Noninvasive Assessment of Left Internal Mammary Artery Graft Patency Using Transthoracic Echocardiography

Abstract

Cardiac catheterization is the only practical method of assessing internal mammary artery graft patency. A noninvasive method would be useful in patients with recurrence of anginal symptoms after coronary artery bypass graft surgery. We hypothesized that transthoracic echocardiography could provide information on blood velocity and anatomy and therefore has the potential to allow measurement of blood flow. High-frequency (5 MHz) transthoracic echocardiography was performed on 41 consecutive patients (mean age, 67 +/- 6 years) who had had left internal mammary artery grafts to the left anterior descending coronary artery (LAD) and were undergoing coronary angiography because of recurrence of anginal symptoms. The results were compared with those from 19 patients (mean age, 58 +/- 11 years) in whom an ungrafted left internal mammary artery was assessed and with those from 15 patients (mean age, 61 +/- 12 years) who had angiographically normal coronary arteries in whom the LAD was studied. Doppler velocity profiles of the left internal mammary graft were obtained in 35 of the 41 study patients (81%). In all cases, a biphasic pattern of blood flow was recorded that corresponded to systole and diastole. Two different flow patterns were observed. In 25 patients with a normal graft or moderate (< 70%) stenosis (group A), blood flow velocity was maximal during diastole. This pattern was also seen in the LAD control group. In 10 patients with severe (> 70%) graft stenosis (group B), blood velocity was maximal during systole, and low velocities were recorded during diastole. This pattern was also seen in the ungrafted internal mammary artery control group. The diastolic fraction of the velocity time integrals for group A was 0.77 +/- 0.07 and for group B was 0.27 +/- 0.01 (P < .05). A diastolic velocity time integral fraction < 0.5 predicted severe stenosis with a sensitivity and specificity of 100%. The ratio of systolic-to-diastolic peak velocities for group A was 0.54 +/- 0.26 and for group B was 3.45 +/- 0.74 (P < .05). A systolic-to-diastolic peak velocity ratio > 1 predicted severe stenosis with a sensitivity of 100% and specificity of 85%. Mean graft blood flow was 63 +/- 21 mL/min. There was no significant difference in mean blood flow between any of the patient groups studied. High-frequency transthoracic echocardiography allows identification of the left internal mammary grafts and measurement of blood flow. Compared with patent grafts or those with moderate lesions, severe stenoses demonstrated different Doppler velocity patterns. Use of this technique may allow noninvasive detection of significant stenoses of the left internal mammary artery graft.