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Ann Thorac Surg 2006;82:771-772
© 2006 The Society of Thoracic Surgeons
Laser Center and Department of Intensive Care Medicine, Academic Medical Center, University of Amsterdam, PO Box 22700, Rm K01-225-2, Amsterdam, 1100DE the Netherlands
(Email: j.f.beek{at}amc.uva.nl).
We thank Dr Horvath [1] for his interest in our work [2]. His comments allow us to address some apparent misunderstandings that seem to persist in the field of transmyocardial laser revascularization (TMLR).
First, experimental and clinical evidence shows that excimer, holmium:yttrium–aluminum–garnet, and CO2 lasers, with widely varying wavelengths from 0.308 to 10.6 micrometers, can create transmyocardial channels with a comparable zone of thermal damage, as well as anginal relief in selected patients. Comparable myocardial damage can also be created by radiofrequency systems, for example, implying that it is likely that also non-laser systems may relieve complaints in selected patients with refractory angina. In "Light and Ice Cream" this view is qualified as incorrect, oversimplified, and nihilistic [1]. However, at our institution, a team of physicists, biologists, and physicians studied laser-tissue interactions for 2 decades, resulting in a reference book on optical-thermal response of laser-irradiated tissue and numerous peer-reviewed publications, including one that addresses laser-tissue interactions in TMLR [3, 4]. On that basis we cannot support the statement by Horvath [1] that the previously mentioned lasers when used in TMLR incite a different tissue reaction and work by different mechanisms.
Second, the mechanism of TMLR is still being debated. Unfortunately, irrespective of the system used, to date there is hardly any clinical evidence that TMLR does result in improved perfusion, which is obviously the optimal treatment of angina. Horvath [1] states that in more than 2,000 patients the demonstrated improvement in response to TMLR can not be attributed to denervation, even though this was investigated in only 8 of these patients. In contrast, in all of the clinical studies investigating TMLR-induced denervation using either positron-emission tomography or 123Iodine MIBG-SPECT, comprising a total of 32 patients (including the 8 patients just previously mentioned), denervation was demonstrated in 67% to 100% of the patients that showed relief of angina. In our study of 8 patients, this result was highly significant (p = 0.0005), and denervation could be attributed to TMLR in 43 of 50 segments (86%) with decreased tracer uptake [5]. The occurrence of reinnervation in some patients at 1 year after TMLR has been reported in one clinical study, but we still found denervation for as much as 16 months postoperatively [5]. Interestingly the denervation hypothesis may explain the short-term and the long-term reduction in angina. Denervation obviously may diminish anginal complaints early after the procedure, but the concomitant improved exercise also may promote arteriogenesis through increased shear stress in pre-existing capillaries [4, 5]. Therefore, despite the minimal clinical evidence for improved perfusion and left ventricular function in the first year after TMLR, this mechanism of exercise-induced arteriogenesis may explain the reported long-term reduction in angina, even when myocardial reinnervation occurs some time after TMLR.
In conclusion, "Light and Ice Cream" beautifully paraphrases that transmyocardial laser revascularization can be performed with various lasers as well as with other devices.
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