Ann Thorac Surg 2003;76:1163-1166
© 2003 The Society of Thoracic Surgeons
Original article: cardiovascular
Mid-term results of combined transmyocardial laser revascularization and coronary artery bypass
Mahmoud Loubani, FRCSIa,
Derek Chin, MRCPb,
Joseph N. Leverment, FRCSa,
Manuel Galiñanes, FRCSa*
a Department of Integrative Cardiovascular Physiology and Cardiac Surgery, Leicester, United Kingdom
b Division of Cardiology, University of Leicester, Glenfield Hospital, Leicester, United Kingdom
Accepted for publication April 9, 2003.
* Address reprint requests to Professor Galiñanes, Department of Integrative Cardiovascular Physiology and Cardiac Surgery, University of Leicester, Glenfield Hospital, Groby Road, Leicester, UK.
e-mail: mg50{at}le.ac.uk
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Abstract
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BACKGROUND: Transmyocardial laser revascularization is increasingly used to treat intractable angina in the absence of graftable vessels; however, its role in combination with coronary artery bypass grafting remains undefined. The aim of this pilot study was to investigate the outcome of the combination therapy at mid-term follow-up.
METHODS: Patients (n = 20) who had elective coronary artery bypass with one or more nongraftable coronary arteries were prospectively randomized to have either coronary artery bypass grafting alone or combination coronary artery bypass grafting plus transmyocardial laser revascularization with a holmium:YAG (yttrium-aluminum-garnet) laser to nongraftable areas. All patients had an exercise tolerance test preoperatively and at 6, 18, and 36 months follow-up. Stress echocardiography was performed on 17 patients at 18 months postoperatively, and regional wall motion score index was calculated in lased and nonlased nonrevascularizable myocardium of the left ventricle at rest and with dobutamine stress.
RESULTS: Both groups of patients were similar in preoperative demographics and operative data. There was no perioperative death. There was no difference between the two groups in angina scoring at 6, 18, and 36 months follow-up. Exercise tolerance improved by a mean of 46.8 ± 20.0 seconds in the coronary artery bypass grafting group versus 199.2 ± 66.5 seconds per patient in the coronary artery bypass grafting plus transmyocardial laser revascularization group (p = 1.8 x10-6) at 6 months; this benefit was maintained at 18 months (157 ± 46.3 versus 61 ± 39.2 seconds; p = 4 x10-4) but was lost at 36 months (57.2. ± 42.1 versus 68.1 ± 46.7 seconds; p = 0.70). The mean values for wall motion score index in the lased and nonlased regions at each stage of dobutamine stress at 18 months after surgery were not statistically significant.
CONCLUSIONS: The combination of coronary artery bypass and transmyocardial laser revascularization improved exercise tolerance in patients in whom complete revascularization could not be achieved by bypass grafting alone in the short term, but this benefit was lost by 36 months postoperatively. The transient improvement in exercise tolerance cannot be explained by changes in contractility in the lased areas.
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Introduction
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Transmyocardial laser revascularization (TMR) has been investigated in several randomized trials [1–9] as the sole therapy for treatment of diffuse coronary artery disease and has been shown to provide benefit with regard to improved angina and survival in comparison to medical therapy alone. A number of nonrandomized studies [10–13] have investigated the use of adjunctive TMR to coronary artery bypass and shown it to be safe. Allen and associates [14] reported on a multicenter randomized trial of TMR combined with coronary artery bypass operations. They found that the procedure was safe, but no benefit was seen with regard to improvement in angina and exercise tolerance. However, there was a reduction in perioperative mortality and an improvement in survival after 1 year of follow-up in the TMR plus coronary artery bypass group. The long-term results of combined TMR and coronary bypass operation remain unclear when complete revascularization cannot be achieved.
In this prospective, randomized controlled study, we investigated the mid-term clinical and functional effects of combining TMR with coronary bypass in patients in whom the use of bypass alone would have achieved incomplete myocardial revascularization.
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Material and methods
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Patient selection
This study was approved by the Leicestershire Health Ethics Committee. Twenty consecutive patients who had elective coronary artery bypass operation with one or more nongraftable dominant coronary arteries and normal left ventricular function with no previous myocardial infarction were prospectively randomized to have either coronary artery bypass grafting (CABG) alone or in combination with transmyocardial laser revascularization (CABG+TMR).
Clinical assessment
All patients were interviewed, the study explained, and informed consent obtained. Angina scores were recorded preoperatively and at 6, 18, and 36 months postoperatively. Exercise tolerance testing using the Bruce protocol was also performed preoperatively and at 6, 18, and 36 months follow-up. ß-blocker medication was withheld for 48 hours before the test. Indications to terminate the test were chest pain, ischemic changes on electrocardiogram, limiting dyspnea, or fatigue. The total exercise time was noted, and the reason for stopping the test documented. The exercise tolerance test was performed on all patients at 6 months but only on 17 patients at 18 and 36 months follow-up.
Operative technique
All patients received standard premedication and anesthetic technique. The chest was opened through a median sternotomy, and the CABG was carried out in routine fashion in all the patients using cardiopulmonary bypass and intermittent cross-clamp fibrillation with mild hypothermia (32°C) for myocardial protection. After completion of the distal anastomoses, the myocardium of the nongraftable areas were lased with the holmium:yttrium-aluminum-garnet laser (CardioGenesis Corp, Sunnyvale, CA). This delivers 2 J of energy per pulse, and three to five pulses were required to traverse the myocardium. The channels were distributed at 1/cm2 throughout the lased area. The laser was synchronized to fire at the peak of the R wave of the electrocardiogram of the patient's beating heart.
Stress echocardiography
Stress echocardiography was performed on 17 patients at 18 months postoperatively, with a mean dobutamine dose of 36 µg · kg-1 · min-1. Digital images were acquired using the quad-loop format on an Agilent 5500 system and an S3 transducer (Philips Medical Systems, the Netherlands). These images were stored on an Agilent Enconcert archive for offline wall motion analysis (1 = normal, 2 = hypokinesis, 3 = akinesis, 4 = dyskinesis) using the 16-segment model of the left ventricle.
Statistical analyses
Data are expressed as mean ± standard deviation. Paired and unpaired Student's t test was used for comparison between the means of the two groups. A p value of less than 0.05 was taken as statistically significant.
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Results
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As seen in Table 1,
both groups of patients were similar in preoperative demographic characteristics and risk factors. Table 2 shows that the two groups of patients had a similar number of grafts, with no differences in cardiopulmonary bypass time, ischemic time, and immediate recovery time. There were no laser-induced arrhythmias noted intraoperatively and no perioperative deaths. The mean number of channels created in the CABG+TMR group was 18.6 ± 4.2 per patient. Table 3
shows that the relief of angina and the improvement in dyspnea class were similar in both groups at 6, 18, and 36 months' follow-up. It also shows that, whereas the exercise tolerance improved by a mean of 46.8 ± 20.0 seconds per patient in the CABG group, the improvement was four times greater (199.2 ± 66.5 seconds) in the CABG+TMR group (p = 1.8 x 10-6) at 6 months postoperatively. This benefit was maintained at 18 months (157.0 ± 46.3 versus 61.0 ± 39.2 seconds; p = 4 x10-4) but was lost at 36 months (57.2. ± 42.1 versus 68.1 ± 46.7 seconds; p = 0.7). Only 1 patient died in the CABG+TMR group at 11 months postoperatively from metastatic colon cancer.
Table 4
shows that, although the wall motion score index of the lased areas after 18 months was lower at each stage of dobutamine stress than in the nonlased areas, this difference did not reach statistical significance.
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Table 4. Postoperative Wall Motion Score Index (WMSI) at Rest and at Low and Peak Doses of Dobutamine for the Lased and Nonlased Nongraftable Areas
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Comment
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The results of this study suggest that the beneficial effect of CABG+TMR in combination on exercise tolerance in the early postoperative period was lost after 36 months. Other investigators [14] reported operative and 1-year survival benefits of CABG+TMR compared with CABG alone, although angina relief and exercise improvement were indistinguishable between the two groups at 1 year follow-up. Many factors could account for the different results on exercise tolerance between our study and that of Allen and associates [14]. For example, the latter, which included 263 patients, was a multicenter study in which different surgeons might have had different criteria for the definition of nongraftable vessels. The fact that more grafts were performed on the CABG alone group than on the CABG+TMR group (the difference approached statistical significance) may support this view. It is also of interest that in their study the inclusion criterion was the presence of isolated coronary artery disease in one or more major vessels or branches that was nongraftable for anatomic reasons, whereas in our study the criterion involved major nongraftable vessels only. Those different criteria might have affected the selection of the patients and the clinical outcome. Furthermore, in their study, only 55% of the patients had both baseline and 12-month exercise treadmill tests available for comparison.
The loss of the beneficial effect on exercise tolerance is difficult to explain, but it might be a consequence of the progression of the ischemic heart disease, although the absence of deterioration in angina does not support this thesis. Another possibility could be a decline in the efficacy of the mechanism responsible for the beneficial effect of TMR; whether this mechanism is an increase in vascularity [15, 16], cardiac denervation [17, 18], or both remains to be determined. The lack of improvement in the wall motion index of the lased areas compared with the nonlased areas at 18 months follow-up suggests that the improvement in exercise tolerance in the CABG+TMR group was not due to amelioration of the contractility of the lased areas. It is clear that to elucidate this issue more investigation is required in order to understand the underlying mechanism of TMR and how this can be sustained. The procurement of this knowledge is essential if TMR is to be considered an adjunct to CABG.
This study is limited by the small sample size, although it was sufficient to demonstrate differences in exercise tolerance between the two groups at 6 and 18 months follow-up. Another limitation might be the lack of assessment of regional perfusion to correlate with wall motion score index.
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Abstract
Introduction
