From the Guidelines
Atrial fibrillation does not have P waves, as the normal P waves seen on an electrocardiogram (ECG) are replaced by irregular, chaotic fibrillatory waves. In atrial fibrillation, the atria are not contracting in a coordinated manner but instead are quivering due to disorganized electrical activity, as stated in the 2024 ESC guidelines for the management of atrial fibrillation 1. This results in the absence of discernible and regular P waves, and irregular activation of the ventricles. The definition of AF is a developing field and ongoing research may allow for pathology-based strategies that could facilitate personalized management in the future.
The key diagnostic features of atrial fibrillation on an ECG include:
- Absence of P waves
- Presence of fibrillatory waves
- Irregular ventricular response These features are consistent across various studies, including the 2006 ACC/AHA/ESC guidelines for the management of patients with atrial fibrillation 1. However, the most recent and highest quality study, the 2024 ESC guidelines, confirms that atrial fibrillation is characterized by the absence of P waves and the presence of irregular fibrillatory waves 1.
The chaotic atrial activity in atrial fibrillation results in irregular ventricular responses, which is why patients with atrial fibrillation typically have an irregularly irregular pulse. The ventricular response depends on electrophysiological properties of the AV node and other conducting tissues, vagal and sympathetic tone, the presence or absence of accessory pathways, and the action of drugs. Regular cardiac cycles (R-R intervals) are possible in the presence of AV block or ventricular or AV junctional tachycardia.
In summary, the absence of P waves and the presence of fibrillatory waves are key diagnostic features of atrial fibrillation, and the most recent guidelines confirm this definition 1.
From the Research
Atrial Fibrillation and P-Wave Characteristics
- Atrial fibrillation (AF) is associated with changes in P-wave morphology and duration, which can be used to predict the risk of AF and its recurrence after treatment 2, 3, 4.
- The P-wave axis, duration, and dispersion are important electrocardiographic markers that can reflect atrial conduction abnormalities and increased risk of AF 3, 4, 5.
- Studies have shown that abnormal P-wave axis, prolonged P-wave duration, and increased P-wave dispersion are associated with an increased risk of AF and its recurrence after catheter ablation 3, 4.
P-Wave Parameters and Atrial Fibrillation Prediction
- P-wave parameters, such as P-wave duration, voltage, dispersion, and terminal force, can be used to predict the success of repeat catheter ablation for paroxysmal atrial fibrillation 6.
- A decrease in P-wave duration and terminal force after repeat ablation can be correlated with successful procedural outcome 6.
- The use of P-wave parameters can help identify patients at high risk of AF recurrence and guide treatment decisions 4, 6.
Treatment Effects on P-Wave Characteristics
- Beta blocker therapy has been shown to decrease P-wave maximum duration and dispersion in congestive heart failure patients, which may reflect a reduction in the probability of atrial fibrillation 5.
- Anti-arrhythmic medication can affect P-wave beat-to-beat variability in patients with paroxysmal AF, which can be used to improve understanding of medication effects on AF 2.