Discussion:
The Schwarz classification is used for guiding therapeutic
considerations in patients with an identified myocardial bridge. This
classification is broken down into types A, B, and C. Type A patients
have an incidental finding of myocardial bridging on angiography without
objective signs of ischemia and do not require treatment. Type B
patients demonstrate ischemia during stress testing and should receive
treatment with beta-blockers or calcium-blockers. Type C patients have
significantly altered intracoronary hemodynamics, with objective signs
of ischemia, including symptoms. These patients should be managed with
medical therapy initially, and if that fails, operative intervention
should be pursued.6
Beta-blockers are useful in patients with myocardial bridging due to
their negative inotropic and chronotropic effects coupled with reduced
sympathetic drive, allowing for increased length of diastolic coronary
filling and reduced compression. Calcium-channel blockers can be used as
an alternative. Nitrates should be used with caution in these patients,
as they increase systolic compression within the bridge while
vasodilating the proximal segment. These altered hemodynamics may
exacerbate retrograde flow thereby reducing the threshold for myocardial
ischemia.
In patient’s refractory to medical therapy, stenting may be considered.
However, significant rates of in stent restenosis have been identified
small numbers of patients. Additional concerns surrounding stenting
include stent fracture, thrombosis, and increased risk of perforation
during deployment, all of which has limited the utility of this
treatment.4,5
A surgical gold standard has not been established for patients with an
isolated myocardial bridge and refractory symptoms due to the infrequent
finding of need for surgical intervention. Coronary artery bypass graft
(CABG) with use of the left internal mammary artery (LIMA) to the LAD
has been described. Concerns regarding the ability of the CABG graft to
remain open due to competitive flow in a patient with non-obstructive
CAD limits enthusiasm for this approach. Alternatively, the literature
suggests that for patients with isolated myocardial bridge, the surgeon
may carefully unroof the intra-myocardial component of the affected
vessel. A perceived benefit of unroofing is that it can be done in
isolation or in combination with CABG if necessary. The unroofing
technique has been shown to be safe and effective in improving symptoms
in a small number of patients. Interestingly, very little is in the
literature regarding the actual angiographic outcome of patients who
undergo surgical unroofing of a myocardial bridge as a result of
significant symptoms. This case report demonstrates complete unroofing
as confirmed by post-operative angiography in addition to significant
symptomatic improvement.