Assessment of coronary blood flow in hypertrophic cardiomyopathy using thrombolysis in myocardial infarction frame count method

Abstract

Background: Coronary microvascular dysfunction has been reported to be present in patients with hypertrophic cardiomyopathy (HCM) despite normal epicardial coronary arteries. In this study we aimed to evaluate coronary blood flow in patients with HCM by means of Thrombolysis In Myocardial Infarction (TIMI) frame count.

Methods: Thirty-two patients with HCM (22 male, 10 female; mean age=48+/-7 years) and 36 healthy control subjects (23 male, 13 female; mean age=49+/-7 years) without any cardiovascular disease were included in the study. All patients and control subjects were selected from individuals who underwent coronary angiography and left heart catheterization in our hospital and were found to have angiographically normal coronary arteries. All patients had an asymmetrically hypertrophic nondilated left ventricle and a basal intraventricular pressure gradient>30 mmHg recorded in the left ventricular outflow tract. A complete transthoracic echocardiographic examination including two-dimensional, M-mode, pulse and continuous Doppler was performed in all patients and control subjects. Coronary flow rates of all subjects were documented by the TIMI frame count method. To obtain corrected TIMI frame count for the left anterior descending (LAD) coronary artery, TIMI frame count for this vessel was divided by 1.7.

Results: Corrected TIMI frame count for the LAD coronary artery was found to be significantly higher in patients with HCM compared to control subjects (35+/-8 vs. 25+/-6, p<0.001). However, we found no significant difference between patients and control subjects regarding TIMI frame counts for the left circumflex (LCx) coronary artery and the right coronary artery (RCA) (LCx: 28+/-6 vs. 26+/-6, p=0.07 and RCA: 26+/-6 vs. 24+/-5, p=0.09). Besides, the corrected TIMI frame count for the LAD coronary artery was found to be significantly correlated with interventricular septal wall thickness (r=0.546, p=0.001) and interventricular septal/posterior wall thickness ratio (r=0.490, p=0.004). However, no significant correlation was detected between the corrected TIMI frame count for the LAD coronary artery and other echocardiographic variables.

Conclusion: We show that patients with HCM had significantly higher corrected TIMI frame counts for the LAD compared to the control subjects. No such difference was detected between the two groups regarding TIMI frame counts for the LCx and RCA, suggesting the presence of regional (interventricular septal) rather than global impairment of coronary blood flow in patients with HCM.