What are the causes of a hyperdynamic flow murmur?

Causes of Hyperdynamic Flow Murmur

Hyperdynamic flow murmurs are primarily caused by conditions that increase cardiac output or blood flow across normal heart valves, including pregnancy, thyrotoxicosis, anemia, arteriovenous fistulas, and cirrhosis with portal hypertension. 1

Characteristics of Hyperdynamic Flow Murmurs

Hyperdynamic flow murmurs typically present with the following features:

• Midsystolic (ejection) murmurs with crescendo-decrescendo configuration
• Start shortly after S1 and end before S2
• Usually heard best at the left sternal border or base of the heart
• Often have a "soft" or "musical" quality
• May vary in intensity with respiration and position changes 1

Major Causes of Hyperdynamic Flow Murmurs

1. Physiological States

• Pregnancy: Increased blood volume and cardiac output lead to hyperdynamic flow murmurs 1
• Childhood/Adolescence: Common innocent murmurs during periods of growth

2. Pathological Conditions

• Anemia: Iron-deficiency anemia causes systolic murmurs due to decreased blood viscosity and compensatory increase in cardiac output 2

  • Particularly common in pediatric populations
  • Murmurs typically resolve after iron therapy and correction of anemia

• Thyrotoxicosis: Characterized by increased metabolic rate and cardiac output 1

• Arteriovenous Fistulas: Create low-resistance circuits, increasing venous return and cardiac output 1

• Liver Cirrhosis with Portal Hypertension: 3, 4

  • Characterized by:
    • Increased cardiac output and heart rate
    • Decreased systemic vascular resistance
    • Low arterial blood pressure
  • Pathophysiology:
    • Portal hypertension leads to development of portosystemic collaterals
    • Increased shear stress in vascular endothelial cells upregulates eNOS, resulting in NO overproduction
    • Vasodilation of systemic and splanchnic circulations reduces systemic vascular resistance
    • Secondary activation of neurohumoral vasoconstrictive systems further aggravates hyperdynamic circulation

• Septic Shock: Can produce hyperdynamic circulation with increased cardiac output 5

• Patent Ductus Arteriosus: In premature infants, can present with hyperdynamic precordium and systolic or systolodiastolic murmurs 6

Differentiation from Pathological Murmurs

Hyperdynamic flow murmurs can be differentiated from pathological murmurs based on:

• Timing (midsystolic vs. holosystolic)
• Response to maneuvers
• Associated clinical findings 1

Response to Maneuvers

Maneuver	Effect on Hyperdynamic Flow Murmurs
Respiration	Right-sided murmurs increase with inspiration; left-sided murmurs are louder during expiration
Valsalva	Most murmurs decrease in intensity
Standing	Most murmurs diminish
Squatting	Most murmurs become louder

Clinical Approach

When evaluating a hyperdynamic flow murmur:

1. Focus on identifying potential underlying causes rather than treating the murmur itself 1
2. Consider echocardiography for definitive diagnosis when the exact cause cannot be determined with certainty
3. Treat the underlying condition:
   • Iron supplementation for anemia
   • Anti-thyroid medications for thyrotoxicosis
   • Management of cirrhosis and portal hypertension
   • Treatment of sepsis if present

Common Pitfalls and Caveats

• Misdiagnosis: Do not mistake a pathological murmur for a hyperdynamic flow murmur. Remember that diastolic murmurs are virtually always pathological and require further cardiac evaluation 1
• Incomplete Evaluation: Always investigate for underlying causes of hyperdynamic flow murmurs, as they may indicate conditions requiring treatment
• Over-investigation: In clear cases of benign flow murmurs (e.g., during pregnancy), extensive cardiac workup may be unnecessary
• Delayed Diagnosis: In pediatric patients with anemia, diagnosis of the underlying condition may be delayed if the murmur is attributed to cardiac pathology 2