In a patient with myocardial bridging and severe mitral regurgitation, what is the optimal management strategy?

Management of Myocardial Bridging with Severe Mitral Regurgitation

The optimal management strategy prioritizes addressing the severe mitral regurgitation first through guideline-directed medical therapy (GDMT) and surgical intervention when indicated, while managing myocardial bridging conservatively with beta-blockers unless it causes refractory ischemic symptoms. 1, 2

Initial Assessment and Classification

Determine whether the mitral regurgitation is primary or secondary through comprehensive echocardiography, as this fundamentally dictates the entire treatment pathway. 2, 3

• Perform transthoracic echocardiography to quantify MR severity using effective regurgitant orifice area (EROA), regurgitant volume, left ventricular dimensions (end-systolic dimension and ejection fraction), and left atrial size 1, 2
• Assess for pulmonary hypertension (pulmonary artery systolic pressure >50 mm Hg), which influences surgical timing 1
• Evaluate for new-onset atrial fibrillation, as this is a reasonable indication for surgery even in asymptomatic patients with severe primary MR 1, 3
• Consider exercise echocardiography if symptoms are present but resting echocardiography shows only moderate MR, as severity can be dynamic 2

For the myocardial bridging component, use intravascular ultrasound (IVUS) or coronary angiography for definitive diagnosis if non-invasive imaging suggests significant compression, though multislice computed tomography offers high sensitivity and specificity non-invasively 4

Medical Management Algorithm

For All Patients (Regardless of MR Type)

Initiate beta-blockers immediately as they serve dual purposes: reducing MR severity and treating myocardial bridging by decreasing systolic compression of the tunneled coronary artery. 2, 5, 6

• Start diuretics as first-line therapy for fluid overload manifestations 2
• Add ACE inhibitors or ARBs, particularly when heart failure symptoms are present 2, 6
• Include aldosterone antagonists if heart failure symptoms persist despite initial therapy 2
• Avoid nitrates entirely, as they worsen symptoms in myocardial bridging by increasing heart rate and contractility, thereby worsening systolic compression 5

For Secondary MR Specifically

Optimize GDMT completely and reassess MR severity before considering any intervention, as secondary MR is highly dynamic and may improve substantially with medical therapy alone. 1, 2, 7

• The severity of secondary MR changes with loading conditions, blood pressure, volume status, ischemia, and heart rate 1
• Consider cardiac resynchronization therapy (CRT) in appropriate candidates (LVEF ≤35%, QRS ≥150 ms), as it may reduce MR severity through increased closing force and resynchronization of papillary muscles 2, 7
• If severe secondary MR persists despite optimal GDMT, transcatheter edge-to-edge repair (TEER) is beneficial in patients with LVEF 20-50%, LV end-systolic dimension ≤70 mm, and pulmonary artery systolic pressure ≤70 mm Hg 1

For Primary MR

Beta-blockers and ACE inhibitors/ARBs provide beneficial effects by lessening MR, preventing deterioration of left ventricular function, and improving survival in asymptomatic patients with moderate to severe primary MR 6

Surgical Intervention Criteria

For Primary Severe MR

Surgery is indicated in the following scenarios, with mitral valve repair strongly preferred over replacement: 1, 2, 8

• Symptomatic patients with severe primary MR (Class I indication) 1, 2
• Asymptomatic patients with LVEF <60% or LV end-systolic dimension >40 mm 1
• Asymptomatic patients with recent-onset atrial fibrillation or pulmonary hypertension (PASP >50 mm Hg) 1, 3
• Asymptomatic patients when likelihood of successful repair exceeds 95% and surgical mortality risk is <1% at an experienced center 1

The rationale for early intervention in asymptomatic patients is that LVEF <60% or LV end-systolic dimension >40 mm already indicate incipient myocardial dysfunction, and outcomes are optimized with intervention before irreversible left ventricular damage occurs 1, 9

For Secondary Severe MR

Surgery is indicated when: 1, 7

• Patient is undergoing coronary artery bypass grafting (CABG) and has LVEF >30% (Class I indication) 7
• Severe secondary MR persists despite optimal GDMT and patient is not a candidate for TEER 1
• LVEF ≤30% may be considered for surgery with CABG, though evidence is weaker (Class IIb) 7

Mitral valve repair with undersized rigid annuloplasty ring is preferred over replacement, as replacement is associated with higher in-hospital mortality (12.5% vs 2.3%) and worse long-term survival (73% vs 92% at 2.5 years) 7, 8

Management of Myocardial Bridging

Beta-blockers are the cornerstone of medical treatment for myocardial bridging and should already be initiated as part of MR management. 5, 6

• Continue beta-blocker therapy indefinitely, as it reduces systolic compression of the tunneled artery 5
• Strictly avoid nitrates, as they paradoxically worsen symptoms by increasing heart rate and contractility 5
• Surgical unroofing or coronary stenting should only be considered if the patient has refractory angina despite optimal beta-blocker therapy and documented significant ischemia 4, 5
• Most patients with myocardial bridging remain asymptomatic or respond well to beta-blockers alone 5

The segment beneath the bridge is protected from atherosclerosis, but the proximal segment is more susceptible to atherosclerotic lesions due to hemodynamic disturbances 5

Follow-Up Protocol

Patients with severe MR require clinical evaluation every 6 months with annual echocardiography to monitor for progression of left ventricular dysfunction or symptoms. 2

• Patients with moderate MR should have clinical evaluation every 6-12 months with annual echocardiography 2
• Serial imaging is essential to detect progressive increase in LV size (end-systolic dimension approaching 40 mm) or decrease in LVEF (approaching 60%), which are indications for surgery even in asymptomatic patients 1
• Reassess MR severity after any change in medical therapy, as secondary MR is particularly dynamic 1, 2

Critical Pitfalls to Avoid

Do not delay surgical intervention in primary MR until symptoms become severe or left ventricular dysfunction is advanced, as this leads to irreversible myocardial damage and worse outcomes. 1, 2, 3

• Failing to recognize that LVEF <60% already indicates myocardial dysfunction in primary MR (normal LVEF should be supranormal due to low afterload) 1
• Using nitrates in patients with myocardial bridging, which worsens symptoms 5
• Failing to optimize GDMT completely before intervening on secondary MR, as severity may improve substantially with medical therapy alone 1, 2
• Choosing mitral valve replacement over repair when repair is feasible, as replacement carries significantly higher mortality 8, 9
• Not recognizing the dynamic nature of secondary MR and making intervention decisions based on a single echocardiogram without reassessment after medical optimization 1, 3