(Jon's Note: PTMR - PERCUTANEOUS TMR - is done via a catheter. TMLR is the same thing but is done surgically, after opening the chest to gain access to the heart. They use different laser systems also.) PTMR Transmyocardial revascularization (TMR) is a technique in which small channels are created between the ischemic heart wall and the left ventricular cavity. The theory came from reptiles - their blood is delivered to the heart by a network of channels directly from the left ventricle. Experiments were done in dogs which led to the idea that this might improve blood flow in people with blocked arteries. A group of patients has emerged who are not candidates for bypass or angioplasty. This group includes patients with severe diffuse coronary disease, small vessel disease, total coronary blockages, and those who have had previous bypass surgery. TMR using a laser is being tested as an alternative for getting more blood flow to ischemic areas of the heart in these patients. To be a candidate for current TMR procedures, patients must meet the following criteria: 1) severe angina (functional class 3 or 4) despite best medical therapy 2) poor candidate for catheter-based angioplasty 3) poor candidate for surgical revascularization Surgical TMLR A recent trial compared results of surgical laser revascularization to medical therapy and reported improved symptoms, improved quality of life, and some evidence of improved cardiac blood flow in the treated areas. Of the surgical TMLR patients, 67% showed improvement in angina compared with 6% of the drug group, and hospitalization for unstable angina was way down - 13% post-TMR versus 72% with medical therapy. However, MUGA in the first 3 months showed a less impressive reduction in reversible defects. In another study, Allen did surgical TMR and reported significant improvement in angina class - 85% vs 18% - and fewer hospitalizations for angina compared with best medical treatment at 6 months. Donovan used dobutamine stress echo to study 12 patients treated with surgical laser TMR and reported improvement in heart contraction in the treated areas of the heart. The physical characteristics of the CO2 laser allow precise tissue removal, but its wavelength does not allow catheter-based use. This limits its use to "open" surgery. Because of this, TMR was begun using Holmium: YAG laser energy, which can be used at much shorter wavelength through flexible fiberoptics. Percutaneous Approach Although trials of catheter based TMR are in the early stages, so far results look good. Percutaneous transluminal myocardial revascularization (PTMR) uses catheter/fiber systems inserted through the groin artery and guided into the left ventricle. Channels (5 mm deep) are created from endocardium to myocardium, not penetrating the epicardium. The goal is to make channels that are smaller in size but similar in effect to channels created by the surgical approach, without the need for "open" surgery or general anesthesia. Complications and death should be lower compared to surgical TMR, where procedural death is between 9-12% PTMR Technique Patients were eligible for the study, if they: 1) had known coronary artery disease not suitable for bypass surgery 2) were in Canadian Cardiovascular Society functional class 3 or 4 3) had inducible ischemia on treadmill test or had unstable angina requiring intravenous nitroglycerin 4) had a preprocedure echo showing more than 9 mm wall thickness of the left ventricular region that was to be lasered and an EF higher than 25 Heparin 7,000 IU is given intravenously to achieve an activated clotting time of at least 280 seconds. A catheter is advanced into the left ventricle and pressures are recorded. An extra stiff guide wire is looped in the left ventricle and the catheter system carefully positioned in the apex. The catheter system is continuously flushed with heparinized saline. Once positioned, the one mm laser fiber is inserted into the guide system and aligned by fluoroscopy (x-ray). Three consecutive pulses are delivered to the endocardial surface. Between 15 and 30 laser channels (3 pulses each) are placed; one channel per one square centimeter, and channels are limited to the lower two-thirds of the left ventricle. The ventricular septum is avoided. Patients are discharged the following day. Percutaneous Trials A recent study focused on patients who had symptoms before PTMR, with 10 in Canadian Cardiovascular Society functional class 3, and 17 in class 4. Before PTMR, 15 patients had symptoms during exercise and 12 had at-rest angina and were on intravenous nitroglycerin. The patients were mostly men. A history of heart attack was present in 55%. An average of 17 channels were created by laser. Regional heart wall motions were unchanged or slightly improved immediately after the procedure. Following the procedure, patients were successfully weaned off intravenous nitroglycerin. The average length of hospital stay was 2 days. There were no procedure-related deaths and no deaths in the 30 day period after the procedure. There were no strokes or sustained ventricular arrhythmias. Of the 27 patients (all class 3 or 4 before the procedure), 15 were in class 1, 3 were class 2 and nine had no angina at one month after PTMR. At 30 days, average functional class improved from 3.6 to 0.7. Ischemia was reduced in 58% and unchanged in 42% of patients. Similar findings were reported by Knopf in 18 patients with medically unresponsive class 3 or 4 angina. There were no procedural deaths and all patients were discharged within 48 hours after the procedure. Average angina class fell from 3.8 at baseline to 1.1 at discharge and was still 1.1 at 6 month follow-up. At 6 months, 88% of patients noted improvement by at least 2 classes in angina severity. Lauer reported similar symptom improvements in 16 patients. Oesterle and Kornowski recently reported similar results using 2 other PTMR systems. Several clinical trials are ongoing. Why Does It Work? Why TMR gives clinical benefit is unknown. Initial studies guessed that open channels would provide continuous blood flow similar to that in alligator hearts. However, the long-term openness of the laser channels is still controversial. A possibility is that laser-induced injury stimulates growth of new blood vessels, called angiogenesis. It is also possible that the angina relief may in part be from damage to the heart's sensory nerves, resulting in an anesthetic effect. Conclusion Based on experience so far, PTMR may be a potential treatment for unresponsive angina in patients not suited to any other revascularization procedure. Developments using angiogenic growth factors are interesting, and the role of growth factors in addition to TMR remains to be seen. Percutaneous Transluminal Myocardial Revascularization: An Emerging Technology Fayaz A. Shawl, MD, Department of Interventional Cardiology and the Cardiology Research Institute, Washington Adventist Hospital Takoma Park Maryland J Invas Cardiol 11(3):169-175, 1999