Can left internal mammary artery side branches affect blood flow rate?

The left internal mammary artery (LIMA) is the most commonly used arterial graft for coronary artery bypass graft (CABG) surgery, and occluding the LIMA side branches during surgery is important to avoid myocardial ischaemia afterwards. In this study we investigated the incidence of patent LIMA graft side branches in our coronary angiography series, and compared LIMA flow rate changes by means of the thrombolysis in myocardial infarction (TIMI) frame count in patients with and without LIMA graft side branches. Patients with a history of CABG surgery and who were scheduled for coronary angiography in our centre between 1 January and 15 December 2006 were enrolled in the study. We compared LIMA graft TIMI frame counts between patients with and without side branches. The incidence of LIMA graft side branches in our study was 18% (seven patients). Mean TIMI frame count was 27.28 +/- 3.4 in patients with LIMA graft side branches and 15.67 +/- 2.3 in patients without. There was a significant difference between the two groups (p < 0.0001). Patients with LIMA graft side branches were more likely to have anterior ischaemia, determined by myocardial perfusion scintigraphy. We suggest that TIMI frame count may be helpful in evaluating the effect of side branches on LIMA graft flow rate. The increased TIMI frame count of a LIMA graft with side branch is associated with insufficient LIMA flow.