av iv

My heart skip skips a beat

HEARTBEATS!!

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)

Ventricular contraction

  • 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)

Ventricular contraction

  • 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