What is annulus paradoxus in echocardiography?

Annulus Paradoxus in Echocardiography

Annulus paradoxus refers to the discordance between mitral annular tissue Doppler velocities and left ventricular filling pressures, where despite elevated filling pressures, the E/e' ratio remains normal or only mildly elevated.

Definition and Mechanism

• Annulus paradoxus is a phenomenon where the expected relationship between mitral annular tissue Doppler velocities (e') and left ventricular filling pressures is disrupted 1
• Normally, as left ventricular filling pressures increase, the E/e' ratio increases proportionally, making it a useful marker for estimating filling pressures 1
• In annulus paradoxus, despite elevated left ventricular filling pressures, the E/e' ratio remains paradoxically normal or only mildly elevated 1

Clinical Context and Occurrence

• Most commonly observed in patients with:
  • Left ventricular hypertrophy, particularly in hypertrophic cardiomyopathy 2
  • Significant mitral annular calcification 3
  • Advanced diastolic dysfunction with restrictive filling patterns 1
  • Some cases of severe aortic stenosis 4

Physiological Explanation

• In normal hearts, the mitral annulus undergoes approximately 25% reduction in area during systole 5, 6
• The annulus has a complex saddle-shaped structure with peaks anteriorly and posteriorly, and nadirs medially and laterally 6
• In conditions causing annulus paradoxus:
  • Annular motion becomes restricted due to calcification or fibrosis 3
  • Septal e' velocities may be particularly affected when there is septal hypertrophy 2
  • The normal relationship between left atrial pressure and mitral annular motion becomes uncoupled 4

Diagnostic Implications

• Recognition of annulus paradoxus is crucial to avoid underestimating left ventricular filling pressures 1
• When annulus paradoxus is suspected, additional parameters should be assessed:
  • Left atrial size (enlarged left atrium suggests elevated filling pressures) 1
  • Pulmonary vein flow patterns (particularly increased atrial systolic reversal) 1
  • Tricuspid regurgitation velocity (elevated suggests increased left-sided pressures) 1
  • Color M-mode flow propagation velocity 1

Clinical Pitfalls and Recommendations

• Relying solely on E/e' ratio in patients with significant left ventricular hypertrophy or mitral annular calcification may lead to underestimation of filling pressures 2, 3
• In patients with hypertrophic cardiomyopathy, the lateral e' velocity may be more reliable than septal e' 2
• When annulus paradoxus is present, a comprehensive assessment of diastolic function using multiple parameters is essential 1
• The 2016 ASE/EACVI diastolic function guidelines recommend using multiple parameters rather than E/e' alone in cases where annulus paradoxus may be present 1

Distinguishing from Other Annular Phenomena

• Annulus paradoxus differs from paradoxical septal motion (seen in LBBB or post-cardiac surgery) where the septum moves paradoxically during systole but septal contractility remains preserved 7
• It also differs from annular dilatation, which is defined as a diastolic diameter >35 mm or >21 mm/m² 5