Functional Assessment of Myocardial Bridging With Conventional and Diastolic Fractional Flow Reserve: Vasodilator Versus Inotropic Provocation.

Background Functional assessment of myocardial bridging (MB) remains clinically challenging because of the dynamic nature of the extravascular coronary compression with a certain degree of intraluminal coronary reduction. The aim of our study was to assess performance and diagnostic value of diastolic-fractional flow reserve (d-FFR) during dobutamine provocation versus conventional-FFR during adenosine provocation with exercise-induced myocardial ischemia as reference. Methods and Results This prospective study includes 60 symptomatic patients (45 men, mean age 57±9 years) with MB on the left anterior descending artery and systolic compression ≥50% diameter stenosis. Patients were evaluated by exercise stress-echocardiography test, and both conventional-FFR and d-FFR in the distal segment of left anterior descending artery during intravenous infusion of adenosine (140 µg/kg per minute) and dobutamine (10-50 µg/kg per minute), separately. Exercise-stress-echocardiography test was positive for myocardial ischemia in 19/60 patients (32%). Conventional-FFR during adenosine and peak dobutamine had similar values (0.84±0.04 versus 0.84±0.06, P=0.852), but d-FFR during peak dobutamine was significantly lower than d-FFR during adenosine (0.76±0.08 versus 0.79±0.08, P=0.018). Diastolic-FFR during peak dobutamine was significantly lower in the exercise-stress-echocardiography test -positive group compared with the exercise- stress-echocardiography test -negative group (0.70±0.07 versus 0.79±0.06, P<0.001), but not during adenosine (0.79±0.07 versus 0.78±0.09, P=0.613). Among physiological indices, d-FFR during peak dobutamine was the only independent predictor of functionally significant MB (odds ratio, 0.870; 95% CI, 0.767-0.986, P=0.03). Receiver-operating characteristics curve analysis identifies the optimal d-FFR during peak dobutamine cut-off ≤0.76 (area under curve, 0.927; 95% CI, 0.833-1.000; P<0.001) with a sensitivity, specificity, and positive and negative predictive value of 95%, 95%, 90%, and 98%, respectively, for identifying MB associated with stress-induced ischemia. Conclusions Diastolic-FFR, but not conventional-FFR, during inotropic stimulation with high-dose dobutamine, in comparison to vasodilatation with adenosine, provides more reliable functional significance of MB in relation to stress-induced myocardial ischemia.

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

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.