What is the management of low flow low gradient aortic stenosis?

Management of Low Flow Low Gradient Aortic Stenosis

Valve replacement is recommended for patients with low flow low gradient aortic stenosis who have symptoms and/or impaired left ventricular systolic function with evidence of flow reserve during low-dose dobutamine stress echocardiography, after excluding pseudo-severe aortic stenosis. 1

Diagnostic Approach

Initial Assessment

• Transthoracic echocardiography with Doppler is the key diagnostic test for evaluating aortic valve area (AVA) when transaortic flow rate is not normal 1
• Low flow low gradient AS is defined by:
  • Small aortic valve area (<1.0 cm²) suggesting severe AS
  • Low mean transvalvular gradient (<40 mmHg) suggesting non-severe AS 2

Types of Low Flow Low Gradient AS

1. Classical low flow low gradient AS:

   • Reduced left ventricular ejection fraction (LVEF <50%)
   • Low stroke volume index (<35 ml/m²) 3
   • Often associated with worse symptomatic status and higher prevalence of eccentric hypertrophy 3

2. Paradoxical low flow low gradient AS:

   • Preserved LVEF (≥50%)
   • Low stroke volume index (<35 ml/m²)
   • Often associated with concentric LV hypertrophy and impaired filling 4

Confirming True Severity

• Low-dose dobutamine stress echocardiography is recommended for classical low flow low gradient AS to:

  • Distinguish true-severe from pseudo-severe AS
  • Assess flow reserve 1, 5
  • Calculate projected valve area at normal flow rate 1

• Multi-detector computed tomography for aortic valve calcium scoring:

  • Recommended especially for paradoxical low flow low gradient AS
  • Thresholds for true-severe AS: ≥2000 AU for men and ≥1200 AU for women 6
  • Particularly useful when stress echocardiography is not feasible or inconclusive 6

Management Algorithm

1. Rule Out Confounding Factors

• Check for measurement errors in echocardiography 6
• Optimize treatment of hypertension before making definitive decisions 6

2. For Classical Low Flow Low Gradient AS (reduced LVEF)

• With flow reserve on dobutamine stress echo and true-severe AS:

  • Valve replacement is strongly recommended 1
  • Shows survival benefit despite higher operative risk compared to high-gradient AS 2

• Without flow reserve:

  • Higher operative mortality but may still benefit from valve replacement
  • Decision should be made by multidisciplinary team 1

3. For Paradoxical Low Flow Low Gradient AS (preserved LVEF)

• If confirmed true-severe AS:
  • Valve replacement is recommended for symptomatic patients (Class IIa indication) 6
  • Consider early intervention in asymptomatic patients with:
    • Markedly reduced stroke volume
    • Myocardial fibrosis on cardiac MRI
    • Poor longitudinal LV function on speckle tracking
    • Moderate to severe LV diastolic dysfunction 6

4. Choice of Intervention

• Surgical Aortic Valve Replacement (SAVR) preferred for:

  • Low surgical risk patients
  • Younger patients
  • Patients with bicuspid aortic valve
  • Presence of other cardiac conditions requiring surgery (multivalvular disease, CAD requiring CABG) 1

• Transcatheter Aortic Valve Replacement (TAVR) preferred for:

  • Inoperable or high-risk patients
  • May be superior to SAVR in patients with low flow low gradient AS 2
  • Lower risk of patient-prosthesis mismatch, but higher risk of paravalvular regurgitation 6

Outcomes and Prognosis

• Classical low flow low gradient AS has approximately 50% 5-year survival rate after TAVR compared to 68% for normal flow high gradient AS 3
• Paradoxical low flow low gradient AS has intermediate prognosis with approximately 62% 5-year survival rate after TAVR 3
• Without intervention, both types of low flow low gradient severe AS have poor outcomes 6, 4

Important Caveats

• The multidisciplinary heart team approach is strongly emphasized for decision-making in these complex cases 1
• Balloon aortic valvuloplasty may be considered as a bridge to definitive valve replacement in hemodynamically unstable patients 1
• Careful assessment is needed to avoid misdiagnosis, particularly in paradoxical low flow low gradient AS which has numerous potential confounders 4
• Valve replacement should not be performed in patients with severe comorbidities where intervention is unlikely to improve quality of life or when life expectancy is <1 year 1