My heart skip skips a beat
The pause is to allow the atria to fully empty into the ventricle.
Heartbeat on an ECG trace
P Interval (Ventricular Diastole)
- Atria and ventricles are relaxed
- blood is flowing into the atria from the veins.
- Atrial pressure increases above that of the ventricle, AV valves open allowing blood to flow into the ventricle
P Wave (Atrial Systole) P-Q
Signal transduction from SA to AV nodes.
- SA node fires
- Atria contract causing atrial systole
- which forces all blood into the ventricles
- emptying the atria.
Q Interval (End of Ventricular Diastole)
Depolarisation of interventricular (IV) septum
- AV valves remain open - all remaining blood squeezed into the ventricles.
- impulse from the SA node reaches the AV node
- which spreads the signal throughout the walls of the ventricles via bundles of His and Purkinje fibres
- R peak is the end of ventricular diastole and the start of systole.
R Interval (Ventricular Systole)
- All blood is now within the ventricles
- so pressure is higher than in the atria - AV valves close
- ventricles start to contract although pressure is not yet high enough to open the SL (semilunar) valves
ST Segment (Ventricular Systole)
- Pressure increases until it equals Aortic pressure,
- SL valves open
- blood is ejected into the Aorta (and pulmonary artery) as ventricles contract
- At this time the atria are in diastole and filling with blood returning from the veins.
- plateau in ventricular arterial pressure
T Wave (Ventricular Diastole)
T= moment of Ventricular repolarisation immediately before ventricular relaxation
- Ventricles relax
- ventricular pressure is once again less than the aortic pressure
- so SL valves close