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Ann Thorac Surg 1999;67:432-436
© 1999 The Society of Thoracic Surgeons

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Original Articles

Transmyocardial laser revascularization: early results and 1-year follow-up

^a Institute of Cardiovascular Diseases, Madras, India

Accepted for publication July 14, 1998.

Address reprint requests to Dr Cherian, Institute of Cardiovascular Diseases, 4-A, Dr. Jayalalitha Nagar, Mogappair, Madras-600 050, India
e-mail: mmmbits{at}giasmd01.vsnl.net.in

	Abstract

Top Abstract Introduction Patients and methods Results Comment References

 
Background. Transmyocardial revascularization using a high-energy CO₂ laser has emerged as a new therapeutic option for patients with severe diffuse coronary artery disease refractory to conventional modes of therapy.

Methods. From December 1994 to September 1997, 102 patients underwent isolated transmyocardial revascularization. The mean age was 56.7 ± 9.2 years and 92.15% were men. Mean preoperative angina class and ejection fraction were 2.6 ± 0.7 and 44.7% ± 10.5%, respectively. Diabetes was present in 49.01% of patients, 32.3% had history of previous myocardial infarction, and 12.7% had undergone a previous coronary artery bypass graft procedure. An average number of 23 ± 8 channels were created in each patient using an 800-W CO₂ laser.

Results. The early mortality was 14.7% and univariate predictors of mortality were age more than 55 years, female sex, creatine kinase more than 1,600 IU, absence of intercoronary collaterals, and mean pulmonary artery pressure greater than 21 mm Hg. At 1-year follow-up there was significant improvement in angina class and effort tolerance but no significant change in left ventricular ejection fraction.

Conclusions. We conclude that transmyocardial revascularization provides symptomatic benefit and improves exercise tolerance in a group of patients suffering from disabling angina not amenable to other modes of treatment. The high early mortality can be brought down with strict patient selection criteria. The mechanism of beneficial effects is uncertain and patency of laser channels is controversial, but laser-induced neoangiogenesis is being looked on as a possible explanation.

	Introduction

Top Abstract Introduction Patients and methods Results Comment References

 
Transmyocardial revascularization (TMR) using a high-energy CO₂ laser, as proposed by Mirhosenini and associates [1] has emerged as a useful alternative mode of therapy for patients with severe refractory angina and coronary anatomy unsuitable for conventional modes of treatment. The procedure is based on the premise that laser-created transmural channels allow blood to flow directly from the left ventricle to the myocardial vascular plexus, thus alleviating ischemia in potentially viable myocardium. Although the early follow-up data from various centers have shown a remarkable symptomatic benefit in angina class [2–4], concrete objective evidence regarding improvement in myocardial perfusion is still lacking. The procedure has also been criticized because of its high early mortality [2, 4, 5], and there have been reports in the literature claiming that these laser-created channels get blocked early postoperatively and that the beneficial effects of this procedure cannot be attributed to "the reptilian heart" phenomenon [6].

We have reviewed the data on patients who have undergone transmyocardial laser revascularization at the Institute of Cardiovascular Diseases and are presenting the early results as well as 1-year follow-up.

	Patients and methods

Top Abstract Introduction Patients and methods Results Comment References

 
From December 1994 to September 1997, 102 patients were offered TMR as a sole mode of myocardial revascularization. During the same period an additional 43 patients underwent combined TMR with coronary artery bypass graft operation (CABG) (Table 1), and they are not included in this study. The mean age of the patients was 56.7 ± 9.2 years and most of the patients were between 51 and 70 years of age (Fig 1). Ninety-four patients were men. The mean preoperative angina class and ejection fraction of the patients were 2.6 ± 0.7 and 44.7% ± 10.5%, respectively, and 9 patients (8.9%) had unstable angina at the time of operation. Patient demographics are outlined in Table 2.

View larger version (22K): [in this window] [in a new window]   Fig 1. Distribution of the patients according to age and number of deaths in each age group.

Patients were operated on using a left anterolateral thoracotomy through the fifth intercostal space. An 800-W CO₂ laser (Heart Laser, PLC Medical Inc, Milford, MA) was used to drill the laser channels using an energy output of 40 J and pulse duration of 50 ms. Of late we have reduced the pulse duration to 25 ms, as an experimental study recently has shown that increasing the pulse duration carries an increased risk of thermal damage to the surrounding tissues [7]. The laser was synchronized to the electrocardiographic signal and fired at the peak of R wave. Transesophageal echocardiography was used to confirm the transmural penetration of laser. Intraoperatively the patients were monitored using continuous electrocardiographic and ST-segment analysis. Pulmonary artery pressures and cardiac index were monitored using a Swan-Ganz thermodilution catheter. Postoperatively cardiac enzymes were measured every 4 hours for 24 hours and the pattern of rise studied.

The patients were extubated after 6 to 8 hours of elective ventilation whenever possible. They were discharged home on the eighth to tenth day and were followed up at 1, 3, 6, and 12 months after operation. At the time of follow-up, data regarding angina class, ejection fraction, and effort tolerance were recorded and analyzed using SPSS (Chicago, IL) statistical package. Thallium myocardial perfusion scans were performed before and after the procedure to assess improvement in regional myocardial perfusion.

Autopsies were performed on 8 patients who died in hospital. Two to four channels were removed in toto from each of the hearts after they were fixed in buffered neutral formalin for 14 days and entire blocks were cut serially from epicardial to endocardial surface.

	Results

Top Abstract Introduction Patients and methods Results Comment References

 
The perioperative parameters are depicted in Table 3. Most of the patients were extubated within 8 to 12 hours of operation. The mean duration of ventilation was 10.2 ± 4.4 hours and the patients stayed in the intensive care unit for a mean of 2.6 ± 1.2 days. They were discharged home on average on the ninth postoperative day. Fifteen patients (14.7%) died within 30 days of operation; the causes of death are shown in Table 4.

A univariate analysis of the predictors of early mortality revealed that female sex, advanced age, and perioperative myocardial infarction were factors significantly affecting the early mortality (Table 5). The mean age of the patients who died was 63.1 years compared with 56.6 years for those who survived the operation. Other variables, such as preoperative angina class, associated risk factors, previous myocardial infarction, and number of laser channels, were not found to be predictors of early mortality. A multivariate logistic regression analysis was performed using SPSS software v.4.0, and only age more than 55 years was found to be a statistically significant predictor of early mortality (odds ratio 7.7; 95% confidence interval = 1.6 to 36.7; p < 0.01). Two patients died during follow-up, one of myocardial infarction and the other of sudden cardiac death.

View larger version (145K): [in this window] [in a new window]   Fig 2. Photomicrograph showing a patent channel. (Hematoxylin and eosin stain, magnification x40.)

View larger version (158K): [in this window] [in a new window]   Fig 3. Photomicrograph showing a channel partly filled with fibrin, and anastomosing with the adjacent sinusoid (arrow). (Hematoxylin and eosin stain, magnification x40.)

Histopathology of serial sections derived from the hearts of the patients who died in the hospital revealed that the epicardial end of the channel appeared depressed and filled with thin or thick bands of fibrin. The most important feature observed was that none of the channels were found to be in straight line. Rather, they were twisted and spiraling, and unless care was taken to cut large sections through and through, there was likelihood to miss the course of the channels and conclude that the channels were closed. The apparent twisting of the channels is presumably caused by the architecture of the cardiac muscle itself. Generally the channels were filled with plasma and erythrocytes separated by fibrin strands (Fig 2). Invariably the channels were found to be communicating with sinusoids (Fig 3) in a large number of areas and entered into sinusoids or opened into the endocardium. The endocardial end did show a few fibrin strands, but these appeared to be of recent origin, indicating patency during life.

	Comment

Top Abstract Introduction Patients and methods Results Comment References

 
The conventional modes of treatment for coronary artery disease, ie, PTCA and CABG procedures, have stood the test of time, and they are known to improve the quality of life as well as longevity. But there remains a substantial group of patients with diffuse small-vessel coronary artery disease, especially in the Indian subcontinent, who cannot be offered these standard modes of treatment. Despite doing multiple endarterectomies, it is often not possible to achieve complete revascularization in these patients, who are usually young and otherwise healthy to lead an active and productive life. For such patients whose daily activities are limited despite maximal medical therapy transmyocardial laser revascularization has a definite role.

Our study differs from other Western reports of TMR in many respects. We are dealing with a younger group of patients (mean age, 56.7 ± 9.2 years), many of whom have diabetes (49.5%) or have undergone TMR as a primary procedure (87.4%) because their diffusely diseased small-caliber vessels are not amenable to PTCA or CABG. This is in contrast to most Western series, in which patients were elderly [2–4] and were considered for TMR only when they had already exhausted their ability to undergo another PTCA or CABG [4].

The operative technique and laser energy used for creating the channels has been fairly standardized in all the series and similar settings were used in the present study also. An experimental study recently has shown that a pulse duration of 25 ms (energy output of 20 J) is sufficient to traverse the human myocardium, which is usually 20 mm thick [7]. Increasing the pulse duration provides only marginal benefit in terms of being able to penetrate the thicker areas of myocardium, and this occurs at an expense of increased thermal damage to the surrounding tissue. Of late we have reduced the pulse duration of 25 ms and transesophageal echocardiography has confirmed trans- myocardial penetration of the laser. The beneficial effects, if any, of this modification are yet to be documented.

The major criticism of this procedure is its high early mortality (reported to be 14% to 18% in various series), which in a significant number of cases has been attributed to perioperative myocardial infarction leading to cardiac failure [2, 4]. Although some degree of rise in cardiac enzymes has been noticed in all cases postoperatively, the analysis of risk factors for early mortality has revealed that patients having creatine kinase more than 1,600 IU and creatine kinases-MB greater than 10% are at higher risk of an unfavorable outcome. The factors contributing to perioperative infarction have been found to be presence of left main coronary artery disease and absence of well-developed intercoronary collaterals. We believe that once the learning curve of the procedure has been overcome and the patient selection criteria are more clearly defined, our early mortality would reduce.

Patients have benefitted symptomatically, and the positive trend in terms of relief of angina has continued at 1-year follow-up. Moreover they have done much better on treadmill testing with both the duration of exercise as well as the metabolic equivalents achieved having improved. This change is most marked and has achieved a statistical significance between 6 months and 1 year of follow-up. This observation may support the theory of laser-induced neovascularization, which requires time to develop and provide its beneficial effects to the myocardium. Thallium perfusion scans were not repeated in this study as they did not show any improvement at 3 months’ follow-up, but now that the data on improvement in exercise tolerance has become available, we are planning to repeat the perfusion scans at 1 year after TMR to evaluate the improvement in regional perfusion.

Patients with impaired left ventricular function (mean pulmonary arterial pressure greater than 21 mm Hg) were found to be at a higher risk of early death, and such patients are not considered as good candidates for isolated TMR. Moreover, there is a marginal drop in ejection fraction at 1-year follow-up, which may tilt the balance in a patient with preexisting left ventricular dysfunction and lead to an unfavorable outcome. For patients with poor left ventricular ejection fraction and left main coronary artery disease we have now adopted a policy of combining TMR with coronary artery bypass grafts to at least one important vessel, and we do not hesitate to perform extensive endarterectomies with onlay patch in such cases, as we believe that this graft supports the myocardium during the early postoperative period and improves the postoperative outcome.

To conclude, we believe there are enough data to suggest that TMR provides symptomatic benefit and improves quality of life as well as the patient’s ability to undergo stress. Although we do not have any evidence at present to show an improvement in regional myocardial perfusion, Cooley and coworkers [8] have demonstrated better subendocardial perfusion after TMR using positron emission tomography scan. The mechanism of beneficial effects provided by TMR is still uncertain and controversial but the focus is shifting toward laser-induced neoangiogenesis [9].

	References

Top Abstract Introduction Patients and methods Results Comment References

 

1. Mirhoseini M., Shelgikar S., Cayton M.M. New concepts in revascularization of the myocardium. Ann Thorac Surg 1988;45:415-420.[Abstract]
2. Horvath K.A., Mannting F., Cummings N., Shernan S.K., Cohn L.H. Transmyocardial laser revascularization: operative techniques and clinical results at two years. J Thorac Cardiovasc Surg 1996;111:1047-1053.[Abstract/Free Full Text]
3. Frazier O.H., Cooley D.A., Kadipasaoglu K.A., et al. Myocardial revascularization with laser. Preliminary findings. Circulation 1995;92(Suppl 2):II-58-II-65.
4. Horvath K.A., Cohn L.H., Cooley D.A., et al. Transmyocardial laser revascularization: results of a multicenter trial with transmyocardial laser revascularization used as sole therapy for end-stage coronary artery disease. J Thorac Cardiovasc Surg 1997;113:645-654.[Abstract/Free Full Text]
5. Smith J.A., Dunning J.J., Parry A.J., Large S.R., Wallwork J. Transmyocardial laser revascularization. J Card Surg 1995;10:569-572.[Medline]
6. Krabatsch T., Schaper F., Leder C., Tulsner J., Thalmann U., Hetzer R. Histological findings after transmyocardial laser revascularization. J Card Surg 1996;11:326-331.[Medline]
7. Jansen E.D., Frenz M., Kadipasaoglu K.A., et al. Laser–tissue interaction during transmyocardial laser revascularization. Ann Thorac Surg 1997;63:640-647.[Abstract/Free Full Text]
8. Cooley D.A., Frazier O.H., Kadipasaoglu K.A., et al. Transmyocardial laser revascularization: clinical experience with 12 months follow-up. J Thorac Cardiovasc Surg 1996;111:791-799.[Abstract/Free Full Text]
9. Monte M., Davel L.E., de Lustig E.S. Inhibition of lymphocyte-induced angiogenesis by free radical scavengers. Free Radic Biol Med 1994;17:259-266.[Medline]

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