What is the management of preload dependence in Hypertrophic Obstructive Cardiomyopathy (HOCM)?

Management of Preload Dependence in Hypertrophic Obstructive Cardiomyopathy (HOCM)

Maintaining adequate preload is critical in HOCM management as decreased preload can worsen left ventricular outflow tract obstruction (LVOTO) and lead to hemodynamic collapse. 1

Understanding HOCM Preload Dependence Physiology

• LVOTO in HOCM is dynamic and highly sensitive to changes in ventricular preload, afterload, and contractility 1
• Decreased preload (from dehydration, diuretics, vasodilators) can worsen LVOTO by:
  • Reducing ventricular cavity size, bringing septal and mitral structures closer together 1
  • Increasing systolic anterior motion (SAM) of the mitral valve 1
  • Exacerbating the Venturi effect that pulls the mitral valve toward the septum 1
• Reduced preload leads to higher outflow gradients, worsened symptoms, and potential hemodynamic compromise 1

Management Strategies for Preload Dependence

General Measures

• Avoid dehydration and excess alcohol consumption 1
• Encourage adequate fluid intake, especially during exercise or hot weather 1
• Avoid arterial and venous dilators, including nitrates and phosphodiesterase type 5 inhibitors 1
• Discontinue vasodilators when possible (ACE inhibitors, ARBs, dihydropyridine calcium channel blockers) 1
• Avoid digoxin due to its positive inotropic effects 1

Pharmacological Management

1. First-line therapy: Non-vasodilating beta-blockers titrated to maximum tolerated dose 1

   • Beta-blockers reduce contractility and improve preload by prolonging diastolic filling 1
   • Examples include propranolol, metoprolol, atenolol 1

2. Alternative first-line: Non-dihydropyridine calcium channel blockers 1

   • Verapamil or diltiazem if beta-blockers are ineffective or not tolerated 1
   • Caution: Verapamil is potentially harmful in patients with severe dyspnea at rest, hypotension, or very high resting gradients (>100 mmHg) 1

3. Advanced therapy options for persistent symptoms: 1

   • Disopyramide (in combination with beta-blockers or calcium channel blockers) 1
   • Cardiac myosin inhibitors (mavacamten) in adult patients 1
   • Septal reduction therapy (surgical myectomy or alcohol septal ablation) 1

4. Diuretic management: 1

   • Use diuretics cautiously and only at low doses when signs of congestion are present 1
   • Aggressive diuresis can be problematic by decreasing preload and augmenting LVOTO 1

Management of Acute Hypotension

• Acute hypotension in HOCM is a medical urgency requiring prompt intervention 1
• Treatment algorithm: 1
  1. Maximize preload with fluid administration
  2. If no response to fluids, administer intravenous phenylephrine or other vasoconstrictors without inotropic activity
  3. Consider combining vasoconstrictors with beta-blockers to dampen contractility and improve preload by prolonging diastolic filling
  4. Avoid inotropic agents that can worsen obstruction

Special Considerations

• Atrial fibrillation can worsen symptoms due to loss of atrial contribution to ventricular filling 1

  • Prompt restoration of sinus rhythm or appropriate rate control is essential 1

• Patients with HOCM are highly dependent on atrial systole for adequate ventricular filling due to impaired ventricular relaxation 1

  • Loss of "atrial kick" in arrhythmias can severely compromise hemodynamics 1

• Septal reduction therapy should be considered for patients with persistent symptoms despite optimal medical therapy 1

  • Surgical myectomy or alcohol septal ablation can provide long-term relief from obstruction 2, 3

Common Pitfalls to Avoid

• Using pure vasodilators (dihydropyridine calcium channel blockers, ACE inhibitors, ARBs) that can worsen LVOTO 1
• Aggressive diuresis without monitoring for worsening obstruction 1
• Using positive inotropic agents (digoxin, dobutamine) that increase contractility and worsen obstruction 1
• Failing to recognize that dobutamine stress testing is not advised for identifying latent LVOTO due to lack of specificity 1
• Inadequate fluid resuscitation during acute hypotensive episodes 1