Hemodynamic Effect of Myocardial Bridging

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yocardial bridging with systolic milking is a frequent finding during coronary angiography. 1 Classically, it is considered a benign congenital anomaly because myocardial perfusion occurs in diastole.Milking is limited to systole and should therefore not impair myocardial perfusion.However, this physiology-based evidence is contradicted by numerous cases of coronary thrombus formation and myocardial infarc-tion, in individuals with pathological findings none other than a myocardial bridging.Pressure-derived fractional flow reserve (FFR) measurement during maximum myocardial hyperemia is an established technique to assess the hemodynamic significance of moderate stenoses in atherosclerotic coronary artery disease. 2 Few data are available concerning its use in myocardial Figure.Left, Midsystolic image of the left coronary artery in anteroposterior view, with 20° of cranial inclination.Just distal to a septal branch, myocardial bridging and "milking" is observed in the left anterior descending artery (encircled in white).Right, End-diastolic view in the same incidence.The segment just distal to the septal branch is smooth and free of atherosclerotic disease.The lower insert of the figure depicts the pressure tracings and their respective values in mm Hg at the level of the aorta (in purple) and in the left anterior descending artery distal to the segment with systolic compression (in green).The ratio of distal pressure to aortic pressure (FFR) is depicted in yellow.Values are mentioned for mean and diastolic pressures (mFFR and dFFR, respectively).The distal measurements were obtained using a 0.014-inch pressure wire, after induction of maximum hyperemia with an intracoronary bolus of adenosine.Left to right: Measurements in baseline condition, during intravenous infusion of dobutamine at 20 g ⅐ kg Ϫ1 ⅐ min Ϫ1 , during intravenous infusion of dobutamine at 30 g ⅐ kg Ϫ1 ⅐ min Ϫ1 and administration of 1 mg of atropine, and finally after intravenous administration of 10 mg of metoprolol.The respective heart rates (bpm) are mentioned in blue.At a dose of 20 g ⅐ kg Ϫ1 ⅐ min Ϫ1 of dobutamine, systolic pressure overshoots distally to the dynamic lesion with a diastolic pressure gradient Ͻ0.75.At the highest dose of dobutamine and after administration of atropine, an important diastolic pressure gradient is seen (55/77ϭ0.71),indicating impaired myocardial perfusion by the myocardial bridge.This gradient disappeared almost instantly after the intravenous administration of metoprolol, despite a higher heart rate than that during the intravenous infusion of dobutamine at a dose of 20 g ⅐ kg Ϫ1 ⅐ min Ϫ1 .

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