Different flow patterns between left and right internal thoracic artery grafts influence the evaluation of severe graft stenosis by transthoracic Doppler echocardiography.

Objective: An increase in the diastolic to systolic flow velocity ratio (D/S) in the proximal left internal thoracic artery (ITA) after coronary artery bypass grafting (CABG) enables noninvasive assessment of graft patency by transthoracic Doppler echocardiography (TTDE). The increase in the D/S can be less pronounced at a site distant from the anastomosis. We postulated that proximal ITA flow patterns differ between the left and right ITAs and that the increase in D/S is less pronounced in the right than in the left proximal ITA.

Methods: Proximal ITA flow was examined by TTDE in 129 consecutive patients after CABG of the left (75) or right (69) ITA to the left coronary artery. The mean D/S of the ITAs was compared with coronary angiography.

Results: The D/S was lower in the group with a patent right ITA than in the group with a patent left ITA (P < .05). The D/S of both the left and right ITAs negatively correlated with angiographic stenosis (r = 0.56 or 0.67, P < .001, respectively). The regression line was significantly shifted downward in the right ITA compared with the left ITA, according to analysis of covariance (P = .01). Graft stenosis was predicted by a D/S of <0.57 and <0.28 with an accuracy of 91% and 97% in the left and right ITAs, respectively.

Conclusion: The patency of both left and right ITA grafts to the left coronary artery can be assessed using TTDE, but different cutoff values of D/S are required to diagnose severe ITA stenosis.