What is the management and treatment approach for a pediatric patient with Shone syndrome, a complex congenital heart defect characterized by a supravalvar mitral membrane, parachute mitral valve, subaortic stenosis, and coarctation of the aorta?

Shone Syndrome: Management and Treatment Approach

Pediatric patients with Shone syndrome require staged surgical interventions throughout life, with initial focus on relieving the most hemodynamically significant obstruction (typically coarctation of the aorta), followed by sequential management of left ventricular outflow and inflow lesions at specialized adult congenital heart disease (ACHD) centers. 1, 2

Definition and Anatomical Components

Shone syndrome consists of four classic left-sided obstructive lesions occurring at multiple levels 3, 1:

• Supravalvular mitral ring (mitral inflow obstruction) 3, 1
• Parachute mitral valve (single papillary muscle with restricted valve mobility) 3, 1
• Subaortic stenosis (left ventricular outflow tract obstruction) 3, 1
• Coarctation of the aorta (aortic arch obstruction) 3, 1

Important caveat: Most patients present with incomplete forms—not all four lesions are always present, but the defining feature is multilevel left-sided obstruction involving both inflow and outflow 2, 4. Associated lesions commonly include bicuspid aortic valve (68-71% of cases) and ventricular septal defects 5, 4.

Diagnostic Evaluation

Transthoracic echocardiography is the primary diagnostic modality and must systematically evaluate all four potential sites of obstruction 1, 6:

• Mitral valve anatomy: Assess for supravalvular ring, parachute configuration, number of papillary muscles, chordal fusion 3, 6
• Left ventricular outflow tract: Identify discrete membrane, fibromuscular ridge, or tunnel-type subaortic stenosis 7
• Aortic arch: Visualize coarctation site, measure gradients, assess collateral flow 3
• Left ventricular function: Evaluate chamber size, wall thickness, systolic and diastolic function 1, 7

Critical pitfall: Pressure gradients across individual lesions may be unreliable because proximal obstruction (mitral stenosis) reduces flow and underestimates distal gradients (subaortic stenosis, coarctation) 2, 6. Careful anatomical assessment is therefore more important than gradient measurements alone.

Additional imaging with cardiac MRI or CT may be needed for aortic arch anatomy and surgical planning 3, 8.

Surgical Management Strategy

Staged Approach to Intervention

Surgery must be performed at specialized ACHD centers by congenital heart surgeons experienced in complex left ventricular outflow tract procedures 3. The surgical approach is typically staged, addressing the most severe obstruction first 2:

First-stage intervention (typically in infancy):

• Coarctation repair is usually the initial procedure (performed in 61% as first intervention) because it is immediately life-threatening and technically straightforward 5, 4
• Indications: Resting gradient >30 mmHg or resting/exercise-induced hypertension 3
• Options include surgical repair or balloon/stent angioplasty 3

Subsequent interventions (childhood through adulthood):

• Subaortic stenosis resection when maximum gradient ≥50 mmHg with symptoms, or with any gradient if causing LV dysfunction or progressive aortic regurgitation 3, 7
• Mitral valve intervention for severe stenosis or regurgitation causing symptoms, pulmonary hypertension, or LV dysfunction 3, 1
• Mitral valve repair is preferred over replacement when anatomically feasible, though parachute mitral valves often require replacement 5, 2

Specific Surgical Indications

For subaortic stenosis 3, 7:

• Maximum gradient ≥50 mmHg with symptoms (Class I indication)
• Maximum gradient <50 mmHg with heart failure, ischemic symptoms, or LV systolic dysfunction (Class I indication)
• Asymptomatic with at least mild aortic regurgitation and maximum gradient ≥50 mmHg (Class IIb—may consider to prevent AR progression)

For coarctation 3:

• Resting gradient >30 mmHg
• Resting or exercise-induced hypertension
• Evidence of significant collateral circulation

For mitral valve lesions 3:

• Symptomatic severe mitral stenosis
• Pulmonary hypertension attributable to mitral obstruction
• Progressive LV dysfunction

Surgical Techniques and Complications

Subaortic stenosis: Circumferential resection of fibrous membrane via transaortic approach; extensive septal myectomy for tunnel-type obstruction; Konno procedure for severe long-segment obstruction 7

Major surgical risks 7, 5:

• Complete heart block (10-15% risk)
• Injury to aortic or mitral valves
• Iatrogenic VSD creation
• Recurrence of subaortic stenosis in ~20% over 10 years, particularly when initial resection performed in childhood

Operative mortality: No deaths at first operation in one series, but mortality increased to 24% after second operation, primarily due to severe mitral valve disease 5. This underscores the importance of careful timing and patient selection for reoperations.

Long-Term Outcomes and Follow-Up

All patients require lifelong follow-up at ACHD centers, typically every 6-12 months for complex cases 3, 1:

• Annual echocardiography to monitor for progression of residual lesions, recurrent obstruction, and ventricular function 1, 7
• Blood pressure monitoring (upper and lower extremity) for recurrent coarctation 3
• Arrhythmia surveillance with ECG and Holter monitoring as indicated 1
• Exercise testing to assess functional capacity and detect exercise-induced hypertension or ischemia 3, 7

Expected Morbidity

Over 70% of patients require reoperation during long-term follow-up 1, 5. Freedom from cardiovascular intervention is only 55% at 10 years, 18% at 20 years, and 8% at 30 years 4.

Common complications in adulthood 4:

• Cardiovascular hospitalizations in 48% (predominantly for arrhythmias or heart failure)
• Recurrent left-sided obstructions requiring intervention
• Progressive aortic regurgitation (60% of adult interventions for aortic valve/LVOT lesions)
• Mitral valve dysfunction (33% of adult interventions)
• Heart transplantation required in 7% by third decade

Endocarditis Prophylaxis

Prophylaxis is recommended for all patients with Shone syndrome (operated or unoperated) given the multiple valve abnormalities and prosthetic materials often present 3.

Pregnancy Considerations

Prepregnancy counseling is essential 3. Repair of significant lesions should be completed before pregnancy when possible 3. Transcatheter intervention may be indicated for unplanned pregnancy with worsening blood pressure or LV failure 3. Avoid estrogen-containing contraceptives 3.

Key Clinical Pitfalls

• Under-recognition: Only 39% of adults with Shone complex were previously diagnosed correctly 4. Maintain high index of suspicion when any left-sided obstructive lesion is identified.
• Masked inflow obstruction: Mitral stenosis may be underestimated because outflow obstruction reduces transmitral flow and gradients 2, 6
• Progressive nature: All components tend to worsen over time, requiring serial interventions 3, 1
• Mortality risk with mitral valve surgery: All operative deaths in one series were secondary to severe mitral valve disease 5, emphasizing the technical difficulty of mitral interventions in this population