Arterial elastance (Ea) is used as a global afterload indicator; which description is accurate?

• A. Ea ≈ end-systolic pressure / stroke volume.
• B. Ea ≈ mean arterial pressure / heart rate.
• C. Ea ≈ end-diastolic pressure / stroke volume.
• D. Ea ≈ stroke volume / cardiac output.

Answer: (A)

Arterial elastance measures afterload as a simple pressure–volume ratio: how much pressure the ventricle must generate to eject a given amount of blood in one beat. The best way to express this is end-systolic pressure divided by stroke volume. End-systolic pressure reflects the arterial pressure the ventricle fights at the end of ejection, and the stroke volume is the amount of blood delivered per beat. A higher end-systolic pressure or a smaller stroke volume increases this ratio, indicating greater afterload the heart has to overcome.

Describing afterload with mean arterial pressure over heart rate mixes a pressure with a rate and isn’t a direct measure of the ventricle’s pressure–volume struggle. End-diastolic pressure represents preload (filling pressure), not afterload, so it doesn’t capture the resistance to ejection. Stroke volume over cardiac output reduces to 1 divided by heart rate, which has no direct link to the pressure the heart must overcome. Therefore, end-systolic pressure divided by stroke volume is the accurate description of Ea as a global afterload indicator.