An Electrocardiogram (EKG or ECG) records the heart’s electrical activity. This non-invasive test assesses heart health by translating electrical signals into a visual tracing. The EKG provides information about the heart’s rate, rhythm, and electrical impulse timing, helping identify various heart conditions.
Understanding EKG Basics
The EKG tracing displays distinct waves and complexes, each representing a specific electrical event. The P wave, typically a small, rounded upward deflection, signifies atrial depolarization. This causes the heart’s upper chambers, the atria, to contract and pump blood into the ventricles.
Following the P wave, the electrical impulse travels through specialized pathways, leading to ventricular depolarization. This is represented by the QRS complex, a sharp, larger deflection on the EKG, reflecting the contraction of the heart’s lower chambers, the ventricles, as they pump blood out to the body. After the ventricles contract, they repolarize. This final electrical event is depicted by the T wave, which appears as another upward deflection following the QRS complex.
Characteristics of a Normal EKG
A normal EKG tracing exhibits a predictable and orderly pattern, often referred to as normal sinus rhythm. In this rhythm, the heart’s natural pacemaker, the sinoatrial (SA) node, initiates the electrical impulses. This results in a regular heart rate, typically ranging from 60 to 100 beats per minute in adults.
A defining feature of normal sinus rhythm is the presence of a distinct P wave preceding every QRS complex. Each P wave should have a consistent shape and occur at a regular interval before its corresponding QRS complex, known as the PR interval. This consistent timing indicates proper electrical conduction from the atria to the ventricles.
The QRS complexes themselves appear narrow and uniform, reflecting efficient and rapid depolarization of the ventricles. The rhythm between successive QRS complexes, known as the R-R interval, is regular, demonstrating the heart’s steady beat. Finally, the T waves are consistently upright and follow each QRS complex, indicating normal ventricular repolarization.
Characteristics of Atrial Fibrillation on EKG
Atrial Fibrillation, or AFib, presents a distinctly different visual pattern on an EKG compared to a normal tracing. A primary characteristic of AFib is an “irregularly irregular” rhythm. This means the time between consecutive QRS complexes varies randomly, lacking any discernible pattern. This irregularity stems from chaotic electrical activity within the atria.
Another hallmark of AFib is the absence of distinct P waves. Instead of organized atrial depolarization, the atria quiver chaotically. This disorganized electrical activity manifests as small, erratic deflections on the EKG baseline, often referred to as fibrillatory waves or “f” waves. These f waves can vary in size, sometimes appearing coarse or fine, or even nearly absent.
The ventricular response in AFib is also often variable, leading to a range of heart rates. While the QRS complexes in AFib are typically narrow, similar to a normal EKG, their irregular spacing is a key indicator of the arrhythmia.
Key Distinctions Between Normal and AFib EKGs
The primary difference between a normal EKG and Atrial Fibrillation lies in rhythm regularity. A normal EKG displays a consistently regular rhythm, with R-R intervals that are uniform. In contrast, an AFib EKG is characterized by an “irregularly irregular” rhythm, where R-R intervals show no predictable pattern.
A second distinction is the appearance of P waves. In a normal EKG, a distinct P wave precedes every QRS complex, indicating organized atrial electrical activity. In AFib, these clear P waves are absent. Instead, the EKG baseline often shows chaotic, small oscillations known as fibrillatory (f) waves, representing disorganized atrial activity.
While QRS complexes typically appear narrow in both, their surrounding electrical activity differs. Regular P waves and consistent R-R intervals define a normal tracing, whereas absent P waves, fibrillatory waves, and irregularly irregular R-R intervals are the hallmarks of Atrial Fibrillation.