Fractional flow reserve guided stenting of a myocardial bridge

To the Editor,

Myocardial bridging (MB) is a common congenital coronary anomaly. The treatment is debated in symptomatic forms. Percutaneous coronary intervention (PCI) could be a possible solution; however, in these cases the major adverse cardiac event rate is high (1).

A 52-year-old man presented with chest pain provoked by emotional stress. Laboratory tests and transthoracal echocardiography were normal. Treadmill test was indicated according to Bruce protocol that demonstrated silent ischemia at 125 Watts workload. Beta blocker was uptitrated (bisoprolol 2.5–10 mg daily).

Despite the oral medical therapy, the patient remained symptomatic. Coronary angiography showed MB in the mid left anterior descendent artery (LAD) with lumen compression (minimal lumen diameter: 0.26 mm, reference vessel diameter: 2.6 mm, and lesion length: 25.4 mm) but without any atherosclerotic lesions. A fractional flow reserve (FFR) measurement proved significant myocardial ischemia (Pd/Pa=0.69). After FFR measurement, the lesion was stented with a 3.0×38 mm paclitaxel eluting stent (Promus Premier, Boston Sci, US) at 14 atm. Control angiography revealed good angiographic result, and final FFR (Pd/Pa=0.96) verified improved hemodynamics. After the procedure, the patient had no complaints and at the 18-months control multislice CT angiography excluded the restenosis.

Drug eluting stent implantation with a longer stent than the visible bridge was safe and effective in this patient during the follow-up period. PCI seems a reasonable treatment in symptomatic MBs; however, patient selection and procedural aspects remain unclear in the absence of comparative clinical trials.

Angina pectoris-like symptoms could be caused by several reasons beyond atherosclerotic coronary disease. To hold the MB responsible for the symptoms, its pathological role must be proved. In a recent publication by Hakkem (2), the FFR measurement was done with dobutamine provocation in the symptomatic bridge. The most severe hemodynamic alteration was found in diastolic FFR; therefore, the authors are suggested to use this value in the MB patients.

Dynamic compression caused by the MB is unique and this kind of coronary lesion differs from other atherosclerotic lesions. The high incidence of procedural failures like stent thrombosis (3), coronary perforation (4), and early restenosis (5) suggest that the stents’ mechanical properties, diameter, and length are the determining factors for a successful intervention. High inflation pressures may be required for optimal stent implantation despite the higher risk of coronary perforation.

Basically the stent recoil means the percentage by which the diameter of a stent decreases from its expanded diameter (when the balloon is inflated at nominal pressure) to its relaxed diameter (when the balloon is retrieved from the stent). We have to calculate with a dynamic stress component as well, which is caused by the myocardium mass above the lesion. The given device’s resistance to this permanent, cyclic force can make a difference between various stent types. On the contrary e.g., the pushability seems to be a less important feature when preparing for stenting a MB on the mid segment of the LAD.