What is the physiologic consequence of the suspected diagnosis in a patient with a history of complete atrioventricular canal/septal defect (AV canal/Septal defect) repair, now presenting with a harsh systolic murmur along the left sternal border?

Right Ventricular Hypertension in a Child with Repaired AV Canal Defect

Right ventricular hypertension is the most likely physiologic consequence of the suspected diagnosis in this 12-year-old child with Down syndrome who had repair of complete atrioventricular canal defect and now presents with a harsh systolic murmur along the left sternal border. 1

Clinical Reasoning

The clinical scenario presents several key findings that point to right ventricular hypertension:

• History of complete AV canal/septal defect repair in infancy 1
• Previously normal echocardiogram with no residual lesions 5 years ago 1
• New harsh systolic murmur along the left sternal border 1
• Patient with Down syndrome (high association with AV canal defects) 1

Suspected Diagnosis and Pathophysiology

• The harsh systolic murmur along the left sternal border strongly suggests subaortic obstruction or left ventricular outflow tract obstruction (LVOTO) 1
• Patients with AV canal defects are morphologically predisposed to subaortic obstruction 2
• Subaortic obstruction can occur naturally in association with abnormal AV valve attachments or may be a consequence of surgery 1

Physiologic Consequences

Why Right Ventricular Hypertension is Most Likely

• In repaired AV canal defects, subaortic obstruction can develop over time, leading to increased resistance to left ventricular outflow 1
• This obstruction creates increased pressure in the left ventricle that is transmitted backward to the pulmonary circulation 1
• The increased pulmonary pressure causes the right ventricle to generate higher pressures to maintain forward flow, resulting in right ventricular hypertension 1
• The harsh systolic murmur along the left sternal border is characteristic of subaortic obstruction rather than mitral regurgitation (which would be more apical) 1

Why Other Options Are Less Likely

• Left atrial dilatation: While this can occur with mitral regurgitation after AV canal repair, the murmur location (left sternal border rather than apex) makes this less likely 1
• Left ventricular dilatation: This would be expected with significant aortic regurgitation or mitral regurgitation, but the murmur characteristics don't support these diagnoses 1
• Left ventricular hypertension: While subaortic stenosis does cause left ventricular hypertension, the question asks for the physiologic consequence of the suspected diagnosis (subaortic stenosis), not the direct effect on the left ventricle 1

Clinical Implications

• Subaortic obstruction in repaired AV canal defects can be progressive 1
• Once the peak Doppler gradient across the subaortic obstruction exceeds 30 mm Hg, it is likely to be progressive 1
• Gradients of 50 mm Hg or more increase the risk for moderate or severe aortic regurgitation 1
• Right ventricular hypertension can eventually lead to right ventricular hypertrophy and potential right heart failure if left untreated 1

Diagnostic Approach

• Echocardiography is the primary imaging modality to confirm the diagnosis 1
• Assessment should include:
  • Subaortic anatomy and gradient measurement 1
  • Left and right ventricular size and function 1
  • Evaluation of the AV valves for residual regurgitation or stenosis 1
  • Measurement of pulmonary artery pressures via tricuspid regurgitation velocity 1

Management Considerations

• Surgical intervention is indicated for symptomatic patients with mean Doppler gradient ≥50 mmHg 1
• Asymptomatic patients should be considered for surgery with:
  • Evidence of left ventricular dysfunction 1
  • Marked left ventricular hypertrophy 1
  • Abnormal blood pressure response on exercise testing 1
• Regular follow-up is essential to monitor progression of obstruction, ventricular function, and development of symptoms 1