighed against the risks of the exposed individuals. For this reason, trial design and study conduct are critically important to ensure that the investigation has the best chance of answering the study question at hand. In the current manuscript, we aim to review issues relating to the conduct of sham-controlled trials and discuss a number of recent examples in the field of interventional cardiology.

Improved myocardial perfusion and cardiac function by controlled-release basic fibroblast growth factor using fibrin glue in a canine infarct model

OBJECTIVE

Angiogenic therapy is emerging as a potential strategy for the treatment of ischemic heart disease but is limited by a relatively short half-life of growth factors. Fibrin glue (FG) provides a reservoir for controlled-release of growth factors. The aim of this study was to evaluate the effects of basic fibroblast growth factor (bFGF) incorporating FG on angiogenesis and cardiac performance in a canine infarct model.

METHODS

Acute myocardial infarction was induced by ligation of the left anterior descending coronary artery (LAD). Group I (n=6) underwent ligation of LAD alone. In Group II, transmural channels were created in the infarct area (n=6). In Group III, non-transmural channels were created to locate FG cylinders containing bFGF (n=6). Eight weeks after operation, myocardial perfusion was assessed by single photon emission computed tomography, cardiac function by echocardiography, and vascular development by immunohistochemical staining.

RESULTS

Total vascular density and the number of large vessels (internal diameter ≥50 μm) were dramatically higher in Group III than in Groups I and II at eight weeks. Only the controlled-release group exhibited an improvement in regional myocardial perfusion associated with lower defect score. Animals in Group III presented improved cardiac regional systolic and diastolic functions as well as global systolic function in comparison with the other two groups.

CONCLUSIONS

Enhanced and sustained angiogenic response can be achieved by controlled-release bFGF incorporating FG within transmyocardial laser channels, thus enabling improvement in myocardial perfusion and cardiac function.

Transmyocardial revascularization ameliorates ischemia by attenuating paradoxical catecholamine-induced vasoconstriction

BACKGROUND

The mechanism by which transmyocardial revascularization (TMR) offers clinical benefit is controversial. We hypothesized that TMR ameliorates ischemia by reversing paradoxical catecholamine-induced vasoconstriction.

METHODS AND RESULTS

Chronic ischemic cardiomyopathy was created in 11 dogs by placing ameroid constrictors on the proximal coronary arteries and their major branches. Six weeks later, 35 channels were created percutaneously in the left circumflex artery region, with the left anterior descending artery region serving as control. At rest, wall thickening and myocardial blood flow did not change in the treated region, whereas they deteriorated in the control bed. Contractile and myocardial blood flow reserve increased in the treated region but deteriorated in the control region. There was diminished iodine 123 metaiodobenzylguanidine uptake and a significant reduction in noradrenergic nerves in the treated region compared with the control region, with a corresponding reduction in tissue tyrosine hydroxylase activity.

CONCLUSIONS

We conclude that the absence of a catecholamine-induced reduction in MBF reserve and contractile reserve in the TMR-treated region with associated evidence of neuronal injury indicates that the relief of exercise-induced ischemia after TMR most likely results from reversal of paradoxical catecholamine-induced vasoconstriction. These findings may have implications in selecting patients who would benefit from TMR.

Additive effect of endothelial progenitor cell mobilization and bone marrow mononuclear cell transplantation on angiogenesis in mouse ischemic limbs

The methods of therapeutic angiogenesis include endothelial progenitor cell (EPC) mobilization with cytokines [e.g., granulocyte colony-stimulating factor (G-CSF)] and bone marrow mononuclear cell (BMMNC) transplantation. Combined angiogenic therapies may be superior to a single angiogenic therapy for the treatment of limb ischemia. Therefore, we investigated whether the angiogenic efficacy of a combination of two angiogenic strategies is superior to either strategy alone. One day after the surgical induction of hindlimb ischemia, mice were randomized to receive either no treatment, EPC mobilization with G-CSF administration, BMMNC transplantation using a fibrin matrix, or a combination of EPC mobilization with BMMNC transplantation using a fibrin matrix. EPC mobilization with G-CSF or BMMNC transplantation using a fibrin matrix significantly increased the microvessel density compared with no treatment. Importantly, a combination of EPC mobilization with BMMNC transplantation using a fibrin matrix further increased the densities of microvessels and BrdU-positive capillaries compared to either strategy alone. Basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF) expression was higher in the EPC mobilization with G-CSF or BMMNC transplantation group than in the no treatment group. The combination therapy of EPC mobilization with G-CSF and BMMNC transplantation resulted in more extensive expression of bFGF and VEGF than the single therapy of either EPC mobilization with G-CSF treatment or BMMNC transplantation. This study demonstrates that the combination therapy of BMMNC transplantation and EPC mobilization potentiates the angiogenic efficacy of either single therapy in mouse limb ischemia models.

Combined Sustained Delivery of Basic Fibroblast Growth Factor and Administration of Granulocyte Colony-Stimulating Factor:Synergistic Effect on Angiogenesis in Mouse Ischemic Limbs

PURPOSE

To investigate whether the efficacy of a single angiogenic therapy (sustained delivery of basic fibroblast growth factor [bFGF] or administration of granulocyte colony-stimulating factor [G-CSF]) can be enhanced further by combining the therapies.

METHODS

One day after surgical induction of hind-limb ischemia, groups of 6 mice were randomized to receive either no treatment, sustained delivery (SD) of bFGF, endothelial progenitor cell (EPC) mobilization with G-CSF administration, or a combination of bFGF SD + G-CSF administration.

RESULTS

G-CSF administration increased significantly (p < 0.05) the number of EPC lineages (CD34 + /AC133 + cells) in both peripheral blood and bone marrow compared to no G-CSF administration. The bFGF SD and G-CSF administration individually increased the capillary and arteriole densities significantly versus no treatment (capillary density: 659 +/- 48/mm2 and 385 +/- 59/mm2, respectively, versus 280 +/- 28/mm2; p < 0.05; arteriole density: 34 +/- 9/mm2 and 41 +/- 6/mm2, respectively, versus 15 +/- 2/mm2; p<0.05). Importantly, bFGF SD + G-CSF further increased the capillary and arteriole densities compared to either strategy alone (capillary density: 786 +/- 40/mm2 versus 659 +/- 48/mm2 and 385 +/- 59/mm2, respectively, p < 0.05; arteriole density: 55 +/- 10/mm2 versus 34 +/- 9/mm2 and 41 +/- 6/mm2, respectively, p < 0.05).

CONCLUSION

This study demonstrates that the combined therapy of sustained bFGF delivery and G-CSF administration potentiates the angiogenic efficacy of either single therapy in mouse hind-limb ischemia models.

A Blinded, Randomized, Placebo-Controlled Trial of Percutaneous Laser Myocardial Revascularization to Improve Angina Symptoms in Patients With Severe Coronary Disease

OBJECTIVES

This study was a randomized, patient- and evaluator-blinded, placebo-controlled trial in patients treated using percutaneous myocardial laser revascularization.

BACKGROUND

Previous studies using similar therapies have been confounded by placebo bias.

METHODS

A total of 298 patients with severe angina were randomly assigned to receive low-dose or high-dose myocardial laser channels or no laser channels, blinded as a sham procedure. The primary end point was the change in exercise duration from baseline examination to six months.

RESULTS

The incidence of 30-day death, stroke, myocardial infarction, coronary revascularization, or left ventricular perforation occurred in two patients in the placebo, eight patients in the low-dose, and four patients in the high-dose groups (p = 0.12); 30-day myocardial infarction incidence was higher in patients receiving either low-dose or high-dose laser (nine patients) compared with placebo (no patients, p = 0.03). At six months, there were no differences in the change in exercise duration between those receiving a sham (28.0 s, n = 100), low-dose laser (33.2 s, n = 98), or high-dose laser (28.0 s, n = 98, p = 0.94) procedure. There were also no differences in the proportion of patients improving to better than Canadian Cardiovascular Society class III angina symptoms at six months. The follow-up visual summed stress single-photon-emission computed tomography scores were not significantly different from baseline in any group and were no different between groups. The modest improvement in angina symptoms assessed by the Seattle Angina Questionnaire also was not statistically different among the arms.

CONCLUSIONS

Treatment with percutaneous myocardial laser revascularization provides no benefit beyond that of a similar sham procedure in patients blinded to their treatment status.

Refractory myocardial ischemic syndromes: patients’ characterization and treatment goals

Experimental strategies such as gene transfer and/or cell transplantation have been explored to enrich collateral perfusion and improve contractility in severely ischemic cardiac patients. Nonetheless, the criteria used to define those patients are not uniform and need to be standardized. The authors propose herein standardized definitions in order to characterize the ‘no option’ ischemic cardiac patients as follows: lack of revascularization options; angina symptoms; limited exercise capacity; perfusion defects; an identifiable target myocardial region. In order to define a favorable clinical effect, the following end points should be the aim of treatment: improved exercise; reduced perfusion defects; improved angina or equivalent symptoms; augmented myocardial stress response; better quality of life parameters following treatment; improved collateral-dependent perfusion. The authors propose that such a systematic approach for patient evaluation should be considered to allow an accurate assessment of treatment efficacy and the comparison of results between alternative myocardial revascularization trials.

Longevity of the placebo effect in the therapeutic angiogenesis and laser myocardial revascularization trials in patients with coronary heart disease

The long-term beneficial effects of placebo therapy were evaluated in angiogenesis and laser myocardial revascularization trials in patients who had end-stage coronary heart disease. Improvements in mean angina class, exercise treadmill time, and quality of life were mostly maintained at 30 +/- 6 months of follow-up. Persistence of effect cannot be used as evidence of efficacy, and double-blinded trials are essential in this patient population.

Treatment of refractory angina pectoris

Refractory angina pectoris is defined as Canadian Cardiovascular Society class III or IV angina, where there is marked limitation of ordinary physical activity or inability to perform ordinary physical activity without discomfort, with an objective evidence of myocardial ischemia and persistence of symptoms despite optimal medical therapy, life style modification treatments, and revascularization therapies. The patients with refractory angina pectoris may have diffuse coronary artery disease, multiple distal coronary stenoses, and or small coronary arteries. In addition, a substantial portion of these patients cannot achieve complete revascularization and continue to experience residual anginal symptoms that may impair quality of their life and increase morbidity. This represents an end-stage coronary artery disease characterized by a severe myocardial insufficiency usually with impaired left ventricular function. As the life expectancy is increasing, patients with angina pectoris refractory to conventional antianginal therapeutics are a challenging problem. We review the nonconventional therapies to treat the refractory angina pectoris, including pharmacotherapy, therapeutic angiogenesis, transcutaneus electrical nerve and spinal cord stimulation, enhanced external counterpulsation, surgical transmyocardial laser revascularization, percutaneous transmyocardial laser revascularization, percutaneous in situ coronary venous arterializations, and percutaneous in situ coronary artery bypass. These therapies are not supported by a large body of data and have only a complementary role; therefore, the aggressive traditional and proven treatment of angina pectoris should be continued along with these therapies, used on an individual basis.

[Long-term results of percutaneous transmyocardial laser revascularization therapy at the University of Vienna Medical Center]

INTRODUCTION

Percutaneous transmyocardial laser revascularization (PTMR) was used for treating patients with therapy refractory angina pectoris who are not amenable for angioplasty or bypass surgery ("no-option patients"). The aim of this study was to evaluate the short- and long-term results of PTMR-interventions performed at the University of Vienna between February 1999 and May 2000.

PATIENTS AND METHODS

Twenty-four "no-option" patients underwent PTMR. The chronically ischemic myocardial areas were determined by perfusion scintigraphy; after coronary angiography and contrast ventriculography 10 patients were treated with the Biosense laser using 3D-NOGA-mapping guidance and 14 patients with the Eclipse laser using biplane fluoroscopic guidance. After an average follow-up period (FUP) of 7.7 +/- 4.2 months, all patients underwent perfusion scintigraphy, coronary angiography and contrast ventriculography. Global and regional left ventricular (LV) function were calculated by the area-length method.

RESULTS

The ischemic myocardial areas of the patients were treated with an average of 16 laser points. In one patient, an intramural hematoma caused by the Biosense laser catheter was observed, in another patient the ventricular wall was perforated by the Eclipse laser (both events were resolved conservatively); during the in-hospital stay 2 patients suffered from severe angina pectoris and in one patient a pacemaker was implanted. During the 7-month-FUP one patient had a myocardial infarction; in one patient a stent implantation, in another one coronary bypass surgery had to be performed (in not-lasered areas), 2 patients died. Thus, the composite MACE rate was 33.3%. Angina class improved significantly during the FUP, but a trend to deterioration of global ejection fraction was observed. The rest and late rest myocardial perfusion remained unchanged.

CONCLUSION

While the angina class of the patients improved significantly, no significant change of myocardial perfusion but a trend to deterioration of LV function after the FUP were observed.

The Society of Thoracic Surgeons practice guideline series: transmyocardial laser revascularization

BACKGROUND

Patients with chronic severe angina refractory to medical therapy who cannot be completely revascularized with either percutaneous catheter intervention or coronary artery bypass graft surgery present clinical challenges. Transmyocardial laser revascularization, either as sole therapy or as an adjunct to coronary artery bypass graft surgery, may be appropriate for some of these patients. Although transmyocardial revascularization has consistently been demonstrated as an efficacious means of relieving angina, the mechanism of its effects are still debated, and criteria for the selection of patients for this novel therapy have not been adequately defined.

METHODS

We reviewed the available evidence to allow us to make recommendations for the appropriate therapeutic applications of transmyocardial revascularization following the format of the American Heart Association and the American College of Cardiology guidelines for diagnostic and therapeutic procedures. Our recommendations were classified as class I, IIA, IIB, or III. For each recommendation we defined the level of supporting evidence as A, B, or C.

RESULTS

We identified class I indications for transmyocardial revascularization as sole therapy and class IIA indications for transmyocardial revascularization as an adjunct to coronary artery bypass graft surgery with levels of evidence A and B, respectively.

CONCLUSIONS

Transmyocardial laser revascularization may be an acceptable form of therapy for selected patients: as sole therapy for a subset of patients with refractory angina and as an adjunct to coronary artery bypass graft surgery for a subset of patients with angina who cannot be completely revascularized surgically.

Chronic effects of transmyocardial laser revascularization in the nonischemic myocardium: a word of caution

BACKGROUND

Transmyocardial laser revascularization (TMLR) has been shown to induce angiogenesis and improve regional myocardial blood flow. However, the biological response to laser of different energy doses in nonischemic myocardium has not been well studied. We study the time course of histological appearance following high- and low-energy TMLR in a rodent model of normal myocardium.

METHODS

The animals were randomized to two groups (high-energy (1.4 J/pulse) TMLR group and low-energy (0.6 J/ pulse) TMLR group). TMLR was applied to the anterolateral wall of the left ventricle. Then the animals were sacrificed (one every 2 or 3 days up to 6 weeks, then one every week) to give a series of hearts from 1 week to 12 weeks following TMLR.

RESULTS

No patent laser channels were identified. All laser channel remnants were composed of granulation tissue, fibrosis, and various amounts of vascular structures. Changes in vascular density demonstrated a similar pattern in both groups over time. The initial increase in vascular density within the laser channel remnants and the surrounding areas was more marked in group I than in group II. Gradual decline of vascular density occurred during a later follow-up. More fibrosis and less vasculature were demonstrated 12 weeks after laser therapy in group I.

CONCLUSION

Angiogenic response to the Holmium:YAG laser in the nonischemic myocardium is nonspecific and unsustainable. TMLR might chronically impair the myocardium function by enhancing regional scar formation. Therefore, we should clearly identify the ischemic area for laser therapy. Reduction of laser energy might prevent this potential complication.

Evaluation of myocardial perfusion and left ventricular function six months after percutaneous transmyocardial laser revascularization: Comparison of two Ho-YAG laser systems with the same wavelength, but different energy delivery and navigation systems

BACKGROUND AND OBJECTIVES

Myocardial perfusion and left ventricular function (LVF) were assessed after percutaneous transmyocardial laser revascularization (PTMR) in patients not amenable to conventional revascularization, with a comparison of two laser systems.

STUDY DESIGN/MATERIALS AND METHODS

PTMR was performed with an Eclipse laser in 15 patients, and with a Biosense DMR in 10 patients. (201)Thallium scintigraphy, coronary angiography, and ventriculography were performed at baseline and at the 7.5+/-4.3-month follow-up. All patients in the Biosense DMR group and 10 in the Eclipse group underwent NOGA mapping before PTMR and after follow-up.

RESULTS

The event-free survival rates were comparable, and the angina scores of all patients improved significantly, but more so in the Biosense DMR group than in the Eclipse group (1.2+/-1.1 vs. 2.3+/-0.9, P < 0.05). Both, the electrical activity assessed by NOGA mapping and the normalized (201)thallium uptake at redistribution improved significantly in the treated segments after Biosense DMR, while the global LVF decreased insignificantly in the Eclipse group.

CONCLUSIONS

PTMR resulted in significant improvements in the clinical symptoms, but the electrical activity improved only in the Biosense DMR group, without transforming to a better LVF.

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.

Laser myocardial revascularization modulates expression of angiogenic, neuronal, and inflammatory cytokines in a porcine model of chronic myocardial ischemia

BACKGROUND

Controversy exists whether transmyocardial laser revascularization (TMR) is associated with angiogenesis or neuromodulation and whether these are time-dependent phenomena. Accordingly, we performed a time-course analysis of the expression of angiogenic and neuronal factors following experimental percutaneous TMR.

METHODS AND RESULTS

Five weeks after placing ameroid constrictors on the circumflex coronary artery, 16 pigs underwent left ventricular mapping guided TMR using Ho:YAG laser (2 J x 1 pulse) at 30 sites directed at the ischemic zones and 11 animals were ischemic controls. Histology and immunostaining were obtained at 1 and 2 weeks (4 TMR and 3 controls at each time point) and at 4 weeks (8 TMR and 5 controls) for vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), nerve growth factor (betaNGF), substance P (SP), and monocyte chemoattractant protein-1 (MCP-1). Immunoreactivity was scored using a digital image analysis system. Factor VIII staining was used for blood vessel counting. Enhanced regional expression of VEGF, bFGF and MCP-1 in the TMR group was noted at 1 and 2 weeks with a threefold increase at 4 weeks following TMR compared to controls. BetaNGF expression in the TMR group was enhanced at 1 and 2 weeks with subsequent decline at 4 weeks to the controls level. SP expression was not significantly different between groups at all time points. There was a twofold increase in the number of blood vessels in the TMR group at 4 weeks, which was not apparent earlier.

CONCLUSIONS

These immunohistological findings suggest that cytokines expression compatible with angiogenesis and neuromodulation occurs early after TMR. Up-regulation of angiogenic and inflammatory cytokines may be more sustained than neuromodulation.

Evaluation of inotropic changes in ventricular function by NOGA mapping: comparison with echocardiography

Assessment of left ventricular (LV) function in the catheterization laboratory is important to optimize treatment decisions and guide catheter-based local therapies. NOGA electromechanical mapping was developed to assess LV contraction during catheterization; however, quantitative analysis of its "local shortening" (LS) algorithm and direct comparison with conventional methods are lacking. We evaluated the accuracy of NOGA-based regional and global function by examining its ability to detect pharmacologically induced changes in contractility compared with echocardiography. Ten anesthetized pigs were paced to ensure a constant heart rate throughout the experiment. Electromechanical maps of the LV and short-axis echocardiograms were obtained 1) at baseline, 2) during intravenous dobutamine, and 3) after intravenous propranolol. NOGA LS and ejection fraction (EF) consistently increased under dobutamine and decreased after propranolol. NOGA LS and NOGA and echocardiography circumferential shortening correlated highly with one another (r > 0.80), as did NOGA EF with echocardiography EF (r = 0.92), although absolute values differed somewhat. Thus NOGA-based global and regional function correlates closely with echocardiography and is sensitive to changes in contractility, but, at the upper end of the scale, LV function is underestimated.

A prospective, multicenter, randomized trial of percutaneous transmyocardial laser revascularization in patients with nonrecanalizable chronic total occlusions

OBJECTIVES

We sought to evaluate the safety and efficacy of percutaneous transmyocardial revascularization (PTMR) in patients with refractory angina caused by one or more chronic total occlusions (CTOs) of a native coronary artery.

BACKGROUND

Previous unblinded, randomized trials of PTMR in patients with end-stage coronary artery disease and refractory angina have demonstrated significant relief of angina and increased exercise duration. Whether such benefits would be realized in blinded patients with less extensive coronary artery disease is unknown.

METHODS

A total of 141 consecutive patients with class III or IV angina caused by one or more chronically occluded native coronary arteries in which a percutaneous coronary intervention (PCI) had failed were prospectively randomized, at 17 medical centers, in the same procedure, to PTMR plus maximal medical therapy (MMT) (n = 71) or MMT only (n = 70). Blinding was achieved through heavy sedation, dark goggles and the concurrent performance of PCI in all patients.

RESULTS

Baseline characteristics were similar between the two groups. A median number of 20 laser channels were created in patients randomized to PTMR. At six months, the anginal class improved by two or more classes in 49% of patients assigned to PTMR and in 37% of those assigned to MMT (p = 0.33). The median increase in exercise duration from baseline to six months was 64 s with PTMR versus 52 s with MMT (p = 0.73). There were no differences in the six-month rates of death (8.6% vs. 8.8%), myocardial infarction (4.3% vs. 2.9%) or any revascularization (4.3% vs. 5.9%) in the PTMR and MMT groups, respectively (p = NS for all).

CONCLUSIONS

In patients with class III or IV angina caused by nonrecanalizable CTOs, the performance of PTMR does not result in a greater reduction in angina, improvement in exercise duration or survival free of adverse cardiac events, as compared with MMT only.

Transmyocardial laser revascularization: a review of basic and clinical aspects

Transmyocardial laser revascularization (TMR or TMLR) is a surgical therapy developed to treat patients with debilitating, medically refractory angina pectoris due to epicardial coronary artery disease that is not amenable to treatment using the traditional methods of percutaneous coronary intervention (PCI) or coronary artery bypass graft surgery (CABG). This technique can also be applied percutaneously [percutaneous myocardial revascularization (PMR) or direct myocardial revascularization (DMR)]. The original hypotheses which motivated development of TMR were that: (i) oxygenated blood could flow directly from the left ventricle and perfuse the myocardium; and (ii) such artificially created channels would remain patent. However, experimental data have refuted both hypotheses. In the face of early reports of marked clinical benefits in terms of relief of anginal symptoms, alternate hypotheses to explain the mechanism have been pursued, including TMR-associated neoangiogenesis and cardiac denervation. Clinically, numerous reports of reduction in frequency and severity of anginal symptoms, improved exercise tolerance and improved quality of life have appeared from nonblind registry-type studies as well as nonblind randomized clinical trials of TMR or PMR versus continued medical therapy. TMR was not associated with a significant improvement in survival compared with medical therapy alone in randomized trials. For example, the prospective, randomized Angina Treatments-Lasers and Normal Therapies in Comparison (ATLANTIC) trial found a 1-year mortality of 5% in 92 TMR-treated patients and 10% in 90 patients treated with medication only. No proof of improved myocardial blood flow in hearts of treated patients is currently available. The first randomized study of PMR was the Potential Angina Class Improvement From Intramyocardial Channels (PACIFIC) trial which found significantly greater improvements in anginal symptoms and exercise tolerance with PMR plus medical therapy, compared with medical therapy alone. The preliminary results of two double-blind studies with PMR/DMR have been presented but have not yet been published in full. Whereas PMR-treated patients did significantly better than sham-treated control groups after 6 months in the Blinded Evaluation of Laser Intervention Electively For angina pectoris (BELIEF) trial, there was no difference after 1 year between DMR-treated patients and those treated with medication only in the DMR In Regeneration of Endomyocardial Channels Trial (DIRECT). Different devices used for revascularization in these two trials may explain the disparity in the results, and therefore the efficacy and tolerability of each device should be judged upon data collected with that particular device.

Alternatives to traditional coronary bypass surgery

Over 1 million percutaneous coronary interventions (PCI) and a half million surgical coronary artery bypass grafting procedures (CABG) are performed in the United States annually for treatment of coronary artery disease. With recent advances in anti-restenosis strategies, the number of PCIs is expected to increase dramatically. Still, these therapies treat relatively discrete coronary lesions. However, there is a relatively large number of patients for whom traditional therapies are not optimal, either because there are diffuse coronary artery lesions, because there are chronic total occlusions, or because, in the instance of bypass surgery, creating proximal or distal anastomoses is problematic. We review three strategies in various stages of development aimed at treating patients not optimally served by traditional forms of revascularization: transmyocardial laser revascularization, angiogenic therapies, and direct ventricle-to-coronary artery bypass.

Could plasmid-mediated gene transfer into the myocardium be augmented by left ventricular guided laser myocardial injury?

Early studies have indicated no correlation between the amount of mechanical injury and the level of myocardial gene expression following direct plasmid vector injection. Recently, however, evidence suggests that combined laser myocardial injury and plasmid-based gene delivery exert synergistic effects on gene expression and activity. The purpose of the study was to determine whether laser-induced myocardial injury followed by transendocardial gene transfer increases gene expression compared to gene transfer alone. We assessed the ability of a plasmid vector to express its transgene after injection into porcine ischemic myocardium with and without preceding laser myocardial injury. Thirteen animals had transendocardial injections of the luciferase reporter gene in a plamid vector using a catheter-based injection system. Injections (0.5 mg per animal, 50 microg per injection site) were divided into 10 sites in the ischemic territory. Eight animals underwent transendocardial laser injury of the ischemic region (2 Joule per pulse x 10 sites) prior to gene delivery. In five animals, gene injection sites were dispersed between laser channels, and in three animals laser and gene delivery were applied in close proximity (< 5 mm) or at the same location. Luciferase activity was measured at 3 and 7 days. Luciferase expression in ischemic zones was markedly elevated at day 3 and 7, and similar whether animals were pretreated using laser injury followed by gene transfer compared to gene transfer alone. Neither same-spot injection nor dispersed gene delivery were associated with augmented gene expression compared to gene transfer alone. Using the above-described catheter-based approach to combine localized laser injury and injection of naked DNA into ischemic myocardium, laser injury did not augment gene expression above levels present with gene transfer alone.

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.

Gene therapy for ischemic heart disease: therapeutic potential

Gene therapy is evolving as an alternative mode to pharmacological intervention in the treatment of cardiovascular diseases. Experimental observations indicating that introduction of genes encoding for angiogenic peptide growth factors could result in improvement in perfusion to ischemic myocardium have led to the initiation of a number of preliminary clinical trials to evaluate this therapeutic modality. Sustained expression of the growth factor product from somatic cells transfected with the DNA for that protein has proven to be one of the major advantages of a gene therapy based approach over administration of the recombinant protein. A number of gene therapy vectors have been developed, prominent among these being adenoviral vectors and naked plasmid DNA. Whereas plasmid DNA results in less efficient transfection, its tolerability profile may be superior to adenoviral vectors. Plasmid DNA is particularly suitable when the gene product to be produced is capable of being secreted by the cell which is producing it. Vascular endothelial growth factor (VEGF) is not only essential to the process of angiogenesis, but, because it can be secreted from intact cells, appears to be ideal for gene transfer therapy aimed at improving perfusion to ischemic myocardium. The DNA can be delivered to the myocardium by intra-arterial or intramuscular injection. At present, direct injection into the muscle either via a small thoracotomy incision or by use of a recently developed percutaneous catheter technique appears to be superior to arterial administration. Several clinical trials based on intramyocardial injection of VEGF DNA in patients with otherwise inoperable coronary artery disease and intractable angina pectoris have recently been completed. These phase I trials have documented the tolerability of gene transfer using plasmid DNA and show promise of being able to improve myocardial perfusion and reduce anginal symptoms in the majority of patients treated thus far. While the trials involving gene transfer via a thoracotomy did not allow for randomization to a placebo group, the recent advent of a percutaneous delivery modality has allowed for randomization which should enhance our ability to determine whether angiogenic gene therapy will prove to be as effective as initial results suggest. In the future, results from such randomized placebo-controlled trials, improvement in vectors utilized for gene transfer and innovative new delivery techniques will undoubtedly enhance the potential of this novel approach to myocardial revascularization.