Transmyocardial Laser Revascularization Research Articles

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.

Improved pain control after cardiac surgery: results of a randomized, double-blind, clinical trial

Objective: We sought to determine whether a continuous regional infusion of a local anesthetic delivered to the operative site would result in decreased levels of postoperative pain and narcotic requirements for patients who undergo a standard median sternotomy for cardiac surgery. Methods A double-blind, randomized, controlled trial was conducted at a single center. Patients who were undergoing elective coronary artery bypass graft surgery alone or combined with laser transmyocardial revascularization received bilateral intercostal nerve blocks with either ropivacaine or saline. At wound closure, 2 catheters with multiple side openings were inserted percutaneously and placed directly over the sternum. The same agent (ropivacaine vs saline) was then administered as a continuous regional infusion for 48 hours through an elastomeric pump. Requirements for postoperative systemic narcotic analgesics and pain assessment scores were recorded for 72 hours after the operation. Secondary outcome measures were hospital length of stay and pulmonary function test results. Pain scores and narcotic use on the second postoperative day were also compared to avoid the confounding influence of anesthesia administered at the time of the operation. Results The total amount of narcotic analgesia required by the ropivacaine group was significantly less than that of the control group (47.3 vs 78.7 mg, respectively; P = .038). The ropivacaine group required less narcotics on postoperative day 2 as well (15.5 vs 29.4 mg, P = .025). The mean overall pain scores for the ropivacaine group were significantly less than the mean overall scores for the normal saline group (1.6 vs 2.6, respectively; P = .005). Patients receiving ropivacaine had a mean length of stay of 5.2 days compared with 8.2 days for patients in the normal saline group ( P = .001). Excluding the data from outliers (length of stay = 39 days), the normal saline group mean length of stay was 6.3 days ( P < .01). There was no difference in assessment of pulmonary function. Conclusion Continuous delivery of local anesthetics significantly improved postoperative pain control while decreasing the amount of narcotic analgesia required in patients who underwent standard median sternotomy. There was also a significant decrease in hospital length of stay, which is likely to result in significant cost reductions.

Mid-term results of combined transmyocardial laser revascularization and coronary artery bypass

Background Transmyocardial laser revascularization is increasingly used to treat intractable angina in the absence of graftable vessels; however, its role in combination with coronary artery bypass grafting remains undefined. The aim of this pilot study was to investigate the outcome of the combination therapy at mid-term follow-up. Methods Patients (n = 20) who had elective coronary artery bypass with one or more nongraftable coronary arteries were prospectively randomized to have either coronary artery bypass grafting alone or combination coronary artery bypass grafting plus transmyocardial laser revascularization with a holmium:YAG (yttrium-aluminum-garnet) laser to nongraftable areas. All patients had an exercise tolerance test preoperatively and at 6, 18, and 36 months follow-up. Stress echocardiography was performed on 17 patients at 18 months postoperatively, and regional wall motion score index was calculated in lased and nonlased nonrevascularizable myocardium of the left ventricle at rest and with dobutamine stress. Results Both groups of patients were similar in preoperative demographics and operative data. There was no perioperative death. There was no difference between the two groups in angina scoring at 6, 18, and 36 months follow-up. Exercise tolerance improved by a mean of 46.8 ± 20.0 seconds in the coronary artery bypass grafting group versus 199.2 ± 66.5 seconds per patient in the coronary artery bypass grafting plus transmyocardial laser revascularization group ( p = 1.8 ×10 −6) at 6 months; this benefit was maintained at 18 months (157 ± 46.3 versus 61 ± 39.2 seconds; p = 4 ×10 -4) but was lost at 36 months (57.2. ± 42.1 versus 68.1 ± 46.7 seconds; p = 0.70). The mean values for wall motion score index in the lased and nonlased regions at each stage of dobutamine stress at 18 months after surgery were not statistically significant. Conclusions The combination of coronary artery bypass and transmyocardial laser revascularization improved exercise tolerance in patients in whom complete revascularization could not be achieved by bypass grafting alone in the short term, but this benefit was lost by 36 months postoperatively. The transient improvement in exercise tolerance cannot be explained by changes in contractility in the lased areas.

Quantification of microembolic signals during transmyocardial laser revascularization

Transmyocardial laser revascularization (TMLR) is known to induce cerebral microembolic signals (MES). We quantified laser induced MES in patients undergoing TMLR during cardiopulmonary bypass for coronary artery bypass grafting (group A) and during TMLR treatment alone (group B). The total number of MES during a single laser application with identical energy was significantly higher in group A compared to group B (P<0.001). Also the peak of MES occurred significantly later in group A (P<0.0001). An increase of laser energy was associated with an increase in numbers of MES particular in group B (r=0.641). Different TMLR modalities generate different amounts of cerebral microembolic signals. Thus, adjustment of TMLR to these modalities may reduce potentially harmful cerebral microemboli and warrants further evaluation.

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.

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.

Quality of life and survival after transmyocardial laser revascularization with the holmium:YAG laser

Background The purpose of the this investigation was to assess postoperative survival and quality of life with transmyocardial laser revascularization (TMR) in high-risk patients. Methods During a 24-month period, 81 consecutive patients underwent either sole therapy TMR (n = 34) or TMR with coronary artery bypass grafting (n = 47) using a holmium:yttrium–aluminum–garnet (YAG) laser. Outcomes were assessed in three high-risk groups, including patients with left ventricular dysfunction (ejection fraction ≤ 0.40) (n = 37), unstable angina (n = 30), and congestive heart failure (n = 33). Disease-specific quality of life was assessed using the Seattle Angina Questionnaire in 58 late survivors and compared with an age-matched cohort undergoing coronary artery bypass grafting only (no TMR) (n = 20). Results Overall mortality was 6% ± 3% (±70% confidence limit) and appeared higher with left ventricular dysfunction (11% ± 5% vs 2% ± 2%), but the difference did not reach statistical significance ( p = 0.17; power = 0.16). There was also no statistical difference with unstable angina (10% ± 6% vs 4% ± 3%; p > 0.53) or congestive failure (9% ± 5% vs 4% ± 3%; p > 0.66). However, survival at 18 months was significantly lower with left ventricular dysfunction (62% ± 9% vs 90% ± 5%; p < 0.003) and congestive failure (48% ± 10% vs 96% ± 3%; p < 0.001). For sole therapy TMR, quality of life was diminished comparing TMR with coronary artery bypass grafting ( p < 0.004) and coronary artery bypass grafting only ( p < 0.002). Conclusions Transmyocardial laser revascularization can be performed in high-risk patients, but survival is significantly impaired in patients with left ventricular dysfunction and congestive failure, and quality of life is diminished without some degree of direct revascularization.

Pro: transmyocardial laser revascularization is best for treatment of severe coronary artery disease

TRANSMYOCARDIAL LASER revascularization (TMLR) has been introduced as a therapeutic option for patients with end-stage coronary disease not amenable to conventional coronary artery bypass grafting. Often patients accepted for this treatment have already undergone multiple percutaneous revascularization procedures as well as surgical revascularization. The idea of creating channels in the myocardium with lasers dates back to 1981,1 and some studies have shown improvement of angina as well as evidence of improved myocardial perfusion by positron emission tomography (PET) scan and dobutamine stress echo. However, the ongoing controversy regarding the efficacy of TMLR may simply indicate that it is not understood which patient populations are most likely to benefit. The mechanism of action is still not well understood. What are the most recent data to support the ongoing application of this treatment?

Transmyocardial laser revascularization: epicardial ECG detection provides efficient R-wave triggering during mobilization of the heart.

In order to achieve an accurate intraoperative ECG detection, a new technique in detecting the trigger-signal was developed. In contrast to the traditional three-lead ECG-configuration, the left leg electrode was connected to a transient epicardial pacemaker electrode on the left-ventricular surface. The Holmium:YAG-Laser for Transmyocardial Laser Revascularization (TMLR) is R-wave-triggered, providing the release of energy only during the refractory period of the heart cycle. However, an exact ECG-triggering during mobilization of the apex and/or posterior wall is difficult to achieve by using conventional ECG-configuration, therefore increasing the risk for mistriggering and induction of arrhythmias during TMLR. Two groups of patients, all undergoing stand alone TMLR-procedures via left minithoracotomy, were compared. Ten patients were operated with the conventional ECG configuration (group 1) and ten patients with the modified epicardial ECG configuration (group 2). In patients of group 1, as a result of a loss of the trigger signal or due to the triggering of artifacts, the incidence of correctly triggered QRS-complexes was 56% of all documented QRS-complexes. In contrast, an excellent triggering was observed in 98% (p < 0.001) in group 2, resulting in a reduction of laser operative time by 35% (p < 0.001) and a decrease in the incidence of intraoperative ventricular fibrillation (0 vs. 3). In conclusion, this new ECG configuration is a simple but effective method in achieving an excellent ECG signal during all stages of TMLR. As a consequence, a reduction in operative time and incidence of ventricular fibrillation can be achieved.

Health Economics and Surgical Care

Health care resources are scarce and yet the demand for them continues to grow. It is inevitable, therefore, that decisions must be taken about how best to deploy resources within the health care sector. The health economist argues that choices between competing health care interventions should be made on the grounds of economic efficiency or cost-effectiveness, i.e. we should choose those interventions which produce the greatest health benefit from the finite resources available. To facilitate such decision-making, it is necessary to have information on both the resource use inputs (or costs) and the benefits (or health outcomes) associated with the health care interventions we wish to choose between. Economic evaluation (which is becoming increasingly common in the health care setting) provides a vehicle for obtaining and synthesising this information. Surgery is constantly evolving. In the face of scarce resources, new technologies should be subject to cost-effectiveness considerations. Economic evaluation has been used to evaluate many surgical interventions, including: • percutaneous transluminal coronary angioplasty • coronary artery bypass grafting • transmyocardial laser revascularization • alternative surgical techniques for the repair of groin hernia • heart, kidney and liver transplantation.

Transmyocardial laser revascularisation and other treatment modalities for angina pectoris.

Ischaemic heart disease is one of the leading causes of morbidity and mortality in the western world. This paper provides an overview of the different treatments for one of the most common manifestations of ischaemic heart disease: angina pectoris. Besides the currently available conventional methods, several alternative treatments are described, with a special focus on transmyocardial laser revascularisation.

Transmyocardial laser revascularization preserves regional myocardial perfusion: an MRI first pass perfusion study.

It is controversial whether transmyocardial laser revascularization (TMLR) improves myocardial perfusion. Therefore, we assessed myocardial perfusion before and after TMLR with quantitative magnetic resonance perfusion imaging (MRPI) in an animal study. One week after partial occlusion of the left circumflex artery (LCx) in 12 pigs, resting perfusion (ml/g/min), perfusion reserve (PR) with adenosine, regional wall thickening (RWT), cardiac output (CO) were quantified with MRI in the LCx (lateral) and LAD (septal) dependent myocardium. Subsequently, six animals were treated with TMLR of the lateral left ventricle (LV). Six animals were left untreated. A final MR was performed 8 weeks later. MRPI data were compared to microsphere-derived blood flow and % LV necrosis (TTC). 'Normal' myocardial perfusion was assessed with MRPI in 12 non-instrumented animals. Resting perfusion prior to TMLR (0.7-0.9+/-0.3) in the LV-lateral myocardium was preserved after TMLR (1.0+/-0.3) and decreased without TMLR (0.3+/-0.1, P<0.05). There was a significant difference (P<0.01) between the TMLR treated and untreated group. Compared to 'normals' (1.2+/-0.2) perfusion of the LV-lateral wall was not different after TMLR but reduced (P<0.02) without TMLR. PR was not different between TMLR-treated (1.4+/-0.9) and untreated (1.9+/-0.6) group but was reduced (P<0.04) compared to PR of 'normals' (2.7+/-0.8). MRPI data and microsphere-derived perfusion were significantly correlated (P<0.01). RWT in the LCx-dependent myocardium improved (P<0.02) after TMLR. CO decreased (P<0.02) and TTC-staining indicated more LV-necrosis without TMLR (6.6+/-1.6 vs. 3.7+/-1.5, P<0.01). TMLR preserves regional myocardial perfusion and improves function as shown with MRPI.

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 CO2laser through a left anterior thoracotomy. Seventeen patients (CABG group) underwent standard CABG. Myocardial oxygenation was determined by measuring intramyocardial partial oxygen pressure (ptiO2). PtiO2was 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 ptiO2was significantly lower in the TMLR group compared with the CABG group (p < 0.05). In both groups ptiO2increased significantly in the postoperative course, whereby ptiO2in the TMLR group was significantly lower compared with the CABG group.Conclusion—Although the exact mechanism of action of TMLR remains unclear, ptiO2and thus oxygen supply in the myocardium increased in patients undergoing TMLR at least in the early postoperative course. However, ptiO2increased to a lesser extent compared with CABG.

Wall Motion and Perfusion Analysis of Transmyocardial Laser Revascularization

ObjectiveObjective—Transmyocardial laser revascularization (TMLR) creates channels in the myocardium. The aim of the treatment is to relieve angina in patients with end-stage coronary artery disease. We studied the effect of TMLR on myocardial function and perfusion with the combination of cine magnetic resonance Imaging (MRf) and thallium scintigraphy.Design—Eight patients with severe triple-vessel coronary artery disease were studied with MRI and thallium scintigraphy before and 6 months after laser treatment.Results—TMLR did not improve global left ventricular (LV) function or myocardial perfusion. However, systolic wall thickening deprived in segments with fixed perfusion defects in 6 months and la ertreatment prevented this deprivation (p = 0.03). In addition single Photon emission computed tomography (SPECT) Imaging indicated that TMLR prevented conversion of reversible into fixed defects.Conclusion—In severe, progressing coronary artery disease TMLR does not improve global LV function or myocardial perfusion, but it preserves systolic wall thickening in fixed defects (scar). It also prevents changes from ischemic myocardial regions to scar.

Transmyocardial laser revascularization combined with vascular endothelial growth factor 121 (VEGF121) gene therapy for chronic myocardial ischemia--do the effects really add up?

Different therapy strategies for coronary disease in conventionally untreatable patients have been developed, among them transmyocardial laser revascularization (TMLR) and the application of growth factors. The objective of our study was to determine whether a combined therapy of TMLR with a vascular endothelial growth factor(121) (VEGF(121)) plasmid is able to stimulate the development of sufficient collateral circulation and hereby to preserve cardiac function. A severe stenosis of the left anterior descending artery was created in healthy pigs. After 1 week, perfusion and regional contractility were assessed at baseline. Afterwards, the ischemic area was treated with TMLR (n=8), intramyocardial injection of naked plasmid DNA encoding VEGF(121) (n=7), or both (n=7). Control animals were left untreated (n=8). After 3 months, the animals were re-examined and underwent immunohistological analysis. The number of capillaries increased only after injection of VEGF(121) plasmid alone compared to untreated ischemia and to the other therapy groups, whereas the number of arterioles was higher following TMLR treatment alone or in combination with VEGF(121) than it was in the case in untreated ischemic animals. However, only combined VEGF(121)+TLMR therapy resulted in an improvement in regional myocardial blood flow in comparison with 1 week ischemia, indicating the efficient development of collateral circulation. In contrast, better regional contractility compared to the 1-week baseline, as well as restoration of the pre-ischemic values, were achieved by both VEGF(121) and combined VEGF(121)+TLMR therapies. This study of chronic myocardial ischemia with a porcine model indicates a synergistic action of TMLR and VEGF(121) gene therapy. Combined treatment alone achieved an increase of regional myocardial perfusion, which accompanied arteriogenesis and corresponded with the restoration of regional function.

The combined use of transmyocardial laser revascularization (TMLR) and fibroblastic growth factor (FGF-2) enhances perfusion and regional contractility in chronically ischemic porcine hearts.

The purpose of this study was to determine the combined effect of transmyocardial laser revascularization (TMLR) and recombinant human basic fibroblastic growth factor (rhFGF-2) treatment in chronically ischemic hearts. To employ this porcine ischemic model, an operative severe stenosis of the left anterior descending artery (LAD) was created (first operation). One week later, the animals were studied at baseline (second operation) by analyzing perfusion (microsphere technique) and regional contractility (ultrasonic crystals). Afterwards, pigs were randomized into one of the four groups: ischemic control group (n = 7), TMLR-group (n = 7), FGF-2-group receiving 500 microg rhFGF-2 (n = 6), and FGF-2 + TMLR-group receiving TMLR with 500 microg rhFGF-2 (n = 6). Twelve weeks later, the animals were re-examined (third operation) and the hearts underwent additionally histochemical and immunohistologic analysis. Three months after therapy, regional myocardial blood flow (RMBF) in the LAD territory was significantly higher at rest in the FGF-2 group and FGF-2 + TMLR group compared to baseline, control and TMLR group (FGF-2 group: 1.17 +/- 0.10 versus baseline 0.28 +/- 0.10, P = 0.028; versus control 0.49 +/- 0.12, P = 0.01; and versus TMLR 0.34 +/- 0.20, P = 0.0081; FGF-2 + TMLR group: 0.88 +/- 0.29 versus baseline 0.41 +/- 0.14, P = 0.028; versus control 0.49 +/- 0.12, P = 0.019 and versus TMLR group 0.34 +/- 0.20 ml/g per min, P = 0.0032). Furthermore, the FGF-2 + TMLR-group demonstrated higher RMBF values in the LAD territory under stress conditions compared to baseline (1.79 +/- 0.69 versus 0.41 +/- 0.14; P = 0.028) and control (1.79 +/- 0.69 versus 0.78 +/- 0.55 ml/g per min; P = 0.038) at the end of the study. In contrast to these groups, RMBF in the control and TMLR group was unchanged. After 3 months, the FGF-2- and FGF-2 + TMLR-groups' regional contractility in the LAD territory revealed an improvement at rest (FGF-2: 84.00 +/- 26.22 versus baseline: 53.76 +/- 13.49, P = 0.003; FGF-2 + TMLR: 104.46 +/- 28.62 versus control: 61.27 +/- 5.13; P = 0.005 and versus TMLR: 59.74 +/- 41.23%; P = 0.041), whereas control and TMLR animals did not show any difference. TMLR as well as FGF-2 + TMLR treatment resulted in an increased number of capillaries and of arterioles in the channel area compared to untreated ischemia (P < 0.005). In contrast to the TMLR- and control group, CO(2)-laser revascularization combined with the application of intramyocardial growth factor, FGF-2, significantly ameliorates perfusion at rest and stress in this model of chronic regional ischemia, whereas sole FGF-2 application showed an improvement at rest only. This was mirrored by an enhancement of regional contractility in the FGF-2 + TMLR- and FGF-2-group at rest.

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

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. 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). 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. 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.

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.

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

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

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

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. 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. 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. 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.