ECG Flashcards
Relate the mechanical events of the cardiac cycle to the ECG
Ventricular filling
AV valves open and blood enters the ventricles (passing filling) 80%
A period of slow filling occurs (diastasis)
Atrial depolarisation occurs and contributes the final 20% of blood called ESV
Marked by the P wave
The PQ interval marks the plateau that allows the ventricles to finish filling before contraction and also allows the wave of electricity to spread to further areas of the conduction sites
Ventricular contraction
As soon as the atria relax, ventriclular depolarisation occurs and marks the QRS complex.
The pressure in the ventricles rises rapidly and sharply closing the Tricuspid and mitral valves shut. As the pressure rises and all valves are closed isovolumetric contraction occurs.
As the pressure in the ventricles exceeds the pressure in the aortic and pulmonary trunk, the aortic and pulmonary valves open and blood is propelled into the circulations.
Note the QRS complex is hiding atrial repolarisation
The period when the aortic and pulmonary valves shut there is a slight increase in pressure called the dicrotic notch.
Ventricular repolarisation
The ventricles repolarise and this marks the T wave.
The heart is in diastole and all valves are shut (isovolumetric relaxation)
During ventricular systole the atria have been passively filling ready ventricular filling when the pressure rises above the ventricles, opening the tricuspid valve.
