RESUMO
AIM: The aim of the study is to evaluate patency and flow reserve by echocardiography in arterial grafts using the left internal mammary artery (LIMA) to the left anterior descending coronary artery (DA). The main limitations in performing this study routinely are the weakness of the Doppler signal and the exact chest localization of the graft. The purposes of the study were: to verify the feasibility of the echo color Doppler method on LIMA; to verify which between the parasternal or supralavicular view is the better approach to obtain a clear signal; to verify the increase of systolic and diastolic flow velocity of LIMA in basal conditions and after infusion of dipyridamole, and if the visualization of the Doppler signal improves after contrast infusion. METHODS: Twenty patients (all males, mean age 63+/-7.8 years) with previous coronary artery bypass in the last 10 years, and without any significant stenosis in the left mammary artery graft as proved by a recent coronary angiogram (within 6 months), were selected for our study. LIMA was evaluated by two echocardiographic approaches. Patients were studied at rest and after pharmacological infusion of dipyridamole using the protocol of 0.56 mg/kg in 4 minutes. Contrast enhancement was infused in order to improve the Doppler signal using Levovist contrast agent at rest and after vasodilatation. Diastolic and systolic peak flow velocities, their ratio and the diastolic and total velocity time integrals were evaluated. RESULTS: The results showed that using the supraclavicular approach we obtained the visualization of the graft at rest in all patients (100%) and using the parasternal approach in 19 out of 20 (95%) even without contrast injection. At rest, the diastolic and systolic peak flow velocities were 0.417+/-0.133 m/s and 0.368+/-0.1291 m/s; their ratio (diastolic/systolic) was 0.882+/-0.7362. The overall and diastolic velocity time integrals were 0.1571+/-0.0645 m and 0.2232+/- 0.0701 m. After dipyridamole infusion we observed in all patients an increase in diastolic and systolic peak flow velocities as expected by 0.582+/-0.342 m/s (p<0.005) and 0.73+/-0.427 m/s (p<0.005). Contrast injection at rest and after peak dipyridamole infusion showed a better and clearer Doppler signal of the graft allowing an easier evaluation of the velocity curves in all patients. In fact using the association dipyridamole-Levovist the velocity ratio and the total and diastolic velocity time integral values were 1.268+/-0.368 (p<0.05), 0.3492+/-0.131 m (p<0.05) and 0.2309+/-0.153 m (p<0.05). CONCLUSION: In conclusion, this new echo-color-Doppler approach seems to be valid for the evaluation of the patency rate and flow reserve of the internal mammary artery graft, and helps to better select patients who really need angiography.
