Sinus Rhythm: This is the most common and normal cardiac rhythm in adults, characterized by a regular rhythm with a rate between 60-100 beats per minute (bpm) and a P wave preceding each QRS complex. It's the default diagnosis unless there's evidence suggesting otherwise.

Ectopic Atrial Rhythm: Originates from a focus outside the sinoatrial (SA) node but within the atria, leading to P waves that are different in morphology from those seen in sinus rhythm. The rate can be regular or irregular.
Wandering Atrial Pacemaker: A rhythm where the site of atrial depolarization shifts between different foci within the atria, leading to varying P wave morphologies and a rate that can be regular or irregular.
Atrial Premature Beats: Early beats originating from the atria that can interrupt a regular sinus rhythm, often followed by a pause before the next beat.

Atrial Fibrillation: Although it presents with an irregularly irregular rhythm and absence of P waves, it's crucial to distinguish from other atrial rhythms due to its implications for stroke risk and anticoagulation therapy.
Paroxysmal Supraventricular Tachycardia (PSVT): A sudden onset, regular, narrow-complex tachycardia that can be mistaken for a rapid sinus or ectopic atrial rhythm but requires different management.
Junctional Rhythm: Originates from the AV junction and can mimic an ectopic atrial rhythm but lacks P waves or has retrograde P waves.

Multifocal Atrial Tachycardia: Characterized by an irregular rhythm with at least three distinct P wave morphologies, each associated with a different focus within the atria.
Chaotic Atrial Tachycardia: A rare condition with multiple ectopic foci firing rapidly, leading to a very irregular rhythm that can be difficult to distinguish from atrial fibrillation.
Atrial Flutter: Although not typically mistaken for sinus or ectopic atrial rhythm due to its characteristic "sawtooth" pattern on ECG, it's a rare but important diagnosis to consider in the differential of atrial arrhythmias.