Coronary Flow Velocity Reserve Using Dobutamine Test for Noninvasive Functional Assessment of Myocardial Bridging

Abstract

Background: It has been shown that coronary flow velocity reserve (CFVR) measurement by transthoracic Doppler echocardiography (TTDE) during dobutamine (DOB) provocation provides a more accurate functional evaluation of myocardial bridging (MB) compared to adenosine. However; the cut-off value of CFVR during DOB for identification of MB associated with myocardial ischemia has not been fully clarified.

Purpose: This prospective study aimed to determine the cut-off value of TTDE-CFVR during DOB in patients with isolated-MB, as compared with stress-induced wall motion abnormalities (VMA) during exercise stress-echocardiography (SE) as reference.

Methods: Eighty-one symptomatic patients (55 males [68%], mean age 56 ± 10 years; range: 27-74 years) with the existence of isolated-MB on the left anterior descending artery (LAD) and systolic MB-compression ≥50% diameter stenosis (DS) were eligible to participate in the study. Each patient underwent treadmill exercise-SE, invasive coronary angiography, and TTDE-CFVR measurements in the distal segment of LAD during DOB infusion (DOB: 10-40 μg/kg/min). Using quantitative coronary angiography, both minimal luminal diameter (MLD) and percent DS at MB-site at end-systole and end-diastole were determined.

Results: Stress-induced myocardial ischemia with the occurrence of WMA was found in 23 patients (28%). CFVR during peak DOB was significantly lower in the SE-positive group compared with the SE-negative group (1.94 ± 0.16 vs. 2.78 ± 0.53; p < 0.001). ROC analyses identified the optimal CFVR cut-off value ≤ 2.1 obtained during high-dose dobutamine (>20 µg/kg/min) for the identification of MB associated with stress-induced WMA, with a sensitivity, specificity, positive and negative predictive value of 96%, 95%, 88%, and 98%, respectively (AUC 0.986; 95% CI: 0.967-1.000; p < 0.001). Multivariate logistic regression analysis revealed that MLD and percent DS, both at end-diastole, were the only independent predictors of ischemic CFVR values ≤2.1 (OR: 0.023; 95% CI: 0.001-0.534; p = 0.019; OR: 1.147; 95% CI: 1.042-1.263; p = 0.005; respectively).

Conclusions: Noninvasive CFVR during dobutamine provocation appears to be an additional and important noninvasive tool to determine the functional severity of isolated-MB. A transthoracic CFVR cut-off ≤2.1 measured at a high-dobutamine dose may be adequate for detecting myocardial ischemia in patients with isolated-MB.

Keywords: coronary flow velocity reserve; dobutamine; myocardial bridging; myocardial ischemia; stress-echocardiography; transthoracic Doppler echocardiography.

Figure 1

The example of coronary flow velocity reserve (CFVR) measurements obtained by transthoracic Doppler echocardiography (TTDE) in the left anterior descending (LAD) artery distal to the myocardial bridging (MB), before and during iv. infusion of high-dose dobutamine (40 µg/kg/min). (A) Coronary angiography revealed myocardial bridging (MB) with severe intramyocardial LAD segment compression (>90% diameter stenosis) during systole; (B) Coronary angiography showed a significant decompression of intramyocardial LAD segment during diastole in the same patient; (C) CFV measurement under basal conditions (CFV baseline), and (D) CFV measurement at peak dobutamine dose (CFV DOB 40). The heart rate under basal conditions was 76 bpm, while during peak dobutamine infusion was 140 bpm (delta-HR 64 bpm). Coronary flow velocity reserve equals 2.96 (CFV DOB 40/CFV baseline = 0.77/0.26 = 2.96). Red arrows showing characteristic diastolic CFV profile during peak dobutamine infusion in the LAD distal to the MB. This phenomenon is characterized by an abrupt acceleration followed by rapid deceleration of the CFV at early-diastole and flow plateau during mid-to-late diastole (“finger-tip” phenomenon). CFV = coronary flow velocity; DOB 40 = dobutamine at 40 µg/kg/min.

Figure 2

Peak coronary flow velocity (CFV) and coronary flow velocity reserve (CFVR) before and during peak dobutamine dose (DOBmax) in relation to stress-echocardiography (SE) results. (A). Scatterplot of peak CFV values under baseline conditions in relations to SE-results; (B). Scatterplot of peak CFV values during DOBmax in relations to SE-results; (C). Scatterplot of CFVR values in relation to SE-results, and (D). Bar graphs of mean CFVR values before and DOBmax in relation to SE-results. The dashed line in panel C represents the ischemic thresholds for CFVR at peak dobutamine dose (2.1). SE− = group of patients without stress-induced ischemia; SE+ = group of patients with stress-induced ischemia.

Figure 3

ROC analysis for assessing the accuracy of coronary flow velocity reserve (CFVR) obtained by transthoracic Doppler echocardiography (TTDE) for detection of stress-induced wall-motion abnormalities (VMA) in MB-patients. The overall diagnostic value of the test was 95% (77/81). ROC = receiver-operating characteristics curve; AUC = area under curve; SE = standard error; CI = confidence interval; Sn = sensitivity; Sp = specificity; PPV = positive predictive value; NPV = negative predictive value. DOBmax = peak dobutamine infusion.

Figure 4

The association between coronary flow velocity reserve (CFVR) obtained by transthoracic Doppler echocardiography (TTDE) and angiographic data (minimal luminal diameter and percent diameter stenosis) in MB-patients, with regards to stress-echocardiography (SE) results. Scatterplots between CFVR and both MLD at end-systole and end-diastole (panels (A,B)), and between CFVR and both percent DS at end-systole and end-diastole (panels (C,D)). Dashed lines represent the ischemic thresholds for CFVR at peak dobutamine dose (2.1), while solid lines represent a linear regression line. MB = myocardial bridging; MLD = minimal luminal diameter; DS = diameter stenosis; SE− = group of patients without stress-induced ischemia; SE+ = group of patients with stress-induced ischemia.