Detection of coronary arteries and evaluation of anastomoses with a commercially available 15-MHz, broadband, linear array transducer.

BACKGROUND

In coronary artery bypass surgery the detection of the target vessels can be difficult due to their intramural location, coverage by adipose tissue, calcification, or fibrous tissue formation. Their identification is especially critical during off-pump coronary artery bypass (OPCAB) and minimally invasive direct coronary artery bypass (MIDCAB) surgeries. Our objectives were to identify whether (1) the epimyocardial use of the broadband linear array transducer CL15-7 allows a clear and rapid identification of the target artery during on-pump coronary bypass (CPB), OPCAB and MIDCAB surgeries; and (2) if this transducer is helpful in investigating the anastomotic morphology with 2D and color flow Doppler.

METHODS

Thirty-two patients without a visually identifiable left anterior descending artery (LAD) were included in the study and epimyocardial ultrasonography was performed. Stabilization of the beating heart was used in 19 patients; in 13 patients, the surgery was carried out with CPB on the arrested heart. Two-dimensional ultrasound alone, or in combination with color Doppler, was used to identify the affected vessel as well as a suitable anastomosis site. Pulsed wave Doppler had to be used occasionally to differentiate between artery and vein. Patency of the anastomoses was established with color Doppler immediately after reinitiating blood flow. An evaluation of the distal graft diameter, its length, and the quality of the anastomosis was made with 2D and color Doppler. Transit-time Doppler flow was used to confirm patency.

RESULTS

The LAD could be identified ultrasonographically in all 32 patients at a depth of 3 to 15 mm. The right coronary artery (RCA) was located at a depth of 3 to 10 mm in the 5 patients where this vessel was to be bypassed. The coronary arteries located on the lateral or posterior aspect of the heart could not be reached due to the shape and rigidity of the transducer handle. The intended anastomosis sites of the LAD and RCA were identified with ultrasound according to their topography and morphology. In all cases the vessel could be dissected and bypassed without undue damage or bleeding. In one OPCAB patient, the LAD was identified in close proximity to the overlying vein along the whole of the anterior wall. This resulted in conversion to CPB, thus facilitating secure exposure of the LAD. The ultrasonographic visibility of the left internal mammary artery to LAD and saphenous vein graft to RCA anastomoses was excellent, and patency correlated well with the transit time flow measurements.

CONCLUSION

The CL15-7 transducer gives excellent near field visibility of the LAD and RCA. This is extremely valuable for the safe dissection of these vessels, especially during off-pump coronary surgery. The anatomical morphology of the anastomoses can be identified but, due to the shape of the transducer handle, only the coronary arteries on the anterior surface of the heart can be evaluated. A flexible, rather than a rigid, hockey stick-shaped handle would eliminate this problem. Training is essential to obtain reliable results.