Low Flow States and Systemic Hypoperfusion

Definition and Diagnosis

Low flow is defined as SVI <35 ml/m² and indicates reduced forward cardiac output per heartbeat indexed to body surface area, according to the European Heart Journal 1, 2, 4
The American College of Cardiology recommends that low-flow, low-gradient severe AS with reduced LVEF (<50%) be defined as SVI <35 ml/m², mean gradient <40 mmHg, AVA <1.0 cm², and LVEF <50% 2, 3, 4
Paradoxical low-flow severe AS with preserved LVEF (≥50%) presents with SVI <35 ml/m², mean gradient <40 mmHg, AVA <1.0 cm², but normal ejection fraction, as stated by the American College of Cardiology 3, 4, 6

The European Heart Journal states that the meaning of SVI depends entirely on the underlying cardiac condition, and that low SVI does not automatically equal systemic hypoperfusion 1, 2, 3
The American College of Cardiology recommends that comprehensive echocardiography be performed to measure AVA, peak velocity, mean gradient, and LVEF, in order to determine the underlying cardiac pathology 3, 5, 6

Each 5 ml/m² reduction in SVI below normal values is associated with a significant increase in mortality risk, according to the American College of Cardiology 5
SVI <30 ml/m² carries independent prognostic significance with significantly reduced 5-year survival, as stated by the American College of Cardiology 6

The American College of Cardiology recommends that aortic valve replacement (SAVR or TAVI) be performed immediately for symptomatic patients with confirmed severe AS (Class I recommendation) 3, 4, 5
Medical management alone is rated "Rarely Appropriate" for symptomatic severe AS, according to the American College of Cardiology 6