What is high output heart failure?

High Output Heart Failure: Definition and Pathophysiology

High output heart failure is a clinical syndrome characterized by symptoms and signs of heart failure occurring in the setting of elevated cardiac output, primarily caused by reduced systemic vascular resistance due to arteriovenous shunting or peripheral vasodilation. 1

Pathophysiological Mechanism

High output heart failure represents a distinct form of heart failure with unique pathophysiology:

• Primary Mechanism: Reduced systemic vascular resistance (SVR) due to:

  • Arteriovenous shunting
  • Peripheral vasodilation 1, 2

• Hemodynamic Consequences:

  • Fall in systemic arterial blood pressure
  • Neurohormonal activation (renin-angiotensin-aldosterone system)
  • Sodium and water retention by kidneys
  • Clinical manifestations of heart failure despite normal or elevated cardiac output 2

• Cardiac Adaptations:

  • Eccentric left ventricular remodeling
  • Elevated natriuretic peptide levels
  • Higher filling pressures
  • Pulmonary hypertension 3

Common Etiologies

The most frequent causes of high output heart failure include:

1. Obesity (31%)
2. Liver disease (23%)
3. Arteriovenous shunts (23%)
4. Lung disease (16%)
5. Myeloproliferative disorders (8%) 3

Other causes include:

• Chronic severe anemia
• Paget's bone disease (multiple small arteriovenous shunts)
• Severe hepatic or renal disorders
• Septic shock
• Thyrotoxicosis 4, 2

Clinical Presentation

Patients with high output heart failure present with typical heart failure symptoms and signs:

• Symptoms:

  • Dyspnea
  • Increased fatigability
  • Exercise intolerance

• Signs:

  • Tachypnea
  • Tachycardia
  • Pulmonary rales
  • Peripheral edema
  • Warm peripheries (distinguishing feature from low-output heart failure)
  • Sometimes low blood pressure (as in septic shock) 4, 2

Diagnostic Features

High output heart failure is characterized by:

• Cardiac output >8 L/min 5
• Normal or elevated ejection fraction
• Reduced systemic vascular resistance
• Elevated filling pressures
• Signs of pulmonary and systemic congestion 3

Clinical Phenotypes

Two distinct phenotypes have been identified:

1. Phenotype with enlarged cardiac chambers (traditional view)
2. Phenotype with normal heart chambers (newer recognition)

Any etiology can present with either phenotype depending on disease evolution 5

Treatment Considerations

Treatment differs significantly from conventional heart failure management:

• Caution with Standard Heart Failure Medications:

  • ACE inhibitors, ARBs, and vasodilatory beta-blockers may worsen the condition by further reducing SVR 1

• Recommended Approaches:

  • Identify and treat the underlying cause (potentially curative)
  • Dietary restriction of salt and water
  • Judicious use of diuretics
  • Avoid vasodilators and positive inotropes 1, 2

Prognosis

High output heart failure is associated with:

• Increased mortality compared to controls (hazard ratio: 3.4)
• Poorest outcomes in patients with the lowest systemic vascular resistance 3

Clinical Pitfalls to Avoid

1. Misdiagnosis: Consider high output heart failure in patients with dyspnea, congestion, and normal ejection fraction, particularly with risk factors like obesity, liver disease, or arteriovenous shunts.

2. Inappropriate Treatment: Standard heart failure medications that cause vasodilation may worsen the condition by further reducing SVR.

3. Missing Treatable Causes: Many etiologies of high output heart failure are potentially curable, making prompt recognition crucial.

4. Overlooking Phenotype Variations: Be aware that high output heart failure can present with either enlarged or normal-sized cardiac chambers.

High output heart failure represents an important and often overlooked cause of clinical heart failure that requires specific diagnostic consideration and tailored management approaches different from conventional heart failure treatment.