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Noninvasive assessment of left and right internal mammary artery graft patency using transthoracic color Doppler echocardiography.

BACKGROUND
The aim of this study was to evaluate the patency of left and right internal mammary artery grafts respectively on the left anterior descending and right coronary artery by noninvasive transthoracic color Doppler echocardiography.


METHODS
Thirty eight patients (34 males, 4 females, mean age 59 +/- 2 years), with a history of coronary artery bypass grafting for a total of 42 mammary artery grafts, were studied by means of color Doppler echocardiography at baseline and after vasodilation with dipyridamole infusion (0.56 mg/kg i.v. over 4 min). The evaluated echocardiographic parameters included: systolic (SPV) and diastolic peak velocities (DPV), systolic (SVI) and diastolic velocity-time integrals (DVI), and the DPV/SPV and DVI/SVI ratios. We also calculated the dipyridamole infusion to baseline ratio of the diastolic peak velocities (DPVdip/DPVbaseline), the index of internal mammary artery graft blood flow reserve and the percent DPV increment as an index of graft stenosis.


RESULTS
On the basis of coronary angiography, two groups were selected: group A (36 mammary grafts) with patent grafts and group B (6 mammary grafts) with moderate or severe stenosis of the grafts. Group A had a predominant diastolic pattern with a DPV of 0.24 +/- 0.13 m/s, whereas group B had a predominant systolic pattern with a reduced DPV of 0.12 +/- 0.03 m/s (p < 0.01). Dipyridamole induced an increase in the DPV respectively of 86.8 +/- 64.4% in group A and 13.8 +/- 15.9% in group B (p < 0.001). Statistical analysis (Mann-Whitney test) revealed a significant difference between the two groups for the baseline DPV (p < 0.01), DVI (p < 0.05), DPV/SPV ratio (p < 0.005), DVI/SVI ratio (p < 0.05), and for the after dipyridamole infusion values: DPV (p < 0.0001), DVI (p < 0.005), DPV/SPV ratio (p < 0.001), and DVI/SVI ratio (p < 0.05). Multivariate analysis showed that the percent DPV increment, the DPVdip/DPVbaseline ratio and the baseline DPV were independent determinants of the stenosis as evaluated at angiography (beta = -0.38, p < 0.01; beta = -0.37, p < 0.01, and beta = -0.33, p < 0.05, respectively; cumulative r2 = 0.25, standard error 0.30 m/s, p < 0.005).


CONCLUSIONS
The echocardiographic evaluation of the mammary grafts is a simple, noninvasive method for the assessment of the graft patency and of the functional status of the vessel. The percent DPV increment and baseline DPV were independent determinants of mammary graft stenosis.