An electrocardiogram (EKG or ECG) is a non-invasive diagnostic test that captures the electrical activity of the heart. It involves placing small electrodes on the skin to detect the heart’s electrical signals. The primary purpose of an EKG is to provide a visual representation of heart health by recording these electrical impulses as a wave pattern on a graph. An “abnormal” EKG means the recorded electrical pattern deviates from what is typical, indicating a possible change in heart function.
The Basics of a Normal EKG
A normal EKG tracing provides a baseline for identifying abnormalities. A typical EKG waveform consists of several distinct components: the P wave, QRS complex, and T wave, each representing a specific electrical event in the heart. The P wave signifies the electrical activation (depolarization) of the atria, the heart’s upper chambers. Following this, the QRS complex represents the rapid electrical activation of the ventricles, the heart’s lower pumping chambers. Finally, the T wave reflects the electrical recovery (repolarization) of the ventricles, preparing them for the next heartbeat.
Specific intervals and segments on the EKG tracing offer additional insights. The PR interval measures the time it takes for an electrical impulse to travel from the atria to the ventricles. The QT interval represents the total duration of ventricular electrical activity, from depolarization through repolarization. The ST segment is the flat line between the QRS complex and the T wave, indicating the period when the ventricles are fully depolarized. A normal heart rate typically ranges between 60 and 100 beats per minute, characterized by a regular rhythm known as normal sinus rhythm, where each QRS complex is preceded by a P wave.
Deviations in Heart Rate and Rhythm
Abnormalities in the heart’s rate and rhythm are frequently detected through an EKG. A heart rate consistently below 60 beats per minute is termed bradycardia, while a rate above 100 beats per minute is called tachycardia. Both bradycardia and tachycardia can be identified by analyzing the spacing between consecutive heartbeats on the EKG.
The EKG reveals various rhythm irregularities, known as arrhythmias. Atrial fibrillation, or AFib, is characterized by an irregularly irregular rhythm and the absence of distinct P waves, replaced instead by chaotic, fine fibrillatory waves; its ventricular rate can vary from 80 to 180 beats per minute. Another arrhythmia, atrial flutter, presents a distinctive “sawtooth” pattern of flutter waves due to rapid atrial activity, around 300 beats per minute. Premature ventricular contractions (PVCs) appear as wide, early, and often bizarre-looking QRS complexes that interrupt the normal rhythm.
Changes in EKG Waveforms and Intervals
The shapes and timings of the EKG’s waveforms and intervals can signal underlying issues. Deviations in the ST segment are significant: ST elevation, where the segment is raised above the baseline, can indicate a myocardial infarction or heart attack. Conversely, ST depression, where the segment is lowered, often suggests myocardial ischemia, meaning reduced blood flow to the heart muscle.
Changes in the T wave, representing ventricular repolarization, also provide important clues. Inverted T waves can be associated with myocardial ischemia, although they can also occur in other conditions like pericarditis or electrolyte imbalances. Abnormally tall or “peaked” T waves may indicate high potassium levels in the blood. Pathological Q waves, which are wider or deeper than normal, can signify a past heart attack, as they reflect dead heart muscle tissue that no longer generates electrical activity.
Interval abnormalities also contribute to the diagnostic picture. A prolonged PR interval indicates a delay in electrical conduction from the atria to the ventricles, a condition known as first-degree AV block. A prolonged QT interval signifies a delay in ventricular repolarization, which can increase the risk of serious ventricular arrhythmias. An enlarged heart chamber, such as in ventricular hypertrophy, can manifest on an EKG as increased QRS voltage or a shift in the electrical axis of the heart.
Underlying Conditions Indicated by Abnormal EKGs
An abnormal EKG serves as a valuable indicator that prompts further medical investigation. Certain EKG patterns are strongly linked to specific cardiac conditions. ST elevation and pathological Q waves are signs of a heart attack, reflecting myocardial damage. Myocardial ischemia, a condition of reduced blood flow to the heart muscle, is often characterized by ST depression or inverted T waves on the EKG.
Arrhythmias like atrial fibrillation and atrial flutter are identified by their distinct EKG rhythm patterns. EKG patterns indicating ventricular hypertrophy or specific arrhythmias can be associated with heart failure.
Electrolyte imbalances, particularly in potassium and calcium levels, can alter EKG waveforms and intervals, leading to changes like peaked or inverted T waves or prolonged QT intervals. Other conditions like inflammation of the heart’s outer lining (pericarditis) can show widespread ST elevation and PR depression. Additionally, certain medications can influence the heart’s electrical activity, resulting in EKG changes such as QT prolongation or altered heart rate and rhythm. An abnormal EKG finding necessitates comprehensive medical evaluation to determine the precise underlying cause.