Assessing coronary blood flow with TIMI frame count method in isolated myocardial bridging

Myocardial bridging (MB) is a congenital anomaly of coronary arteries and its functional significance remains controversial. Using the TIMI frame count (TFC) method, the authors investigated whether the coronary blood flow velocity is decreased in MB. The study included 18 patients (group 1; 12 men and 6 women; mean age 50 +/-6 years) who had angiographically proven MB and otherwise normal coronary arteries and 20 subjects (group 2; 13 men and 7 women; mean age 50 +/-7 years) with normal-appearing coronary arteriograms. TFC of each group was determined and correlation between TFC and various factors including percent systolic narrowing, age, gender, body mass index, blood pressure, and echocardiographic parameters (ejection fraction, left-right ventricle wall thickness, and diameters) was investigated. Baseline characteristics were similar in the groups. All of the MB was localized to the left anterior descending (LAD) artery. Corrected TFC(LAD) frame count (CTFC) was significantly higher in group 1 than in group 2 (24.7 +/-2.1 vs 22.1 +/-1.9 frames/s, p = 0.001). Circumflex and right coronary artery frames counts were similar in the groups (22.4 +/-2.4 vs 21.3 +/-2.3 frames/s, p = 0.18, 23.1 +/-2.2 vs 23.4 +/-2.1 frames/s, p = 0.7) On correlation analysis, there was no correlation between TFC and the factors investigated. CTFC of patients with MB was higher than of those with normal coronary arteries, irrespective of the degree of systolic narrowing. This may suggest that coronary blood flow is decreased in patients with MB compared to patients having normal coronary arteries.