Direct CO2 laser "revascularization" of the myocardium

The prospective clinical and scintigraphic assessment of patients with preserved left ventricular systolic function after transmyocardial laser revascularisation

AIM

To analyse the clinical outcome and myocardial perfusion and function after transmyocardial revascularisation (TMR) in patients with normal left ventricular function and multivessel coronary artery disease non-amenable for standard revascularisation.

METHOD AND RESULTS

Twenty three severely symptomatic patients (CCS score median 4) with normal left ventricular systolic function but coronaries non-amenable for either PTCA or CABG were subjected to TMR. The angina score, left ventricular systolic and diastolic function in radionuclide ventriculography at rest, exercise tolerance and myocardial perfusion--Thallium-201 SPECT (adenosine stress 74 and 37 MBq under nitrate cover) were evaluated before and 3, 6, 12 months post-operatively. After an average of 40 +/- 12 (range 14-56) TMR channels angina score decreased significantly (p< 0.0001) and the exercise tolerance increased (from 6.0 +/- 4.5 to 9.1 +/- 4.6 after 6 months, p< 0.05) in 21 patients. During the follow up period two patients had a myocardial infarction and one committed suicide after 6 months. Ejection fraction dropped significantly only after 1 year post-TMR from 70 +/- 13 to 63 +/- 0.13%, p < 0.05. The overall perfusion improved initially in 14 patients with subsequent deterioration in time. The changes in segmental perfusion were not associated with the symptomatic improvement.

CONCLUSION

Transmyocardial revascularisation in patients with normal ejection fraction may improve the angina class, exercise tolerance and overall but not segmental perfusion and does not show any immediate effect on left ventricular function.

A mathematical model for the laser treatment of heart disease

Transmyocardial laser revascularisation (TMLR) is used to treat patients with severe coronary artery disease. A laser is used to create narrow tunnels within ischemic heart muscle in an attempt to reperfuse the area with oxygenated blood directly from the left-ventricular chamber. It has been hypothesised that initially blood flow through the patent tunnels plays an important role in the efficacy of the treatment (J. Am. College Cordiol. 25(1) (1995) 258) and Waters (J. Fluid Mech. 433 (2001) 193) developed a simple mathematical model to show that this blood flow enhances the quantity of oxygenated blood drawn into the tunnel and the subsequent delivery of oxygen to the tissue. To date, however, the optimum parameter values for this clinical technique have not been determined, e.g. the radius of the laser-drilled tunnels and their relative spacing. We present a mathematical model to determine the distribution of oxygen for a wide range of the governing parameters. Our results indicate that the tunnel radius has a significant effect on the degree of tissue reperfusion and predictions for the optimum tunnel spacing are made.

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.

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.

Potential use of ultrasound in creating transmyocardial channels

Although the mechanisms of the clinical benefits of transmyocardial laser revascularization (TMLR) are considered to be angiogenesis with increased perfusion, denervation and placebo effect, it is unknown whether laser energy is a prerequisite in obtaining these beneficial effects. The present study investigated whether it is possible to create transmyocardial channels and induce angiogenesis by ultrasound. Myocardium was penetrated with an ultrasonically activated surgical blade by advancing the blade tip perpendicularly to the left ventricular free wall of the beating heart of 6 mongrel dogs. The power of ultrasound was set at either the lowest or highest of the system. The animals were killed 30 min (acute; n=3) and 2 weeks (chronic; n=3) after channel creation. Holmium:YAG laser, which is currently used for clinical TMLR, was used to create myocardial channels in 4 other dogs, which were also killed 30 min (n=2) and 2 weeks (n=2) after channel creation. The areas of acute channel core, acute thermal damage and chronic fibrosis were compared between the laser and ultrasound channels by Masson's trichrome stain. Factor VIII and proliferating cell nuclear antigen (PCNA) immunostaining were carried out on the samples obtained from chronic animals. The density of vessels and that of proliferating vascular endothelial cells and vascular smooth muscle cells around the channels were measured. The area of acute core was larger in the lowest and highest outputs of ultrasound than in laser channels (0.78+/-0.09, 1.0+/-0.12 vs 0.38+/-0.04 mm2; p<0.01). The area of acute damage in both laser and the highest output of ultrasound channels was greater than in the channels produced by the lowest output of ultrasound (4.43+/-0.28, 4.63+/-0.44 vs 2.90+/-0.29 mm2; p<0.01). The ratio of acute damage area to acute core area was greater in laser channels than in either type of ultrasound channel (16.86+/-1.66 vs 6.04+/-0.67, 7.86+/-1.07; p<0.01) and the area of chronic fibrosis was greater (3.23+/-0.20 vs 1.59+/-0.18, 2.24+/-0.20 mm2; p<0.01). Factor VIII and PCNA immunostaining revealed new vessels not only inside the areas of chronic fibrosis, but also in the surrounding myocardium, in both laser and ultrasound channels. Ultrasound created transmyocardial channels histologically similar to laser channels and angiogenesis was induced in the normal myocardium surrounding ultrasound channels.

A review of the literature: transmyocardial laser revascularization

BACKGROUND AND OBJECTIVE

Transmyocardial laser revascularization is an investigational procedure that improves chronic angina that is not amenable to other forms of therapy. The theorized mechanism is an increased supply of oxygenated blood to the myocardium via the creation of left ventricular transmural channels. The objective of this review is to facilitate an understanding of the current work published in the literature on the subject of transmyocardial laser revascularization.

METHODS

Using Melvyl Medline, all pertinent literature associated with transmyocardial laser revascularization was sought and reviewed.

CONCLUSION

The research in transmyocardial laser revascularization is growing. The results of the current work in animals is conflicting with some showing a benefit from this procedure and others that refute its effectiveness. This may be the outcome of differing methodology, which has yet to be evaluated. Although the results of human trials are positive, the overall effectiveness in comparison with the conventional forms of therapy has not been addressed. It is, therefore, a procedure worthy of continued study.

Long- and short-term effects of transmyocardial laser revascularization in acute myocardial ischemia

BACKGROUND AND OBJECTIVE

This study examined the effect of transmyocardial laser revascularization (TMLR) on infarct size and global and regional left ventricular (LV) function.

STUDY DESIGN/MATERIALS AND METHODS

Acute ischemia was induced in 24 dogs by ligating the left anterior descending artery. TMLR was done through a left thoracotomy in 12 dogs. The 12 control dogs had ligation only. Global and regional LV function were measured before ligation, then at 6 hours or 3 months after ligation. We calculated the volumetric ratio of damaged myocardium to myocardium at risk (Vd/Vr).

RESULTS

At 6 hours, global compensation despite regional dyskinesia was universal; Vd/Vr was the same in control and TMLR dogs. At 3 months, global function during stress was significantly higher in TMLR dogs than in control dogs (P < .05); regional contractions were synergic only in TMLR dogs; mean Vd/Vr was significantly lower in TMLR dogs.

CONCLUSION

TMLR limits infarct expansion and improves long-term global and regional function after acute ischemia.

Early postoperative changes in regional systolic and diastolic left ventricular function after transmyocardial laser revascularization: a comparison of holmium:YAG and CO2 lasers

OBJECTIVES

The purpose of this study was to determine the short-term effects of transmyocardial laser revascularization (TMR) on regional left ventricular systolic and diastolic function, myocardial blood flow (MBF) and myocardial water content (MWC).

BACKGROUND

Clinical studies of TMR have noted a significant incidence of cardiac complications in the early postoperative period. However, the early post-treatment effects of laser therapy on the myocardium and their potential contribution to postoperative cardiac morbidity are unknown.

METHODS

Swine underwent holmium:yttrium-aluminum-garnet (holmium:YAG) (n = 12) or carbon dioxide (CO2) (n = 12) laser TMR. Regional systolic function for the lased and nonlased regions was quantitated using preload recruitable work area (PRWA) and regional diastolic function with the ventricular stiffness constant alpha.

RESULTS

Preload recruitable work area was significantly decreased in the lased regions both 1 (59.8+/-13.0% of baseline, p = 0.02) and 6 h (64.2+/-9.4% of baseline, p = 0.02) after holmium:YAG TMR. This decreased PRWA was associated with a significant reduction in MBF to the lased regions (13.2% reduction at 1 h, p = 0.02; 18.4% decrease at 6 h post-TMR, p = 0.01). These changes were not seen after CO2 laser TMR. A significant increase in MWC (1.4+/-0.3% increase with holmium:YAG, p = 0.004; 1+/-0.2% increase with CO2, p = 0.002) and alpha (217.4+/-44.2% of baseline 6 h post-holmium:YAG TMR, p = 0.05; 206+/-36.7% of baseline 6 h post-CO2 TMR, p = 0.03) was seen after TMR with both lasers.

CONCLUSIONS

In the early postoperative setting, impaired regional systolic function in association with regional ischemia is seen after TMR with a holmium:YAG laser. Both holmium:YAG and CO2 lasers are associated with increased MWC and impaired diastolic relaxation in the lased regions. These changes may explain the significant incidence of early postoperative cardiac morbidity. The impact of these findings on anginal relief and long-term outcome are not known.

Transmyocardial laser revascularization combined with coronary artery bypass grafting: a multicenter, blinded, prospective, randomized, controlled trial

OBJECTIVE

We sought to assess the safety and efficacy of transmyocardial revascularization combined with coronary artery bypass grafting in patients not amenable to complete revascularization by coronary bypass alone.

METHODS

A total of 263 patients whose standard of care was coronary artery bypass grafting and who had one or more ischemic areas not amenable to bypass grafting were prospectively randomized to receive coronary bypass of suitable vessels plus transmyocardial revascularization to areas not graftable (n = 132) or coronary bypass alone with nongraftable areas left unrevascularized (n = 131). Group preoperative demographics and operative characteristics were similar.

RESULTS

The operative mortality rate after coronary bypass/transmyocardial revascularization was 1.5% (2/132) versus 7.6% (10/131) after coronary bypass alone (P =.02). Patients undergoing both coronary bypass and transmyocardial revascularization required less postoperative inotropic support (30% vs 55%, P =.0001) and had a trend toward fewer insertions of intra-aortic balloon pumps (4% vs 8%, P =.13) than did patients having coronary bypass alone. Multivariable predictors of operative mortality were coronary artery bypass alone (odds ratio, 5.3; 95% confidence interval, 1.1-25.7; P =.04) and increased age (odds ratio, 1.1; 95% confidence interval, 1. 0-1.2; P =.03). One-year Kaplan-Meier survival (95% vs 89%, P =.05) and freedom from major adverse cardiac events defined as death or myocardial infarction (92% vs 86%, P =.09) favored the combination of coronary bypass and transmyocardial revascularization. Baseline to 12-month improvement in angina and exercise treadmill scores was similar between groups.

CONCLUSIONS

In a prospective, randomized, multicenter trial, transmyocardial revascularization combined with coronary artery bypass grafting in patients not amenable to complete revascularization by coronary bypass alone was safe; however, angina relief and exercise treadmill improvement were indistinguishable between groups at 12 months of follow-up. Operative and 1-year survival benefits observed after adjunctive transmyocardial revascularization require confirmation by a larger validation study, which is ongoing.

Myocardial laser revascularization: the controversy and the data

The clinical and experimental data relevant to the theoretical mechanisms and clinical results of laser myocardial revascularization are reviewed. Both transmyocardial and percutaneous approaches are considered. Both types result in a reduction in anginal symptoms in patients refractory to conventional therapy and are likely to act through common pathways. The proximate mechanisms for the transmyocardial revascularization effect most likely relate to myocardial inflammation, secondary stimulation of growth factors, and denervation of the myocardium.

Transmyocardial laser revascularization: current status

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

Transmyocardial laser revascularization does not denervate the canine heart

BACKGROUND

Transmyocardial laser revascularization has been used as an indirect approach to improve myocardial perfusion in patients with refractory angina not amenable to conventional therapy. Three mechanisms have been proposed for its therapeutic effects: direct perfusion of the ischemic myocardium through patent channels; induction of angiogenesis; and regional denervation. We sought to determine whether transmyocardial laser revascularization modifies afferent and efferent axonal function within the affected myocardium.

METHODS

Studies were performed in 9 dogs that were artificially ventilated and underwent thoracotomy. Changes in ventricular dynamics and intrinsic cardiac neuronal activity were monitored before and after creating 20 transmural channels in the left ventricular ventral free wall with a holmium:yttrium-aluminum-garnet laser in response to three stimuli: application of veratridine or bradykinin to the epicardial sensory neurites of intrinsic cardiac afferent neurons; sympathetic or parasympathetic efferent neuronal activation either electrically (4 V, 10 Hz, 5 ms) or chemically (nicotine, 5 microg/kg intravenously), and direct cardiomyocyte beta-adrenergic receptor stimulation (isoproterenol hydrochloride, 5 microg intravenously).

RESULTS

Sensory neurites of right atrial afferent neurons in the studied epicardial region responded similarly to chemical stimulation before and after transmyocardial laser revascularization. Transmyocardial laser treatment did not reduce local ventricular contractile responses to direct activation of sympathetic or parasympathetic efferent neurons by electrical or chemical means, nor did it affect cardiomyocyte augmentor responses elicited by exogenous beta-adrenergic receptor challenge.

CONCLUSIONS

As transmyocardial laser revascularization does not affect afferent or efferent axonal function in the affected ventricle, the efficacy of this form of therapy cannot be ascribed to local denervation.

Myocardial scarring after transmyocardial laser revascularization: A potential mechanism of clinical improvement?

BACKGROUND AND OBJECTIVE

The morphological evolution of transmyocardial laser channels was analyzed in a pig model.

MATERIALS AND METHODS

Five channels were created in the lateral wall of the left ventricle of 12 animals, using a Ho:YAG laser. In half of the animals, an additional infarction was induced in the same area. Animals were sacrificed at one-week intervals until week 5 and the critical regions of the left ventricular wall were subjected to microscopic computed morphometrical analysis.

RESULTS

There was no clearly patent lumen at any stage. Cross-sectional area of the channels fell from 8.5 +/- 1.2 mm(2) at day 0 to 2.1 +/- 0.1 mm(2) at day 35. From day 7 onward, the channel area was gradually replaced by granulation tissue and the proportion of the channel occupied by granulation scar tissue increased from 37 +/- 2% at day 7 to 100% at day 28. In the subgroup with concomitant infarction, granulation tissue of both channel and infarction became indistinguishable from day 14 onward.

CONCLUSIONS

These results suggest strongly that channel patency is not the mechanism of angina relief after transmyocardial laser revascularization with Ho:YAG laser.

Are there vascular density gradients along myocardial laser channels?

BACKGROUND

Clinical studies suggest that transmyocardial laser revascularization may improve regional blood flow of the subendocardial layer. The vascular growth pattern of laser channels was analyzed.

METHODS

Twenty pigs were randomized to undergo ligation of left marginal arteries (n = 5), to undergo transmyocardial laser revascularization of the left lateral wall (n = 5), to undergo both procedures (n = 5) or to a control group (n = 5). All the animals were sacrificed after 1 month. Computed morphometric analysis of vascular density of the involved area was expressed as number of vascular structures per square millimeter (+/-1 standard deviation).

RESULTS

The vascular density of the scar tissue of the laser channel was significantly increased in comparison with myocardial infarction alone: 49.6+/-12.8/mm2 versus 25.5+/-8.6/mm2 (p < 0.0001). The vascular densities of subendocardial and subepicardial channel areas were similar: 52.9+/-16.8/mm2 versus 46.3+/-13.6/mm2 (p = 0.41). The area immediately adjacent to the channels showed a vascular density similar to that of normal tissue: 6.02+/-1.7/mm2 versus 5.2+/-1.9/mm2 (p = 0.08). In the infarction + transmyocardial laser revascularization group, the channels were indistinguishable from infarction scar.

CONCLUSIONS

Scars of transmyocardial laser revascularization channels exhibit an increased vascular density in comparison with scar tissue of myocardial infarction, which does not extend into their immediate vicinity. There was no vascular density gradient along the longitudinal axis of the channels.

Diagnosis, incidence, and clinical significance of early postoperative ischemia after transmyocardial laser revascularization

BACKGROUND

Clinical improvement after transmyocardial laser revascularization (TMR) is typically delayed, and patients therefore remain at risk for ischemic events after the procedure. The purpose of this study was to define the range of creatine phosphokinase (CPK) and CPK-MB enzyme elevation after TMR and to assess the incidence of early postoperative ischemic events.

METHODS

Twenty-one patients undergoing isolated TMR were evaluated for 48 hours after surgery with serial CPK and CPK-MB enzymes and 12-lead electrocardiograms for evidence of myocardial ischemia or injury. Clinically evident postoperative ischemic events including angina pectoris, myocardial infarction (MI), and cardiac death were recorded as well.

RESULTS

Eleven patients (52.4%) had ischemic electrocardiographic changes in the first 48 hours after TMR. Ischemia was clinically silent in 7 (63.6%) of these 11 patients. Cardiac death occurred in 1 patient (4.8%) as a result of acute MI. Nonfatal MI occurred in an additional 4 patients (19.0%). Of the 5 patients with MI, 4 had angina pectoris versus no angina in the 16 patients without MI (P =.02). All patients had elevated CPK and CPK-MB levels after TMR: however, peak CPK (P =.02) and CPK-MB (P =. 005) levels were significantly higher for patients suffering postoperative MI compared with those without MI.

CONCLUSIONS

Transient ischemia occurs frequently after TMR and is clinically silent in the majority of patients. Patients with postoperative MI are more likely to have symptomatic ischemia as well as significant cardiac enzyme elevation. The combination of 12-lead electrocardiogram and cardiac enzymes appears to have significant merit for the diagnosis of myocardial ischemia and infarction after TMR. These studies should be obtained in all patients undergoing TMR for the first 48 hours after surgery.

Perioperative morbidity and mortality after transmyocardial laser revascularization: incidence and risk factors for adverse events

OBJECTIVES

The purpose of this study was to describe the incidence and spectrum of perioperative cardiac and noncardiac morbidity and mortality after transmyocardial laser revascularization (TMR) and to identify predictors of these adverse clinical events.

BACKGROUND

Clinical studies have demonstrated the efficacy of TMR for relieving angina pectoris, although no study to date has specifically addressed the associated perioperative morbidity and mortality.

METHODS

Between October 1995 and August 1997, 34 consecutive patients with end-stage coronary artery disease (CAD) underwent isolated TMR. The majority of patients (94%) had class III or IV angina pectoris, and two patients (6%) had unstable symptoms preoperatively. Patient records were reviewed for fatal and nonfatal adverse cardiac and noncardiac events.

RESULTS

Perioperative death occurred in two patients (5.9%) due to cardiogenic shock complicating acute myocardial infarction. Perioperative cardiac morbidity occurred in 16 patients (47.1%); noncardiac morbidity was seen in 12 patients (35.3%). Preoperative unstable angina was the only variable predictive of perioperative death (p = 0.005). Cardiac (p = 0.005) and noncardiac (p < 0.001) morbidity rates were significantly higher for the initial 15 patients undergoing the procedure. Other predictors of perioperative complications included lack of postoperative treatment with a furosemide infusion (p < or = 0.04) and preoperative unstable angina (p = 0.05).

CONCLUSIONS

Perioperative mortality in patients undergoing isolated TMR is low. Transmyocardial laser revascularization patients are at higher risk for adverse perioperative cardiac and noncardiac events, likely reflecting the lack of immediate benefit from the procedure in the setting of severe CAD. These patients merit vigilant surveillance for adverse events and aggressive medical management in the perioperative period.

Neovascularization after transmyocardial laser revascularization in a model of chronic ischemia

BACKGROUND

The mechanism of clinical improvement after transmyocardial laser revascularization (TMR) is unknown. One hypothesis holds that TMR causes increased myocardial perfusion through neovascularization. This study sought to determine whether angiogenesis occurs after TMR in a porcine model of chronic myocardial ischemia.

METHODS

Six miniature pigs underwent subtotal left circumflex coronary artery occlusion to reduce resting blood flow to 10% of baseline. After 2 weeks in the low-flow state, dobutamine stress echocardiography and positron emission tomography were performed to document ischemic, viable myocardium. The animals then underwent TMR and were sacrificed 6 months later for histologic and immunohistochemical analysis.

RESULTS

Histologic analysis of the lased left circumflex region demonstrated many hypocellular areas filled with connective tissue representing remnant TMR channels. Histochemical staining demonstrated a highly disorganized pattern of neovascularization consistent with angiogenesis located predominantly at the periphery of the channels. Immunohistochemical analysis confirmed the presence of endothelial cells within neovessels. Vascular density analysis revealed a mean of 29.2+/-3.6 neovessels per high-power field in lased ischemic myocardium versus 4.0+/-0.3 (p<0.001) in nonlased ischemic myocardium.

CONCLUSIONS

This study provides evidence that neovascularization is present long term in regions of ischemic, viable myocardium after TMR. Angiogenesis may represent the mechanism of clinical improvement after TMR.

Transmyocardial laser-revascularization: experimental studies on prolonged acute regional ischemia

OBJECTIVE

This experimental study in pigs was undertaken to answer the question whether TMLR after acute myocardial infarction may improve regional myocardial perfusion, left ventricular function and diminish myocardial necrosis in the area at risk.

METHODS

Thirty open-chest anesthetized pigs were observed for 6 h, six pigs served as controls. In 24 pigs, occlusion of the left anterior descending artery (LAD) beyond the first diagonal branch was performed: seven pigs had LAD occlusion only (ischemia group), and 17 pigs were treated by TMLR (using a CO2-laser, energy: 40 J) prior to coronary occlusion; nine pigs received one laser channel (1 mm diameter) per cm2 (laser group 1) and eight pigs two channels per cm2 in the LAD territory (laser group 2). Regional myocardial blood flow by microspheres, function (franc starling curves), histochemical assessment (triphenyl tetrazolium chloride, TTC and histology), were performed.

RESULTS

The lased pigs were less prone to ventricular fibrillation (laser group 2, 38%; laser group 1, 56%; ischemic group, 100%; P < 0.05), and showed a significant smaller area of necrosis (TTC) in the area at risk (laser group 1, 23%; laser group 2, 14%; vs. ischemia group, 31%; P < 0.01). There was no significant difference between laser-treated and ischemia hearts regarding the amount of blood flow into the infarcted LAD region and the maximal left ventricular stroke work index after 6 h (P = n.s). Regional myocardial blood flow: ischemia group, 4 +/- 5 ml/100 g/min; laser group 1, 3 +/- 10 ml/100 g/min, and laser group 2, 2 +/- 10 ml/100 g/min; maximal left ventricular stroke work index: ischemia group, 1.8 mJ/g; laser group 1, 2.1 mJ/g and laser group 2, 2.1 mJ/g.

CONCLUSIONS

This model of acute regional ischemia demonstrates that CO2-laser revascularization diminish significantly the incidence of ventricular fibrillation and necrosis in the area at risk, and does not change regional myocardial perfusion and global left ventricular function. This experiment indicates that TMLR may be an alternative in treating advanced ischemic heart disease.

Electron-microscopic findings after transmyocardial laser revascularization in an acute ischemic pig model

OBJECTIVE

The clinical benefit in terms of angina reduction after transmyocardial laser revascularization (TMLR) in patients with diffuse coronary artery disease who are not candidates for conventional procedures has been proved. The exact mechanisms of TMLR however, are still unknown. The aim of this study was to investigate the cellular changes in relation to intramyocardial partial oxygen pressure (ptiO2) after TMLR in a model of acute ischemia in pigs by electron microscopical methods (TEM).

METHODS

Seven pigs were included in this study (five animals with acute myocardial ischemia and additional TMLR and two animals with acute myocardial ischemia and without TMLR for control). Acute ischemia was induced by ligation of diagonal branches of the left anterior descending artery (LAD). Intramyocardial partial oxygen pressure was measured before induction of ischemia and thereafter continuously for up to 6 h in all animals. Biopsies of all animals were taken before induction of ischemia and thereafter at 30 min, 3 and 6 h. Analysis of the myocardial ultrastructure was focused on mitochondria, cell nucleus, T-tubules and myofibrils.

RESULTS

Ultrastructural changes were seen in all animals. At 6 h after induction of ischemia, mitochondria showed a destruction of the internal as well as the external membrane and of the cristae. The nuclei showed margination of the chromatin. Myofibrils were characterized by ruptures in the Z-stripes. Lipid droplets as an indicator of ischemia could be identified. PtiO2 between 40 and 80 mmHg before intervention decreased down to 0-2 mmHg within the first 9 min after diagonal branch ligation and did not increase even after TMLR.

CONCLUSIONS

In this acute ischemic model using pigs, TEM evaluation following TMLR proves irreversible changes of the myocardial ultrastructure. Furthermore, TMLR was not able to increase ischemically induced decrease of ptiO2. These data provide some evidence that TMLR thus, may not be able to ameliorate acute ischemia at least in the pig model. Further investigations are needed to investigate the effect of TMLR in chronic myocardial ischemia.

Transmyocardial laser revascularization using the Holium-YAG laser for treatment of end stage coronary artery disease

OBJECTIVE

Transmyocardial Laserrevascularization (TMLR) is a treatment for end-stage coronary artery disease, that is not eligible for surgery or PTCA. The experience with TMLR using the Holium YAG laser is presented.

METHODS

Transmyocardial Laserrevascularization (TMLR) was performed in 28 patients with end stage coronary artery disease, using a new Holium YAG Laser. All patients were refractory to a maximum of medical treatment. In 16 patients TMLR was used as the sole therapy with a mean of 28 +/- 4 laser created channels (group A). In 12 patients TMLR was combined with coronary artery bypass graft surgery with a mean of 17 +/- 2 channels and 1.3 +/- 0.2 grafts (group B). Preoperative and postoperative examination included angina classification, exercise test and thallium scan.

RESULTS

Postoperative demographics were as follows: (a) age 55-71 years (mean 63.9 +/- 6.5 years); (b) Canadian Cardiovascular Society Angina Scale (CCS) mean 3.3 +/- 0.5; (c) ejection fraction 35-71% (mean 54 +/- 13.7%). All patients had an peri- and postoperative course without major complications and a duration of hospitalization of 8.2 +/- 1.9 days. Minor complications were a clinically silent myocardial infarction n = 1, atrial arrhythmia n = 2 and pneumothorax n = 2. A follow-up at 3-12 months was completed in 23 patients (82%). Only one patient died 5 months after surgery (cardiac related death). In all remaining patients CCS had improved with a mean of 1.6 +/- 0.3, P < 0.01. The exercise tolerance test (bicycle) improved in 17 patients with a mean 26.5 +/- 6.5 watt, P < 0.01. The ejection fraction did not significantly improve. The repeated thallium scan did not show an improvement of perfusion in the lasered area to a significant level. Subjective benefit from the treatment was confirmed by 21 patients.

CONCLUSION

Based on these results it is concluded that TMLR with the Holium-YAG laser is a safe therapy for the treatment of end stage coronary artery disease. The postoperative clinical results are comparable to that achieved with the CO2-laser in terms of reducing angina symptoms and improving exercise tolerance and quality of life. However. relief of symptoms is not correlated to objective findings of cardiac function.

Transmyocardial laser revascularisation in acutely ischaemic myocardium

OBJECTIVE

Although recent experience suggests that transmyocardial laser revascularisation (TMLR) relieves angina, its mechanism of action remains undefined. We examined its functional effects and analysed its morphological features in an animal model of acute ischaemia.

METHODS

A total of 15 pigs were randomised to ligation of left marginal arteries (infarction group, n = 5), to TMLR of the left lateral wall using a holmium:yttrium-aluminium garnet (Ho:YAG) laser (laser group, n = 5), and to both (laser-infarction group, n = 5). All the animals were sacrificed 1 month after the procedure. Haemodynamics and echocardiography with segmental wall motion score were carried out at both time intervals (scale 0-3: 0, normal; 1, hypokinesia; 2, akinesia; 3, dyskinesia). Histology of the involved area was analysed.

RESULTS

Laser group showed no change of the segmental wall motion score of the involved area 30 min after the laser channels were made (score: 0 +/- 0). Infarction and laser infarction groups both showed a persistent and definitive increase of the segmental wall motion score (at 30 min: 1.6 +/- 0.3 and 2 +/- 0, respectively; at 1 month: 1.8 +/- 0.2 and 1.8 +/- 0.4, respectively). These increases were all statistically significant in comparison with baseline values (P < 0.5), however comparison between infarction and laser-infarction groups showed no significant difference. On macroscopic examination of the endocardial surface, no channel was opened. On histology, there were signs of neovascularisation around the channels in the laser group, whereas in the laser-infarction group the channels were embedded in the infarction scar.

CONCLUSIONS

In this acute pig model, TMLR did not provide improvement of contractility of the ischaemic myocardium. To the degree that the present study pertains to the clinical setting, the results suggest that mechanisms other than blood flow through the channels should be considered, such as a laser-induced triggering of neovascularisation or neural destruction.

Percutaneous transmyocardial revascularization

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

[Transmyocardial laser revascularization--an innovative pathophysiologic concept]

In patients with coronary artery disease where standard revascularization procedures are not appropriate, transmyocardial laser revascularization (TMLR) represents an innovative technique which is currently validated worldwide. Initially, it has been assumed that myocardial perfusion of ischemic regions could be instantly improved by inducing TMLR channels, which, however, might not be confirmed in ongoing studies. Indeed, the gain in O2 diffusion surface obtained by 20 patent TMLR channels is only 6 cm2 which accounts for just 0.01% of the total capillary surface (47000 cm2) of the myocardium. Instead, a chronic structural remodeling of myocardial regions, adjacent to TMLR channels and mediated by TMLR-induced expression of vascular endothelial growth factor (VEGF), may occur leading to neocapillarization of ischemic myocardium irrespective of the long-term patency of TMLR channels and, thereby, would improve myocardial perfusion (Figure 1). Six weeks following TMLR in the pig, patent TMLR channels were not observed. Instead, a marked degree of reparative fibrosis was found at the site of TMLR-treated myocardial regions (Figure 2). It is, however, not known, whether ischemic conditions would affect chronic channel patency. TMLR combined with intramyocardial administration of 0.5 microgram VEGF between the laser-induced channels resulted in few patent channels (Figure 3). The apparently low efficacy of VEGF applied as protein could be attributed to degradation of VEGF by local peptidases. In addition to VEGF, other growth factors and the interaction of endothelial cells and the extracellular matrix need to be considered. Of particular relevance appears alpha v beta 3-integrin which is needed for adhesion of endothelial cells to extracellular matrix components and is, therefore, required for neocapillarization. Among various other growth factors associated with neoangiogenesis, TGF-beta 1 and PDGF-BB are involved in the formation of extracellular matrix anchoring newly formed vessels. Thus, the expression of VEGF and alpha V beta 3-integrin in myocardial regions surrounding TMLR channels appears to be of major importance for the development of neoangiogenesis within the ischemic myocardium. Whether concomitant therapeutical strategies, i. e., gene transfer leading to over-expression of VEGF, will optimize the TMLR procedure by improving neoangiogenesis remains to be elucidated in future experimental studies.

The development of surgery of the coronary circulation: the Bigelow Lecture

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Clinical data and histological features of transmyocardial revascularization with CO2-laser

OBJECTIVE

TMR is a modern therapeutic approach in the treatment of patients with severe chronic ischemic cardiac disease. Clinical data from world-wide over 1800 TMR-treated patients shows that TMR can improve cardiac status in cases without preoperative congestive heart failure. The mechanisms underlying beneficial TMR-effects are not well understood.

METHODS

The 61 patients of the Hamburg University TMR-trial were treated with a CO2-laser. Clinically, both a 6 and a 12 months follow-up were performed. Pathologically, hearts from four patients who died 3 (2 persons), 16 and 150 days after TMR, respectively, were examined by trichrom-and immunostaining (anti-collagen types I and III).

RESULTS

In a 6 months follow-up clinical data indicates that TMR was able to improve clinical status in 50 of 61 laser-treated patients (82%), whereas 5 (8.2%) did not show any benefit evaluated by CCS grading and six (9.8%) died. CCS grade reduction was found in 22 patients with a 12 months follow-up (28 patients still in evaluation). Days 30, mortality amounted to 6.5%; late mortality (over 30 days) was 3.3%. Histopathological investigations revealed tissue remodeling comparable with different stages of wound healing. The cicatricial tissue in the original laser-created channels displayed a stronger immunostaining for collagen type III than for type I.

CONCLUSIONS

Clinically, TMR improves cardiac function in some patients with severe ischemic cardiac disease, but pathophysiological data as well as morphological features from human myocardium could not explain this phenomenon. Therefore, TMR treatment should be used only as 'the last chance' in patients with severe angina pectoris.

Thoracoscopic transmyocardial laser revascularization

BACKGROUND

Transmyocardial laser revascularization is a promising surgical technique used to treat nonreconstructable ischemic heart disease. Recent clinical data show that this technique improves the regional perfusion of ischemic myocardium and reduces angina. Presently, transmyocardial laser revascularization requires an open, lateral thoracotomy. We report here the use of thoracoscopic techniques to perform transmyocardial laser revascularization in a closed chest fashion.

METHODS

Five Yorkshire farm pigs underwent left chest thoracoscopic exploration and pericardiotomy. A specialized laser handpiece then was introduced into the chest and thoracoscopic transmyocardial laser revascularization was performed (one channel per square centimeter) using an 800-W CO2 laser.

RESULTS

Video analysis and gross pathology revealed that the anatomic area accessible to thoracoscopic transmyocardial laser revascularization included the entire left ventricular free wall distributions of the left anterior descending, left circumflex, and posterior descending arteries, from base to apex. Standard hematoxylin and eosin staining confirmed the creation of complete and patent 1-mm-diameter transmural channels throughout these distributions.

CONCLUSION

We have shown that transmyocardial laser revascularization can be performed effectively and safely by thoracoscopy, and that this less invasive technique may reduce morbidity and provide a more cost-effective alternative therapy for nonreconstructable ischemic heart disease.

Physiology, histology, and 2-week morphology of acute transmyocardial channels made with a CO2 laser

BACKGROUND

Transmyocardial revascularization with a CO2 laser appears to improve symptoms in patients with refractory angina. However, it remains controversial as to whether blood flow through the channels is the mechanism of benefit, especially in the acute setting.

METHODS AND RESULTS

Three protocols were used to test whether blood flows through transmyocardial CO2 laser revascularization channels. First, channels were made in excised, cross-perfused dog hearts (n = 5) using a CO2 laser (The Heart Laser; PLC Systems Inc, Milford, MA; 40 J/pulse) followed by ligation of the proximal left anterior descending coronary artery. Colored microspheres injected into the left ventricular chamber failed to detect any significant transmyocardial blood flow. In the second protocol (n = 4), laser channels were created in the left anterior descending artery territory, the left anterior descending artery was ligated, and the hearts were excised after 24 hours. Triphenyltetrazolium chloride staining revealed that no viable myocardium was detected around the laser channels in the ischemic myocardium. Finally, channels examined 2 weeks after creation in normal (n = 6) or ischemic (n = 4) myocardium did not maintain their original caliber but were invaded by granulation tissue, which included a large amount of smaller vascular spaces and vessels of various sizes.

CONCLUSIONS

Transmyocardial laser revascularization channels made with this CO2 laser did not provide acute myocardial perfusion or preserve myocardial viability in the face of acute ischemia. Channel morphology changes dramatically within the first 2 weeks. To the degree that these findings pertain to human myocardium, the results suggest that transmyocardial blood flow may not be the mechanism of benefit of this procedure, particularly in the acute setting.

Transmyocardial laser revascularization: results of a multicenter trial with transmyocardial laser revascularization used as sole therapy for end-stage coronary artery disease

BACKGROUND

Transmyocardial laser revascularization was used as the sole therapy for patients with ischemic heart disease not amenable to percutaneous transluminal coronary angioplasty or coronary artery bypass grafting. This technique uses a carbon dioxide laser to create transmyocardial channels for direct perfusion of the ischemic heart.

METHODS

Since 1992, 200 patients, at eight hospitals in the United States, have undergone transmyocardial laser revascularization. The patients have a combined 1560 months of follow-up for an average of 10 +/- 3 months per patient. Their age was 63 +/- 10 years and their ejection fraction was 47% +/- 12%. Eighty-two percent had at least one previous bypass graft operation and 38% had a prior angioplasty. Preoperatively, the patients underwent nuclear single photon emission computed tomography perfusion scans to identify the extent and severity of their ischemia. These scans were repeated at 3, 6, and 12 months. Angina class, admissions for angina, and medications were recorded.

RESULTS

The perioperative mortality was 9%. Angina class decreased significantly from before treatment to 3, 6, and 12 months (p < 0.001). Likewise, there was a significant decrease in the number of perfusion defects in the treated left ventricular free wall. Concomitantly, there was a significant decrease in the number of admissions for angina in the year after the procedure when compared with the year before treatment (2.5 vs 0.5 admissions per patient-year).

CONCLUSION

These combined results indicate that transmyocardial laser revascularization provides angina relief, decreases hospital admissions, and improves perfusion in patients with severe coronary artery disease.

Laser-tissue interaction during transmyocardial laser revascularization

BACKGROUND

The clinical procedure known as transmyocardial revascularization has recently seen its renaissance. Despite the promising preliminary clinical results, the associated mechanisms are subject to much discussion. This study is an attempt to unravel the basics of the interaction between 800-W CO2 laser radiation and biological tissue.

METHODS

Time-resolved flash photography was used to visualize the laser-induced channel formation in water and in vitro porcine myocardium. In addition, laser-induced pressures were measured. Light microscopy and birefringence microscopy were used to assess the histologic characteristics of laser-induced thermal damage.

RESULTS

The channel depth increased logarithmically with time (ie, with pulse duration) in water and porcine myocardium. Pressure measurements showed the occurrence of numerous small transients during the laser pulse, which corresponded with channel formation, as well as local and partial channel collapse during the laser pulse. Twenty millimeters of myocardium was perforated in 25 ms. Increasing the pulse duration had a small effect on the maximum transversable thickness, but histologic analysis showed that thermal damage around the crater increased with increasing pulse duration.

CONCLUSIONS

Several basic aspects of the interaction of high-power CO2 laser radiation with myocardial tissue and tissue phantoms were studied in vitro. Although the goal of this study was not to unravel the mechanisms responsible for the beneficial effects of transmyocardial revascularization, it provided important information on the process of channel formation and collapse and tissue damage.

Percutaneous method of laser transmyocardial revascularization

Laser transmyocardial revascularization (TMR) creates conduits from the left ventricular cavity into the myocardium and has been forwarded as a potential method of perfusing ischemic myocardium. The procedure typically employs a CO2 laser to produce transmyocardial channels from the epicardial to the endocardial surface via an open thoracotomy. Preliminary studies in animals and human subjects have yielded promising results, and clinical trials evaluating the long-term efficacy of the procedure are in progress. We now report the use of a percutaneous method of TMR using a laser delivered through a novel catheter system. To assess the feasibility of performing percutaneous TMR, studies were performed on 15 adult canine subjects utilizing a holmium:YAG laser. Via a femoral artery approach, novel laser catheters were introduced into the left ventricular cavity under fluoroscopic guidance. Biplane coronary angiography, ventriculography, and transesophageal echocardiography were employed to direct catheters to specific regions and assess the efficacy of creating transmyocardial channels. Multiple channels could be created in the anterior, lateral, inferoposterior, and septal regions as demonstrated by contrast ventriculography with confirmation by subsequent gross and histologic examination. The procedure was tolerated well without any ventricular dysfunction or sustained ventricular arrhythmias. We have demonstrated that laser transmyocardial revascularization via a percutaneous approach is feasible with creation of channels from the endocardial surface of the left ventricle into the myocardium. On gross and histological examination, these channels are similar in appearance to those created by the currently employed open chest, epicardial method of TMR.

Patient care and expectations for recovery after transmyocardial laser revascularization

Transmyocardial laser revascularization is an investigational cardiovascular surgical procedure that has been trialed in the United States since 1991. The procedure involves the use of a high-energy carbon dioxide (CO2) laser to penetrate ischemic myocardium of the left ventricle. The successful formation of patent laser channels results in the formation of a new circulation within the myocardium. This angiogenesis has shown to improve perfusion to the previously oxygen-deprived tissue. To date, more than 500 patients have undergone this procedure in the United States, and approximately 1,500 cases have been performed in Europe, Asia, and the Middle East. The perioperative nursing care for these patients is multifaceted, including, but not limited to, the need for noninvasive assessment skills, effective pain management, and thorough discharge teaching. Unlike other cardiovascular procedures, this surgery does not immediately repair the ischemic areas; recovery is an insidious process. A realistic understanding of this surgery is needed to assist the patient throughout his or her hospitalization and to properly prepare the individual for expectations of recovery after discharge.

Transmyocardial laser revascularization. Histological features in human nonresponder myocardium

BACKGROUND

The creation of transmyocardial channels from the epicardium to the left ventricular cavity with the use of a CO2 laser is a modern approach in the treatment of patients with chronic ischemic cardiac disease. The histological features of human myocardium at different times after transmyocardial laser therapy have not been previously described. We had the opportunity to examine hearts from patients who died without clinical evidence of a persistent therapeutic effect at 3, 16, and 150 days after transmyocardial laser revascularization (TMR) respectively.

METHODS AND RESULTS

We grossly localized the laser-created channels in unfixed and formalin-fixed tissue. Three ventricular levels were defined for cutting the hearts into four segments. Then, transmural blocks were excised and cut crosswise and lengthwise for histological investigation through the use of established staining methods. On day 3, laser-induced channels were filled with abundant granulocytes and thrombocytes, fibrinous network, and detritus and were surrounded by severe myocardial necrosis. Furthermore, the epicardial and endocardial portions were obstructed by fibrinous network and microclots. Granulocytes were mostly absent on day 16; in addition, the channels were filled with erythrocytes or fibrinous network. On day 150, we observed a string of cicatricial tissue admixed with a polymorphous blood-filled capillary network and small veins, which very rarely had a continuous wrinkled link to the left ventricular cavity.

CONCLUSIONS

We found different stages of wound healing in human nonresponder myocardium after TMR, resulting in scarred tissue that displayed capillary network and dilated venules without evidence of patent and endothelialized laser-created channels. Experimental studies are necessary to analyze the morphological basis for TMR-mediated effects in human responder myocardium.

Transmyocardial laser revascularization: clinical experience with twelve-month follow-up

We are investigating a new technique for myocardial revascularization in which an 800 W carbon dioxide laser is used to drill 1 mm diameter channels into a beating heart after left thoracotomy. Clotting occludes the channels on the subepicardium, and in the long-term setting, blood from the left ventricular cavity flows through these channels to perfuse the ischemic subendocardium. To test the efficacy of this technique in a preliminary clinical trial, we used it as sole therapy for 21 consecutive patients. All patients had hibernating myocardium, reduced coronary flow reserve, or both, had distal diffuse coronary artery disease, and had angina refractory to normal therapy. Eight patients were excluded from follow-up because of death (n=5), rerevascularization (n=2), or diaphragmatic paralysis resulting in postoperative respiratory incapacity (n=1). In the remaining 13 patients available for follow-up, the mean angina class (Canadian Cardiovascular Society) was 3.7 +/- 0.4 before operation and 1.8 +/- 0.6 12 months after operation (p < 0.01). Mean resting left ventricular ejection fraction was 48% +/- 10% before operation and 50% +/- 8% at 12-month follow-up. At 12 months, resting mean subendocardial/subepicardial perfusion ratio had increased by 20% +/- 9% in septal regions treated by laser but decreased by 2% +/- 5% in untreated regions (n=11, p <.001). These results suggest that revascularization by this laser technique positively affects subregional myocardial perfusion and may result in clinical benefits for patients with reversible myocardial ischemia. Studies to date have not demonstrated significant changes in global and regional ventricular contractile function.

Does blood flow through holmium:YAG transmyocardial laser channels?

BACKGROUND

Early reports indicate that transmyocardial laser revascularization improves symptoms in patients with refractory angina. However, there is little experimental evidence of whether blood flow through channels is the mechanism of action.

METHODS

Endocardial channels were made in the distribution of the left anterior descending coronary artery in canine hearts (n = 5) using a holmium:yttrium-aluminum garnet laser. Hearts were excised acutely while perfused in a retrograde fashion from a second dog so that the aortic valve always remained closed. The proximal left anterior descending coronary artery was ligated. To measure direct transmyocardial blood flow, colored microspheres were injected into the left ventricular chamber.

RESULTS

The number of spheres per gram of tissue in the channel region was significantly higher than in the control region (low load, 302.5 +/- 169.0 versus 41.8 +/- 59.4; high load, 208.4 +/- 138.3 versus 5.8 +/- 11.7; both, p < 0.05). However, the estimated regional blood flow through the channels was extremely low (<0.01 mL/g/min. In the chronic setting (n = 4) (2-week survival), no flow as detected through the channels, and the endocardial entry points were closed.

CONCLUSIONS

Transmyocardial blood flow does not appear to occur through channels made with the holmium:yttrium-aluminum garnet laser. It remains to be determined whether this is the case with other types of lasers.

Transmural channels can protect ischemic tissue. Assessment of long-term myocardial response to laser- and needle-made channels

BACKGROUND

We previously found that transmural laser channels failed to acutely increase myocardial blood flow. Nevertheless, this method is being used to treat patients with coronary artery disease who are unable to undergo angioplasty or bypass graft surgery and in cases in which previous surgery has failed. To reconcile the lack of an acute increase in blood flow with beneficial effects claimed in patients, our hypothesis was that the channel-making process might, over time, stimulate a protective effect, possibly by the growth of new vessels linking channels to the existing circulation. We tested this hypothesis in rat hearts, which have little native collateral circulation.

METHODS AND RESULTS

We made six transmural channels in the left ventricle of each heart using a 400-micrometer-diameter optic fiber coupled to a holmium:yttrium-aluminum-garnet laser or a 400-micrometer-diameter syringe needle. Two months after the channels were made, rats were randomized to either an infarct-size study or analysis of myocardial capillary density. We challenged any induced protective mechanism by acutely occluding the left coronary artery for 90 minutes, followed by 4.5 hours of reperfusion. The artery was then reoccluded, and pigment was injected into the circulation to delineate tissue perfused by the occluded vessel and to detect perfusion via the channels. We used triphenyltetrazolium staining to determine the amount of muscle necrosis and the location of muscle protection. Infarct size in needle-treated hearts was smaller than in controls (15 +/- 6% versus 40 +/- 3% of the left ventricle, P<.01). Infarct size in laser-treated hearts (27 +/- 5%) did not differ significantly from controls; however, all eight laser-treated hearts showed evidence of muscle protection in areas adjacent to channels. We found that the laser-made channels were associated with more fibrosis than the needle-made channels (mean width of fibrosis 430 +/- 50 versus 180 +/- 30 micrometer, P<.0001), and, in tissue remote from channels, fibrosis was increased more in laser-treated hearts (3.6 +/- 0.3%) versus both control (2.5 +/- 0.2%) and needle-treated (2.5 +/- 0.3%) hearts (P<.05). In addition, muscle disarray was seen adjacent to channel-associated fibrosis. We observed injected pigment within fibrosis associated with the channels and in surrounding myocardium. We also found vessels that appeared to be connected to channels; however, there was no overall increase in capillary density.

CONCLUSIONS

We were able to protect the heart against coronary artery occlusion by making transmural channels 2 months before occlusion. Channels created by a needle provided greater protection than channels created by a laser, probably because they caused less initial injury. Our results are consistent with the concept that the channels were able to provide blood flow to the tissue directly from the ventricular cavity; however, we cannot rule out the possibility that other mechanisms of protection may be involved.

Recovery and viability of an acute myocardial infarct after transmyocardial laser revascularization

OBJECTIVES

The short- and long-term effectiveness of transmyocardial laser revascularization was evaluated in the setting of an acute myocardial infarction.

BACKGROUND

Theoretically, transmyocardial laser revascularization allows direct perfusion of the ischemic area as ventricular blood flows through the channels to the myocardium.

METHODS

Infarcts were created by coronary occlusion in 30 sheep. Eighteen of these sheep were studied to assess short-term efficacy. The infarct was reperfused after 1 h by either removing the occlusion or by laser drilling using a high power carbon dioxide laser. The occlusions were left in place for the control group. To monitor regional recovery, percent systolic shortening was measured. To evaluate long-term effectiveness, 12 additional sheep underwent creation of an infarct. Six were treated with the laser, and six were untreated. The animals were restudied 30 days later.

RESULTS

In the short-term experiment, the control and reperfusion groups exhibited no recovery of regional contractility. The laser group demonstrated improvement throughout the recovery period. There was a significant difference in the area of necrosis within the same area at risk (reperfusion group 44 +/- 6% and control group 39 +/- 5% vs. laser group 6 +/- 2%). After 30 days, none of the control animals showed evidence of contraction in the infarct, whereas the laser-treated animals did. Histologic analysis of the laser-treated infarcts revealed patent channels surrounded by viable myocardium. The control-group infarcts were necrotic and scarred.

CONCLUSIONS

On the basis of both short- and long-term improved contractility, as well as diminished necrosis in the area at risk, these results indicate that transmyocardial laser revascularization may be an alternative method of treating ischemic heart disease.

Cardiovascular applications of laser technology

Laser technology has been evaluated for the treatment of coronary artery disease, ventricular and supraventricular arrythmias, hypertrophic cardiomyopathy, and congenital heart disease. Developments in laser angioplasty, laser thrombolysis, transmyocardial laser revascularization, photochemotherapy, laser treatment of arrhythmias and/or laser diagnostics are directed at improving upon conventional non-laser approaches, and providing new therapeutic and diagnostic options. This review will summarize the current status of the multiple applications of laser technology for cardiovascular diagnosis and therapy.

Prevention of acute regional ischemia with endocardial laser channels

Laser myocardial revascularization has been shown to reduce mortality and infarct size after left anterior descending coronary artery (LAD) ligation in dogs. It has not been shown to improve myocardial contractility in acute ischemia. In this study a holmium-yttrium-aluminum garnet laser (wavelength, 2.14 microns) was used to create nontransmural myocardial channels from the endocardial surface in the ischemic regions of the canine left ventricle. Twelve mongrel dogs (6 controls, 6 laser myocardial revascularizations) underwent 90 minutes of LAD ligation followed by 6 hours of reperfusion. The ischemic region was determined by methylene blue injection during brief LAD occlusion. Laser myocardial revascularization averaged three channels per square centimeter in the ischemic region created using 12 J/channel (600 mJ/pulse, 10 Hz) before LAD ligation. Contractility was assessed from regional preload recruitable stroke work (RPRSW), using pairs of segment length ultrasonic transducers in the ischemic and the nonischemic regions. Two-dimensional echocardiography corroborated with segmental length findings. In control dogs, the ischemic region was dyskinetic during LAD ligation and reperfusion. Dyskinesis of the ischemic region during systole produced negative values for regional stroke work, and RPRSW was considered zero. In 4 of 6 laser-revascularized dogs, RPRSW remained positive in the ischemic region. Two dogs had intermittent dyskinesis. The difference between laser-revascularized and control dogs in ischemic region RPRSW was significant (p < 0.01 by Fischer's exact test).(ABSTRACT TRUNCATED AT 250 WORDS)

Laser-mediated transmural myocardial channels do not salvage acutely ischemic myocardium

OBJECTIVES

We sought to determine whether the presence of transmural laser-made channels could provide blood flow to ischemic myocardium.

BACKGROUND

Laser-made transmural channels have been used in patients to restore blood flow to ischemic myocardium. Whether such channels actually relieve ischemia is unclear. We therefore tested the concept in an animal model of acute ischemia.

METHODS

Eighteen dogs underwent 6 h of permanent coronary artery occlusion. At 30 min after occlusion, 8 dogs were randomized to the laser-treated group (30 to 40 transmural channels, 1 mm in diameter, were made in the cyanotic area using a holmium: yttrium-aluminum-garnet laser), and 10 were randomized to the control group (no treatment). Transmural blood flow was measured before and after treatment using radiolabeled microspheres. Regional segment shortening and myocardial lactate content were measured in four of the control and two of the laser-treated dogs. Infarct size was measured in all animals using triphenyltetrazolium chloride staining.

RESULTS

Laser channels failed to increase blood flow to ischemic tissue. After laser channels were made, mean transmural flow averaged 0.10 +/- 0.03 versus 0.11 +/- 0.03 ml/min per g in treated versus control dogs, respectively. Furthermore, infarct size was similar in both groups (46 +/- 6% vs. 43 +/- 7%, respectively, of the myocardium at risk, p = NS). In addition, the presence of laser channels neither improved regional myocardial function nor enhanced washout of accumulated lactate.

CONCLUSIONS

Direct laser revascularization of the heart did not provide any immediate benefit to ischemic myocardium in this canine model of coronary artery occlusion. Thus, it is doubtful that direct laser-mediated myocardial revascularization would be of immediate benefit in the treatment of patients with acute ischemia.

Septal myectomy with a carbon dioxide laser for hypertrophic cardiomyopathy

Septal myectomy with a noncontact carbon dioxide laser for hypertrophic cardiomyopathy is described. This technique results in improved visualization of the septum as the laser beam is held outside the heart and the resecting laser beam can always be clearly seen. We believe this approach provides an improved method of septal myectomy in hypertrophic cardiomyopathy.