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Ann Thorac Surg 2001;72:822
© 2001 The Society of Thoracic Surgeons
a McGill University Health Centre, The Montreal General Hospital, 1650 Cedar Ave, Room C9-169, Montreal, PQ H3G 1A4, Canada
e-mail: mdiumusica{at}mcgill.ca
It is in fact rather amazing that few have looked at the dose-response relationship in all the experimental studies and clinical trials for transmyocardial laser revascularization (TMR) until this time. No new drug would have been accepted and approved without dose-response data. Perhaps this is because we surgeons are more used to an all-or-none response: you do not worry about dose-response when you repair a valve or close a ventricular septal defect (VSD). Studying the outcome of laser TMR as a function of channel density allows one to choose the optimal number of laser punctures that should be made. Otherwise it is simply arbitrary. But in the case of TMR, there is another reason why such a study may be important. In spite of the FDA approval of this procedure and reports from centers worldwide of its efficacy in reducing anginal symptoms, the reasons why such results are obtainable remains highly controversial. The most serious challenging data come recently from the first blinded randomized DIRECT trial [1]. During cardiac catheterization, patients were randomized in a blinded fashion to receive low-dose or high-dose density (10 to 15 and 20 to 25 channels per zone) endocardial laser punctures or a mock procedure. Although improvements were noted across all study groups, the investigators reported no difference in functional and symptomatic responses among these groups, suggesting a significant placebo effect. The dose-response findings in such a study are valuable in strengthening the possibility that the procedure and outcome may or may not have a cause-and-effect relationship, rather than merely an association.
This interesting paper by Hamawy and colleagues raises many additional questions. They showed that the densities of excimer laser channels created from the epicardial side in an ischemic myocardial segment had a positive relationship with the magnitude of neovascularization and increased blood flow. The contradiction between this observation and the results of DIRECT trial may be because the endpoints looked at in this study (angiogenesis) are not relevant to the clinical outcome endpoints for the DIRECT trial (angina relief and functional improvement); or because the route of TMR (epicardial versus endocardial approach) or the laser energies used were different. But if so, how? Furthermore, if the angiogenesis induced by TMR is due to an inflammatory response following tissue trauma created by laser punctures, why not use a cheap needle, which can also cause similar although less trauma and angiogenesis, and simply increase the puncture density to match the effect of a laser? The intense scrutiny that TMR continues to receive is appropriate. If this procedure, which requires the use of an expensive device, is not valid, we should know. On the other hand, solid confirmation of this approach will justify its wider application in order to offer relief for patients who suffer from intractable angina.
References
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