The heart is controlled by its own internal electrical system. When medical concerns arise, doctors use the electrocardiogram (EKG) to assess the health of the heart muscle and its rhythm. This common diagnostic tool provides a snapshot of the heart’s electrical activity, helping to identify a wide range of cardiac issues quickly and safely during emergency medicine and routine health screenings.
Defining EKG and ECG
The electrocardiogram uses two abbreviations: EKG and ECG. Both terms refer to the same procedure and are used interchangeably. ECG is the English-based abbreviation, using the “C” from “Cardio.”
EKG is derived from the original German spelling, Elektrokardiogramm. This German term was adopted because pioneering research was conducted by German-speaking scientists. In the United States, EKG is often favored to prevent confusion with the EEG (Electroencephalogram), which measures brain activity.
What the Test Measures
The heart generates an electrical current to coordinate its function. This electrical system begins with the sinoatrial (SA) node, the heart’s natural pacemaker located in the upper right chamber. The SA node initiates an electrical impulse that spreads through the upper chambers (atria) and then passes to the lower chambers (ventricles).
This flow of electricity causes the heart muscle to contract and pump blood. The EKG machine uses electrodes placed on the skin to detect the electrical changes resulting from the heart’s depolarization and repolarization cycle. The resulting graph captures the strength and timing of these signals. Physicians analyze this data to determine if the heart’s electrical conduction system is working correctly, identifying abnormal rhythms, muscle damage, or problems with blood supply.
How an EKG is Performed
A standard EKG procedure, often called a 12-lead EKG, requires no special preparation. The patient lies still, usually on their back, in a relaxed position. A technician places ten small, sticky electrodes onto the skin: six across the chest and four on the arms and legs.
These electrodes connect by wires to the EKG machine, which records the electrical activity. The term “12-lead” refers to the twelve different electrical perspectives, or views, of the heart created by combining the signals from the ten electrodes. This multi-angle recording allows doctors to pinpoint the location of any electrical abnormalities. The test is entirely non-invasive, does not send electricity into the body, and is usually completed within minutes.
Understanding the Waveform
The EKG output is a graph composed of distinct waves and intervals representing one complete cardiac cycle, or heartbeat. This waveform is labeled P, Q, R, S, and T.
The P wave is the first small upward deflection, signifying the electrical impulse spreading through the atria and causing them to contract. The sharp, central spike is the QRS complex, which represents the electrical activation of the ventricles, the heart’s main pumping chambers. The final component is the T wave, which shows the ventricles’ repolarization, or electrical recovery, as they prepare for the next beat. Doctors analyze the shape, duration, and intervals between these waves to measure heart rate and rhythm, detect muscle damage, or identify irregular heartbeats called arrhythmias.