Novel revascularization therapies--TMLR and growth factor-induced angiogenesis monitored with cardiac MRI

Magnetic resonance quantitative myocardial perfusion reserve demonstrates improved myocardial blood flow after angiogenic implant therapy

PURPOSE

The purpose of this study is to follow myocardial angiogenesis temporally using quantitative magnetic resonance first pass perfusion imaging and compare this with the "gold standard" of radioactive microspheres in a random subset of animals.

MATERIALS AND METHODS

Ameriod constrictors were placed around the left circumflex in 15 pigs to induce an ischemic area. Two groups were randomized to receive either a sham operation or treatment with angiogenic implants inserted into myocardium in the distribution of the left circumflex artery (LCX). These implants are designed to induce myocardial angiogenesis. Magnetic resonance first pass perfusion imaging was performed at baseline and also after treatment with either sham or implant therapy by using first pass perfusion imaging with a TurboFLASH sequence. Absolute myocardial blood flow was derived by applying a quantitative Fermi function model. Radioactive microspheres were also injected into a random subset of animals to measure myocardial blood flow.

RESULTS

Angiogenic implant therapy increased absolute myocardial blood flow in the left circumflex territory relative to baseline and sham treated groups during adenosine infusion. Myocardial blood flows measured with radioactive microspheres was increased significantly in both the LCX and LAD territories during stress. Myocardial Perfusion reserve was also significantly increased in both the LCX and left anterior descending territories relative to baseline. Ejection Fraction during stress with dobutamine infusion increased significantly in the implant therapy group while that in the sham group was not affected.

CONCLUSION

Quantitative MR myocardial first pass perfusion imaging can be used to track the development of angiogenesis as corroborated by radioactive microspheres. Angiogenic implant therapy is a new device based therapy that has potential to protect an ischemic region by accelerating angiogenesis although further research is necessary with this device.

Transmyocardial laser revascularization causes sustained VEGF secretion

Transmyocardial laser revascularization (TMR) using a carbon dioxide (CO(2)) laser has been shown to relieve angina, increase vascular density, and improve myocardial contraction. A study of 28 patients receiving TMR was conducted to monitor vascular endothelial growth factor (VEGF) levels with the goal of clarifying the relationship between TMR, the amelioration of angina, and vascular density. Serum VEGF levels were measured during four periods (preoperative, postoperative, convalescence, and late) in these 28 patients who received sole therapy TMR for un-revascularizable ischemic angina and the levels were compared with the control group consisting of 10 nonischemic thoracotomy patients. Twelve of the 28 patients had previous coronary artery bypass graft(s); 10 had unstable angina, and 1 had an ejection fraction less than 30%. Overall, angina class was reduced from 3.8 +/- 0.9 to 1.0 +/- 0.9 (P < 0.01) at the 1-year follow-up. There were no perioperative mortalities; however, there was one late mortality. The results show that VEGF levels were higher in the convalescence and late periods. Specifically in the late period, VEGF levels in TMR therapy patients surpassed those of the control group and normalized VEGF levels were three times higher in the late period than preoperatively. The sustained VEGF secretion observed in this study may help to explain why CO(2) TMR therapy causes locally increased vascular density and angina relief.

Autologous Bone Marrow-Derived Stem Cell Therapy in Combination with TMLR. A Novel Therapeutic Option for Endstage Coronary Heart Disease: Report on 2 Cases

We report 2 cases in which patients with coronary heart disease not amenable for conventional revascularization underwent transmyocardial laser revascularization (TMLR) and implantation of AC133+ bone-marrow stem cells. The reason for using TMLR in combination with stem cell application is to take advantage of the synergistic angiogenic effect. The local inflammatory reaction induced by TMLR should serve as an informational platform for stem cells and may trigger their angiogenic differentiation. Functional analysis of myocardial performance after treatment in these 2 cases revealed dramatic improvement of the wall motion at the site of the TMLR and stem cell application. Because TMLR does not enhance myocardial contractility and there was no angiographic evidence of major collaterals to the ischemic region in either patient, we assume that the synergistic effect of stem cells and TMLR-induced angiogenesis occurred; however, our assumption is of a speculative nature. We think that TMLR in combination with stem cell transplantation might become a novel revascularization therapy for ischemic myocardium.