Interpretation of ECG Waveform with Respect to Electromechanical Activity of the Heart
Introduction
Electrocardiography (ECG) records the electrical activity of the heart.
The mechanical activity of the heart (contraction and relaxation) occurs as a result of this electrical
activity.
This relationship is known as electromechanical coupling.
P Wave – Atrial Activity
Electrical Activity: Atrial depolarization.
Mechanical Activity: Atrial contraction (atrial systole), pushing blood into the ventricles.
PR Interval – AV Conduction
Electrical Activity: Impulse conduction from atria through AV node to ventricles with a short delay.
Mechanical Activity: Completion of ventricular filling before ventricular contraction.
QRS Complex – Ventricular Activity
Electrical Activity: Ventricular depolarization.
Mechanical Activity: Ventricular contraction (ventricular systole) and ejection of blood into
pulmonary artery and aorta.
ST Segment – Ventricular Systole
Electrical Activity: Ventricles are fully depolarized (isoelectric phase).
Mechanical Activity: Maximum ventricular contraction and blood ejection.
T Wave – Ventricular Recovery
Electrical Activity: Ventricular repolarization.
Mechanical Activity: Ventricular relaxation (diastole) and beginning of ventricular filling.
QT Interval – Total Ventricular Activity
Electrical Activity: Total time of ventricular depolarization and repolarization.
Mechanical Activity: Represents total ventricular systole.
Summary Table
P wave – Atrial depolarization → Atrial contraction
PR interval – AV delay → Ventricular filling
QRS complex – Ventricular depolarization → Ventricular contraction
ST segment – Full depolarization → Blood ejection
T wave – Ventricular repolarization → Ventricular relaxation
Conclusion
The ECG waveform provides a clear representation of the electrical events of the heart,
each of which triggers a specific mechanical response. Proper interpretation of ECG
helps in understanding normal and abnormal cardiac function.