Electrocardiography

The Electrocardiogram or EKG or ECG is a way of monitoring the heart with electrodes on the skin of your body. It graphs a waveform of action potentials produced from the cardiac muscle fibers during each heartbeat. Electrodes are placed on the arms and legs and six positions on the chest to record the EKG. The EKG amplifies the electrode signal and produces a waveform like this.


The first is the P wave which is a small upward deflection that represents atrial depolarization. A fraction of a second after the P wave begins the atria contract. The second wave is the QRS complex. This begins as a downward deflection (Q) then a large upward triangular deflection (R) then ends in another downward deflection (S). The QRS complex represents ventricular depolarization as the action potential goes through the ventricular fibers. Very quickly after the start of the QRS the ventricals start to contract. The last wave is a upward dome shaped deflection called the T wave. It represents ventricular repolarization and occurs right before the ventricles relax.

The EKG is useful in diagnosing abnormal rhythems and conduction patterns, or used to monitor patients recovering from a heart attack. It can also be used to detect a fetus.