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J Thorac Cardiovasc Surg 2000;119:540-549
© 2000 Mosby, Inc.
SURGERY FOR ACQUIRED CARDIOVASCULAR DISEASE |
From the Departments of Cardiothoracic Surgery, St Vincent Hospital, Indiana Heart Institute,a Indianapolis, Ind; University of Louisville, Jewish Heart & Lung Institute,b Louisville, Ky; Cooper Hospital,c Camden, NJ; Redding Medical Center,d Redding, Pa; Fairfax Hospital,e Falls Church, Va; Kaiser Permanente Medical,f Los Angeles, Calif; Terrebonne General Medical Center,g Houma, La; St Vincent’s Medical Center,h Jacksonville, Fla; Sutter Memorial Hospital,i Sacramento, Calif; and Sentara Norfolk General Hospital,j Norfolk, Va.
Address for reprints: Keith B. Allen, MD, 8333 Naab Rd, Suite 300, Indianapolis, IN 46260 (E-mail: cvsurgeon{at}iquest.net ).
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Abstract |
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 Top Abstract IntroductionPatients and methodsResultsDiscussionAppendixAppendix: DiscussionReferences |
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Introduction |
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TopAbstractIntroductionPatients and methodsResultsDiscussionAppendixAppendix: DiscussionReferences |
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1-4 In one series only the presence of diseased but nongrafted arteries significantly influenced event-free survival, as defined by the absence of death, recurrent angina, myocardial infarction (MI), and the need for repeat CABG. 3
In 4 prospective randomized trials, transmyocardial revascularization (TMR) significantly improved angina compared with continued medical therapy 5-8 when used as the sole therapy to treat ischemic heart disease not amenable to CABG or percutaneous transluminal coronary angioplasty (PTCA). Considering the success of TMR as a sole therapy, we hypothesized that in patients with one or more target areas not amenable to grafting, CABG plus TMR (CABG/TMR) would be safe and result in decreased adverse cardiac events. Several nonrandomized studies with adjunctive TMR have been reported. 9-12 This summary reports the findings at 1 year of follow-up of a single-blinded, prospective, randomized, multicenter trial designed to assess the safety and efficacy of CABG/TMR in patients who would be incompletely revascularized by CABG alone.
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Patients and methods |
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TopAbstractIntroductionPatients and methodsResultsDiscussionAppendixAppendix: DiscussionReferences |
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The institutional review boards of each participating center and the Food and Drug Administration (FDA) approved the study, which was monitored by a blinded independent data and safety committee. Informed consent was obtained from each patient.
Inclusion criteria were isolated coronary artery disease with one or more major vessels or branches not bypassable for anatomic reasons (distal or diffuse disease) and the presence of viable myocardium surrounding the nonbypassable vessels. Exclusion criteria were as follows: severe chronic obstructive pulmonary disease (forced expiratory volume in 1 second < 55% of predicted value); non–Q-wave or Q-wave MI within 2 or 3 weeks of enrollment, respectively; severe arrhythmia uncontrolled by a device or medication; and decompensated cardiac failure.
Randomization
A total of 266 patients were prospectively randomized to receive either CABG alone or CABG of suitable vessels plus TMR of areas not amenable to grafting. Randomization occurred before surgery and was computer generated and stratified by sex and ejection fraction (EF; 
40% > 40%). Patients were blinded for 1 year after surgery as to whether they received adjunctive TMR. After randomization, 3 patients were identified as having violated protocol and were excluded from further analyses. Protocol violations included 2 patients randomized to CABG alone (1 patient received CABG/TMR for compassionate reasons and 1 patient received an unanticipated concomitant mitral valve replacement), and 1 patient was randomized to CABG/TMR and withdrew from the study before surgery. Therefore, for study purposes, 132 patients received CABG/TMR, and 131 patients received CABG alone. The two treatment groups had similar demographics, including predicted operative mortality rates determined by Parsonnet 13 risk modeling (Table I).
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Baseline data and follow-up
Baseline data, in addition to patient demographics, included the following: EF determined by radionuclide ventriculography, echocardiography, or cardiac catheterization; angina class determination, according to Canadian Cardiovascular Society definition; and a symptom-limited modified Bruce exercise treadmill test. Patients unable to perform a baseline exercise treadmill test because of angina (n = 83) were assigned values of zero minutes and one metabolic equivalent (MET).
Patients underwent clinical follow-up at 3-, 6-, and 12-month intervals after surgery. At each interval, patients were evaluated for major adverse cardiac events, angina class, and occurrence of repeat CABG, PTCA, or both. A modified Bruce exercise treadmill test was obtained at 12 months for comparison with baseline values.
Follow-up for operative mortality rates and 30-day and 1-year major adverse cardiac events was 100% (263/263), 100% (263/263), and 89% (235/263), respectively. Paired baseline and 12-month exercise treadmill tests were available for comparison in 55% (135/243) of patients. Angina assessment was complete at 3, 6, and 12 months on 86% (215/250), 79% (195/247), and 84% (204/243) of patients, respectively.
Operative procedure
The CABG procedure and postoperative care were center specific and not different between groups within each center. Patients randomized to CABG alone had viable target areas which were served by vessels not amenable to grafting left untreated. Patients randomized to receive adjunctive TMR had CABG performed on suitable vessels and TMR channels placed every square centimeter in viable areas unable to be grafted.
Adjunctive TMR was performed by using a 20-W pulsed holmium:yttrium-aluminum-garnet (holmium) laser (Eclipse Surgical Technologies, Sunnyvale, Calif). Laser energy was delivered with a flexible 1-mm optical fiber. Laser calibrations were set to deliver 6 to 8 W of laser energy at 5 pulses/s; typically, 3 to 8 pulses were required to traverse the myocardium. Laser energy application was controlled with a foot switch and not gated to the cardiac cycle. In this series adjunctive TMR was performed while patients were receiving cardiopulmonary bypass (CPB). TMR was performed either on an arrested heart before placement of grafts (n = 19) or after the completion of grafts (n = 112). Median laser time was 6 minutes (5th percentile, 3 minutes; 95th percentile, 12 minutes) during which an average of 25 ± 10 channels were created.
Statistical analysis
All statistical analyses were carried out by using SAS software (SAS Institute, Inc, Cary, NC). Demographic and baseline variables were analyzed by using a 2-sample t test for continuous variables and the 
2, Fisher exact, or Cochran-Mantel-Haenszel tests for qualitative variables. A goodness-of-fit test was used to compare predicted versus actual operative mortality rates within each treatment group. Differences in operative mortality rates and adverse events between groups were determined by using the Fisher exact test. Kaplan-Meier survival estimates were used to analyze mortality rates at 1 year, as well as freedom from major adverse cardiac events (death and MI) at 30 days and 1 year. Statistical differences in Kaplan-Meier survival estimates were determined by using the Wilcoxon-Gehan test. The Cox method of multivariate logistic regression was used to determine predictors of operative mortality and to determine predictors of 1-year freedom from mortality, MI, or severe angina (class III or IV). Variables used for these analyses were as follows: prior CABG, diabetes, sex, age, treatment arm, preoperative EF of 35% or greater or less than 35%, and the presence of endarterectomies.
The distribution of angina classes for each group at baseline and each follow-up interval was analyzed by using the Cochran-Mantel-Haenszel test. Differences between groups in the proportions of patients in each angina class were determined by using the Fisher exact test.
Net change from baseline to 12 months in exercise treadmill test duration and METs were calculated for each patient. Differences between groups were analyzed with a 2-sampled t test.
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Results |
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TopAbstractIntroductionPatients and methodsResultsDiscussionAppendixAppendix: DiscussionReferences |
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Additional cardiac procedures aimed at treating angina were required in 3 patients during follow-up. Two patients, one from each group, underwent subsequent PTCA; one patient randomized to CABG alone underwent subsequent TMR with a carbon dioxide laser and ultimately underwent cardiac transplantation.
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Discussion |
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TopAbstractIntroductionPatients and methodsResultsDiscussionAppendixAppendix: DiscussionReferences |
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5-8 The safety and efficacy of TMR combined with CABG in patients who would be incompletely revascularized by CABG alone have been more difficult to assess because of the influence of adjacent bypass grafts and lack of randomized control arms in previous studies. 9-12 In this single-blinded, prospective, randomized, multicenter trial, patients who received CABG/TMR had reduced operative and 1-year mortality rates, required less postoperative left ventricular support, and experienced enhanced 30-day freedom from major adverse cardiac events when compared with CABG alone. However, at 1-year follow-up, freedom from major adverse cardiac events, angina relief, and improvement in exercise treadmill duration and METs were similar between groups.
The early benefits observed after CABG/TMR must be analyzed in the context of potential study limitations. Randomization for this study occurred preoperatively. Even if randomization had occurred intraoperatively, the surgeon’s belief in TMR could influence surgical conduct and bias decisions regarding whether a vessel was bypassable. In an attempt to achieve as complete a revascularization as possible in the group undergoing CABG alone, surgeons might increase the operative mortality rate by performing more technically questionable grafts or more endarterectomies. Because surgeons cannot be blinded, this limitation is difficult to circumvent in any adjunctive TMR trial. In this study, however, operative characteristics were similar between groups; there were no obvious differences between groups with regard to time on bypass, number of vessels bypassed, distribution of coronary arteries grafted, or number of endarterectomies performed (Table II
). Furthermore, the operative mortality rate in the group undergoing CABG alone was similar to the mortality rate predicted by using Parsonnet risk modeling. The operative mortality rate observed in the group undergoing CABG alone may be perceived as excessive in light of the patients’ well-preserved left ventricular function, but the predicted operative mortality rate in both groups reflects the significant comorbidities commonly associated with diffuse coronary artery disease. Participants in this study were not ideal candidates for CABG because the diffuse nature of their coronary artery disease limited complete conventional revascularization. The diffuse nature of their coronary artery disease is emphasized by the use of endarterectomies in 9% (23/263) of patients in this series. As determined by using Parsonnet risk modeling, the actual mortality rate in the control group was similar to the predicted mortality rate (7.6% vs 6.6%, P = .5). By contrast, the operative mortality rate after CABG/TMR tended to be less than the predicted rate (1.5% vs 6.3%, P = .06). Multivariable predictors for operative mortality rate in this series were CABG alone and increased age.
The early benefits of adjunctive TMR observed in this trial are similar to results seen in previous animal studies, which suggested TMR channels were acutely patent. Sen and colleagues 14,15 reported improved survival and reduced MI size after mechanical acupuncture and left anterior descending artery ligation in dogs. Mirhoseini and Cayton 16 reproduced Sen’s study but used a carbon dioxide laser to create transmural channels. The 83% survival of dogs treated with TMR and acute left anterior descending ligation contrasted sharply with the fatal outcomes observed in all dogs treated with left anterior descending ligation alone. Horvath and associates, 17 using a carbon dioxide laser, observed reduced MI size and improved regional contractility after TMR in an acute ischemic ovine model. They attributed the benefits of TMR to patent laser channels, which were verified histologically. Endocardial laser revascularization in dogs has also demonstrated preservation of myocardial function during acute ischemia, which was attributed to improved nutritive perfusion through laser channels. 18 More recently, acute channel patency after percutaneous myocardial revascularization in human subjects has been demonstrated with ventriculography (Fig 3). 19
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20,21 using microspheres, have been unable to demonstrate perfusion through acute laser channels. Kohmoto and colleagues 22 confirmed the conduction of blood through laser channels created in dogs for up to 2 weeks before closure but concluded that the amount of perfusion through these channels would not have physiologic significance. That conclusion was based on the assumption that channel blood flow was 1-way from the left ventricle to the myocardial capillary network, rather than in a to-and-fro pattern.
Long-term benefits regarding angina and exercise tolerance are more difficult to assess after CABG/TMR because of the strong positive influence of bypass grafting on both groups. As expected, both groups experienced significantly improved angina and exercise treadmill test scores at 12 months compared with baseline values. Although patients undergoing CABG/TMR tended to have less class III or IV angina at 12 months of follow-up (P = .11), overall angina class distribution and exercise treadmill scores were similar between groups. When TMR was used as sole therapy, a significant improvement (>1.5 minutes) in exercise treadmill duration was observed when compared with medical therapy alone. 6 As bypass grafts deteriorate, longer follow-up will determine whether adjunctive TMR slows the inevitable return of angina for patients not completely revascularized by CABG alone.
The mechanism of TMR remains controversial. Compelling theories include laser energy–induced angiogenesis, 23,24 sympathetic denervation, 25,26 and laser channel patency. 16,17,27 The mechanism may be multifaceted and may be influenced by the presence of adjacent bypass grafts.
In this prospective, randomized, multicenter trial, TMR combined with CABG in patients who were not amenable to complete revascularization by CABG alone was observed to be safe. The operative and 1-year survival benefits observed after adjunctive TMR require confirmation by a larger validation study, which is ongoing.
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Appendix |
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TopAbstractIntroductionPatients and methodsResultsDiscussionAppendixAppendix: DiscussionReferences |
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Central Baptist Hospital, Lexington, Ky, S. P. Saha, MD (10)
Cooper Hospital, Camden, NJ, A. J. DelRossi, MD (39)
Deborah Heart and Lung, Browns Hill, NJ, G. Laub, MD, M. Grosso, MD (4)
Fairfax Hospital, Falls Church, Va, E. A. Lefrak, MD (20)
Hoag Hospital, Newport Beach, Calif, D. Zusman, MD (1)
Huntington Hospital, Los Angeles, Calif, V. Starnes, MD (4)
University of Louisville Hospital and Jewish Heart and Lung Institute, Louisville, Ky, R. D. Dowling, MD (16)
Kaiser Permanente Medical, Los Angeles, Calif, T. A. Pfeffer, MD (16)
Lankenau Hospital, Wynnewood, Pa, S. Goldman, MD (7)
Maimonides Hospital, Brooklyn, NY, M. W. Connolly, MD (5)
North Ridge Hospital, Fort Lauderdale, Fla, H. Dennis, MD (10)
Phoenix Memorial Hospital, Phoenix, Ariz, J. Hessel, MD (5)
Redding Medical Center, Redding, Calif, F. Realyvasquez, MD (39)
Sacred Heart Hospital, Spokane, Wash, S. L. Selinger, MD (1)
Sentara Norfolk General Hospital, Norfolk, Va, S. Szenptetery, MD (12)
St Francis Hospital, Beach Grove, Ind, D. Raess, MD (5)
St John’s Hospital, Springfield, Ill, J. Schneider, MD (8)
St Joseph’s Hospital, Atlanta, Ga, D. Murphy, MD (2)
St Patrick’s Hospital, Missoula, Mont, C. M. G. Duran, MD (2)
St Vincent Hospital, Indiana Heart Institute, Indianapolis, Ind, K. B. Allen (21)
St Vincent’s Medical Center, Jacksonville, Fla, M. Mostovych, MD (10)
Sutter Memorial Hospital, Sacramento, Calif, D. Schuch, MD (12)
Terrebonne General Medical Center, Houma, La, T. L. Fudge, MD (11)
Washington Hospital Center, Washington, DC, S. Boyce, MD (3)
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Appendix: Discussion |
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TopAbstractIntroductionPatients and methodsResultsDiscussionAppendixAppendix: DiscussionReferences |
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I am pleased, in spite of early work to the contrary presented by those using the holmium laser, that the concept of channel patency, which has been our idea of this mechanism over the last 8 years of work with the carbon dioxide laser, seems to be confirmed in this study. Certainly that is the only thing that I believe could explain the acute benefit. We are doing a similar randomized study with the carbon dioxide laser in a course of high-risk patients, 60% redo operations, 20% on preoperative intra-aortic balloon pump, that shows a similar mortality benefit.
I have a few questions related to the presentation, and I would like to first comment on how this nongraftable area was determined in general. As you know, most vessels can always be grafted. Whether they require an endarterectomy or whether they are less desirable for bypass, of course, is another issue. I wonder if any perfusion studies were done to demonstrate lack of perfusion or poor perfusion in these areas and viability and if that was of some assistance in determining the areas to be lazed.
The concept of ventricular perforation seems important. It seems to me to be difficult to obtain information with regard to perforation and whether perforation was achieved. I would like for you to comment further how, without the use of the echo, this was determined.
Because you have had experience with both of these modalities, I would like further observations as to the use of these modalities in the operative theater.
Dr Allen. Thank you, Dr Frazier, for those kind comments. We owe a great deal to Dr Frazier’s pioneering work in this area, and he is to be congratulated on the data that have come out of his institution.
With regard to his first question regarding how nongrafted areas were determined, no perfusion studies were used in this study. Neither the Eclipse nor Atlantic trials, which are randomized trials with a holmium laser as sole therapy compared with medical management in patients with refractory angina not amenable to conventional surgery, were able to demonstrate improved perfusion. The PLC carbon dioxide laser (PLC Systems Inc, Milford, Mass) has demonstrated weekly improved perfusion. We felt that it was not reasonable to use perfusion in this type of a trial because of the difficulty in separating the influence of bypass grafts versus TMR channels. The areas that were determined to be ungrafted were based on surgeon review of the angiogram and the intraoperative evaluation of the vessels. As noted, a significant number of patients (almost 10%) in this series required extensive endarterectomies.
Now I will turn to your second question on how penetration was confirmed without use of transesophgeal echocardiography. The carbon dioxide laser requires a full ventricle to disperse the collimated beam of energy that goes through in one shot. The holmium:YAG laser is a pulsed laser that fires 5 pulses per second, and it takes about 5 to 8 pulses to traverse the myocardium. With just a few cases, it is very easy on a beating heart to learn the tactile and auditory sensation as to when penetration takes place. When it is done on an arrested heart, as was commonly done in this series, you obviously lose that auditory sensation because the ventricle is not full and beating, but the tactile sensation is still clearly there. In addition, TEE is less helpful when a sternotomy is used because the heart is lifted out of the pericardial cavity to reach the lateral wall. It is very interesting that when you look at the heart during retrograde perfusion after the laser channels have been placed, there is perfuse bleeding from the laser channels.
Your final question was regarding comparisons of the holmium carbon dioxide lasers. I gained experience with the carbon dioxide laser during training in Dr Najafi’s program in Chicago and have now used the holmium laser in over 200 patients at the Indiana Heart Institute in Indianapolis. In my experience, both lasers are extremely efficacious and do a very good job at meeting their end points. On the basis of independent review by the FDA of both the PLC and Eclipse randomized trials using TMR as sole therapy, there was not any difference between the two modalities.
Dr Craig R. Smith (New York, NY). First, Dr Allen and his coworkers are to be congratulated for being the first group to demonstrate a nonsubjective benefit for TMR that occurs in the first month. This is a surprising finding. I did not intend to mention the experimental issues, but because we have been subjected to the percutaneous myocardial revascularization canine ventriculogram from Dr Oesterie, I feel I must point out that there is no compelling experimental evidence of perfusion through these channels, which actually provides nutritive blood flow to muscle, and I invite the audience to check out the data. I acknowledge that this statement represents a retraction of early data from my own laboratory published about 6 years ago.
I grant that this study may show that there is acute perfusion associated with channels occurring by some mechanism that is unmasked in this setting, perhaps having to do with an increase in global perfusion resulting from bypass grafts, and this may in fact be an important contribution. However, let’s look at some of the variables in this randomized study.
The study was carried out in 24 centers. I think it is common in any center for two surgeons to disagree about the graftability of a vessel. Consider just one scenario. A surgeon evaluating a coronary branch, thought angiographically to be nonbypassable, opens the vessel and finds it can indeed by bypassed. Is that patient randomized or not? When is the patient randomized? Is the region treated with laser or not? This is just one example of multiple opportunities, in a study design of this sort, for the strength of the surgeon’s belief in the treatment to affect behavior. It is important for us to know more about the details of the randomization: when did it occur, were there patients withdrawn from the protocol, and how many were withdrawn?
I am certainly prepared to be proven wrong by having these findings confirmed in other trials, but the mortality benefit is such a surprising finding that we need more assurance about the study design.
Dr Allen. In answer to your first question, there is no doubt that the mechanism of TMR is controversial. A commonly quoted article from your institution, with Dr Burkhoff as senior author, states that channels are not patent in the long-term. Within the body of the article, however, it clearly states that for 2 weeks microspheres traverse the channels when an isolated heart model is used, showing that at least for a 2-week period, acute channels are patent. In another commonly quoted article by Hardy, which also used microspheres and concluded that channels were not patent, he clearly demonstrated that channels were acutely patent for 5 days. They may not stay open for very long, but they may stay open long enough to give you some of the acute benefit that we observed in this study.
With regard to your second question, when we statistically looked at the results between the 24 centers, the centers did not influence the results. Randomization was done before surgery. Surgeons evaluated the angiogram, made a determination as to whether they thought they could completely revascularize that patient, and then that patient was randomized. Three patients were withdrawn from the study as detailed in the paper.
Dr Keith A. Horvath (Chicago, Ill). Nice presentation, Dr Allen. I agree that the combination therapy provides a method to achieve a more complete revascularization; however, the expected and observed mortality rates that you quote for the patients undergoing CABG alone are somewhat high. Having previously seen the demographics for your patients and using those demographics and the relative risks from the Society of Thoracic Surgeons (STS) database, a 2.3% mortality rate is what would be predicted, and the surprising result you are getting is not the 1.5% mortality rate with the combined procedure but the 7.5% for CABG alone. This 7.5% mortality rate brings up the following question: would those patients have been better served by being treated with laser alone or even continuing their medical therapy because both your work and that in other multi-institutional trials with sole therapy with the laser have shown that the 30-day mortality rate is less than 7.5% for those patients?
Echoing what Dr Smith has said, having evaluated a number of these patients and approving them for combined procedures, we have a 40% rate of conversion from a preoperative plan of CABG plus laser to CABG alone, because the vessels were found intraoperatively to be graftable, and I have to congratulate your cardiologists and surgeons for having a 100% agreement between the preoperative angiography and the intraoperative findings.
Regarding the mechanism, there are no articles, even with careful reading of the discussion sections, the bibliographies, and the footnotes that demonstrate that using a holmium:YAG laser creates patent channels with any substantial perfusion benefit.
Dr Allen. Thank you for your comments, Dr Horvath. I have heard them before when I presented the preliminary findings of this study at the AHA last fall.
It is interesting that you were able to obtain STS mortality data on the basis of the demographics presented at last year’s AHA, because we certainly were not. All of the data points that are needed to do an accurate STS mortality estimation are not available for this study because they were not collected prospectively. Therefore if you put in left ventricular function, sex, and age, the STS database spits back "incomplete data." Therefore it is very interesting that you were able to do it but we were not.
We were, however, able to prospectively collect the smaller number of data points required for both Parsonnet and O’Connor risk modeling, and what they showed was that a higher operative mortality rate is expected in this population, as was also alluded to by Dr Frazier. It is not unreasonable in this population to expect the mortality rate that we saw.
I think the other thing that is very important to emphasize is that regardless of the predicted mortality rate, this is a prospective randomized trial.
Dr Graeme L. Hammond (New Haven, Conn). Dr Allen, this comment is to support your work and addresses the question of function of channels that are created in the heart. Our work carried out 28 years ago on the intact beating canine heart and published in the American Journal of Physiology clearly shows that under normal conditions little or no blood enters the myocardium through pre-existing myocardial sinusoids left over from the phylogenetic development of the mammalian heart. On the other hand, as ischemia progresses and coronary flow and pressure decrease, 5% to 10% of myocardial perfusion arises directly from the left ventricular lumen, and this is under circumstances in which no channels were created by the laser. Accordingly, I believe the physiologic setup is there and can be enhanced by the laser treatment of the myocardium.
Dr Allen. Thank you for your comments.
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Acknowledgments |
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Footnotes |
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References |
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TopAbstractIntroductionPatients and methodsResultsDiscussionAppendixAppendix: DiscussionReferences |
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