MR CHARACTERIZATION OF BLOOD-FLOW IN NATIVE AND GRAFTED INTERNAL MAMMARY ARTERIES

In the postoperative patient with anginal symptoms, differentiation be tween bypass graft compromise and nonischemic causes has until now bee n accomplished only by means of x-ray angiography. A noninvasive test is clearly desirable. The authors used a cine phase-contrast (PC) magn etic resonance (MR) imaging technique to characterize blood flow in na tive and grafted internal mammary arteries (IMAs). Ten volunteers and 15 patients who had recently undergone IMA coronary artery bypass graf ting were imaged. Cine PC MR imaging was performed in the transaxial p lane at the level of the pulmonary artery bifurcation. Flow in both IM As was quantified and expressed as a percentage of cardiac output meas ured in the ascending aorta. In the 15 patients, flow analysis was per formed in both the native and grafted IMAs. In the volunteers, IMA blo od flow ranged from 2. 1 % to 4.3 % of cardiac output on the left (mea n, 3.5%) and 2. 1 % to 5. 1 % (mean, 3.5%) on the right. There was con siderable intersubject variability, with coefficients of variation of 10.7 % for the left and 12.3 % for the right IMA. Intrasubject variabi lity was limited, with estimated common standard deviations of 0.45 % of cardiac output (range, 0.2%-1.1 %) for the left and 0.39% (range, 0 .1%-0.6%) for the right IMA. Flow in grafted IMAs was identified in 13 of 15 patients. In one of two patients without demonstrable IMA graft flow, cardiac catheterization confirmed lack of flow. IMA graft flow varied from 28 to 164 mL/min (mean, 80.3 ml/min). This study shows the feasibility of using cine PC MR imaging as a quantitative method of e valuating blood flow in IMA coronary artery bypass grafts.