Percutaneous method of laser transmyocardial revascularization

Transmyocardial Revascularization: Peril and Potential

Transmyocardial laser revascularization is a technique for the treatment of patients with chronic angina pectoris that is refractory to medical therapy and who are not eligible for surgical intervention. Percutaneous myocardial revascularization is a less-invasive catheter-based procedure that has been adapted from transmyocardial laser revascularization. Six prospective randomized clinical trials have been performed with transmyocardial laser revascularization and 5 have been performed using percutaneous myocardial revascularization. All of the transmyocardial laser revascularization and 4 of the percutaneous myocardial revascularization studies showed a significant improvement in angina class; however, results for improved survival, increased exercise tolerance, improved ejection fraction, and improved myocardial perfusion were less definitive. Transmyocardial laser revascularization has significant potential for morbidity and mortality. This article summarizes the results of the randomized trials, explains the current theories for the mechanism of transmyocardial laser revascularization, and discusses its current role in treatment for patients, considering the evidence that currently exists.

Usefulness and safety of percutaneous myocardial laser revascularization for refractory angina pectoris

This prospective, double-blind, randomized, sham-controlled trial was designed to control for patient and investigator bias in assessing symptomatic improvement after percutaneous myocardial laser revascularization (PMLR) therapy. Eighty-two patients with stable angina pectoris (class III or IV) not amenable to conventional revascularization and with evidence of reversible ischemia, ejection fraction >/=25%, and myocardial wall thickness >/=8 mm were randomized to either PMLR with optimal medical therapy (n = 40) or to a sham procedure with optimal medical therapy (n = 42). With the exception of 1 laser technician, all patients, investigators, and assessors were blinded to treatment through the 12-month follow-up. The primary end point was restricted to Canadian Cardiovascular Society angina class improvement to limit the number of patients exposed to a sham procedure. Secondary assessments included medication usage, quality of life, exercise testing, ejection fraction, and hospitalizations. The incidence of serious adverse events, as determined by cardiac event-free survival at 12 months, was similar between groups. At 12 months, Canadian Cardiovascular Society angina scores improved by >/=2 classes in significantly more PMLR-treated patients than sham control patients (35% vs 14%, p = 0.04). Angina-specific quality-of-life measures were significantly higher in the PMLR group at each follow-up (p <0.05). Exercise and medication usage was similar between groups at 12 months. We conclude that PMLR therapy is reasonably safe and effective as symptomatic improvement in patients refractory to medical therapy, and that the clinical benefit is not attributable to placebo effect or investigator bias.

Alternative therapeutic strategies for patients with severe end-stage coronary artery disease not amenable to conventional revascularization

Although there have been remarkable advances in medical therapy, percutaneous coronary interventions, and coronary artery bypass graft surgery, complete revascularization remains a challenge given the more complex coronary artery disease prevalent in contemporary practice. The lack of donors for cardiac transplantation will fuel the search for effective alternative strategies for dealing with patients with severe ischemic heart disease not amenable to conventional revascularization techniques. Percutaneous laser revascularization clearly diminishes anginal symptoms; however, the blinded trials have provided conflicting results, with one study showing a definite decrease in angina and another suggesting that the placebo effect may play a major role in this modality. Similarly, surgical transmyocardial laser revascularization is limited by the lack of consistent improvement in objective measurements of ischemia and the potential confounding mechanisms of denervation and the placebo effect, and thus should be reserved for only the most highly selected patients. Although enhanced external counterpulsation is associated with an improvement in anginal symptoms and exercise tolerance, this modality is limited by its availability, tolerability, and rigid exclusion criteria. Of the alternative strategies available, therapeutic angiogenesis holds the most promise. However, the long-term results of ongoing randomized clinical trials require further scrutiny. Novel methods for vascular reconstruction are evolving techniques, but should be viewed currently as mainly experimental methods. The common goals of these new treatment options would be to reduce symptoms, decrease morbidity, and potentially improve mortality by reducing ischemia through favorably impacting myocardial oxygen supply and demand. The optimal management of patients with severe end-stage coronary artery disease not amenable to conventional revascularization techniques will continue to remain a challenge for the clinician and will be the main focus of basic cardiovascular research and clinical trials in the new millennium.

Percutaneous myocardial laser revascularization in patients with refractory angina pectoris

This study aimed to determine the safety and efficacy of percutaneous myocardial laser revascularization (PMLR). Seventy-three patients with stable angina pectoris (class III or IV) who were unsuitable for conventional revascularization and had evidence of reversible ischemia by thallium-201 scintigraphy, ejection fraction of > or =25%, and myocardial wall thickness > or =8 mm were randomized to optimal medical therapy alone (n = 37) or PMLR with optimal medical therapy (n = 36). Patients were followed up at 3, 6, and 12 months. The primary end point was exercise time. Secondary end points included angina scores, left ventricular ejection fraction, quality of life, changes in medical therapy, and hospitalizations. All 36 patients randomized to PMLR underwent the procedure successfully with no periprocedure deaths. One patient developed sustained ventricular tachycardia that required electrical cardioversion, and 1 patient developed cardiac tamponade that required surgical drainage. At 12 months, exercise times improved by 109 seconds in the PMLR group but decreased by 62 seconds in the control group (p <0.01). Angina scores improved by 2 classes in 36% of PMLR-treated patients at 12 months compared with 0% of the control patients (p <0.01). We conclude that PMLR is a relatively safe procedure that provides patients with symptomatic angina relief and improvement in exercise capacity and quality of life.

Myocardial laser revascularization for the treatment of end-stage coronary artery disease

Myocardial laser revascularization is a novel therapeutic technique aimed at delivering oxygenated blood via a series of channels to the ischemic regions of the heart. These channels may be created surgically or via a less invasive percutaneous approach. In patients with end-stage coronary artery disease, both transmyocardial laser revascularization (TMR) and percutaneous myocardial laser revascularization (PMR) have been associated with a reduction in symptoms, improved exercise tolerance, and enhanced quality of life. However, the mechanism of action of laser therapy is incompletely understood, the results of objective cardiac perfusion measurements are inconclusive, and multiple randomized trials have failed to demonstrate an increase in survival. In addition, the positive results seen in TMR trials have been questioned because of a lack of blinding, raising the possibility that the benefit may have been due to the placebo effect. Finally, two recent sham-controlled, randomized clinical trials of PMR have not shown any benefit of the procedure, but instead have highlighted the important role of the placebo effect in the response to PMR. Further research is, therefore, needed to elucidate the value of myocardial laser revascularization.

Myocardium tissue ablation with high-peak-power nanosecond 1,064- and 532-nm pulsed lasers: influence of laser-induced plasma

BACKGROUND AND OBJECTIVES

We investigated the mechanism and characteristics of porcine myocardium tissue ablation in vitro with nanosecond 1,064- and 532-nm pulsed lasers at laser intensities up to approximately 5.0 GW/cm(2). Particular attention was paid to study the influence of the laser-induced plasma on the ablation characteristics. The applicability of these two lasers to transmyocardial laser revascularization (TMLR) was discussed.

STUDY DESIGN/MATERIALS AND METHODS

Porcine myocardium tissue samples were irradiated with 1,064- and 532-nm, Q-switched Nd:YAG laser pulses, and the ablation depths were measured. The temporal profiles of the laser-induced optical emissions were measured with a biplanar phototube. For the ablated tissue samples, histological analysis was performed with an optical microscope and a polarization microscope.

RESULTS

The ablation efficiency at 1,064 nm was higher than that at 532 nm. The ablation threshold at 1,064 nm (approximately 0.8 GW/cm(2)) was lower than that at 532 nm (approximately 1.6 GW/cm(2)), in spite of the lower absorption coefficient being expected at 1,064 nm. For the 1,064-nm laser-ablated tissues, thermal damage was very limited, while damage presumably caused by the mechanical effect was observed in most of the cases. For the 1,064-nm laser ablation, the ablation threshold was equal to the threshold of the laser-induced optical emission (approximately 0.8 GW/cm(2)), while for the 532-nm laser ablation, the optical emission threshold ( approximately 2.4 GW/cm(2)) was higher than the ablation threshold.

CONCLUSIONS

We considered that for the 1,064-nm laser ablation, the tissue removal was achieved through a photodisruption process at laser intensities of > approximately 0.8 GW/cm(2). At laser intensities of > 3.0 GW/cm(2), however, the ablation efficiency decreased; this can be attributed to the absorption of incoming laser pulses by the plasma. For the 532-nm laser ablation, the tissue removal was achieved through a photothermal process at laser intensities of > approximately 1.6 GW/cm(2). At laser intensities of > 2.4 GW/cm(2), a photodisruption process may also contribute to the tissue removal, in addition to a photothermal process. With regard to the ablation rates, the 1,064-nm laser was more suitable for TMLR than the 532-nm laser. We concluded that the 1,064-nm Q-switched Nd:YAG laser would be a potential candidate for a laser source for TMLR because of possible fiber-based beam delivery, its compact structure, cost effectiveness, and easy maintenance. Animal trials, however, have to be carried out to evaluate the influence of the tissue damage.

Nanosecond, high-intensity pulsed laser ablation of myocardium tissue at the ultraviolet, visible, and near-infrared wavelengths: in-vitro study

BACKGROUND AND OBJECTIVE

A large number of clinical trials of transmyocardial laser revascularization (TMLR) have been conducted to treat severe ischemic heart diseases. A variety of laser sources have been used or tested for this treatment, however, no comprehensive study has been performed to reveal the mechanism and the optimum laser irradiation condition for the myocardium tissue ablation. There have been reported limited experimental data of the high-intensity pulsed laser ablation of myocardium tissues.

STUDY DESIGN/MATERIALS AND METHODS

A 1064-nm Q-switched Nd:YAG laser and its 2nd (532 nm), 3rd (355 nm), and 4th (266 nm) harmonics were used for ablation experiments. At each wavelength, 25 laser pulses irradiated the porcine myocardium tissue samples at a constant laser intensity (peak laser power divided by laser spot area) of approximately 2 GW/cm(2) and the ablation depths were measured. During ablation, laser-induced optical and acoustic emissions were measured to investigate the ablation mechanism at each laser wavelength. For the ablated tissues, histological observation was made with a polarization optical microscope.

RESULTS

It was shown that the ablation efficiency did not directly depend on the linear absorption coefficient of the tissue; the ablation depth was maximized at 355 and 1064 nm, and minimized at 532 nm. Strong laser-induced optical and acoustic emissions were observed for the 266- and 1064-nm laser irradiations. The histology showed that thermal denaturation of the tissue near the ablation walls decreased with decreasing wavelength for 266, 355, and 532 nm, but it was limited for 1064 nm.

CONCLUSION

At the laser intensity of approximately 2 GW/cm(2), ablation characteristics were drastically changed for the different laser wavelengths. The results indicated that for 266, 355, and 532 nm, the tissue removal was achieved mainly through a photothermal process, but for 266 nm the intense laser-induced plasma formation would result in a reduced laser energy coupling to the tissue. For 1064 nm, a photodisruption was most probable as a dominant tissue removal process. Because of the high ablation rate and limited thermal denaturation, the 355- and 1064-nm lasers could be potential laser sources for TMLR, although further investigation is needed to discuss the clinical issues.

Transmyocardial coil implants: a novel approach to transmyocardial revascularization

BACKGROUND

Transmyocardial laser revascularization (TMLR) has potential benefit for patients with end-stage coronary artery disease and intractable angina not amenable to conventional revascularization techniques. Neovascularization has been proposed to occur around the laser channels. Our aim was to determine the feasibility of a novel nonlaser myocardial revascularization technique and its effect on angiogenesis in a nonischemic porcine model.

METHODS

In the first phase, six transmyocardial stainless steel coil implants (TMI) were deployed to the lateral wall of the left ventricle in each of 6 pigs. The animals were sacrificed at 8 and 12 weeks, with a single animal dying prematurely at 4 weeks, and the myocardium was assessed for new vessel growth. In the second phase, 8 implants were deployed in each of 12 pigs with regular fluoroscopic follow-up until sacrifice at 2 weeks to assess implant stability.

RESULTS

The deployment procedure was safe and feasible with no complications evident. A significant increase in new vessels at implant sites with 5.43 +/- 3.67, 4.97 +/- 2.44, and 3.57 +/- 2.29 seen per high power field at 12, 8, and 4 weeks, respectively, compared to 1.00 +/- 1.06 (p < 0.0001) in control myocardium. There was no evidence of implant migration in Phase 2.

CONCLUSIONS

TMIs can feasibly be deployed in the nonischemic pig model with a high success rate. The presence of angiogenesis at the implant site and the maintenance of this reaction for 3 months implies that TMI may offer an alternative to TMLR while providing a platform for delivery of angiogenic factors.

Intracardiac catheter 2-D arrays on a silicon substrate

The design, fabrication, and characterization of a 7 MHz, two-dimensional (2-D) array transducer built on a silicon substrate is described. The array fits inside a 9-French (2.9 mm O.D.) catheter for use in real-time intracardiac volumetric imaging. The -6 dB fractional bandwidth of the transducer is 30%, the 50 ohm pitch-catch insertion loss is 78 dB, and the interelement crosstalk is -25 dB. Real-time volumetric images in phantoms and in-vitro images of a sheep heart have been acquired yielding measured spatial resolution of 2 mm at a depth of 1 cm. The cardiac structures imaged include ventricular chambers, interventricular septum, mitral and tricuspid valves and real-time 3-D rendered volumes of the tricuspid valve in the open and closed position.

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.

Clinical outcome of a cohort of patients eligible for therapeutic angiogenesis or transmyocardial revascularization

BACKGROUND

Newer methods of coronary revascularization are being investigated in patients who are not candidates for coronary artery bypass grafting or percutaneous intervention. Our objective was to determine the proportion of patients eligible for newer methods of revascularization and determine their 1-year clinical outcome.

METHODS

Five hundred consecutive charts and angiograms from patients undergoing diagnostic angiography for coronary artery disease from January to May of 1998 were reviewed to assess the suitability for revascularization. Patients ineligible for conventional revascularization were followed up for 1 year.

RESULTS

Fifty-nine patients of the 500 studied were identified who had refractory ischemia but were not candidates for traditional revascularization. The 59 patients ineligible for traditional methods of revascularization had a rehospitalization rate of 128% (76 total hospitalizations), a 25.5% rate of myocardial infarction (15 of 59), and a mortality rate of 16.9% (10 of 59).

CONCLUSIONS

The prognosis of many patients eligible for newer methods of revascularization on maximal medical therapy is poor.

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.

Histologic signatures of thermal injury: applications in transmyocardial laser revascularization and radiofrequency ablation

BACKGROUND AND OBJECTIVE

Cardiac treatments such as transmyocardial laser revascularization and radiofrequency ablation cause thermal injury. We sought to provide quantitative histologic methods of assessing such injury by using the inherent birefringence of cardiac muscle and collagen; specifically, to exploit the connection between thermal injury and the loss of birefringence.

STUDY DESIGN/MATERIALS AND METHODS

We quantified tissue birefringence changes in vitro for temperatures up to 130 degrees C. This information was used to assess thermal injury associated with myocardial channels made in vitro. We then measured in vivo cardiac injury 30 minutes and 3 days after radiofrequency exposure.

RESULTS

Birefringence decreased above 60 degrees C for muscle and above 70 degrees C for collagen. Temperatures above 80 degrees C were associated with collagen fiber straightening and above 95 degrees C with little muscle birefringence. Injury adjacent to laser channels was greatest parallel to cell orientation. In vivo, muscle with reduced birefringence was surrounded by cells exhibiting focal birefringence increases (contraction bands). Early injury assessment marked by birefringence changes corresponded to lesion size at 3 days.

CONCLUSION

Polarized light revealed histologic temperature signatures corresponding to irreversible muscle injury and collagen denaturation.

Transmyocardial laser revascularization

Transmyocardial laser revascularization is an alternative treatment option for patients with refractory angina who are not suitable candidates for more conventional coronary intervention or surgery. The laser creates channels that provide blood flow from the left ventricular chamber to areas of ischemic myocardium. Results have been impressive with patients reporting a reduction in angina of two classes according to the Canadian Heart Association Angina Classification. Care of the patient post transmyocardial laser revascularization procedure is comparable to that of other cardiac surgery patients. Innovations in this relatively new procedure include less invasive approaches and using it as an adjunctive or delivery modality for gene therapy.

Percutaneous transmyocardial laser revascularisation for severe angina: the PACIFIC randomised trial. Potential Class Improvement From Intramyocardial Channels

BACKGROUND

Percutaneous transmyocardial laser revascularisation (PTMR) is a proposed catheter-based therapy for refractory angina pectoris when bypass surgery or angioplasty is not possible. We undertook a randomised trial to assess the safety and efficacy of this technique.

METHODS

221 patients with reversible ischaemia of Canadian Cardiovascular Society angina class III (61%) or IV (39%) and incomplete response to other therapies were recruited from 13 centres. Patients were randomly assigned PTMR with a holmium:YAG laser plus continued medical treatment (n=110) or continued medical treatment only (n=111). The primary endpoint was the exercise tolerance at 12 months. Analyses were by intention to treat.

FINDINGS

11 patients died and 19 withdrew; 92 PTMR-group and 99 medical-treatment-group patients completed the study. Exercise tolerance at 12 months had increased by a median of 89.0 s (IQR -15 to 183) with PTMR compared with 12.5 s (-67 to 125) with medical treatment only (p=0.008). On masked assessment, angina class was II or lower in 34.1% of PTMR patients compared with 13.0% of those medically treated. All indices of the Seattle angina questionnaire improved more with PTMR than with medical care only. By 12 months there had been eight deaths in the PTMR group and three in the medical treatment group, with similar survival in the two groups.

INTERPRETATION

PTMR was associated with increased exercise tolerance time, low morbidity, lower angina scores assessed by masked reviewers, and improved quality of life. Although there is controversy about the mechanism of action, and the contribution of the placebo effect cannot be quantified, this unmasked study suggests that this palliative procedure provides some clinical benefits in the defined population of patients.

Results of clinical trials of transmyocardial laser revascularization versus medical management for end-stage coronary disease

BACKGROUND DATA

Over 5,000 patients worldwide have undergone transmyocardial laser revascularization (TMR) since 1990 for the treatment of myocardial ischemia due to end-stage coronary artery disease. Recently, four prospective randomized controlled clinical trials have reported their results in comparing TMR to maximal medical therapy. The purpose of this review is to provide an update and comparison of the results of these trials.

METHODS

Patients with severe angina were randomized to treatment by laser TMR (carbon dioxide or holmium YAG) or continuing on maximum medical therapy. All patients were followed for a year and had reassessment of angina class and quality of life at that time.

RESULTS

All of the trials demonstrated that TMR provided significant relief of angina when compared to medical management. Additional objective data in the form of exercise tolerance and myocardial perfusion scanning was used to support the symptomatic improvement.

CONCLUSION

Symptomatic improvement is seen for patients with severe diffuse coronary artery disease treated by TMR.

Transmyocardial revascularization aggravates myocardial ischemia around the channels in the immediate phase

We examined whether transmyocardial revascularization (TMR) relieves myocardial ischemia by increasing regional perfusion via the transmural channels in acute canine experiments. Regional blood flow during transient coronary ligation (2 min) was compared before and 30 min after TMR, and at the third transient ischemia the mid-left ventricle (LV) was cut and immediately frozen along the short axis for the analysis of NADH fluorescence in the regions around the TMR channels. In low-resolution analysis (2-4 g tissue or 2-3 cm(2) area), regional perfusion was not significantly altered after TMR, and NADH fluorescence was observed throughout the ischemic region without significant spatial variation. High-resolution analysis (2.8 mg, 1 mm x 1 mm) revealed that the flow after TMR was lower, and NADH fluorescence was higher in the regions close to the channels (1-2 mm) than in the regions 3-4 mm away from them. Creating TMR channels did not improve the regional perfusion and rather aggravated the local ischemia in the vicinity of the channels in the immediate phase.

Transmyocardial laser revascularization in the treatment of myocardial ischemia

Since 1990, over five thousand patients worldwide have undergone transmyocardial laser revascularization (TMR) for the treatment of myocardial ischemia due to end-stage coronary artery disease. Recently four prospective randomized controlled clinical trials have reported their results in comparing TMR to maximal medical therapy. All of the trials demonstrated that TMR provided notable relief of angina when compared to medical management. Additional objective data in the form of exercise tolerance and myocardial perfusion scanning are used to support the symptomatic improvement. Although the trials are similar, they are not identical, and this review provides an update and comparison of their results.

[The practical clinical guidelines of the Sociedad Española de Cardiología on interventional cardiology: coronary angioplasty and other technics]

Interventional cardiology has had an extraordinary expansion in last years. This clinical guideline is a review of the scientific evidence of the techniques in relation to clinical and anatomic findings. The review includes: 1. Coronary arteriography. 2. Coronary balloon angioplasty. 3. Coronary stents. 4. Other techniques: directional atherectomy, rotational atherectomy, transluminal extraction atherectomy, cutting balloon, laser angioplasty and transmyocardial laser and endovascular radiotherapy. 5. Platelet glycoprotein IIb/IIIa inhibitors. 6. New diagnostic techniques: intravascular ultrasound, coronary angioscopy, Doppler and pressure wire. For the recommendations we have used the classification system: class I, IIa, IIb, III like in the guidelines of the American College of Cardiology and the American Heart Association.

Transmyocardial laser revascularization: current status

Transmyocardial laser revascularization (TMLR) has been widely evaluated for treatment of the ischemic myocardium either in conjunction with coronary artery bypass grafting or as sole therapy. Clinically, it has shown significant improvement for angina symptoms, but the mechanism by which this modality works is unknown at this time. The original premise on which transmyocardial revascularization was established depended on its ability to essentially generate channels that would directly carry blood from the ventricle into the ischemic myocardium. This theory, however, has not been substantiated, so other mechanisms have been postulated. This article gives a historical perspective on the advent of transmyocardial revascularization and the many animal and human studies that have paved the way for its clinical use. Current controversies are examined, along with the new advances in laser technology and where the future of TMLR is headed.

Transmyocardial revascularization: the fate of myocardial channels

Attempted cardiac revascularization through laser-made channels has gained considerable recent notoriety. Although the treatment reduces angina, its ability to enhance perfusion is unclear, and the mechanism of action unknown. The fate of the channels appears an obvious place to look for insight. Therefore, this review focuses on temporal and spatial changes in channel morphology. An appreciation of the natural history of the channels not only has potential to elucidate mechanisms, but also to provide the basis for optimization of channel-making.

Catheter-based percutaneous myocardial laser revascularization in patients with end-stage coronary artery disease

OBJECTIVES

This study evaluates the feasibility and safety of a catheter-based laser system for percutaneous myocardial revascularization and analyses the first clinical acute and long-term results in patients with end-stage coronary artery disease (CAD) and severe angina pectoris.

BACKGROUND

In patients with CAD and intractable angina who are not candidates for either coronary artery bypass grafting (CABG) or percutaneous transluminal coronary angioplasty (PTCA), transmyocardial laser revascularization (TMR) has been developed as a new treatment that results in reduced angina pectoris and increased exercise capacity. However, surgical thoracotomy is required for TMR with considerable morbidity and mortality.

METHODS

A catheter-based system has been developed that allows creation of laser channels in the myocardium from within the left ventricular cavity. Laser energy generated by a Holmium: YAG (Cardiogenesis Corporation, Sunnyvale, California) laser was transmitted to the myocardium via a flexible optical fiber capped by an optic lens. The optical fiber was maneuvered to the target area under biplane fluoroscopy through a coaxial catheter system permitting movement in three dimensions.

RESULTS

Thirty-four patients with severe CAD not amenable to either CABG or PTCA and refractory angina pectoris (Canadian Cardiologic Society [CCS] Angina Scale Class III-IV) were included in the study. Ischemic regions were identified by coronary angiography and confirmed by thallium scintigraphy. The percutaneous myocardial revascularization (PMR) procedure was successfully completed in all patients. In 29 patients, one vascular territory of the left ventricle and in 5 patients, two vascular territories were treated. Eight to fifteen channels were created in each ischemic region. Major periprocedural complications were limited to an episode of arterial bleeding requiring surgical repair. There was one death early after PMR, due to a myocardial infarction (MI) in a nontreated region. Clinical follow-up at 6 months (17 patients) demonstrated significant improvement of angina pectoris (CCS class before PMR: 3.0+/-0.0, six months after PMR: 1.3+/-0.8, p<0.0001) and increased exercise capacity (exercise time on standard bicycle ergometry before PMR: 384+/-141 s, six months after PMR: 514+/-158 s, p<0.05), but thallium scintigraphy failed to show improved perfusion of the laser treated regions.

CONCLUSIONS

Percutaneous myocardial revascularization is a new safe and feasible therapeutic option in patients with CAD and severe angina pectoris not amenable to either CABG or PTCA. Initial results show immediate and significant improvement of symptoms and exercise capacity but evidence of improved myocardial perfusion is still lacking.

Direct myocardial revascularization and angiogenesis--how many patients might be eligible?

This study examines the proportion of patients with ischemic heart disease who may be candidates for the newer modalities of revascularization. A significant proportion (approximately 5%) of patients who undergo coronary angiography at tertiary referral centers may be eligible for newer methods of therapy.

Percutaneous transmyocardial laser revascularization: an overview

Transmyocardial revascularization (TMR) is a novel strategy designed to improve anginal symptoms and enhance myocardial perfusion by applying laser energy directly into the ischemic myocardium. Preliminary surgical experiences using TMR have indicated a significant reduction in angina severity, improved quality of life, and some evidence of improved myocardial perfusion in refractory coronary ischemic syndromes. Possible mechanisms to explain the clinical benefit include stimulated angiogenesis, local myocardial denervation, or both. The goal of catheter-based TMR is to create nontransmural endomyocardial channels smaller in size but comparable in tissue effect to the surgical TMR procedure. At present, most percutaneous TMR experiences seem very promising, although derived from nonrandomized registries with a relatively small number of patients. More rigorous assessments of objective and subjective endpoints derived from ongoing larger randomized clinical trials are needed to render definitive conclusion about the validity of this therapeutic strategy in patients with refractory coronary ischemic syndromes. Cathet. Cardiovasc. Intervent. 47:354-359, 1999.

Transmyocardial and percutaneous myocardial revascularization: current and future role in the treatment of coronary artery disease

Transmyocardial revascularization (TMR) is a new treatment modality under evaluation in patients with severely symptomatic, diffuse coronary artery disease, in whom the potential for medical or interventional management has been exhausted. Preliminary clinical trials show improved ischemic symptoms within the first 3 months in about 70% of TMR-treated patients. The original proposed mechanism of surgical or catheter-based TMR (percutaneous myocardial revascularization [PMR]) was that channels mediate direct blood flow between the left ventricular cavity and ischemic myocardium. However, several alternative explanations for the clinical success of TMR have recently been suggested, including improved perfusion by angiogenesis, an anesthetic effect by nerve destruction, and a potential placebo effect. This article reviews the clinical role of TMR/PMR, its possible pathophysiologic mechanisms, and its controversies. It provides an overview of the actual scientific and clinical status of TMR and details future directions.

Transmyocardial revascularization with holmium laser

Sixteen patients with angina refractory to medical therapy who were not considered suitable for standard revascularization underwent transmyocardial revascularization with holmium laser. The average age of the patients was 63.2 +/- 10.5 years. All of them had angina class 3 or 4, and 9 (56%) had previously undergone an aortocoronary bypass grafting. Four patients died during the 6-month follow-up period (25%). Among the survivors, anginal class decreased to class 2 or 1 at the 6th month (p = 0.002). Ejection fraction did not change. The ischemic burden by Holter decreased from 85.3 +/- 656 to 5.5 +/- 9.7 min (p = 0.046). Myocardial perfusion with 201Tl single photon emission computed tomography (SPECT) images at rest and after dipyridamole showed a significant improvement among the ischemic treated segments (p = 0.015). Baseline ejection fraction was somehow lower in nonresponsive than in responsive patients (33 +/- 13 vs. 49 +/- 10, p = 0.052). We conclude that transmyocardial laser revascularization with holmium laser is effective in treatment in ischemic patients not amenable to surgery or percutaneous procedures, as previously reported with CO2 laser. Further investigation is needed to determine which clinical profiles identify the patients for whom this therapy is suitable.

Initial results of laser-based percutaneous myocardial revascularization for angina pectoris

Results of a 30-patient pilot study of a recently developed percutaneous myocardial revascularization approach are described. The feasibility and positive safety profile of percutaneous myocardial revascularization are clearly demonstrated, with no mortality associated with the treatment or in the immediate post-treatment period and an incidence of only 1 major complication.

Beyond stents: third-generation coronary devices

Despite extraordinary growth in percutaneous transluminal coronary angioplasty (>400,000 cases in United States in 1997) patients are still routinely referred for bypass grafting in large numbers. Why? Second-generation devices (directional coronary atherectomy, high-speed rotational atherectomy [Rotablator], and stents) have expanded the application of percutaneous catheter treatment of coronary disease. Specifically, highly eccentric lesions in large vessels, heavily calcified lesions, and coronary dissections can be effectively treated with these devices. Stents have substantially reduced the incidence of restenosis, but this benefit is largely confined to vessels more than 3 mm in diameter and stenoses less than 20 mm in length. A third generation of coronary devices has evolved in the late 1990s in response to continuing failures of conventional balloon angioplasty, atherectomy, and stenting. The failures of the 1990s were (1) restenosis, including in-stent restenosis, (2) chronic total occlusions, (3) diffuse small-vessel disease, and (4) aged vein graft disease. In response to these challenges novel devices are being developed: (1) for restenosis, intracoronary radiation therapy (brachytherapy); (2) for chronic total occlusions, Prima Laser wire; (3) for diffuse small-vessel disease, percutaneous myocardial laser revascularization; and (4) for aged vein grafts, antiembolization devices. Each of these new catheter technologies will need to be economically and clinically reconciled with the multitude of minimally invasive surgical revascularization techniques that are rapidly evolving.

Current perspectives on direct myocardial revascularization

Direct myocardial revascularization (DMR), either surgical or catheter-based, uses lasers to create channels between ischemic myocardium and the left ventricular cavity to improve perfusion and decrease angina. This technique can also be used to deliver drugs to the damaged tissue. Candidates include patients with chronic, severe, refractory angina and those unable to undergo conventional surgical revascularization or angioplasty because remaining conduits or acceptable target vessels are lacking. Although the mechanism of action of DMR is still not known, several theories have been proposed, including stimulated angiogenesis. Late sequelae also remain to be determined. Channel characteristics differ depending on whether they were created by carbon dioxide or holmium/yttrium-aluminum-garnet (Ho: YAG) lasers. Catheter-based DMR obviates thoracotomy and anesthesia and, in systems that can create electromechanical maps, fluoroscopy. Phase I clinical trials are now under way to evaluate catheter-based DMR, with endpoints that include improvement in symptoms of angina, exercise capacity, and radionuclide myocardial perfusion.

Detection and assessment of laser-mediated injury in transmyocardial revascularization

When channels are made through the myocardium with a laser, tissue surrounding the channels is injured. Thus, methods of examining and quantifying the histologic changes caused by laser-mediated injury are required both for comparison of different channel making protocols and also to help understand the mechanisms of transmyocardial revascularization. The two principal components of the myocardium, collagen and muscle, are both normally birefringent. This optical property can be exploited with the use of polarized light microscopy to assess tissue structure at the cellular and subcellular levels allowing several different types of injury to be detected. Increases in tissue temperature above 60 degrees C for muscle and 70 degrees C for collagen decrease their birefringence and, hence, result in decreased brightness when viewed with polarized light. Lower temperatures may cause cell membrane injury, calcium overload, and the formation of contraction bands, which appear as areas of increased birefringence. In this way, the extent of thermal injury can be assessed. The same optical properties can be used to measure cell and fiber orientation and, hence, enable assessment of mechanical disruption of the tissue after ablation. Long-term remodeling of the myocardium in the form of scar formation, increased interstitial fibrosis, and muscle disarray can also be quantified. The ability to measure the acute injury and the long-term structural consequences of that injury with the use of polarized light microscopy should prove vital in determining the optimal laser "dose" required and may also reveal information on the mechanism(s) of benefit found with transmyocardial revascularization.

Percutaneous transmyocardial revascularization

Transmyocardial revascularization (TMR) is a potential therapy for patients with severe angina pectoris and coronary anatomy deemed unsuitable for traditional revascularization techniques. Investigations of TMR are reviewed with emphasis on studies relevant to the development of a percutaneous, catheter-based transmyocardial revascularization procedure (PMR). The results of the preliminary animal studies and description of the PMR procedure are discussed. The recently initiated human PMR protocol is summarized and possible future investigative directions are outlined.