Expansion
Rapid filling, diastasis and atrial systole
Expansion
- Rapid (early) filling - about 70 to 80 per cent of the total, driven by the pressure gradient once the atrioventricular valve opens; corresponds to the E wave on Doppler and to S3 if audible
- Diastasis - a slow plateau of passive filling; the first phase to be lost when the heart rate rises
- Atrial systole - the atrial kick, contributing the final 10 to 20 per cent; corresponds to the A wave and to S4 if audible
Two clinical points follow. Losing the atrial kick in atrial fibrillation matters little in a normal heart but can precipitate decompensation in a stiff, hypertrophied one, where it may contribute 30 to 40 per cent of filling.
And because diastasis disappears first, tachycardia encroaches progressively on the efficient early filling phase, which is why rate control improves output in diastolic dysfunction.