Transmyocardial revascularization devices: technology update

Abstract

Transmyocardial laser revascularization (TMR) emerged as treatment modality for patients with diffuse coronary artery disease not amendable to percutaneous or surgical revascularization. The procedure entails the creation of laser channels within ischemic myocardium in an effort to better perfuse these areas. Currently, two laser devices are approved by the US Food and Drug Administration for TMR - holmium:yttrium-aluminum-garnet and CO2. The two devices differ in regard to energy outputs, wavelengths, ability to synchronize with the heart cycle, and laser-tissue interactions. These differences have led to studies showing different efficacies between the two laser devices. Over 50,000 procedures have been performed worldwide using TMR. Improvements in angina stages, quality of life, and perfusion of the myocardium have been demonstrated with TMR. Although several mechanisms for these improvements have been suggested, evidence points to new blood vessel formation, or angiogenesis, within the treated myocardium, as the major contributory factor. TMR has been used as sole therapy and in combination with coronary artery bypass grafting. Clinical studies have demonstrated that TMR is both safe and effective in angina relief long term. The objective of this review is to present the two approved laser devices and evidence for the safety and efficacy of TMR, along with future directions with this technology.

Keywords: angiogenesis; coronary artery disease; laser; revascularization.

Figure 1

Illustration showing left thoracotomy and exposure of the heart for TMR. Notes: The handpiece and 1 mm transmural channels in the myocardium are shown. The channels are created one per square centimeter, beginning inferiorly and moving superiorly to the anterior section of the heart. Total channel number depends on size and ischemic territory. Abbreviation: TMR, transmyocardial revascularization.

Figure 2

Transmyocardial revascularization lasers. Notes: (A) Heart Laser CO₂ Transmyocardial Revascularization System (Novadaq Technologies Inc., BC, Canada). (B) SolarGen TMR Ho:YAG Laser System (CardioGenesis Corporation, Foothill Ranch, CA, USA) with associated fiberoptic handpiece. Abbreviations: Ho:YAG, holmium:yttrium–aluminum–garnet; TMR, transmyocardial revascularization.

Figure 3

Illustration of CO₂ laser. Notes: Energy from the laser is delivered via hollow tubes and is reflected by mirrors to reach the epicardial surface of the heart. Transmural channels are created using a single 20 J pulse.

Figure 4

Stop-action photography of laser pulses. Notes: (A) Stop-action photography of laser pulses created with the CO₂ laser. The CO₂ laser creates a clean and straight channel within the tissue. (B) Stop-action photography of laser pulses created with the Ho:YAG laser. The Ho:YAG laser creates wider explosive ablations within the tissue. Abbreviation: Ho:YAG, holmium:yttrium–aluminum–garnet.

Figure 5

Angina relief at 12 months. Notes: Summary of angina relief in five randomized controlled trials at 1-year follow-up as defined by a decrease of two or more angina classes. Column graph illustrates differences between medical management and transmyocardial revascularization plus medical management groups. Corresponding P-values are shown below the bars. Abbreviations: MM, medical management; TMR, transmyocardial revascularization.

Figure 6

Procedural timeline for NIH Clinical Trial (NCT01557543) in patients undergoing TMR plus direct mesenchymal stem cell injections. Notes: Preoperative MRI and echocardiography are done along with bone marrow harvest 3 weeks before TMR procedure. Mesenchymal stem cells are isolated from bone marrow and expanded ex vivo. Following laser channel creation during TMR, mesenchymal stem cells are injected into the ischemic myocardium. Follow-up MRI and echocardiography are done at 1 month, 3 months, 6 months, and 12 months and compared to baseline imaging. Abbreviations: MRI, magnetic resonance imaging; NIH, National Institutes of Health; TMR, transmyocardial revascularization.