Shone Syndrome

Introduction

Shone Syndrome is a rare congenital heart disease characterized by the presence of multiple obstructive anomalies of the left ventricular outflow tract. Originally described as a combination of four defects, it is now considered a variable condition that can include different anomalies obstructing blood flow from the left ventricle to the aorta. This pathology can manifest in a **complete form**, when all four classic defects are present, or **incomplete form**, when only some of these anomalies are present.
Shone Syndrome is rare, accounting for less than 1% of congenital heart diseases. It can be diagnosed at birth in severe cases or later in childhood or adulthood in cases with mild or progressive obstructions.

Anatomy and Pathophysiology

The main anomalies in Shone Syndrome include:

• Supravalvular mitral ring: a fibrous structure that reduces the opening of the mitral valve, causing stenosis.
• Parachute mitral valve: an anomaly of the papillary muscles, which converge at a single point, limiting mitral valve mobility.
• Subaortic stenosis: narrowing of the left ventricular outflow tract.
• Aortic coarctation: narrowing of the proximal aorta, creating an obstacle to systemic blood flow.

These anomalies lead to **left ventricular overload**, which can cause **ventricular hypertrophy, heart failure, and progressive valvular dysfunction**. In severe cases, systemic blood flow obstruction can result in **organ hypoperfusion and early heart failure**.

Signs and Symptoms

The symptoms depend on the severity of the obstructions:

• In newborns with severe forms: **heart failure, cyanosis, and hypovolemic shock**.
• In older children: **exercise-induced dyspnea, growth retardation, and fatigue**.
• Presence of a **heart murmur**, often detectable within the first months of life.

Diagnosis

Echocardiography is the primary diagnostic test, capable of identifying valvular and vascular anomalies. Other useful tests include:

• Electrocardiogram (ECG): signs of left ventricular hypertrophy.
• Cardiac MRI: useful for a detailed evaluation of the aortic arch and the severity of coarctation.
• Cardiac catheterization: performed in complex cases to define anatomy and pressure gradients.

Treatment

Treatment is **personalized** based on the anomalies present and may include:

• Mitral valvuloplasty: to improve blood flow through the mitral valve.
• Resection of subaortic stenosis: to reduce the obstruction in the left ventricular outflow tract.
• Aortic coarctation repair: through stent angioplasty or surgical correction.
• Long-term monitoring: to assess obstruction progression and the need for additional interventions.

Prognosis

The prognosis depends on the severity of the obstructions and the effectiveness of the treatment. With proper management, survival is good, but many patients require multiple interventions throughout their lives. The main complications include **progressive valvular dysfunction, left ventricular hypertrophy, and systemic hypertension**.

References
1. Shone J.D. et al. The Developmental Complex of "Parachute Mitral Valve," Supravalvular Ring of Left Atrium, Subaortic Stenosis, and Coarctation of Aorta. Am J Cardiol. 1963;11:714-725.
2. Brown J.W. et al. Surgical Treatment of Shone's Anomaly: A 27-Year Experience. Ann Thorac Surg. 2005;80(2):769-774.
3. García-Montes J.A. et al. Shone's Complex: Experience in Diagnosis and Treatment. Rev Esp Cardiol. 2006;59(3):284-287.
4. Chen Q. et al. Long-Term Outcomes in Patients with Shone's Syndrome. J Thorac Cardiovasc Surg. 2020;160(4):1125-1135.
5. Van Mierop L.H. et al. Pathophysiology and Surgical Management of Shone's Complex. Pediatr Cardiol. 2019;40(5):805-815.
6. Bove E.L. et al. Shone's Syndrome: Surgical Challenges and Innovations. J Am Coll Cardiol. 2018;72(6):245-259.