Like skeletal muscle, your heart can’t do what it does without electricity. In fact, the electrical activity in the heart provides us the means to study the heart under various conditions and pathologies. It can also be used to diagnose various heart diseases and conditions.
What Is An Electrocardiogram?
To measure and quantify electrical activity in the heart, we turn to the electrocardiogram (ECG). An ECG is a graphic record of the changes in magnitude and direction of the electrical current generated by the depolarization and repolarization of the atria and ventricles. The electrical current is readily detected by non-invasive electrodes attached to the skin. No pain or blood necessary!
What Does The Electrocardiogram Record?
Depolarization refers to the change in electrical charge within the heart cells, going from negative to positive (discharge). Becoming positively charged is depolarization and when the cell goes back to its negative charge, that’s repolarization (recharge). It all has to do with ions moving across the cell membrane. The heart’s electrical activity and consequent mechanical pumping of blood is continuous and occurs in cycles. Each cycle consists of a depolarization phase and a repolarization phase. When you look at an ECG tracing, you can distinguish each of the cardiac cycles.
A normal cardiac cycle ECG is comprised of the following:
- P wave (atrial depolarization/atrium contract)
- QRS complex (ventricular depolarization/ventricles contract)
- T wave (ventricular repolarization/ventricles relax)
These waves and complexes are “pictures” of the electrical activity. An R-R interval is the distance (time elapsed) between the R waves of two consecutive cardiac cycles and is normally used when determining heart rate.
