An electrocardiogram (ECG or EKG) is a simple, non-invasive test that records the electrical signals generated by the heart. It provides a visual representation of the heart’s rhythm and electrical pathways, acting as a snapshot of its current function. When a result is labeled “abnormal,” it means the tracing shows a variation from the expected normal pattern. An abnormal finding is not a final diagnosis but rather a starting point for a physician to investigate the underlying cause.
How the ECG Measures Heart Function
The heart’s function relies on a coordinated electrical impulse that starts in the atria and travels to the ventricles, triggering a contraction. The ECG machine translates this electrical activity into a continuous line tracing composed of distinct waves and segments. Analyzing the shape, size, and timing of these features allows healthcare providers to assess the heart’s electrical health.
The P wave represents the electrical activation (depolarization) of the atria. Following this is the QRS complex, which signifies the depolarization of the ventricles, leading to their powerful contraction. The final wave is the T wave, representing the electrical recovery (repolarization) of the ventricles as they relax.
The time intervals between these waves, such as the PR and QT intervals, are also measured to ensure the electrical signal is traveling at the correct speed through the conduction system. An abnormality is identified when any of these waves or intervals deviate from their established normal measurements.
Abnormalities Related to Rate and Rhythm
Abnormal ECG findings often relate to the heart’s rate and rhythm, which govern the timing and regularity of the beats. A normal adult heart rate falls within 60 to 100 beats per minute, following a consistent, regular pattern known as sinus rhythm. Deviations from this standard indicate an arrhythmia, or irregular heartbeat.
Tachycardia is classified as a heart rate consistently above 100 beats per minute. This fast rate can be a normal response to exertion, but it may also signal an underlying issue like fever or certain heart conditions. Conversely, bradycardia is a heart rate below 60 beats per minute. This slow rate can indicate problems with the heart’s natural pacemaker or be a side effect of certain medications.
An irregular rhythm, where the beats are unevenly spaced, is another frequent abnormality. Atrial fibrillation (AFib) is a common example, characterized by rapid, chaotic electrical activity in the atria. These timing issues suggest a dysfunction in the heart’s electrical impulse generation, affecting the overall pace and coordination.
Abnormalities Related to Conduction and Structure
Abnormalities in the shape and segment of the ECG tracing often point to problems with the heart’s physical structure or blockages in the electrical pathways. These changes can indicate damage to the heart muscle itself. Reduced blood flow (ischemia) can cause the ST segment—the area between the QRS complex and the T wave—to appear depressed below the baseline.
More serious injury, such as an acute heart attack (myocardial infarction), causes the ST segment to be noticeably elevated, indicating significant muscle damage. Another structural issue involves hypertrophy, or the thickening of the heart muscle, often due to long-standing high blood pressure. This enlargement alters the electrical signal’s strength, causing the QRS complex to appear unusually tall.
Disruptions in the heart’s electrical wiring, such as a bundle branch block, are visible as a widened QRS complex. These blocks occur when the electrical impulse is delayed or completely blocked from traveling down one of the main pathways to the ventricles. The resulting detour forces the signal to spread more slowly, stretching the QRS complex beyond its normal duration.
Interpreting an Abnormal Result
Receiving an abnormal ECG result requires consultation with a physician, who will place the finding into the context of a patient’s symptoms, medical history, and physical examination. The ECG is a screening tool, and an abnormality does not automatically confirm a serious heart diagnosis. Sometimes, an abnormal reading is a normal variation for a particular individual or a temporary effect of stress, certain medications, or an electrolyte imbalance.
If the abnormality suggests a potential underlying condition, the physician will typically recommend further diagnostic testing. Common follow-up procedures may include an echocardiogram, which uses sound waves to create moving images of the heart’s structure and function. A Holter monitor records the heart’s electrical activity continuously over 24 to 48 hours to catch intermittent rhythm problems. A stress test may also be performed to observe the heart’s response to exertion, which helps determine if blood flow issues are present.