What is Shone syndrome in pediatric patients?

What is Shone Syndrome?

Shone syndrome (also called Shone complex or Shone anomaly) is a rare congenital heart disease characterized by multiple levels of left-sided heart obstructions, classically consisting of four specific lesions: supravalvular mitral ring (or supramitral membrane), parachute mitral valve, subaortic stenosis, and coarctation of the aorta. 1

Core Anatomical Components

The syndrome involves serial obstructive lesions affecting left ventricular inflow and outflow:

• Supravalvular mitral ring: A fibrous membrane above the mitral valve that restricts left atrial outflow 1, 2
• Parachute mitral valve: Abnormal mitral valve where chordae attach to a single or dominant papillary muscle, creating functional stenosis 1, 3
• Subaortic stenosis: Fibrous or fibromuscular obstruction below the aortic valve in the left ventricular outflow tract 1
• Coarctation of the aorta: Narrowing of the aortic arch, typically in the postductal region 1, 2

Clinical Presentation Patterns

Most patients present in infancy or early childhood with symptoms of heart failure, but late presentations into adulthood are well-documented when lesions are incomplete or less severe. 3, 4

Key presenting features include:

• Congestive heart failure in infancy with feeding difficulties and failure to thrive 3
• Treatment-resistant hypertension in adolescents and adults, often the first clue to diagnosis 2, 4
• Progressive dyspnea and exercise intolerance as obstruction worsens over time 5
• Cardiac murmurs detected on routine examination 6

Incomplete Forms and Associated Lesions

The complete four-lesion syndrome is uncommon; most patients present with incomplete variants having 2-3 of the classic lesions. 3, 4

Frequently associated abnormalities include:

• Bicuspid aortic valve present in approximately 63% of cases 1, 3
• Ventricular septal defect occurring in up to 67% of patients 3
• Left ventricular hypertrophy secondary to chronic outflow obstruction 1
• Mitral regurgitation in addition to stenosis from valve abnormalities 5

Pathophysiology and Natural History

The syndrome creates progressive left-sided heart obstruction at multiple levels:

• Elevated left atrial pressure from mitral inflow obstruction leads to pulmonary venous hypertension and pulmonary hypertension 1
• Left ventricular pressure overload from outflow obstruction causes hypertrophy and eventual diastolic dysfunction 1
• Systemic hypertension results from coarctation, often severe and difficult to control medically 2, 4

Pulmonary hypertension in Shone syndrome historically carried poor prognosis, but recent series show 5- and 10-year survival rates of 88% and 83% respectively in mid-term survivors, suggesting elevated pulmonary vascular resistance is not a major issue after successful intervention. 1

Diagnostic Approach

Transthoracic echocardiography is the primary diagnostic modality and should assess:

• Mitral valve anatomy including papillary muscle configuration and presence of supravalvular ring 1, 7
• Left ventricular outflow tract for subaortic membrane or stenosis 7
• Aortic arch anatomy and gradient across coarctation site 1
• Left ventricular size, function, and degree of hypertrophy 7

Cardiac MRI or CT angiography is essential to fully delineate aortic arch anatomy, collateral vessels, and associated vascular anomalies 1, 2, 4

Cardiac catheterization is reserved for cases where noninvasive imaging is inconclusive or when hemodynamic assessment is needed before intervention 1

Management Principles

Surgical intervention is typically required at multiple stages throughout life, with over 70% of patients requiring reoperation during follow-up. 5

Indications for intervention include:

• Symptomatic patients with any significant gradient across obstructive lesions 1, 7
• Resting gradient >30 mmHg across coarctation or subaortic stenosis 1, 7
• Progressive left ventricular dysfunction or severe hypertrophy attributable to obstruction 7
• Severe mitral stenosis with symptoms or pulmonary hypertension 1

Operative mortality is low (0%) at first operation but increases to 24% after second operation, with deaths primarily related to severe mitral valve disease. 3

Long-Term Outcomes and Follow-Up

All patients require lifelong cardiology follow-up by adult congenital heart disease specialists regardless of surgical status 7

Key surveillance includes:

• Annual echocardiography to detect recurrent obstruction at any level, which occurs in approximately 65% of patients 5
• Blood pressure monitoring at rest and with exercise, as residual hypertension is common despite adequate coarctation repair 1
• Assessment for arrhythmias and heart block, particularly after subaortic resection 7

Recurrence of obstruction occurs in approximately 20% over 10 years, particularly when initial resection is performed in childhood. 7

Despite high reoperation burden, ventricular function is preserved in the majority of patients, with >60% requiring no cardiac medications and 93.5% freedom from death or transplant at long-term follow-up. 5

Important Clinical Pitfalls

• Misdiagnosis as essential hypertension in adults with incomplete forms lacking obvious murmurs 2, 4
• Failure to screen for all four lesions when one component is identified 1, 6
• Underestimation of mitral valve disease severity, which drives operative mortality 3
• Inadequate long-term follow-up missing recurrent obstruction that develops years after initial repair 5