What does an undulating baseline with no visible P waves on a 12-lead EKG indicate?

An undulating baseline with no visible P waves on a 12-lead EKG is characteristic of atrial fibrillation. In this arrhythmia, the normal electrical conduction between the atria and ventricles is disrupted. Instead of clear, distinct P waves that indicate atrial depolarization, the tracing shows an irregularly wavy baseline, which results from chaotic electrical activity in the atria. This absence of organized atrial contraction results in an irregularly irregular ventricular response, which is a hallmark finding in atrial fibrillation.

In contrast, atrial flutter typically presents with a “sawtooth” pattern of P waves, referred to as flutter waves, rather than the undulating baseline expected in atrial fibrillation. Second-degree heart block generally shows a pattern of dropped beats but maintains visible P waves, and Wolff-Parkinson-White syndrome is characterized by a delta wave and a short PR interval, which are not consistent with the description of an undulating baseline and absent P waves.