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J Thorac Cardiovasc Surg 1998;115:1392
© 1998 Mosby, Inc.
LETTERS TO THE EDITOR |
To the Editor:
I read with interest the article titled "Transmyocardial Laser Treatment Denervates Canine Myocardium (J Thorac Cardiovasc Surg 1997;114:883-90) by Kwong and associates. The authors concluded that laser treatment destroys cardiac nerve fibers and that this may contribute to the reduced angina pectoris seen clinically. This was an elegant experiment, but conclusions from the results of animal experiments must be complemented by observations in human beings. In the past 4 years, my colleagues and I have carried out transmyocardial revascularization for the relief of class IV angina, unresponsive to maximum medical therapy and unsuitable for coronary bypass or angioplasty, in 295 patients. A carbon dioxide laser was used in 228 patients and a holmium–yttrium-aluminum-garnet (YAG) laser in 67. Preinfarction angina was present in 111 patients who did not respond to treatment, including intravenous heparin and nitroglycerin for at least 1 week. The operative mortality for the carbon dioxide laser was 3.7% for patients in stable condition (0% last year) and 12.8% for those in unstable condition. By 1 year dipyridamole (Persantine) thallium studies showed increased vascularity as compared with the preoperative state in 55% of the patients. Angina relief progressively increased, so that by 3 months two thirds of the patients either had no angina or class I or II angina, by 6 months 75%, and by 1 year 90%. In fact, at 1 year 40% had no angina, 31% had class I, and 21% had class II angina. The late mortality (12 to 48 months) was only 7%, and the patients remained in the angina class that was present at 1 year. With the carbon dioxide laser, it is more difficult to create a channel through the entire thickness of the myocardium when there is a heavy fat layer in the epicardium. It is fascinating that in one patient in whom no channels reached the ventricular cavity, as confirmed by transesophageal echocardiography, the angina decreased to class II by 3 months; a second patient in whom only seven channels reached the cavity had no angina 1 year later.
With the holmium-YAG laser, the operative mortality was 4.8% for patients in stable condition and 16.7% for those in unstable condition because of problems with low cardiac output, myocardial infarction, and ventricular fibrillation, which have since been overcome by changes in the intraoperative and postoperative care. However, the increase in perfusion seen on the thallium study was not as marked as in the patients treated with the carbon dioxide laser, only 40% showing improvement. In addition, although by 1 year 90% of the patients treated with the holmium-YAG laser had improved by at least two angina classes, only 21% had no angina, 27% were in class I, and 45%, or one half, were in class II.
In light of these observations in this large series of patients, including progressive improvement in angina class over the first year and relief of angina despite failure of the laser channels to reach the ventricular cavity, I conclude that these circumstances indicate an ongoing process over the first year, stimulated by the interaction of the laser with the myocardial tissue. This favors a mechanism of vascular neogenesis, as well as the development of connections between preexisting intramyocardial collaterals, which could improve the distribution of blood supply. The reptilian theory would not apply when no channels or very few reached the ventricular cavity. In addition, there is conflicting evidence about the patency of the channels from animal experiments, as well as from human postmortem examinations. Furthermore, if denervation is the primary factor, it should have an immediate effect that would be maintained at a constant level throughout the year, or possibly even decline somewhat. To the contrary, my associates and I warn all our patients that they will still have angina for some time after the operative procedure, but that it will gradually and slowly decrease in frequency and severity. Finally, the differences in results between the two lasers warn us that various energy sources do not necessarily have the same effect on myocardial tissue. Hence all new techniques will have to be judged by results observed over time.
Director, The Heart InstituteAudubon HospitalLouisville, KY 4021712/8/89668
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