Atrial fibrillation, often called AFib, is a common heart rhythm disorder where the heart’s upper chambers beat erratically. An electrocardiogram, or EKG, is a diagnostic tool for detecting this condition, providing a visual representation of the heart’s electrical activity.
Atrial Fibrillation Explained
Atrial fibrillation is an irregular and often rapid heart rhythm originating in the heart’s upper chambers, the atria. Instead of contracting in an organized fashion, the atria quiver chaotically, a process called fibrillation. This disorganized electrical activity leads to inefficient pumping of blood from the atria into the lower chambers, the ventricles.
The normal heartbeat begins with a single electrical impulse from the sinus node in the right atrium. In AFib, multiple sites within both atria fire electrical impulses, sometimes at rates exceeding 400 beats per minute. This uncoordinated electrical activity causes the atria to twitch rather than contract effectively. Consequently, blood can pool in the atria, increasing the risk of blood clot formation and potentially leading to complications such as stroke.
How an Electrocardiogram Works
An electrocardiogram, or EKG, is a non-invasive medical test that records the heart’s electrical activity. This test involves placing electrodes, typically 10 to 12 adhesive patches, on the skin of the chest, arms, and legs. These electrodes detect the electrical changes that occur as the heart muscle depolarizes and repolarizes during each heartbeat.
The electrical signals transmit through wires to an EKG machine, which converts them into a wave pattern displayed on a screen or printed on paper. A normal EKG tracing exhibits a predictable series of waves that repeat with consistent timing. These waves include the P wave, representing the electrical impulse spreading across the atria and their contraction; the QRS complex, indicating the electrical activity as the ventricles contract; and the T wave, showing the ventricles relaxing and recovering after beating.
Recognizing Atrial Fibrillation on an EKG
Identifying atrial fibrillation on an EKG involves observing specific abnormalities. A defining feature of AFib is the absence of distinct P waves, which normally represent organized atrial contraction. Instead, the EKG may show chaotic, irregular deflections known as fibrillatory waves or “f waves,” or an erratic, undulating baseline between QRS complexes.
A second indicator is an “irregularly irregular” R-R interval. This means the time between consecutive QRS complexes, which represent ventricular beats, is completely unpredictable and lacks any discernible pattern. Unlike other irregular rhythms, AFib’s irregularity is absolute.
The ventricular rate in AFib is also variable, often ranging from 100 to 180 beats per minute, due to the erratic impulses reaching the ventricles. While the QRS complexes themselves appear normal in shape and duration, their irregular timing is a clear sign of AFib. The combination of absent P waves and an irregularly irregular R-R interval forms the hallmark of atrial fibrillation on an EKG.
Various EKG Approaches for AFib
Different EKG monitoring approaches detect atrial fibrillation, particularly when the condition occurs intermittently or without noticeable symptoms. The standard 12-lead EKG is used for immediate diagnosis if AFib is present during the brief recording period, which typically lasts only about 10 seconds. This test provides a snapshot of the heart’s electrical activity from multiple angles.
When AFib episodes are sporadic or asymptomatic, a Holter monitor is used. This portable device records the heart’s electrical activity continuously, usually for 24 to 48 hours, but sometimes for up to 7 days or longer. Patients wear the device under clothes while engaging in daily activities, allowing for the capture of intermittent rhythm disturbances that a standard EKG might miss.
For less frequent episodes, an event monitor is often prescribed. This portable device can be worn for weeks or months and records the heart’s electrical activity only when activated by the patient experiencing symptoms, or automatically when an irregular rhythm is detected. For very rare episodes, an implantable loop recorder (ILR) may be used. This device is placed under the skin and can continuously monitor and record heart rhythm for up to three years.