An electrocardiogram, commonly known as an ECG or EKG, is a straightforward, non-invasive medical test. It records the heart’s electrical signals, providing a visual representation of its activity. An ECG assesses the heart’s electrical health, helping identify patterns that might suggest underlying issues.
Understanding Heart Electrical Activity
The heart functions as a pump, and its rhythmic contractions are orchestrated by a sophisticated internal electrical system. Specialized cells within the heart generate electrical impulses, initiating each heartbeat. These impulses begin in the sinoatrial (SA) node, often called the heart’s natural pacemaker, located in the upper right chamber. The electrical signal then travels through the upper chambers (atria), causing them to contract and push blood into the lower chambers (ventricles).
The impulse briefly pauses at the atrioventricular (AV) node before rapidly spreading to the ventricles, triggering their contraction and pumping blood out to the body. An ECG machine detects these electrical impulses through small sticky patches called electrodes, which are placed on the skin, typically on the chest, arms, and legs. These electrodes are connected to a machine that translates the electrical activity into a wavy line graph, displayed on a screen or printed on paper.
What a Normal ECG Looks Like
A normal ECG tracing displays a predictable pattern of waves and segments that reflect the healthy sequence of the heart’s electrical events. The tracing typically features three main components: the P wave, the QRS complex, and the T wave. Each of these waves corresponds to specific electrical activities within the heart’s chambers.
The P wave is the first small, rounded upward deflection on the ECG and represents the electrical activation (depolarization) of the heart’s upper chambers, the atria, as they contract. Following the P wave, there is a brief flat line called the PR segment, which indicates the time it takes for the electrical signal to travel from the atria to the ventricles. A normal PR interval, which includes the P wave and PR segment, typically ranges from 0.12 to 0.20 seconds.
Next, the QRS complex appears as a sharp, prominent deflection, usually with a downward dip (Q wave), a tall upward spike (R wave), and a final downward dip (S wave). This complex signifies the electrical activation (depolarization) of the heart’s lower, larger pumping chambers, the ventricles, as they contract. A normal QRS complex is typically narrow, usually less than 0.12 seconds wide, indicating efficient electrical conduction through the ventricles.
Finally, the T wave is another rounded, upward deflection that follows the QRS complex. This wave represents the electrical recovery or resetting (repolarization) of the ventricles, preparing them for the next heartbeat. In a healthy heart, these waves occur in a consistent rhythm, and the heart rate generally falls within 60 to 100 beats per minute at rest. A “normal” ECG pattern indicates that the heart’s electrical signals are generated and conducted properly.
Why an ECG is Performed
Doctors frequently use an ECG as a diagnostic tool, often when a patient experiences symptoms related to heart health. For instance, an ECG may investigate chest pain, shortness of breath, or a sensation of a fluttering or racing heart, known as palpitations. Dizziness, weakness, or unexplained fatigue can also prompt an ECG to evaluate the heart’s electrical activity.
Beyond investigating symptoms, an ECG is a routine part of many medical assessments. It can be used to check overall heart health during a physical examination or as a pre-surgical evaluation to ensure the heart can tolerate the stress of an operation. For individuals with known heart conditions, ECGs help monitor the condition’s progression or assess how well certain medications or treatments, such as a pacemaker, are working.