Myocardial revascularization with laser. Preliminary findings

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.

Transmyocardial laser revascularization (TMLR) in patients with unstable angina and low ejection fraction

OBJECTIVE

Does perioperative use of the intraaortic balloon pump (IABP) improve the postsurgical outcome of patients presenting with endstage coronary artery disease, unstable angina and low ejection fraction transferred for transmyocardial laser revascularization (TMLR)?

METHODS

TMLR, as sole therapy combined with the perioperative use of an intraaortic balloon pump has been assessed in seven patients with endstage coronary artery disease, unstable angina and low ejection fraction (EF < 35%). Six out of seven patients had signs of congestive heart failure. These patients are compared with 23 patients with endstage coronary artery disease, stable angina and EF > 35%, who were treated with TMLR as sole therapy without the use of IABP. The creation of transmural channels was performed by a CO2-laser. All patients were evaluated by hybrid positron emission tomography (perfusion SPECT and viability PET) and ventriculography preoperatively. Echocardiography, clinical status and hemodynamic assessment by Swan Ganz catheter were performed perioperatively.

RESULTS

The perioperative mortality of this combined procedure (TMLR and IABP) was zero. Three out of seven patients had pneumonia with complete recovery. Swan Ganz catheter examinations showed deterioration of LV-function after TMLR intraoperatively and improvement after 2 h and further after 6 h on ICU (P < 0.05). In contrast, a decrease of LV-function in sole TMLR patients with an EF > 35%) has not been observed. Patients with EF < 35% needed the IABP for 2.3 days and moderate dose catecholamines for a mean of 3.0 days. The postoperative EF and resting wall motion score index (WMSI) of all analysed LV segments (evaluated by echocardiography) did not change compared to baseline (EF 31.3+/-2.6 preop. to 32.8+/-3.2 postop.; WMSI: 1.75+/-0.14 at baseline to 1.71+/-0.17 postop.). The average Canadian Angina Class at the time of discharge decreased from 4.0+/-0 (baseline) to 2.3+/-0.5 (P < 0.05) and the NYHA-Index from 3.9+/-0.3 to 2.7+/-0.5. No patient had signs of angina pectoris, whereas two patients still had signs of congestive heart failure.

CONCLUSIONS

The reported data support our concept to start IABP preoperatively in patients with reduced LV contractile reserve in order to provide cardiac support during the postoperative phase of reversible decline of LV-function induced by TMLR.

Myocardial angiogenesis as a possible mechanism for TMLR efficacy

Despite advances in the treatment of ischemic heart disease, there still exists a significant number of individuals for whom bypass surgery or angioplasty are not options. Transmyocardial laser revascularization (TMLR) is a promising technology that has already been shown to reduce symptoms in patients with chronic ischemic heart disease that is not amenable to conventional therapies. Although it appears that TMLR can provide symptomatic relief of angina in selected patients, the mechanism by which TMLR is thought to work is unclear. Recently it has been postulated that TMLR induces an angiogenic response and, perhaps, improves local perfusion to ischemic myocardial territories. A brief overview of the biology of myocardial angiogenesis is presented.

Transmyocardial laser treatment denervates canine myocardium

BACKGROUND

In patients with refractory angina who are not candidates for conventional revascularization, transmyocardial laser treatment reduces angina significantly in the early postoperative period. We hypothesized that transmyocardial laser treatment damages cardiac nerve fibers that convey the pain of angina pectoris.

METHODS

Left thoracotomy was performed in sixteen adult mongrel dogs. Treatment groups included animals in which a portion of the left ventricle underwent creation of transmyocardial channels with a holmium:yttrium-aluminum-garnet laser (n = 5) or chemical destruction of cardiac nerves by application of phenol to the epicardium (n = 5). Sham-operated negative control animals underwent thoracotomy and pericardiotomy alone (n = 6). Cardiac afferent nerve function was assessed by epicardial application of bradykinin, a potent algesic, before treatment and 2 weeks after the operation. The resulting central nervous system-mediated decrease in systemic mean arterial pressure was measured. Cardiac innervation of treated and untreated left ventricular myocardium was further assessed by immunoblot analysis performed with an antibody against tyrosine hydroxylase, a sympathetic nerve-specific enzyme.

RESULTS

Before treatment, changes in systemic arterial pressure were seen with bradykinin stimulation in all dogs. Two weeks after treatment, no hemodynamic response was seen after stimulation of laser- or phenol-treated areas, but a normal response was seen after stimulation of untreated areas in these same animals and in negative control animals. Immunoblots demonstrated loss of tyrosine hydroxylase in regions of phenol and laser treatment.

CONCLUSION

Transmyocardial laser treatment destroys cardiac nerve fibers, which may contribute to the reduced angina pectoris seen clinically.

Improvement in inducible ischemia during dobutamine stress echocardiography after transmyocardial laser revascularization in patients with refractory angina pectoris

OBJECTIVES

The purpose of this ongoing study is to determine whether transmyocardial laser revascularization (TMLR) can lessen inducible ischemia and improve contractile reserve in patients with refractory angina pectoris.

BACKGROUND

TMLR is an emerging surgical technique for the treatment of myocardial ischemia and angina pectoris not amenable to conventional percutaneous or surgical revascularization. Objective data documentating a reduction in ischemia during noninvasive stress testing after TMLR are rare.

METHODS

Fifteen patients with severe coronary artery disease unsuitable for treatment with standard revascularization techniques were studied with dobutamine stress echocardiography (DSE) before TMLR. Of the 12 patients who underwent TMLR, DSE was repeated at 3 months postoperatively in 11 patients and at 6 months in 9 patients. Stress echocardiograms were analyzed for inducible ischemia, with calculation of the wall motion score index (WMSI). Heart rate and dobutamine dose achieved at peak stress were also assessed as indexes of stress tolerance.

RESULTS

Compared with that before TMLR, wall motion at rest for all myocardial segments did not change significantly after TMLR, although there was a mild improvement in the WMSI of the lased myocardial regions ([mean +/- SD] 1.64 +/- 0.34 after vs. 1.78 +/- 0.34 before TMLR, p < 0.05). Overall WMSI at peak stress improved markedly after TMLR (1.70 +/- 0.30 after vs. 2.06 +/- 0.31 before TMLR, p < 0.002), with the improvement in WMSI limited to the lased segments only (1.47 +/- 0.31 after vs. 2.15 +/- 0.34 before TMLR, p < 0.0004). The improvement in WMSI with stress resulted primarily from a decrease in the percentage of ischemic segments (47% before vs. 23% after TMLR, p < 0.0008), with no change in the percentage of infarcted segments (23% before vs. 26% after TMLR). Heart rate (83 +/- 5 beats/min before vs. 102 +/- 21 beats/min after TMLR, p = 0.01) and dobutamine infusion rate (26 +/- 9 micrograms/kg body weight per min before vs. 34 +/- 9 micrograms/kg per min after TMLR) achieved at peak stress also increased postoperatively, consistent with improved stress tolerance. The reduction in ischemic wall motion abnormalities and improved stress tolerance persisted at 6 months, without evidence of further improvement or deterioration of function over time.

CONCLUSIONS

TMLR performed in patients with refractory angina pectoris reduces ischemic wall motion abnormalities and improves stress-induced tolerance during dobutamine echocardiography. These beneficial effects persist up to 6 months postoperatively.

[Transmyocardial laser revascularization and rehabilitation]

Transmyocardial laser revascularization (TMLR) is a new technique for patients with CAD or heart attack to revascularize ischemic areas of the myocardium in which the localisation or the condition of the vessels does not allow bypass grafting. This study shows the results in observation of patients before and during the first 3 months after TMLR. Of 110 patients operated on from 1994 to 1996, 86 were evaluated for well being (quality of life), using NYHA- and CCS-classification, stress test and nitril-scintigraphy at rest and under stress conditions. 51 patients, of whom 11 were females, underwent TMLR combined with coronary artery bypass graft (CABG). 35 male patients were treated singularly with TMLR. The average age in both groups was 59 years (+/- 23). All patients were subject to phase I rehabilitation in specialised institutions after being mobilised in the operating hospital. The evaluations took place on the day of admission to the hospital prior to surgery, within 10 days after surgery and 3 months following. The average stay in the rehabilitation-institution was between 4 and 6 weeks. Our findings demonstrate that both groups profited from the procedures, while the TMLR/CABG group showed a faster recovery and a better outcome. In comparison to 57% of the TMLR group, 85% of the patients in the TMLR/CABG group reported an improvement ranging from good to significant in quality of life assessments. The TMLR/CABG rated from an average of initially 3.4 (+/- 0.6) to 2.1 (+/- 0.8) after 3 months at NYHA- and 3.3 (+/- 0.7) to 1.7 (+/- 0.8) at CCS-classification. The TMLR group rated from 3.6 (+/- 0.5) to 2.4 (+/- 0.8) in NHYA- and from 3.4 (+/- 0.5) to 1.9 (+/- 0.7) on the CSS-scales. A remarkable improvement was noted in the stress test with an increase in power and endurance from 21 to 89 watts for the combined group and 8 to 81 watts for the TMLR treated patients, who generally recovered more slowly. The perfusion scan showed the same tendencies as previously reported but in some cases the results were not congruent with other findings. Overall, our findings indicate that there is a benefit for terminally symptomatic CAD patients after TMLR, but an observation period of 3 months does not allow for final conclusions on this matter. Rehabilitation seems to be of value for TMLR-patients since they have shown a markedly better performance following 3-month treatment, but further data from clinical randomised trials are needed to determine the influence of TMLR with short- and long-term rehabilitation on the prognosis of the disease.

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

Images

[Histomorphology after transmyocardial laser revascularization]

From 11/1994 to 4/1997 we enrolled 140 patients with diffuse CAD refractory to maximum antianginal therapy who are not candidates for PTCA or CABG for transmyocardial laser revascularisation (TMLR). Of these patients aged 63.5 +/- 15 years, 98 had coronary 3-vessel disease, and the average left ventricular ejection fraction was 44%. Eleven out of these 140 patients died from different reasons (pneumonia, myocardial infarction, septicemia). Seven patients who died between the 1st and 20th postoperative day underwent a postmortem examination with histological analysis of the areas treated by TMLR. On the seven investigated ventricles a total of 220 channels were created. The predominant finding in specimens within five days after TMLR was recently closed channels. Furthermore, a zone of necrosis with an average extension of 500 microns on each side of the channel was evident. Many changes were noticeable in specimens from patients who died two or three weeks after TMLR. Freshly clotted material had been replaced by a granular tissue of variable density. High macrophage and monocyte activity was evident. The extent of this cellular activity could be depicted by staining with a special proliferation marker, such as MiB. On the one hand numerous dividing macrophages were observed, on the other, active fibroblasts indicative for the transformation into scar-like tissue. After staining for type-4-collagen, typical for the basal membrane of capillaries, a large number of stained structures was noticeable in the closed channel lumen. Numerous garlandlike structures became visible under higher magnification. By CD 31 incubation, these structures, were found to be lined with endothelium. Further research will be required to indicate whether the laser channels later are partially or completely open, from where the capillaries are supplied, and whether they even connect to the ventricle lumen. But in conclusion, it seems unlikely, that TMLR follows the mechanism of the amphibian heart.

[Transmyocardial laser revascularization in stable and unstable angina pectoris]

Endstage coronary artery disease still remains a therapeutic challenge. An increasing number of patients is no longer amenable for direct revascularization by PTCA or coronary bypass surgery and does also no longer respond to maximum medical therapy. This fact has directed the interest again towards surgical techniques of indirect revascularization, which had been introduced by Beck and other surgeons more than 60 years ago. Among these attempts we can also find transmyocardial needle punctures, firstly performed by Sen in Bombay. In the early eighties it was Mirhoseini, who used a laser for creating these transmural channels, primarily in combination with coronary bypass surgery at the arrested heart and later on together with Crew as a sole therapy at the beating heart. The idea behind this transmyocardial laser revascularization (TMLR) was a "reptilization" of the human heart, which meant a direct blood supply from the ventricle into the ischemic myocardium. Whereas this theory has not proven to be true, as the surface area of these channels is not sufficient for the nutrition of the surrounding myocardial tissue by diffusion or convection, different models have been developed by anatomical, experimental and clinical studies, such as the connection between the laser channels and intramyocardial vessels or capillaries, analogous to ventriculo-coronary connections in human anatomy or pathology as for example those connections described in children with pulmonary atresia and intact ventricular septum or the Thebesian veins. Moreover the laser trauma may also simply contribute to the induction of neoangiogenesis. While the function of TMLR is still not clearly defined, clinical studies in the United States and also in other countries have proven the clinical efficacy in a cohort of severely diseased patients undergoing this procedure. Accordingly more than 2/3 of all patients after TMLR showed a significant improvement of more than 2 angina classes (CCS) as well as a decrease in medication and hospitalization. Moreover there was also a reduction of ischemic areas demonstrated by szintigraphy and, in one study from Houston, also by positron emission tomography. While the overall mortality in all those studies is still considerably high, a reduction could be achieved by a stricter selection of patients excluding especially those with a severely impaired left ventricular function. As demonstrated by preliminary data from the last phase III FDA-study, TMLR may even reduce long-term mortality compared to maximum medical therapy in a randomized group of patients. Our own experiences in 134 patients also confirmed a significant reduction of angina after TMLR alone (n = 67) or in combination with bypass surgery (n = 67) with the majority of patients being in angina class 1 and 2 (CCS) 6 months after surgery. All of these patients were in angina class 3 and 4 before surgery. Nuclear scans could demonstrate an improved perfusion in more than 40%. Further studies as well as other clinical and also experimental investigations have still to be awaited, before the definitive role of TMLR within the armamentarium against coronary artery disease can be determined. However, it is already a therapeutic option for those highly symptomatic patients, who cannot be offered a different treatment modality.

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.

Laser light delivery systems for medical applications

For medical applications, the choice of a delivery system will be governed by the characteristics of the laser system on the one hand and the tissue application on the other. The most important parts are the beam guide and the target optics. Most lasers have wavelengths in the visible and near-infrared and can be transported by silica fibres. For the mid- and far-IR other fibre materials or hollow waveguides are used. At the end of the waveguide or fibre, an optically active component is present to direct the beam and to control the power density on the target tissue. The laser beam can be delivered either by focusing handpieces and scanning devices to treat superficial areas or through microscopes, endoscopes and flexible fibres to treat areas almost anywhere inside the human body. The characteristics of the delivery systems can be determined looking at beam properties, transmission and thermal properties. The delivery of continuous wave or pulsed laser energy, contact or non-contact, will determine the contribution of optical, thermal and mechanical effects to the tissue. The practical use of laser delivery systems is illustrated by various clinical applications.

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.

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.

Blood flow capacity via direct acute myocardial revascularization

The concept of direct myocardial revascularization, achieving myocardial perfusion through means other than the normal coronary vasculature, has a long history with the most widely investigated technique being the Vineberg procedure; current interest centers around the encouraging preliminary clinical results obtained with transmyocardial laser revascularization. Despite significant previous research, the acute blood flow potential through the direct myocardial route remains unknown. Nontransmural laser channels were made in the distal LAD territory from the epicardial surface of 5 mongrel dogs to which an internal mammary artery was connected. A flow probe was placed on the distal most portion of the artery and an intercostal branch was cannulated for infusion of colored microspheres. Measurements were taken under baseline conditions and following LAD and epicardial collateral ligation. Under all conditions, blood flow pattern was of a to-and-fro nature. At baseline, there was an average 0.60 +/- 0.24 ml/min net flow into the myocardium which was all contained within 0.5 cm of the central channel with a final myocardial perfusion of 0.011 +/- 0.016 ml/min/g. Following induction of ischemia average flow increased to 1.41 +/- 0.51 ml/min which extended as far as 1 cm from the channel with a final myocardial perfusion of 0.22 +/- 0.19 ml/min/g. In conclusion, a limited amount of acute myocardial perfusion can be achieved by the present technique of direct myocardial revascularization and the amount of flow is highly dependent upon the amount of flow through the native circulation.

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.

One-month histologic response of transmyocardial laser channels with molecular intervention

BACKGROUND

Transmyocardial revascularization reduces the symptoms and morbidity of patients with endstage ischemic heart disease. The mechanism is postulated to be the formation of transmural left ventricular channels through which oxygenated blood directly perfuses the myocardium. New techniques for molecular enhancement of angiogenesis and endothelial cell motility may represent strategies to augment this clinical benefit.

METHODS

Triads of transmyocardial revascularization channels were placed in eight separate nonischemic sites on the hearts of 7 pigs weighing 68 to 78 kg, which were allowed to recover and were then sacrificed at 28 days. In addition, one triad pair was injected with vascular endothelial growth factor, and two triad pairs received an adenovirus vector with or without the gene encoding for human profilin, which increases endothelial cell motility and adhesion. The remaining triad pair stood untreated (laser only). The histologic changes were graded (0 through 3) by an independent pathologist without knowledge of the treatment modality. Profilin production and vascular endothelial growth factor activation using a tyrosine kinase assay were monitored.

RESULTS

Transmyocardial revascularization alone resulted in a significant injury response (p < 0.01), including increased vascularity without patent channels. Vascular endothelial growth factor increased surrounding inflammation (p < 0.01) without improving vascularity or patency. Profilin content in tissues was increased but nonspecifically because inflammation resulting from adenovirus also induces higher profilin concentrations.

CONCLUSIONS

The clinical benefit of transmyocardial revascularization may result simply from a nonspecific histologic response to injury. Molecular interventions appear to stimulate more inflammation but no additional angiogenesis. Further improvement in the clinical benefit of transmyocardial revascularization awaits the successful stimulation of a true angiogenic response.

Histological findings after transmyocardial laser revascularization

In recent time, it has become more and more probable that patients with severe diffuse coronary artery disease, who are not candidates for aortocoronary bypass surgery or percutaneous transluminal coronary angioplasty procedures, can benefit from transmyocardial laser revascularization (TMR). But the underlying principle of TMR still remains unclear. This study reports on a histological analysis of eight patients, in whom a total of 250 channels had been created, who died after TMR. The TMR channels were created by a CO2 laser surrounded by a zone of necrosis with an extent of about 500 microns. In the hearts of patients who died in the early postoperative period (1 to 7 days postoperative), almost all channels were closed by fibrin clots, erythrocytes, and macrophages. There were no obvious connections between the channels and the ventricular cavity. In specimens from patients, who died 2 or more weeks after the procedure, a granular tissue with high macrophage and monocyte activity was observable. Within this tissue, we observed a developing network of capillaries. Otherwise, the tissue filling the channels did not substantially differ from scar tissue. We failed to observe connections between the ventricular cavity and the new capillaries. Whether these vessels within the closed channels have any impact on myocardial perfusion remains unclear, but it seems unlikely that the clinical effects of TMR are based on the principle of the amphibian heart.

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.