How do you increase the cardiac index (CI) in patients with hypertrophic cardiomyopathy (HCM) and systolic anterior motion (SAM)?

Management of Cardiac Index in HCM with Systolic Anterior Motion

In patients with hypertrophic cardiomyopathy (HCM) and systolic anterior motion (SAM), increasing cardiac index requires reducing left ventricular outflow tract obstruction (LVOTO) through beta-blockers as first-line therapy, followed by non-dihydropyridine calcium channel blockers or disopyramide if needed, with invasive septal reduction therapy reserved for drug-refractory cases with gradients ≥50 mm Hg. 1, 2

Pathophysiology of Reduced Cardiac Index in HCM with SAM

The cardiac index in HCM with SAM is compromised by several interrelated mechanisms:

• Dynamic LVOTO caused by SAM of the mitral valve leaflets contacting the hypertrophied septum
• Increased LV systolic pressure and prolonged ventricular relaxation
• Elevated LV diastolic pressure and diastolic dysfunction
• Secondary mitral regurgitation from distorted mitral valve coaptation
• Myocardial ischemia due to supply-demand mismatch

These factors collectively reduce forward cardiac output and impair cardiac index 1.

Medical Management Algorithm

First-Line Therapy:

• Non-vasodilating beta-blockers (e.g., propranolol)
  • Mechanism: Reduce contractility, heart rate, and LVOT gradient
  • Dosing: Titrate to maximum tolerated dose
  • Target: Heart rate 55-65 bpm at rest 2

Second-Line Therapy (if beta-blockers insufficient):

• Non-dihydropyridine calcium channel blockers (e.g., verapamil)
  • Mechanism: Improve ventricular relaxation and diastolic filling
  • Caution: Use with extreme care in severe obstruction due to potential vasodilation 2, 3
  • Benefit: Improved left ventricular diastolic function specifically noted in HOCM patients 3

Third-Line Therapy:

• Disopyramide (added to beta-blockers)
  • Mechanism: Negative inotropic effect reduces LVOT gradient
  • Administration: Usually combined with beta-blockers 2

Volume Management:

• Maintain adequate preload
• Avoid dehydration which worsens obstruction
• Avoid vasodilators which can exacerbate LVOTO 1

Invasive Management Options

For patients with drug-refractory symptoms and LVOT gradients ≥50 mm Hg:

Septal Reduction Therapy:

• Surgical septal myectomy

  • Gold standard for severe, drug-refractory LVOTO
  • Reduces septal thickness and eliminates SAM
  • Post-procedure LVOT gradients can be reduced to <10 mm Hg 1, 4

• Alcohol septal ablation

  • Alternative for high-surgical-risk patients
  • Creates controlled infarction of basal septum 1

Mitral Valve Interventions:

• MitraClip therapy

  • Emerging approach targeting SAM directly
  • Can significantly reduce both basal peak gradients (from 65±25.5 to 7.7±5.0 mmHg) and provoked gradients (from 145.3±8.1 to 23.2±7.6 mmHg) 5

• Surgical mitral valve repair techniques

  • May be combined with myectomy in selected cases
  • Options include anterior mitral leaflet extension, edge-to-edge repair, or chordal cutting 6

Monitoring Effectiveness

• Echocardiography with Doppler to assess LVOT gradient at rest and with provocation
• Measurement of cardiac index via right heart catheterization in selected cases
• Clinical assessment of exercise capacity and symptoms 1

Important Caveats

• Avoid dobutamine for identifying latent LVOTO due to lack of specificity 1
• Avoid vasodilators which can worsen obstruction by decreasing afterload 1, 7
• Catecholamine excess can dramatically worsen LVOTO even in otherwise normal ventricles 7
• Careful monitoring required when using verapamil in patients with severe obstruction due to potential vasodilation 2, 3
• In patients with severe left ventricular dysfunction, the negative inotropic effects of medications may not be counterbalanced by afterload reduction 3

By systematically addressing the pathophysiologic mechanisms of reduced cardiac index in HCM with SAM, clinicians can effectively improve hemodynamics and symptoms in these challenging patients.