Non-invasive evaluation of mammary artery flow reserve and adequacy to increased myocardial oxygen demand

Objective: To evaluate the flow reserve and adequacy to meet myocardial requests in stress conditions of mammary artery-left anterior descending (IMA-LAD) grafts using a non-invasive method. Methods: Patients (20) with angiographic evidence of normofunctioning left IMA-LAD grafts were submitted to dypiridamole Tl201 myocardial scintigraphy and concomitant transthoracic echo-doppler evaluation of the IMA flow at a mean interval of 32.5 months after surgery. Results: Under basal conditions, the mean peak and end flow velocities in systole were 0.39 and 0.06 m/s, respectively In diastole, the mean peak and end flow velocities were 0.27 and 0.02 m/s and mean tele-diastolic flow velocity was 0.14 m/s, with a mean systolic/diastolic ratio of 1.51. After dypiridamole infusion, mean systolic velocities were 0.47 (peak) and 0.23 (end) m/s, respectively +20 and +283%, whereas mean diastolic velocities were 0.56 (peak) and 0.06 (end) m/s, +107 and +200%, respectively. Mean tele-diastolic flow velocity increased to 0.32 m/s (+ 128%) and the systolic-diastolic index changed to 0.85. In all cases no significant scintigraphic evidence of induced ischemia was demonstrated in the LAD region. Conclusions: Transthoracic echo-doppler evaluation combined with Tl201 myocardial scintigraphy is a useful tool for the assessment of IMA flow reserve and adequacy to stress conditions. In the late postoperative period, the IMA shows the possibility of increasing the flow velocity, almost 2-fold; the increase in flow is prevalently diastolic and leads to a complete reversal of the physiological systolic/diastolic flow ratio. The flow reserve of IMA is always able to meet the augmented myocardial oxygen demand after dypiridamole infusion.