Why can't you give inotropes to patients with Hypertrophic Obstructive Cardiomyopathy (HOCM)?

Why Inotropes Should Not Be Given to Patients with HOCM

Positive inotropic agents are harmful in patients with Hypertrophic Obstructive Cardiomyopathy (HOCM) as they aggravate dynamic outflow obstruction, increasing the risk of hemodynamic instability, worsening symptoms, and potentially causing life-threatening complications. 1

Pathophysiological Mechanism

• HOCM is characterized by dynamic left ventricular outflow tract obstruction (LVOTO), which can be worsened by factors that increase contractility 1
• Positive inotropic agents increase myocardial contractility, which directly exacerbates the existing LVOT gradient in HOCM patients 1
• Inotropes accelerate left ventricular ejection, increasing the hydrodynamic force on the protruding mitral leaflet, promoting earlier and more severe mitral-septal contact 2
• This worsening obstruction can lead to hemodynamic collapse, especially in patients with high resting gradients (>80-100 mmHg) 1

Clinical Evidence and Guidelines

• The 2024 AHA/ACC guideline explicitly states that positive inotropic agents are harmful in HOCM patients and should be avoided to reduce the risk of hemodynamic instability (Class 3: Harm recommendation) 1
• FDA labeling for inotropes like milrinone specifically warns against use in patients with hypertrophic subaortic stenosis, stating they "may aggravate outflow tract obstruction" 3
• The 2020 AHA/ACC HCM guideline identifies positive inotropic agents as relatively contraindicated in patients with symptomatic obstructive HCM 1

Management Principles for HOCM

• The cornerstone of HOCM management is the use of negative inotropic agents, which decrease LVOT obstruction by:

  • Reducing contractility
  • Slowing left ventricular ejection acceleration
  • Delaying mitral-septal contact 2

• First-line pharmacologic therapy includes:

  • Non-vasodilating beta-blockers titrated to maximally tolerated doses 1
  • Non-dihydropyridine calcium channel blockers (verapamil, diltiazem) if beta-blockers are ineffective or not tolerated 1
  • Disopyramide in combination with beta-blockers or calcium channel blockers for persistent symptoms 1, 4

Hypotension Management in HOCM

• If hypotension develops in HOCM patients:
  • Prioritize intravenous fluid administration to correct hypovolemia 1
  • Use alpha-agonists (phenylephrine, vasopressin) rather than beta-agonists 1
  • Consider intraoperative echocardiography to evaluate LVOT obstruction 1
  • In selected cases, intravenous beta-blockade may be necessary to reduce LV contractility and relieve obstruction 1

Perioperative Considerations

• Factors that must be avoided in HOCM patients undergoing surgery include:

  • Positive inotropic agents (contraindicated) 1
  • Tachycardia (reduces diastolic filling time) 1
  • Reduced preload (hypovolemia) 1
  • Reduced afterload (vasodilation) 1

• Established negative inotropic agents should be continued throughout the perioperative period 1

Common Pitfalls to Avoid

• Using inotropes for hypotension in HOCM patients - this can precipitate hemodynamic collapse 1, 3
• Discontinuing negative inotropic medications (beta-blockers, calcium channel blockers) perioperatively 1
• Excessive diuresis, which reduces preload and can worsen LVOT obstruction 1
• Using vasodilators (ACE inhibitors, ARBs, dihydropyridine CCBs) which can worsen symptoms by reducing afterload 1

In summary, the use of positive inotropic agents in HOCM directly contradicts the therapeutic goal of reducing contractility and LVOT obstruction. Their use can precipitate hemodynamic deterioration and should be strictly avoided in favor of fluid resuscitation and alpha-agonist vasopressors when managing hypotension in these patients.