Valvulo-arterial impedance

Zva · Derived: Zva = (SBP + AS mean gradient) / SVi

Normal range & thresholds

<3.5 mmHg·m²/mL normal global afterload. ≥3.5 raised; ≥4.5 associated with roughly doubled risk of death or AVR in asymptomatic AS, independent of stenosis severity ^[113,158].

Pathophysiology

The LV in AS faces two resistances in series — the valve and the arterial tree. Zva expresses the systolic pressure the LV generates per millilitre of indexed stroke volume, capturing both. It explains why symptoms and LV dysfunction appear at ‘moderate’ gradients in hypertensive or stiff-artery patients ^[113].

Raised by

• Severe AS, especially paradoxical low-flow; hypertension; low SVi

Lowered by

• Normal flow and normal arterial load; after AVR

Technique & pitfalls

• BP at the time of the Doppler study; SVi from LVOT; mean gradient from multi-window CW.

Pseudo-change & artefact

• Uncontrolled BP on the day; SVi error; hypertension lowers the transvalvular gradient.

Treatment thresholds

Not a guideline intervention criterion itself; supports Heart Team decisions in asymptomatic or discordant AS alongside cardiac-damage staging ^[6,58].

Next step

• Control BP and re-grade; calcium score if low-gradient (card 69); staging (card 70).

Drugs

Antihypertensives lower the arterial component; nothing lowers the valve component except intervention.

Reversibility

Falls immediately after AVR; arterial component persists.