The internal mammary artery bypass--the principles of preoperative and postoperative diagnosis using colour-duplex ultrasound.

Background: The aim of the study was the assessment of functional characteristics of the left internal mammary artery (LIMA) bypass in patients after coronary artery bypass grafting (CABG) in comparison with the native LIMA using colour-duplex ultrasound as the non-invasive diagnostic method.
Methods: We examined 303 patients after myocardial revascularization with the internal mammary artery bypass using the Hewllett Packard 2500, 5500 ultrasound units. Using the 7.5 MHz linear transducer we detected the LIMA from the left supraclavicular approach. We assessed the peak systolic velocity (PSV--cm/s), peak diastolic velocity (PDV--cm/s), end-diastolic velocity (EDV--cm/s) and we calculated the peak systolic/peak diastolic velocity ratio (SDVR) and resistance index RI (PSV-EDV/PSV). The obtained parameters were compared with the native LIMA flow characteristics of the 70 consecutive patients before CABG.
Results: We observed the transformation of internal mammary artery flow from the predominantly systolic high resistance type of the native LIMA, to the low resistance biphasic waveform after its use as a coronary artery graft. We detected a significant increase of diastolic flow velocities and a significant decrease of resistance and of the SDVR ratio. In dysfunctional grafts we found a decrease of diastolic flow and an increase of LIMA resistance and SDVR.
Conclusion: The colour-duplex ultrasound is a perspective non-invasive method for the postoperative follow-up of patients with the LIMA graft. It allows the assessment of the bypass flow characteristics, functional status and patency and it could contribute to the early diagnosis of bypass failure. (Fig. 6, Tab. 4, Ref. 21.)