What are the signs and symptoms of Hypertrophic Cardiomyopathy (HCM) in pediatric patients?

Signs and Symptoms of Hypertrophic Cardiomyopathy in Pediatric Patients

The presentation of hypertrophic cardiomyopathy (HCM) in pediatric patients is heterogeneous, with the most common clinical manifestations being heart murmurs and palpitations, while some children may present with aborted sudden cardiac death as their first symptom. 1

Clinical Presentation

Common Symptoms

• Heart murmur - Often the first sign detected during routine examination
• Palpitations - Frequently reported by older children
• Chest pain - Particularly with exertion
• Dyspnea - Especially during exercise
• Syncope - Particularly concerning when exercise-related or unexplained
• Fatigue - May be overlooked as non-specific

Physical Examination Findings

• S4 heart sound - Common in obstructive HCM 2
• Systolic ejection murmur - Typically heard best at the left sternal border and apex
• Dynamic murmur - Changes with Valsalva maneuver or standing (increases with decreased preload)
• Abnormal blood pressure response to exercise - May indicate higher risk

Age-Related Presentation Patterns

Infants (<1 year)

• Often present with:
  • Congestive heart failure
  • Feeding difficulties
  • Failure to thrive
  • Higher likelihood of metabolic or syndromic causes 3, 4
  • Generally worse prognosis than older children 4

Children and Adolescents

• May be asymptomatic and detected through:
  • Family screening
  • Incidental finding of ECG abnormalities
  • Evaluation for heart murmur
• Symptomatic presentations include:
  • Exercise intolerance
  • Chest pain with exertion
  • Palpitations
  • Syncope (particularly concerning)

Diagnostic Findings

ECG Abnormalities

• Left ventricular hypertrophy
• ST-segment and T-wave abnormalities
• Pathological Q waves
• Conduction abnormalities
• Ventricular pre-excitation (particularly in metabolic forms)

Echocardiographic Features

• Left ventricular wall thickness >2 standard deviations from predicted mean (z-score >2) 5
• Various patterns of hypertrophy:
  • Asymmetric septal hypertrophy (most common in non-syndromic HCM)
  • Concentric hypertrophy (more common in syndromic forms) 1
• Left ventricular outflow tract obstruction (present in approximately 25% of pediatric cases) 1
• Diastolic dysfunction
• Mitral valve abnormalities (elongation, systolic anterior motion)

Arrhythmias

• Non-sustained ventricular tachycardia (≥3 consecutive ventricular beats at ≥120 BPM lasting <30 seconds)
• For pediatric patients, a VT rate exceeding baseline sinus rate by >20% is considered significant 5

Risk Factors for Sudden Cardiac Death

Particularly important to identify in pediatric patients:

• Maximum left ventricular wall thickness ≥30 mm or z-score ≥6 5
• Unexplained syncope (especially with exertion)
• Non-sustained ventricular tachycardia on monitoring
• Family history of HCM-related sudden death
• Abnormal blood pressure response to exercise
• Extensive late gadolinium enhancement on cardiac MRI (≥15% of LV mass) 5
• Genotype-positive status (harboring pathogenic/likely pathogenic variants) 5

Special Considerations in Pediatric HCM

• Etiology is more diverse than in adults:

  • Sarcomeric mutations (most common in older children)
  • Metabolic disorders (glycogen storage diseases, lysosomal storage diseases)
  • RASopathies and other malformation syndromes
  • Neuromuscular disorders
  • Mitochondrial diseases 3

• Presentation varies by underlying cause:

  • Metabolic/syndromic HCM: typically presents in infancy/early childhood
  • Neuromuscular disorders: more commonly diagnosed in adolescence 6

Monitoring Recommendations

Regular assessment should include:

• Clinical examination with 12-lead ECG and echocardiography every 1-2 years
• Ambulatory ECG monitoring annually or every 6 months if left atrial dilation ≥45 mm
• Exercise stress testing (in children >7-8 years who can cooperate) to assess:
  • Exercise capacity
  • Provocable LVOT obstruction
  • Blood pressure response
  • Exercise-induced arrhythmias 5

Important Pitfalls to Avoid

1. Missing the diagnosis in children with focal hypertrophy - Up to 5% of pediatric HCM cases may be missed by echocardiography alone but detected by CMR 5

2. Overlooking non-sarcomeric causes - Unlike adults, children have a higher prevalence (up to 35%) of non-sarcomeric causes that may require specific treatments 3

3. Inadequate family screening - As most cases are familial, evaluation of first-degree relatives should be routine 6

4. Underestimating risk in asymptomatic children - HCM can develop during childhood despite previously normal evaluations, necessitating serial monitoring 5