Case #24 - Should patients with myocardial bridging be considered for surgical revascularization?

Maria Margarita Gonzales, Luiz Mastrocolla, William Chalela, Cláudio Meneghetti and João Vitola

50 yo man presents with an 8 y history of exercise induced chest tightness, sometimes occuring at rest. At age 42 yo, underwent coronary angiography for the same symptoms, revealing myocardial bridge involving the Mid LAD and no atherosclerotic lesions. Was managed initially with beta blockers with no relief of symptoms. At age 49 yo his symptoms increased in frequency and intensity. Myocardial Perfusion Imaging using rest/exercise one day 99Tc-Sestamibi (figure 1) demonstrated severe and extensive ischemia in the anteroseptal, septal and apical regions, partially fixed at rest.
His rest ECG is shown on figure 2a and 2b. His exercise and early recovery ECGs, performed during the same stud,y showed ST elevation up to 10 mm (figures 2c, 2d, 2e) while the patient complained of limiting chest pain. New coronary angiography performed (figure 3 and 4) revealing again myocardial bridge in the LAD and no atherosclerotic disease. He was treated now with beta blocker (atenolol 50 mg/day), calcium channel blocker (amlodipine 5 mg/day) and statins (sinvastatin 20 mg/day). Symptoms persisted and repeated MPI unchanged. . Surgical revascularization with a left internal mammary to the LAD was performed. Symptoms resolved. Repeat MPI performed 2 months later was normal (figure 5), disappearing ST changes on the ECG during exercise (figure 6).

Set 1/3

Question 1 - It is true to say regarding patients with myocardial bridge:
a. Flow occurs in diastole and bridge compromises flow during systole, therefore it never causes ischemia.
b. Myocardial bridge is often a cause of ischemia requiring stenting
c. Myocardial bridge rarely causes severe ischemia, but when it occurs it may require myocardial revascularizationd. None of the above

The answer is:
c. Myocardial bridge rarely causes severe ischemia, but when it occurs it may require myocardial revascularization

Discussion and literature review

Myocardial bridging is an anatomical variation in which a coronary artery takes a course within a segment of the myocardium that compresses the lumen during ventricular systole despite a normal appearance during diastole. Interestingly, myocardial bridging is present in up to 78% of autopsy cases [1], [2] and in 0.5% to 16% of patients examined by coronary angiography [3], [4]. Myocardial bridging most frequently occurs on the LAD. Although most patients are asymptomatic, myocardial bridges may cause ischemia and related complications, including myocardial stunning, infarction, arrhythmia, AV block, transient LV dysfunction and sudden death [5]. Although, it was believed that the affected coronary is compressed only in systole, IVUS has demonstrated that the vessel narrowing continues even in early diastole, which might account for myocardial ischemia distal to the bridge [6].
Nitroglycerine, administered during angiography increases the sensitivity for the diagnosis of myocardial bridges compromising blood flow [7]. The proposed mechanisms are an increase in vessel wall compliance and decrease in aortic pressure.
Few studies have reported evaluation of myocardial bridges with MPI. In two small retrospective studies [8], [9] no abnormalities were found with stress 201Tl imaging. However, when myocardial bridges cause ischemia, stress-induced perfusion defects are present on MPI and resolve after the affected artery is bypassed [10].
References
[1] Bezzera AJ, Prates JC, Didio LJ. Incidence and clinical significance of bridges of myocardium over the coronary arteries and their branches. Surg Radiol Anat 1987;9:273-280.

[2] Ferreira AG Jr, Trotter SE, Konig B Jr, et al. Myocardial bridges : morphological and functional aspects. Br Heart J 1991;66:364-367.
[3] Noble J, Bourassa MG, Petitclerc R, et al. Myocardial bridging and milking effect on the left descending coronary artery : normal variant or obstruction. Am J Cardiol 1976;37:993-999.

[4] Kramer JR, Kitazume H, Proudfit WL, et al. Clinical significance of isolated coronary bridges: benign and frequent condition involving the left descending coronary artery. Am Heart J 1982;103:283-288.

[5] Tortoledo F Stented bridge: another golden gate for the interventional cardiologist. Cathet and cardiovascul intervent 2002, 56:64-65
[6] Ge J, Erber R, Ruprecht HJ, et al. Comparison of intravascular ultrasound and angiography in the assessment of myocardial bridging. Circulation 1994;89:1725-1732.
[7] Erbel R, Treese N, Alken G, et al. Provocation of myocardial bridging in patients with normal coronary arteries by nitroglycerin and orciprenalin. Eur Heart J 1985; 6 (suppl):71.
[8] Ahmad M, Merry SL, Haibach H. Evidence of impaired myocardial perfusion and abnormal left ventricular function during exercise in patients with isolated systolic narrowings of the LAD artery. Am J Cardiol 1981;48:832-836.
[9] Greenspan M, Iskadrian AS, Catherwood E, et al. Myocardial bridging of the LAD artery: Evaluation using exercise thallium-201 myocardial scintigraphy. Cathet Cardiovasc Diagn 1980;6:173-180.

[10] Berry JF, von Mering GO, Schmalfuss C, et al. Systolic compression of the left descending coronary artery: a case series, review of the literature, and therapeutic options including stenting. Catheter Cardiovasc Interv 2002;56:58-63.

ANSWERS GIVEN FOR CASE # 24

1 - c - c. Myocardial bridge rarely causes severe ischemia, but when it occurs it may require myocardial revascularization
2 - Myocardial bridge rarely causes mild ischemiawhich needs PTCA.

1 - c - c. Myocardial bridge rarely causes severe ischemia, but when it occurs it may require myocardial revascularization
2 - C. It is rare myocardial bridge to cause ischemia