Angiogenesis is enhanced in ischemic canine myocardium by transmyocardial laser revascularization

Effects of needle puncturing on re-vascularization and follicle survival in xenotransplanted human ovarian tissue

BACKGROUND

Ovarian tissue transplantation can restore fertility in young cancer survivors, however the detrimental loss of follicles following transplantation of cryopreserved ovarian tissue is hampering the efficiency of the procedure. This study investigates whether needle puncturing prior to transplantation can enhance revascularization and improve follicle survival in xenotransplanted human ovarian cortex.

METHODS

Cryopreserved human ovarian cortex pieces (N = 36) from 20 women aged 24-36 years were included. During the thawing process, each piece of tissue was cut in halves; one half serving as the untreated control and the other half was punctured approximately 150-200 times with a 29-gauge needle. The cortex pieces were transplanted subcutaneously to immunodeficient mice for 3, 6 and 10 days (N = 8 patients) and for 4 weeks (N = 12 patients). After 3, 6 and 10 days, revascularization of the ovarian xenografts were assessed using immunohistochemical detection of CD31 and gene expression of angiogenic factors (Vegfα, Angptl4, Ang1, and Ang2), and apoptotic factors (BCL2 and BAX) were performed by qPCR. Follicle density and morphology were evaluated in ovarian xenografts after 4 weeks.

RESULTS

A significant increase in the CD31 positive area in human ovarian xenografts was evident from day 3 to 10, but no significant differences were observed between the needle and control group. The gene expression of Vegfα was consistently higher in the needle group compared to control at all three time points, but not statistically significant. The expression of Ang1 and Ang2 increased significantly from day 3 to day 10 in the control group (p < 0.001, p = 0.0023), however, in the needle group this increase was not observed from day 6 to 10 (Ang2 p = 0.027). The BAX/BCL2 ratio was similar in the needle and control groups. After 4-weeks xenografting, follicle density (follicles/mm³, mean ± SEM) was higher in the needle group (5.18 ± 2.24) compared to control (2.36 ± 0.67) (p = 0.208), and a significant lower percentage of necrotic follicles was found in the needle group (19%) compared to control (36%) (p = 0.045).

CONCLUSIONS

Needle puncturing of human ovarian cortex prior to transplantation had no effect on revascularization of ovarian grafts after 3, 6 and 10 days xenotransplantation. However, needle puncturing did affect angiogenic genes and improved follicle morphology.

Effects of Er:YAG laser treatment on re-vascularization and follicle survival in frozen/thawed human ovarian cortex transplanted to immunodeficient mice

PURPOSE

The huge loss of ovarian follicles after transplantation of frozen/thawed ovarian tissue is considered a major drawback on the efficacy of the procedure. Here we investigate whether Er:YAG laser treatment prior to xenotransplantation can improve re-vascularization and subsequently follicle survival in human ovarian tissue.

METHODS

A total of 99 frozen/thawed human ovarian cortex pieces were included of which 72 pieces from 12 woman were transplanted to immunodeficient mice. Tissues from each woman were included in both an 8-day and an 8-week duration study and treated with either full-beam laser (L1) or fractionated laser (L2), or served as untreated controls. Vascularization of the ovarian xenografts were evaluated after 8 days by qPCR and murine Cd31 immunohistochemical analysis. Follicle densities were evaluated histologically 8 weeks after xenografting.

RESULTS

Gene expression of Vegf/VEGF was upregulated after L1 treatment (p=0.002, p=0.07, respectively), whereas Angpt1, Angpt2, Tnf-α, and Il1-β were significantly downregulated. No change in gene expression was found in Cd31/CD31, ANGPT1, ANGPT2, ANGTPL4, XBP1, or LRG1 after any of the laser treatments. The fraction of Cd31 positive cells were significantly reduced after L1 and L2 treatment (p<0.0001; p=0.0003, respectively), compared to controls. An overall negative effect of laser treatment was detected on follicle density (p=0.03).

CONCLUSIONS

Er:YAG laser treatment did not improve re-vascularization or follicle survival in human ovarian xenografts after 8 days and 8 weeks grafting, respectively. However, further studies are needed to fully explore the potential angiogenic effects of controlled tissue damage using different intensities or lasers.

Transmyocardial revascularization (TMR): current status and future directions

Purpose

Cardiac surgeons are increasingly faced with a more complex patient who has developed a pattern of diffuse coronary artery disease (CAD), which is refractory to medical, percutaneous, and surgical interventions. This paper will review the clinical science surrounding transmyocardial revascularization (TMR) with an emphasis on the results from randomized controlled trials.

Methods

Randomized controlled trials which evaluated TMR used as sole therapy and when combined with coronary artery bypass grafting were reviewed. Pertinent basic science papers exploring TMR's possible mechanism of action along with future directions, including the synergism between TMR and cell-based therapies were reviewed.

Results

Two laser-based systems have been approved by the United States Food and Drug Administration (FDA) to deliver laser therapy to targeted areas of the left ventricle (LV) that cannot be revascularized using conventional methods: the holmium:yttrium-aluminum-garnet (Ho:YAG) laser system (CryoLife, Inc., Kennesaw, GA) and the carbon dioxide (CO₂) Heart Laser System (Novadaq Technologies Inc., (Mississauga, Canada). TMR can be performed either as a stand-alone procedure (sole therapy) or in conjunction with coronary artery bypass graft (CABG) surgery in patients who would be incompletely revascularized by CABG alone. Societal practice guidelines have been established and are supportive of using TMR in the difficult population of patients with diffuse CAD.

Conclusions

Patients with diffuse CAD have increased operative and long-term cardiac risks predicted by incomplete revascularization. The documented operative and long-term benefits associated with sole therapy and adjunctive TMR in randomized trials supports TMR's increased use in this difficult patient population.

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.

Surgical therapy for heart failure

Today's healthcare delivery system is challenged with an escalating number of heart failure patients who have exhausted medical therapy and overwhelmed the limits of organ transplantation. Scientific and technological advances over the last 20 years have now brought new surgical options to this vast patient population, ranging from ventricular restoration surgery to surgical gene therapy and beyond. This article reviews the myriad of surgical options that are available to these patients, their benefits and shortcomings, as well as potential future directions.

Long-Term Outcomes After CABG With Concomitant CO2 Transmyocardial Revascularization in Comparison With CABG Alone

OBJECTIVES

: Transmyocardial revascularization (TMR) has been used as an isolated or adjunctive revascularization therapy in patients presumed to have nonbypassable coronary artery disease. The purpose of this study is to evaluate the short- and midterm mortality for patients with complete revascularization using TMR and coronary artery bypass grafting (CABG) compared with those patients with incomplete CABG revascularization and to document long-term follow-up in patients receiving TMR + CABG.

METHODS

: Seventy TMR + CABG patients were cohort matched with 70 patients undergoing isolated CABG with circumflex coronary artery disease, but with no bypassable distal targets, from 1999 to 2005 at Emory University Hospital. The data were retrospectively reviewed from a database after being prospectively entered. Results are presented in mean ± standard deviation, and Kaplan-Meier curves were created for long-term all-cause mortality.

RESULTS

: The TMR + CABG patients had a similar incidences to the CABG only group for preoperative ejection fraction (50.9 ± 11.2% vs. 50.7 ± 10.3%, P = 0.93), number of grafts (2.6 ± 1.1 vs. 2.5 ± 1.3, P = 0.5), and number of diseased vessels (2.8 ± 0.3 vs. 2.9 ± 0.4, P = 0.26). Off-pump surgery was used more often in the CABG alone group versus the TMR combined with CABG group (74.3% vs. 41.4%, P < 0.001). Postoperatively, there was no statistical difference among the TMR + CABG and the CABG alone groups for intensive care unit length of stay (4.3 ± 7.8 days vs. 2.6 ± 3.4 days, P = 0.026), postsurgical length of stay (7.6 ± 6.1 days vs. 6.8 ± 4.5 days, P = 0.31), stroke events (1.4% vs. 1.4%, P = 1.00), myocardial infarction (4.3% vs. 2.9%, P = 0.65), and 30-day mortality (5.7% vs. 4.3%, P = 0.70). Long-term survival rate was not statistically significant. In addition, 4-year follow-up in the TMR + CABG group had symptom improvement with reduction in New York Heart Association classification for class III/IV (P < 0.0001, baseline vs. 4-year follow-up).

CONCLUSIONS

: The combination of TMR and CABG for complete revascularization is safe and carries no further risk to patients compared with CABG only. CABG + TMR patients tend to have increased resource utilization. Long-term follow-up shows similar survival between the groups. TMR can be a useful adjunct to CABG for complete revascularization.

Intramyocardial partial oxygen pressure in patients undergoing transmyocardial laser revascularization and bypass surgery

OBJECTIVE

Numerous investigations could not clarify the exact mechanism of transmyocardial laser revascularization (TMLR). The aim of this study was to investigate, whether TMLR leads to an increase of myocardial oxygenation in comparison to patients undergoing coronary artery bypass grafting (CABG).

DESIGN

Twelve patients (TMLR group) underwent TMLR alone with an 800 W CO2 laser through a left anterior thoracotomy. Seventeen patients (CABG group) underwent standard CABG. Myocardial oxygenation was determined by measuring intramyocardial partial oxygen pressure (ptiO2 ). PtiO2 was measured online and mean values at 1, 24, 32, and 48 h postoperatively were compared with baseline before intervention. Parameters influencing ptiO2 (arterial pO2, hemodynamic parameters, hemoglobin) were recorded.

RESULTS

Mean baseline ptiO2 was significantly lower in the TMLR group compared with the CABG group (p < 0.05). In both groups ptiO2 increased significantly in the postoperative course, whereby ptiO2 in the TMLR group was significantly lower compared with the CABG group.

CONCLUSION

Although the exact mechanism of action of TMLR remains unclear, ptiO2 and thus oxygen supply in the myocardium increased in patients undergoing TMLR at least in the early postoperative course. However, ptiO2 increased to a lesser extent compared with CABG.

Myocardial Laser Revascularization in the Year 2000 as seen by a Norwegian Specialist Panel. The Process of Evaluating and Implementing New Methods in Clinical Practice

OBJECTIVE

In Norway "Transmyocardial laser revascularization" as a routine method was prohibited by the Ministry of Health in 1995 due to lacking evidence of treatment effect and concerns about procedural morbidity and mortality. In 1999 Norwegian health authorities asked for a re-evaluation of the method based on a systematic review of literature.

METHODS

Medline and Embase were searched and a total of 267 articles were identified. Publications were classified by an expert panel according to type of study and importance for the project.

RESULTS

Based on the literature review the panel concluded that heart laser treatment does not have a life-saving effect, nor does it improve myocardial function. However, the method has a considerable short-term symptomatic effect, the mechanism of which is not understood. Neoangiogenesis, denervation and placebo may play a role. Based on the report the Norwegian health authorities recommended use of this method be restricted to scientific trials only.

CONCLUSIONS

Based on a systematic literature review it was concluded that the only documented effect of heart laser treatment is symptom relief, the mechanism for which is unclear. It could partly or totally be a placebo effect. A conflict of interest may arise when new technologies are to be implemented in health care. The communication between professionals evaluating scientific results and decision makers is challenging. Quality assurance of this process may be obtained by use of expert panels working under the auspices of an official institution.

Non-invasive Monitoring of Angiogenesis in Cardiology

Angiogenesis plays an important role in the pathophysiology of atherosclerosis and after myocardial infarction. Furthermore, angiogenesis has been the focus of many therapeutic strategies. In view of that, a direct and clear understanding of the role of these pathways in the living subject is needed. Molecular Imaging has emerged as a powerful tool to study biological processes non-invasively. In this review, evidence will be presented and discussed on the feasibility of different molecular imaging strategies to study the involvement of angiogenic pathways in the assessment of the atherosclerotic disease and as a tool to assess angiogenic therapy. Focus will be placed on those imaging modalities with the potential to be translated to clinical use.

Assisting the failing heart

Anesthesiologists increasingly encounter patients who have a spectrum of heart failure ranging from stable chronic heart failure to acute heart failure to cardiogenic shock. Improved medical therapy has increased the survival of patients who have chronic heart failure but not of patients who have acute heart failure. New surgical techniques and mechanical devices may offer alternatives to certain patients who have refractory heart failure This article provides an overview of established and newer pharmacologic and nonpharmacologic therapies and surgical interventions to manage patients who have heart failure, including the perioperative management of heart transplantation and ventricular assist devices.

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.

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.

Angiogenic therapy for coronary artery and peripheral arterial disease

Neovascularization in chronically ischemic adult cardiac and skeletal muscle results from the processes of angiogenesis, arteriogenesis and vasculogenesis. Therapeutic angiogenesis describes an emerging field of cardiovascular medicine whereby new blood vessels are induced to grow to supply oxygen and nutrients to cardiac or skeletal muscle rendered ischemic as a result of progressive atherosclerosis. Various techniques have been utilized to promote new blood vessel growth in the heart and extremities, including mechanical means such as surgical or percutaneous myocardial laser revascularization, angiogenic growth factor therapies involving members of the vascular endothelial growth factor and fibroblast growth factor families, and more recently, cellular-based therapies using stem cells known as endothelial progenitor cells or angioblasts. The following review discusses each of these treatment strategies in detail including both preclinical and clinical data for their use in peripheral arterial and coronary artery disease.

Direct left ventricle-to-coronary artery stent restores perfusion to chronic ischemic swine myocardium

BACKGROUND

Direct left ventricle (LV)-to-coronary artery shunts (VSTENT) have been proposed as an alternative means of myocardial revascularization. The goal of this study was to examine quantitative changes in myocardial perfusion and possible mechanisms of revascularization with an LV-to-coronary shunt.

METHODS

Ameroid occluders were implanted on the proximal left anterior descending coronary artery (LAD) of 6 pigs to create chronic ischemia. Four weeks later, a VSTENT was placed to directly connect the distal LAD with the LV chamber. Animals survived for an additional 3 weeks and received periodic bromodeoxyuridine (BrdU) injections to identify dividing cells to identify and quantify angiogenesis. Regional myocardial perfusion (RMP) was measured with color microspheres under adenosine vasodilatory stress before and 3 weeks after VSTENT implantation. Vascularity was assessed histologically by an overall vascularity index and a growth index reflecting the density of BrdU-positive vascular cells.

RESULTS

Three weeks after VSTENT placement, RMP improved from 38.4% +/- 19.6% of non-ischemic flow to 86.8% +/- 13.7% in treated animals (P < .05). This benefit was accompanied by histological evidence of increased vascularity and vascular proliferation. Four of 5 animals had patent and functional devices at the end of the study.

CONCLUSION

Chronic VSTENT placement improves RMP and may promote arterial remodeling in chronically ischemic porcine myocardium.

Release of cardiac biochemical markers after percutaneous myocardial laser or sham procedures

BACKGROUND

Percutaneous myocardial laser (PML) reduces symptoms in patients with intractable angina. PML leads to a certain loss of viable myocardium, we therefore assessed if troponin or cardiac markers release may explain the clinical effect, and furthermore assessed the markers release during percutaneous sham procedures.

METHODS

Eighty-two patients with chronic refractory angina were randomized to either percutaneous myocardial laser or a true sham procedure. Cardiac markers were assessed before the procedure, and (1/2), 2, 4, 6, and 10-12 h postprocedure.

RESULTS

Troponin I increased to median peak levels (range) of 4 (0.6-43) microg/L in the laser group vs. 1.5 (0.1-5.9) microg/L, p=0.001, and creatine kinase MB to 14 (6-357) microg/L vs. 11 (3-40) microg/L, p<0.05, within and between-group comparison, the rise of CK-MB occurred significantly earlier in the sham group, 3.8 vs. 2.5 h. A time-dependent between-group difference was only detected for troponin. 88% of sham and 100% of laser patients had marker levels above reference limits. There was no correlation between the number of laser/sham created channels, biomarker levels postprocedure, and changes in left ventricular ejection fraction or angina improvement during 12 months of follow-up.

CONCLUSIONS

The release of cardiac markers is not related to relief of angina after myocardial laser. The use of intracardiac catheters induces a considerable marker release, which is not caused by acute ischemia.

Guidelines for the Clinical Use of Transmyocardial Laser Revascularization

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 (CABG) are clinically challenging. Transmyocardial laser revascularization (TMR), as sole therapy or as an adjunct to CABG, may be appropriate therapy for these patients. The recommendations are based on a review of the available evidence including expert consensus opinions. The author follows the format of the American Heart Association and the American College of Cardiology guidelines for diagnostic and therapeutic procedures. There are class I indications for sole therapy TMR and class IIA indications for TMR as an adjunct to CABG. TMR is indicated for selected patients: as sole therapy for a subset of patients with refractory angina. It also may be effective as an adjunct to CABG for a subset of patients with angina who cannot be completely revascularized surgically.

Targeted Therapeutic Applications of Acoustically Active Microspheres in the Microcirculation

The targeted delivery of intravascular drugs and genes across the endothelial barrier with only minimal side effects remains a significant obstacle in establishing effective therapies for many pathological conditions. Recent investigations have shown that contrast agent microbubbles, which are typically used for image enhancement in diagnostic ultrasound, may also be promising tools in emergent, ultrasound-based therapies. Explorations of the bioeffects generated by ultrasound-microbubble interactions indicate that these phenomena may be exploited for clinical utility such as in the targeted revascularization of flow-deficient tissues. Moreover, development of this treatment modality may also include using ultrasound-microbubble interactions to deliver therapeutic material to tissues, and reporter genes and therapeutic agents have been successfully transferred from the microcirculation to tissue in various animal models of normal and pathological function. This article reviews the recent studies aimed at using interactions between ultrasound and contrast agent microbubbles in the microcirculation for therapeutic purposes. Furthermore, the authors present investigations involving microspheres that are of a different design compared to current microbubble contrast agents, yet are acoustically active and demonstrate potential as tools for targeted delivery. Future directions necessary to address current challenges and advance these techniques to clinical practicality are also discussed.

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.

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.

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.

Digital Radiographic Quantification of Myocardial Blood Flow Around a Transmyocardial Laser Channel in Rabbit Hearts

BACKGROUND

A mechanism underlying the benefits of transmyocardial laser revascularization (TMLR) has been presumed to be improvement in perfusion. We evaluated myocardial blood flow around a laser channel using digital radiography combined with a 3H-labeled desmethylimipramine ([3H]DMI) deposition.

METHODS AND RESULTS

A laser channel was created in the left ventricular wall using a YAG-laser in 6 non-ischemic rabbit hearts. After 8 weeks, [3H]DMI(1.11 MBq) was injected into the left atrium and the TMLR-treated myocardium was sectioned. Another 6 hearts were examined as controls. We measured [3H]DMI density in arbitrary units with digital radiography in the channel remnant, the surrounding area and a remote area. Flow distribution was quantified by the coefficient of variation of flows (CV). The surrounding area had the highest density (p < 0.001) and the lowest CV (p < 0.001), and had higher density (p < 0.001) and lower CV (p < 0.001) than the controls. There was no transmural difference in the density in all domains. The CV increased with depth in the remote area, as well as in controls (p < 0.001), but there was no transmural difference in the surrounding area.

CONCLUSIONS

The TMLR increases myocardial blood flow and decreases flow heterogeneity in the surrounding area. The disappearance of transmural difference in flow heterogeneity might indicate the remodeling of microcirculation to improve regional oxygen delivery.

Transmyocardial Revascularization

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

Only transient increase of vascular growth factors and microvascular density after percutaneous myocardial laser

OBJECTIVE

We tested the hypothesis that percutaneous myocardial laser may stimulate microvascular growth in areas surrounding the laser channels.

METHODS

We conducted a study of 24 domestic pigs, which underwent percutaneous myocardial laser to left ventricular myocardium using holmium:YAG laser. The pigs were sacrificed in groups of four after one day, 3-4 days, one week, three weeks and six weeks. Frozen sections from both normal and treated myocardium were prepared for immunofluorescence microscopy and stained with antibodies against von Willebrand factor, vascular endothelial growth factor (VEGF) and Extra Domain-A cellular fibronectin (ED-AcFN). Microvascular density (MVD) and vascular area (VA) were determined in sections stained with antibodies against von Willebrand factor VIII using a digitised image analysis system. When determined in laser treated areas, channel core remnants were excluded from analysis.

RESULTS

Within the laser channel remnants and in the tissue closely surrounding these, expression of VEGF and ED-AcFN increased significantly after treatment at one, 3-4, and seven days and decreased to normal at three and six weeks. Expression of ED-AcFN was detected adjacent to endothelial cells of microvessels. The original laser channels were rapidly invaded by granulation tissue. There was no sign of recanalization at any stage during the six weeks. Morphometric analysis showed no increase in MVD and VA in the myocardium surrounding the laser channels.

CONCLUSION

An increase of VEGF and ED-AcFN after myocardial laser is transient and is not associated with increase of MVD or VA in myocardium not involving laser channel remnants.

What is the Optimal Channel Density for Transmyocardial Laser Revascularization?

BACKGROUND

Transmyocardial laser revascularization (TMR) has demonstrated reproducible relief of angina in patients with end-stage coronary disease. However, the optimum dose or channel density has not been elucidated.

METHODS

Using a porcine model of chronic myocardial ischemia, 14 animals were treated with CO2 TMR and randomized as follows: group 1 was 1 channel per 2 cm2; group 2 was 1 channel per 1 cm2; and group 3 was 2 channels per 1 cm2. Left ventricular myocardial viability and function were assessed by magnetic resonance imaging (MRI) and echocardiography pretreatment, and repeated 6 weeks later.

RESULTS

The MRI assessment of group 1 (1 channel/2 cm2) and group 2 (1 channel/cm2) demonstrated similar improvement in segmental contractility posttreatment of 12.11% +/- 5.15% and 12.47% +/- 9.51%, respectively. In contrast, group 3 (2 channels/cm2) showed significantly worse segmental contractility posttreatment: -18.52% +/- 7.16% (p = 0.01). Echocardiographic imaging revealed significant improvements in wall thickening in the ischemic zone for group 1 at 0.91 +/- 0.07 cm pretreatment versus 1.30 +/- 0.09 cm posttreatment, (p = 0.01); and for group 2 at 0.93 +/- 0.11 cm versus 1.42 +/- 0.18 cm, (p = 0.01). No significant improvement in wall thickening was seen in group 3 (0.84 +/- 0.06 cm versus 0.88 +/- 0.09 cm, p = n.s.).

CONCLUSIONS

These data corroborate the empiric finding of an effective therapeutic dose range for TMR, 1 channel per 1 to 2 cm2. These results also demonstrate a detrimental effect when channel density is increased above the clinical standard of 1 channel per cm2 to a density of 2 channels per 1 cm2.

Improved myocardial function after transmyocardial laser revascularization according to cine magnetic resonance in a porcine model

OBJECTIVE

This study was undertaken to demonstrate that transmyocardial laser revascularization of hypoperfused myocardium improves regional and global myocardial function.

METHODS

Cine magnetic resonance imaging was used to monitor regional wall thickening (in millimeters) and cardiac output (in milliliters per kilogram per minute). Cine magnetic resonance imaging was performed before and 8 weeks after transmyocardial laser revascularization was applied to the hypoperfused lateral wall of the left ventricle (target area) in a porcine model (n = 9, transmyocardial laser revascularization group). A second group of animals was left untreated (n = 8, control group).

RESULTS

Regional wall thickening in the target area improved after transmyocardial laser revascularization (0.7 +/- 0.3 mm to 3.7 +/- 1.9 mm, P <.02) and was significantly higher (P <.01) after transmyocardial laser revascularization than in the control group, in which it did not improve (0.5 +/- 0.6 mm to 0.5 +/- 1.2 mm). Accordingly, cardiac output and microsphere-derived myocardial blood flows were significantly higher than in the control group (P <.01), and the amount of triphenyltetrazolium chloride-stained myocardium was lower (P <.01).

CONCLUSION

Cine magnetic resonance imaging demonstrates improved global and regional myocardial function after transmyocardial laser revascularization in a porcine model.

The effect of percutaneous transmyocardial laser revascularization on left ventricular function in a porcine model of hibernating myocardium

BACKGROUND

Hibernating myocardium is defined as a state of persistently impaired myocardial function at rest due to reduced coronary blood flow that can partially or completely be restored to normal if the myocardial oxygen supply/demand relationship is favorably altered. Percutaneous laser revascularization (PMR) is an emerging catheter-based technique that involves creating channels in the myocardium, directly through a percutaneous approach with a laser delivery system, and has been shown to reduce symptoms in patients with severe refractory angina; however, its effect on improving regional wall motion abnormalities in hibernating myocardium has not been clearly established. We sought to determine the effect of PMR using the Eclipse System (Cardiogenesis) on left ventricular function in a porcine model of hibernating myocardium.

METHODS

A model of hibernating myocardium was created by placement of an ameroid constrictor in the proximal left anterior descending artery of a 35 kg male Yorkshire pig. The presence of hibernating myocardium was confirmed with dobutamine stress echocardiography (DSE) and defined as severe hypocontractility at rest, with an improvement in systolic wall thickening with low-dose dobutamine in myocardial regions with a subsequent deterioration in function at peak stress (biphasic response). After the demonstration of hibernating myocardium, PMR was performed in the area of hypocontractile function, and the serial echocardiography was performed. The echocardiograms were reviewed by an experienced echocardiologist blinded to the results, and regional wall motion was assessed using the American Society of Echocardiography Wall Motion Score. Six weeks after PMR, the animal was sacrificed and the heart sent for histopathologic studies.

RESULTS

A comparison of the regional wall motion function of the area distal to the ameroid constrictor and in the contralateral wall at baseline, post-ameroid placement, and post-PMR was performed. Hibernating myocardium was demonstrated 4 weeks after ameroid placement by DSE. Coronary angiography demonstrated a discrete 90%stenosis in the proximal LAD at the site of ameroid constrictor placement without evidence of collaterals. Using PMR, 17 bursts were successfully delivered to the anterior wall distal to the ameroid constrictor. Four weeks after PMR, there was improvement in wall motion function in the region distal to the ameroid placement by echocardiography. Histopathologic analysis demonstrated the absence of myocardial infarction in the anterior wall distal to the ameroid constrictor.

CONCLUSIONS

The performance of PMR in a porcine model of hibernating myocardium is feasible and is associated with an improvement regional wall motion function after 4 weeks.

Transmyocardial Laser Therapy: A Strategic Approach

BACKGROUND

Coronary artery bypass and percutaneous intervention have become the established methods of coronary revascularization in treating angina pectoris. Subsets of angina patients, however, are not amenable to either of these procedures. Transmyocardial laser revascularization (TMR) has been developed as a potential treatment to address such patients, and clinical research to date illustrates the success of TMR for this patient group.

STRATEGIC PLAN SUMMARY

Although the symptoms of ischemic heart disease manifest themselves in a variety of ways, the best results with TMR are seen in patients with severe angina rather than in patients with silent ischemia or congestive heart failure. Potential TMR patients receive diagnostic tests to determine if and where the therapy should be applied. A recent cardiac catheterization is required to document the status of and the coronary-system suitability for the planned intervention. It is not appropriate to assume that a patient with nonbypassable, noninterventional coronary artery disease has to be relegated to medical therapy only. Additionally, echocardiography demonstrates the status of cardiac valves and segmental wall motion activity. This knowledge allows the surgeon to determine the sequence of surgery and if abnormalities are present. Once the decision to use TMR use has been made, there are 2 approaches--sole therapy or adjunctive therapy. TMR is not to be substituted for a feasible bypass graft, but the best time to make this decision may well be during the surgery itself, because grafts that appear surgically feasible on an angiogram may be less feasible after the chest has been opened. The decision to perform sole-therapy TMR in the absence of bypassable vessels clearly must be made before opening the chest. Whether to use cardiopulmonary bypass (CPB) and the sequence in which to perform TMR and bypass grafts are based on surgeon preference. The advantage of performing TMR on CPB is that channels can quickly be lased without pause. A potential advantage of performing TMR before bypass grafts is that "channel leak" (bleeding) can be minimized by the conclusion of the surgery. Complete revascularization has become technically more difficult because of the increasing use of percutaneous approaches and because patients are being referred for coronary artery bypass grafting much later in the course of their coronary disease progression than before. TMR may well be a viable alternative to bypassing a heavily diseased, previously intervened, small-diameter coronary artery. Thus, a model in which myocardial perfusion is considered within the context of the natural circulation can be conceived as an alternative to a model in which circulation is altered by interventional, surgical, and/or transmyocardial methods. TMR has been shown to be effective in accomplishing a complete revascularization when the restoration of circulation to ischemic territories with interventional therapy, bypass surgery, or a combination of both has been ineffective. We recommend that interested users follow this "complete revascularization strategy" algorithm for all ischemic vessels being considered for interventional or surgical treatment. Running each diseased vessel through this thought process will ensure that available treatment options are considered in the optimization of a patient's outcome.

CONCLUSION

The use of TMR for angina relief has evolved into a clinically proven technology that has enabled physicians to address difficult revascularization cases with a therapy that is safe and effective.

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.

Mechanisms and Results of Transmyocardial Laser Revascularization

Transmyocardial laser revascularization (TMR) is a technique that has been performed on over 10,000 patients around the world. Most of the patients were not suffering from heart failure. TMR is principally used for the treatment of angina, but in patients with significant reversible ischemia that is not amenable to conventional therapy, TMR may also improve myocardial function. The results of using TMR as a treatment for angina show a dramatic improvement in symptoms and quality of life. This paper reviews the current status of TMR techniques, mechanisms and results.

Regional Cardiac Sympathetic Innervation Early and Late After Transmyocardial Laser Revascularization

BACKGROUND

Prior experimental and clinical studies have drawn disparate conclusions regarding the effects of transmyocardial laser revascularization (TMR) on regional cardiac innervation in the treated regions. Regional afferent denervation has been proposed as a potential mechanism of action of the procedure, although this as yet remains unproven. The purpose of the present study was to evaluate regional myocardial sympathetic innervation both early (3 days) and late (6 months) after TMR.

METHODS

Mini-swine in the early group were randomized to be sacrificed 3 days after holmium:YAG TMR (n = 5) or sham thoractomy (n = 3). In the late group, mini-swine with hibernating myocardium in the left circumflex (LCx) region were randomized to sham redo-thoracotomy (n = 5), TMR of the LCx distribution with a carbon dioxide (n = 5), holmium:YAG (n = 5), or excimer (n = 5) laser. Six months postoperatively the animals were sacrificed. Additional animals in both the early (n = 2) and late (n = 2) groups served as age- and weight-matched normal controls. Immunohistochemistry and Western blot analysis for tyrosine hydroxylase (TYR-OH), a neural-specific enzyme found in sympathetic efferent nerves and a commonly used anatomic marker of regional innervation, were performed on lased and nonlased LCx and septal regions.

RESULTS

Immunohistochemical staining for TYR-OH was markedly diminished in the lased myocardial regions 3 days after TMR. This staining was significantly reduced compared to untreated septal regions, sham-operated, and normal LCx myocardium. Quantitative immunoblotting confirmed a significant reduction in TYR-OH (p < 0.05) protein concentration in the lased regions 3 days after TMR. On the contrary, TYR-OH staining was present in LCx myocardium surrounding the laser channels of all animals in all groups 6 months postoperatively. Staining was not different from controls. Similarly, there was no difference in LCx TYR-OH protein concentration between the normal, sham, or 6 months postoperative lased groups (p > 0.2 by one-way ANOVA).

CONCLUSIONS

TMR-treated myocardium demonstrates anatomic evidence of regional sympathetic denervation 3 days postoperatively, although myocardium lased with each of the three lasers currently in clinical use is reinnervated by 6 months as evidenced by immunoblotting and immunohistochemistry for TYR-OH. These results suggest that mechanisms other than denervation may account for the long-term reductions in angina seen after TMR.

Evolving revascularization approaches for myocardial ischemia

Stable angina pectoris secondary to ischemic heart disease is a common and disabling condition. Medical therapy aims to relieve symptoms, improve exercise capacity, and decrease cardiac events by reducing myocardial oxygen demand or improving coronary blood supply to the ischemic myocardium. If medical treatment is inadequate, invasive revascularization procedures to improve coronary perfusion are considered. Percutaneous transluminal coronary angioplasty (PTCA) and coronary artery bypass graft (CABG) surgery are well-established and widely used myocardial revascularization techniques. Recent advances in PTCA have attempted to address the problem of restenosis, initially through the deployment of bare metal intracoronary stents and, more recently, with drug-eluting stents. Developments in CABG have focused on reducing the invasiveness of the procedure and minimizing the incidence of serious complications. Refinements include the use of mechanical stabilizers, endoscopic harvesting of conduit vessels, robotic telemanipulation systems, and fully automated anastomotic devices. Surgical laser transmyocardial revascularization and therapeutic angiogenesis represent newer approaches to coronary revascularization. Therapeutic angiogenesis aims to deliver an angiogenic growth factor or cytokine to the myocardium to stimulate collateral blood vessel growth throughout the ischemic tissue. The angiogenic factor may be administered as a recombinant protein or as a transgene within a plasmid or gene-transfer vector. Ongoing angiogenic gene therapy clinical trials are evaluating which factors, vectors, and delivery techniques hold the greatest promise for management of patients with chronic stable angina.

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.

Endocardial cryotherapy as a novel strategy of improving myocardial perfusion in a patient with severe coronary artery disease

Patients with intractable angina pectoris due to end-stage coronary artery disease who are not amenable to conventional revascularization provide a therapeutic challenge. We describe the first published case of a young patient with intractable coronary artery disease that was successfully treated by endocardial cryotherapy.

Technetium 99m-labeled tetrofosmin and iodine 123-labeled metaiodobenzylguanidine scintigraphy in the assessment of transmyocardial laser revascularization

OBJECTIVE

Transmyocardial laser revascularization is a new technique that improves symptoms in patients with refractory angina not amenable to conventional revascularization. The aim of this study was to assess whether transmyocardial laser revascularization produces changes in innervation, perfusion scintigraphy, or both that could explain the benefit to patients.

METHODS

Sixteen patients (12 men and 4 women; mean age, 60 +/- 8 years) with coronary artery disease were studied. Transmyocardial laser revascularization was performed in 39 myocardial areas supplied by a stenotic vessel. A technetium 99m-labeled tetrofosmin stress-rest tomographic scan and iodine 123-labeled metaiodobenzylguanidine planar scans were performed before and after transmyocardial laser revascularization (3 and 12 months later) to evaluate myocardial perfusion and innervation. Stress and rest perfusion images were quantified on a polar map. Ischemia uptake was also defined as the difference between rest and stress uptake for each area. Innervation planar images were visually analyzed and semiquantified.

RESULTS

A significant decrease in angina class from baseline was observed at 3, 6, and 12 months after transmyocardial laser revascularization (P <.005). A significant decrease in ischemia uptake was also found between the pre-transmyocardial laser revascularization and the post-transmyocardial laser revascularization studies in treated areas (P <.001). A significant improvement in stress myocardial perfusion at 3 and 12 months after transmyocardial laser revascularization was only found in treated areas that were considered ischemic in the pre-transmyocardial laser revascularization study (P <.05). At 3 months, a significant myocardial innervation worsening was observed in treated areas (P <.001), with partial recovery at 12 months (P <.05).

CONCLUSION

The transmyocardial laser revascularization mechanism involves both perfusion improvement and denervation, mainly at 3 months, that partially recovered at 12 months.

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.

Role of MMPs and plasminogen activators in angiogenesis after transmyocardial laser revascularization in dogs

We examined the role of matrix metalloproteinases (MMPs), tissue inhibitors of MMP (TIMPs), and plasminogen activator (PA) in transmyocardial laser revascularization (TMLR)-induced angiogenesis. TMLR was accomplished with a carbon dioxide laser in seven dogs whose left anterior descending coronary artery (LAD) was ligated. Seven control dogs underwent only LAD ligation, and four dogs underwent a sham operation, consisting only of a left thoracotomy. Two weeks later, transmural myocardial samples were harvested from the distributions of the LAD and the left circumflex artery for substrate zymography, immunohistochemical staining, and in situ zymography. MMP-1, MMP-2, TIMP-1, TIMP-2, and urokinase-type PA levels in the distribution of the LAD were higher in the laser group than in the control or sham group. Counts of von Willebrand factor-positive microvessels and smooth muscle alpha-actin-positive arterioles demonstrated that the angiogenesis and ateriogenesis was promoted in the laser group and correlated directly with the number of MMP-stained microvessels. We conclude that TMLR induces the expression of MMPs, TIMPs, and urokinase-type PA and that these proteinases play an important role in angiogenesis after TMLR.

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.

Effect of transmyocardial laser revascularization on myocardial perfusion and left ventricular remodeling after myocardial infarction in rats

PURPOSE

To monitor perfusion changes in remote myocardium caused by transmyocardial laser revascularization (TMLR) and to investigate the influence of TMLR on left ventricular morphology and function.

MATERIALS AND METHODS

The coronary arteries were ligated in 32 Wistar rats. Eight weeks later, cine magnetic resonance (MR) imaging was performed in both the treatment (n = 12) and control group (n = 8). TMLR was then performed in the remote myocardium in the treated group. Twelve weeks after myocardial infarction, cine MR imaging, including dobutamine-induced (10 micro g per kilogram of body weight per minute via the tail vein) stress, was repeated and followed with hemodynamic measurements in both groups and with perfusion MR imaging (in-plane resolution, 140 x 140 micro m) of the isolated heart at rest and during nitroglycerin-induced stress in the TMLR group (n = 10).

RESULTS

Left ventricular dilatation and hypertrophy were enhanced in the TMLR group (change in end-diastolic volume at 8-12 weeks: control group, 24.6 micro L +/- 16.7 and TMLR group, 81.7 micro L +/- 15.7; change in left ventricular mass: control group, 54.5 mg +/- 19.2 and TMLR group, 124.1 mg +/- 30.7; P <.03 for both). Ejection fractions at rest were approximately equal (control group, 40% +/- 2; TMLR group, 38% +/- 2; P value not significant), but during dobutamine-induced stress, the ejection fraction was higher in the TMLR group (54.4% +/- 4.9; control group, 47.4% +/- 4.8; P <.05). TMLR-treated areas were better perfused than was untreated myocardium (difference in perfusion: TMLR-treated vs control region, 3.89 mL/min/g +/- 0.83 at rest vs 2.29 mL/min/g +/- 1.06 during nitroglycerin-induced stress; P <.05 for both). Hemodynamic measurements revealed no differences between groups.

CONCLUSION

High-spatial-resolution perfusion MR imaging depicted a significant perfusion improvement after TMLR. Post-myocardial infarction remodeling of the left ventricle was found to be enhanced.

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.

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.

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.

Contrast ultrasound targeted drug and gene delivery: an update on a new therapeutic modality

The effective delivery of intravascular drugs and genes to regions of pathology is dependent on a number of factors that are often difficult to control. Foremost is the site-specific delivery of the payload to the region of pathology and the subsequent transport of the payload across the endothelial barrier. Ultrasound contrast agent microbubbles, which are typically used for image enhancement, are capable of amplifying both the targeting and transport of drugs and genes to tissue. Microbubble targeting can be achieved by the intrinsic binding properties of the microbubble shells or through the attachment of site-specific ligands. Once microbubbles have been targeted to the region of interest, microvessel walls can be permeabilized by destroying the microbubbles with low-frequency, high-power ultrasound. A second level of targeting specificity can be achieved by carefully controlling the ultrasound field and limiting microbubble destruction to the region of interest. When microbubbles are destroyed, drugs or genes that are housed within them or bound to their shells can be released to the blood stream and then delivered to tissue by convective forces through the permeabilized microvessels. An alternative strategy is to increase payload volume by coinjecting drug- or gene-bearing vehicles, such as liposomes, with the microbubbles. In this manifestation, microbubbles are used for creating sites of microvessel permeabilization that facilitate drug or gene vehicle transport. Recent work in the emerging field of contrast ultrasound-based therapeutics, with particular emphasis on the delivery of drugs and genes to tissue through microvascular networks is reviewed.

Do transmyocardial and percutaneous laser revascularization induce silent ischemia? An assessment by exercise testing

BACKGROUND

Transmyocardial and percutaneous laser revascularization (TMR, PTMR) may reduce angina and increase exercise tolerance in otherwise untreatable angina patients, although the mechanism is unknown and the placebo effect may be significant. One other proposed mechanism is cardiac denervation leading to silent ischemia.

METHODS

Electrocardiograms obtained during symptom-limited exercise (ETT, modified Bruce protocol) at baseline and 12 months were analyzed (blinded core laboratory) from 182 patients randomized to TMR (n = 92) or medical therapy alone (MED(TMR), n = 90) and 219 patients randomized to PTMR (n = 109) or medical therapy alone (MED(PTMR), n = 110).

RESULTS

Exercise duration increased 1 year after TMR or PTMR relative to medically treated patients (6.8 +/- 3.4 min vs 8.6 +/- 3.5 min for TMR; 7.3 +/- 3.1 min vs 9.1 +/- 3.6 min for PTMR, P <.05). At baseline, 20% of TMR and MED(TMR) subjects had ST depression >1.0 mm, >80% had angina during exercise, but only 3% had ST changes without chest pain (silent ischemia). This did not change after TMR. In the PTMR group, more subjects exercised to >1.0 mm ST depression (from 17% to 34%, P <.05), with no change in MED(PTMR), but the proportion with silent ischemia did not change in either group.

CONCLUSION

Exercise tolerance improved after TMR and after PTMR. Relative to PTMR, TMR more effectively suppressed pain during exercise and ischemic ST depression. However, neither TMR nor PTMR induced significant silent ischemia. These results suggest that denervation may not be a significant factor contributing to angina relief after these procedures. The contribution of the placebo effect was not determined by these results.