Chronic stable angina transmyocardial revascularization
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As the survival of patients with primary coronary events continue to increase, the number of patients presenting with refractory ischemia despite maximal medical therapy and unsuitable for further traditional revascularization techniques also continues to rise. Transmyocardial revascularization (TMR) is one of the emerging techniques that has been studied in many randomized trials and has shown to reduce the incidence of recurrent angina, increase exercise tolerance time and improve quality of life. TMR can be performed using either a laser beam or a percutaneous approach. However, only laser TMR is currently FDA approved.
Mechanism of Benefit
Direct myocardial revascularization involves a series of transmural endo-myocardial channels through the heart muscle that carries blood from the ventricular cavity into the myocardium to improve myocardial revascularization. Following TMR, the outside of the heart muscle seals up immediately. In time, as these channels heal, they stimulate the creation of new small vessels or capillaries (angiogenesis). Other mechanism of benefit in TMR is thought to be sympathetic denervation.
- Across various studies, researchers have found that the mortality rates range from 5 to 20% and the peri-operative mortality ranges between 5 to 12%.
- In a small subset of studies, researchers found different stages of wound healing in human nonresponder myocardium after TMR. This, they concluded, resulted in scarred tissue that displayed capillary network and dilated venules without evidence of patent and endothelialized laser-created channels.
- TMR could be performed using either a carbon dioxide or holmium: YAG laser known as laser TMR or by a percutaneous approach with a catheter referred as percutaneous TMR.
- Another way to perform TMR is through epicardial surgical approach. This can be done alone or in combination with CABG.
Transmyocardial revascularization is an alternative procedure for patients with severe refractory angina who remain symptomatic despite receiving maximal medical therapy and/or refractory patients with normal to mildly reduced left ventricular function and who are unsuitable for revascularization with either PCI or CABG.
- Although it has been hypothesized that TMR induced angiogenesis caused improved myocardial perfusion, there is no evidence that the procedure would alter the left ventricular performance, which is often the result of clinically significant improved myocardial perfusion.
- Animal studies suggest that TMR has been has been shown to partially denervate the cardiac nerve fibers.
Supportive Trial Data
- The six randomized trials that compared TMR with medical therapy in patients with refractory angina, demonstrated significant clinical benefit associated with TMR; however, the extent of improvement varied and myocardial perfusion was improved only in five of the six trials.
- Laser TMR was shown to provide significant symptomatic benefit but no improvement in the exercise capacity.
- Patients with refractory angina who underwent laser TMR and received continued medical therapy, demonstrated a significantly better outcome with respect to improvement in angina, survival free of cardiac events, freedom from treatment failure, and freedom from cardiac-related re-hospitalization.
- In the DIRECT trial, 298 patients with severe angina and unsuitable for CABG or PCI, were randomly assigned to receive either low-dose or high-dose myocardial laser channels or no laser channels, and blinded as a control procedure. The study demonstrated that treatment with percutaneous myocardial laser revascularization provided no benefit in comparison to continued medical therapy in terms of clinical outcome, quality of life and improvement in exercise duration.
|"1. Surgical laser transmyocardial revascularization (TMR). (Level of Evidence: A)"|
2011 ACCF/AHA/SCAI Guidelines: Transmyocardial Revascularization to Improve Symptoms (DO NOT EDIT)
|"1. Transmyocardial laser revascularization performed as an adjunct to CABG to improve symptoms may be reasonable in patients with viable ischemic myocardium that is perfused by arteries that are not amenable to grafting.  (Level of Evidence: B)"|
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