Asian Cardiovasc Thorac Ann 1999;7:23-26
© 1999 Asia Publishing EXchange Pte Ltd
Transmyocardial Laser Revascularization as Sole Therapy in Coronary Disease
Li Zhi, MD,
Ren Li Jie, MD,
Wang Bing, MD,
Xu Wen Ting, MD,
Li Guang Ying, MD
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Department of Cardiovascular Surgery Wanjie Hospital Zibo, Shandong People's Republic of China China
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For reprint information contact: Li Guang Ying, MD Tel: 86 533 465 0000 Ext. 8211 Fax: 86 533 465 0830 Department of Cardiovascular Surgery, Wanjie Hospital, Zibo, Shandong Province 255213, People's Republic of China.
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Abstract
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This prospective study evaluated the medium-term efficacy of transmyocardial laser revascularization as the sole therapy in patients with ischemic heart disease. A carbon dioxide laser was used to create channels through ischemic areas of the myocardium in 33 patients with a mean age of 58.8 ± 10.4 years. The mean left ventricular ejection fraction determined by echocardiography was 44.8% ± 14%. Preoperatively, the patients underwent coronary artery angiography, single photon emission computed tomography perfusion scans, and positron emission tomography metabolism scans to determine the extent and severity of ischemia and myocardial viability. Total follow-up of 327 patient-months was obtained for 26 patients with a mean follow-up of 12.6 ± 9 months. The scans were repeated at 3, 6, 12, and 24 months postoperatively. The perioperative mortality was 9% due to ventricular fibrillation. Morbidity was minimal. The number of perfusion defects decreased significantly after treatment and there was a significant increase in myocardial viability in the treated left ventricular free wall. The success rate, defined as a decrease of 2 angina classes, was approximately 80% during the follow-up, reflected in a significant decrease in the number of admissions for angina in the year after the procedure (mean, 0.5 ± 0.4) compared with the previous year (mean, 2 ± 1.1) and in decreased use of antianginal medications.
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Introduction
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The technique of transmyocardial laser revascularization (TMLR) creates transmural channels through ischemic myocardium to allow direct perfusion of the myocardium with ventricular blood.1 Since the pioneering work of Mirhoseini and Clayton2 in 1981, the ability of trans-myocardial revascularization alone to provide relief of angina and improve myocardial perfusion has been assessed in patients with disabling angina refractory to medical therapy and untreatable by conventional means of revascularization.3–5 In August 1998, the US Food and Drug Administration approved the use of a high-power 1000-watt carbon dioxide laser (The Heart Laser; PLC Medical Systems, Franklin, MA, USA) for trans-myocardial revascularization in cases of chronic stable angina not amenable to conventional therapy. This prospective study was designed to evaluate the short-term and medium-term efficacy of TMLR with The Heart Laser as the sole therapy in patients with ischemic heart disease.
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Patients and Methods
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Between June 1996 and June 1998, we performed TMLR as the sole therapy in 33 patients with end-stage coronary artery disease. The indications for TMLR were: diffuse multi-vessel coronary artery disease not amenable to percutaneous transluminal coronary angioplasty (PTCA) or coronary artery bypass grafting (CABG); refractory angina after maximum medical therapy; small vessel disease not amenable to CABG; new angina after PTCA or CABG in patients unsuited or unwilling to undergo repeat PTCA or CABG; and coronary artery anatomy suitable for CABG but the patients had heparin allergy, high risk factors for cardiopulmonary bypass, or a strong preference for TMLR.
Before the procedure, all patients underwent cardiological examination, electrocardiography, echocardiography, coronary artery angiography, single photon emission computed tomography (SPECT) perfusion scans, and positron emission tomography (PET) metabolism scans to determine the extent of ischemia and myocardial viability. SPECT myocardial perfusion images were obtained after Persantine-load images followed by injection of technetium-99m sestamibi. The left ventricular free wall was divided into 5 segments: anterior; posterior; lateral; inferior; and apex. In each segment, the degree of perfusion was calculated as a percentage of normal. PET myocardial metabolism scans, the gold standard for identifying myocardial viability, were obtained at rest with fasting and glucose loading. Fluorine-18 fluoro-2-deoxy-D-glucose was injected and the degree of myocardial viability was calculated as a percentage in each segment.6,7 The patient demographics are listed in Table 1
. Preoperatively, 67% of the patients were in Canadian Cardiac Society (CCS) angina class IV and 33% were in class III.
Under standard general anesthesia, all patients were intubated, a transesophageal echocardiography (TEE) probe was inserted, and radial artery and central venous lines were used for monitoring. A baseline TEE study was performed to evaluate ventricular function and valvular disease. TEE was used to confirm transmyocardial penetration of the laser beam. The patients were placed in a 45-degree right lateral decubitus position and underwent a left anterolateral thoracotomy through the 5th or 6th intercostal space, depending on the location of the point of maximal impulse. The pericardium was opened and dissected free of the heart. On the basis of the preoperative SPECT and PET scans, the area of reversible ischemia was exposed.
TMLR was carried out using The Heart Laser that delivers 850 watts of peak power to the tissue, the maximum output is 80 joules, and the pulse width varies from 1 to 99 msec. The laser energy is absorbed by the blood in the ventricle and this produces an acoustic image analogous to steam that is readily visible by TEE in the long-axis 4-chamber view. This TEE image denotes transmyocardial penetration. Only laser shots verified by TEE were considered to have traversed the myocardium. The operative settings were an average pulse energy of 41 ± 10 joules and a pulse width of 48 ± 10 msec. The laser was aimed with a helium-neon laser guidance placed against the epicardium before firing. The laser was triggered to fire on the R wave of the electrocardiographic cycle when the ventricle was maximally distended with blood and electrically quiescent, to avoid arrhythmias. On average, 31 ± 8 pulses were delivered and the penetrative rate was 97%. Channels of 1 mm in diameter were created in a distribution of approximately one per cm2. Hemorrhage from the channels was controlled with direct finger pressure or an epicardial suture if pressure was not adequate.
The patients were requested to return at 3, 6, 12, and 24 months after the operation for physical examination, review of medications, assessment of angina class, and SPECT and PET scans. The follow-up scans were compared with the preoperative baseline scans and changes in the number of involved segments were calculated. The septum was not treated by TMLR and thus served as a control for each patient. Angina class, medications, and admissions for angina were assessed by interview and questionnaire.
The baseline and follow-up data were compared and analyzed by the Wilcoxon signed rank test and the paired Student t test. Differences were considered significant when the value of p was less than 0.05. The results were reported as mean ± standard deviation with two-sided p values.
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Results
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Follow-up was achieved in 26 of the 33 patients for a mean of 12.6 ± 9 months (total, 327 patient-months). SPECT scans were obtained after 3, 6, 12, and 24 months of follow-up. Angina class data were complete for 26 patients at 3 months, 21 patients at 6 months, 17 patients at 12 months, and 5 patients at 24 months. SPECT studies were complete for 20 patients (100 segments), 20 (100 segments), 15 (75 segments), and 4 patients (20 segments) at 3, 6, 12, and 24 months respectively. The PET studies were complete for 11 patients (66 segments), 6 (30 segments), 4 (20 segments), and 4 (20 segments) at 3, 6, 12, and 24 months respectively.
Postoperative morbidity from the procedure was minimal. No intraoperative laser-induced arrhythmias occurred. There was a 12% incidence of atrial fibrillation after the operation (4 patients). One patient (3%) had acute left ventricular failure that improved after 24 hours on medical treatment. One patient (3%) had mild mitral regurgitation as a result of laser injury to the chordae; this did not require treatment and at the 6-month follow-up, the patient was symptom-free. No patient had myocardial infarction, reoperation for bleeding, wound infection, or pneumonia. The majority of patients were extubated within 24 hours after the operation (mean duration of intubation, 0.8 ± 1.2 days). The mean intensive care unit stay was 1 ± 1.2 days and the mean hospital stay was 15 ± 8 days. Three deaths (9%) occurred between the 1st and 17th day after the procedure. The cause of death in all cases was ventricular fibrillation. These 3 patients had unstable angina, low left ventricular ejection fractions (33% to 37%), and angiographically demonstrated triple-vessel coronary disease. The other 30 patients are currently alive.
All patients were restarted on their preoperative medications immediately after TMLR. One year later, 50% of the patients have decreased their usage of cardioactive medications (nitrates, beta blockers, or calcium channel blockers), while the others have continued to use the same dosages. In the year before TMLR, there was an average of 2 ± 1.1 admissions for angina in this group of patients. In those patients with a full year of follow-up, there was a significant decrease in the number of admissions, with an average of 0.5 ± 0.4 admissions for angina after treatment with TMLR (p < 0.001). Mean CCS angina class decreased significantly at 3, 6, 12, and 24 months compared to the preoperative status (p < 0.001) as shown in Figure 1. There was a marked redistribution of patients from CCS angina class III and class IV before treatment to classes 0 to II after 6 months. In one-third of the patients, angina was totally eliminated and did not recur during the follow-up. Based on the criterion that a decrease of two angina classes after the operation is considered a success, the procedure had a success rate of 81% for patients at 3 months (21/26 patients, p < 0.001), which was sustained at 6 months (16/21 patients, p < 0.001), 12 months (15/17 patients, p < 0.001), and 24 months (4/5 patients, p < 0.001).
The results of the preoperative and postoperative SPECT perfusion scans and PET metabolism scans are depicted in Figures 2 and 3. There was a significant decrease in the number of segments with perfusion defects in the treated left ventricular free wall after the procedure (p < 0.001), which was maintained during the 24 months of follow-up. PET scans indicated that myocardial viability was significantly increased in the laser-treated segments (p < 0.001) throughout the follow-up period. Scans of the untreated septum reveal no significant change.
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Figure 2. Mean changes in myocardial perfusion determined by single photon emission computed tomography.
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Discussion
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The success of any type of myocardial revascularization is based on improvement in the delivery of oxygenated blood to the ischemic area. The traditional methods of improving myocardial perfusion include PTCA, CABG, and medical therapy. However, some patients may have diffuse small vessel disease and others may have surpassed their ability to undergo angioplasty or CABG. TMLR was developed from knowledge of myocardial sinusoids and the thebesian system.8 The laser-induced channels create myocardial neovascularization as well as stimulating further vessel formation to carry oxygenated blood to the ischemic areas and these channels can maintain long-term patency.9 This treatment offers a solution to the management of patients with end-stage coronary artery disease who are not suitable candidates for PTCA or CABG and who suffer angina refractory to maximal medical treatment.
Most of the patients in our study were referred from other hospitals and categorized as inoperable, unsuitable for further PTCA, or in an unacceptably high-risk group for cardiopulmonary bypass. Some patients who had developed recurrent angina after CABG or PTCA would not accept a repeat procedure and opted for TMLR. Most Chinese patients are unwilling to undergo major surgery such as CABG because of their traditional beliefs but they are willing to accept the limited incision required for transmyocardial revascularization. We feel that if the coronary anatomy is suitable for TMLR, their choice of this procedure should be accepted. Patients with high risk factors for cardiopulmonary bypass include those with low left ventricular ejection fractions (below 30%), hypertension, diabetes, or compromised function of the liver, kidney or lung. In addition, because heparin is necessary for anticoagulation during cardiopulmonary bypass, patients with heparin allergy should also be considered for TMLR as a safer alternative.
This study demonstrated improvements in angina class, perfusion, and myocardial metabolism that persisted for 24 months after the procedure. These improvements were reflected in the decreased use of antianginal medication and fewer admissions for angina. We conclude that TMLR is indicated as sole therapy for severe angina in patients with end-stage coronary artery disease.
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References
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Abstract
Introduction
