Definition
Diastole (Greek for “expansion”) is the relaxation and filling phase of the heart chambers (ventricles). It is in contrast to systole (the tensing and ejection phase of the heart) and serves to prepare it. The filling phase during diastole is followed by the expulsion phase in systole.
Structure of the diastole
In general, diastole begins with the slackening of the chamber muscles and the simultaneous closure of the two pocket valves connecting to the major arteries. Thus, the blood from the atria cannot flow directly into the large arteries, but is first collected in the two chambers. In ECG, diastole is the phase between the end of the T-wave and the beginning of the Q-wave.
More precisely, the diastole is divided into 4 different phases:
- The relaxation phase, also known as isovolumetric relaxation, is the period directly after the contraction of the heart chambers. During this phase, both the sail and the pocket valves are closed. In the ECG, this phase appears between the end of the T-wave and the middle of the TP stretch.
In the echocardiogram, the relaxation phase can be seen at the end of the systolic outflow.
- This is followed by the early filling phase, which is also called active diastole. The two heart chambers (ventricles) suck the blood from the atria through the open sail valves. In the ECG, this phase is found between the middle of the TP stretch and the beginning of the P-wave.
In the echocardiogram this phase is represented by the E-wave.
- Diastasis is also partly still counted to the early filling phase. In the ECG it is represented by the P-wave, in the echo by the phase between E-wave and A-wave.
- This is followed by the late filling phase. Here the two atria contract until they become flaccid and the two chambers are completely filled.
The sail valves between atrium and ventricle close again to prevent blood from flowing back from the ventricles into the atria, and the expulsion phase can begin. In the ECG this phase is represented by the P-R distance, in the echo it is the A-wave. Now both chambers are filled with blood and the expulsion phase (systole) can begin.
