An electrocardiogram (ECG or EKG) is a non-invasive test that records the electrical signals of the heart. These signals coordinate the heart’s contractions, enabling it to pump blood effectively. The primary purpose of an ECG is to check for underlying heart problems by visualizing these electrical patterns. An “abnormal ECG” indicates that the recorded electrical activity deviates from what is considered typical. It is important to understand that an abnormal reading does not automatically signify a severe condition, but it does warrant further medical investigation to determine its cause and significance.
Disruptions in the Heart’s Electrical Activity
Abnormal ECG readings can stem from issues within the heart’s electrical conduction system. The heart has a natural pacemaker that generates electrical impulses that travel along specific pathways to coordinate its pumping. Disruptions to this system can lead to various irregularities.
Rhythm disturbances, known as arrhythmias, are a common cause of abnormal ECGs. These include tachycardia, where the heart beats too fast, such as in atrial fibrillation (characterized by an irregular and rapid heartbeat) or supraventricular tachycardia (a fast heart rate originating above the ventricles). Conversely, bradycardia refers to a heart beating too slowly. Irregular rhythms also encompass premature beats, like premature atrial contractions (PACs) originating from ectopic sites in the atria, or premature ventricular contractions (PVCs), which are extra beats originating in the ventricles.
Beyond rhythm, problems with the electrical pathways, known as conduction blocks, can alter the ECG pattern. For instance, bundle branch blocks occur when there is an interruption in electrical impulses traveling to the ventricles, such as left bundle branch block (LBBB) or right bundle branch block (RBBB), both causing a widened QRS complex. Atrioventricular (AV) blocks delay or interrupt signals from the atria to the ventricles.
Heart Muscle and Blood Flow Conditions
Physical changes to the heart muscle or problems with its blood supply are frequent causes of abnormal ECG patterns. When the heart muscle is damaged or strained, its ability to conduct electrical signals changes, leading to detectable deviations on an ECG.
Myocardial ischemia and infarction are significant conditions that manifest on an ECG. Ischemia refers to reduced blood flow to the heart muscle, which can cause changes in the ST segment and T-waves. A myocardial infarction, or heart attack, occurs when blood flow to a part of the heart muscle is severely reduced or blocked, causing tissue damage or death. This often results in characteristic ST segment elevation or depression, T-wave inversions, and pathological Q waves.
Conditions affecting the heart muscle structure, such as cardiomyopathy, can also lead to abnormal ECGs. Cardiomyopathy involves the heart muscle becoming enlarged, thickened, or rigid, impairing its pumping ability. Heart failure, where the heart cannot pump enough blood, often presents with abnormal electrical patterns due to strain and remodeling of the heart muscle. Severe valvular heart disease can cause chamber enlargement and subsequent ECG changes.
Influences from Outside the Heart
An abnormal ECG reading can sometimes result from factors that originate outside the heart but still affect its electrical function.
Electrolyte imbalances are a common non-cardiac cause. Minerals such as potassium, calcium, and magnesium are crucial for electrical signaling of heart cells. When levels are imbalanced, they can interfere with the heart’s electrical activity, leading to abnormal ECG patterns.
Certain medications can also influence the heart’s electrical rhythms. Some drugs, such as antidepressants, antiarrhythmics, and even certain cold medications, can alter heart rate, rhythm, or conduction pathways, resulting in ECG changes. These drug-induced changes can range from minor deviations to more significant rhythm disturbances.
Disorders of the thyroid gland can impact heart function. An overactive thyroid (hyperthyroidism) can lead to a faster heart rate, while an underactive thyroid (hypothyroidism) can cause a slower rate, both reflected in an ECG. Severe lung conditions, like pulmonary embolism or chronic obstructive pulmonary disease (COPD), can place strain on the heart, particularly the right side. This increased strain can manifest as specific ECG changes, such as right axis deviation or P-wave abnormalities.
Normal Variations and Non-Serious Findings
An “abnormal” ECG does not always indicate a serious underlying disease. Many factors can cause deviations from the typical pattern without medical concern.
Some common findings are benign variants of normal heart activity. For example, early repolarization is an ECG pattern frequently seen in healthy individuals, especially athletes. Athletic heart syndrome, involving physiological changes from intense training, can appear abnormal but is a normal adaptation.
Technical issues during the test can also lead to misleading results. Poor electrode placement, patient movement, or electrical interference can create artifacts or distortions, making the ECG appear abnormal. These issues are usually easily identified and corrected.
Physiological influences, such as stress, anxiety, or digestion, can temporarily affect heart rate and rhythm. These transient changes can cause minor deviations on an ECG not reflecting underlying heart disease. When an ECG shows an unexpected result, doctors consider it one piece of information. They combine it with a patient’s symptoms, medical history, physical examination, and other diagnostic tests to form a complete picture and determine the appropriate course of action.