Assessment of left internal mammary artery graft patency and flow reserve after minimally invasive direct coronary artery bypass

Despite its merits, minimally invasive direct coronary artery bypass surgery (MIDCAB) has been criticized for variable left internal mammary artery (LIMA) graft patency rates, prompting the frequent use of postoperative LIMA angiography. Noninvasive transthoracic Doppler interrogation of LIMA grafts has recently been shown to have utility for assessing patency and flow reserve after conventional bypass surgery, but data after MIDCAB has been limited. The objective of this study was to assess LIMA graft anatomy and physiology in 54 patients after MIDCAB using angiography and noninvasive LIMA Doppler imaging. The right internal mammary artery (RIMA) was studied as a control. LIMA flow reserve in response to adenosine was evaluated in a subgroup of 18 randomly chosen patients with patent grafts. LIMA angiographic patency was 93%. Forty-four patients (81%) had obtainable LIMA Doppler data. Patent grafts had a diastolic dominant flow pattern with a peak diastolic/systolic velocity ratio of 1.3 ± 0.6 and a percent diastolic time-velocity integral (TVI) of 70 ± 11%. These data were significantly different than the RIMA control values of 0.2 ± 0.1 and 30 ± 10%, respectively (p <0.05). Occluded grafts had absent flow or a systolic dominant pattern. Adenosine-induced increases in LIMA peak diastolic velocity from 48 ± 20 to 105 ± 28 cm/s (p <0.05 vs baseline) and diastolic TVI from 21 ± 10 to 37 ± 19 cm (p <0.05 vs baseline), yielding adenosine/baseline ratios of 2.4 ± 0.9 and 2.0 ± 0.7, respectively, which was consistent with normal flow reserve. The diastolic flow velocity reserve response was inversely related to baseline diastolic flow (r = -0.69). In conclusion, MIDCAB can be associated with a high rate of LIMA patency and favorable physiologic Doppler flow patterns. Correlation of these findings to long-term patient outcome after MIDCAB is warranted.