From the Guidelines
In atrial fibrillation (AFib), P waves are absent from the ECG, replaced by chaotic, rapid electrical activity in the atria that appears as an irregular baseline or "fibrillatory waves" on the ECG, as defined by the 2014 AHA/ACC/HRS guideline for the management of patients with atrial fibrillation 1.
Key Characteristics of AFib
- The surface ECG shows absolutely irregular RR intervals, i.e., RR intervals that do not follow a repetitive pattern, as stated in the 2010 ESC guidelines for the management of atrial fibrillation 2.
- There are no distinct P waves on the surface ECG, with some apparently regular atrial electrical activity possibly seen in some ECG leads, most often in lead V1 2.
- The atrial cycle length, when visible, is usually variable and < 200 ms (≥300 bpm), indicating rapid and irregular atrial activity 2.
Clinical Implications
The absence of P waves and presence of fibrillatory waves is a defining diagnostic feature of AFib, reflecting the lack of coordinated atrial contraction, which contributes to the increased risk of thrombus formation in the atria, particularly the left atrial appendage, leading to the increased stroke risk associated with AFib, as noted in the 2014 AHA/ACC/HRS guideline 1.
Diagnostic Evaluation
When evaluating a patient with suspected AFib, it is essential to look for the absence of distinct P waves before each QRS complex, an irregular ventricular rhythm, and the presence of fibrillatory waves, which may be coarse or fine depending on the case, as described in the 2010 ESC guidelines 2.
From the Research
P Waves in Atrial Fibrillation
- Atrial fibrillation (AF) is characterized by rapid and disorganized atrial activation leading to impaired atrial function, which can be diagnosed on an EKG by lack of a P-wave and irregular QRS complexes 3.
- The absence of P waves in AF is due to the disorganized atrial activation, which prevents the formation of a coherent P wave 3.
- In AF, the normal P wave is replaced by fibrillatory waves, which are small, irregular, and rapid deflections on the EKG 3.
Diagnosis and Treatment
- The diagnosis of AF is typically made using an electrocardiogram (ECG), which shows the absence of P waves and irregular QRS complexes 3.
- Treatment of AF typically involves a combination of rate control, rhythm control, and anticoagulation therapy to prevent stroke and other complications 4, 5, 6.
- Rate control therapy aims to slow the ventricular rate, while rhythm control therapy aims to restore and maintain sinus rhythm 4, 5, 6.
Electrical and Pharmacological Cardioversion
- Electrical cardioversion is a procedure that uses electrical shocks to convert AF to sinus rhythm, and is often used in patients with symptomatic AF 5, 7.
- Pharmacological cardioversion uses medications such as ibutilide, flecainide, or propafenone to convert AF to sinus rhythm, and is often used in patients with less severe symptoms 5, 7.
- Antiarrhythmic drugs such as amiodarone, sotalol, and propafenone can be used to maintain sinus rhythm after cardioversion, but may have potentially serious adverse effects 4, 5, 6.