Rate refers to events per minute, which for the heart means beats per minute (bpm).
The ventricular rate and the atrial rate are often the same, and "heart rate" often means the ventricular rate.
If the atrial rate and the ventricular rate differ we have a disorder of impulse formation or conduction or both
This refers to the timing of a series of events. The events can be regular or irregular or occur in patterns. The term is used in music, where we speak of a syncopated rhythm (strong beats become weak and vice versa) or three quarter time. In poetry we talk about iambic pentameter. The same meaning is used in electrocardiography: regular rhythm, irregular rhythm or a "irregularly irregular" rhythm.
The term is also applied to the origin(s) and conduction of impulses in the heart. The latter use of the term has replaced the original term for impulse formation and conduction, the "mechanism of the heart beat" or just "the mechanism". Thus we refer to atrial rhythms, supraventricular rhythms, junctional rhythms and ventricular rhythms.
The frequently used term "normal sinus rhythm" implies that the atrial rhythm has a normal origin and normal conduction in the atria, that the conduction of the impulse through the atrioventricular node is normal, and that conduction through the His-Purkinje system to the ventricles is also normal.
The commonly used term "rapid atrial fibrillation" (or RAF) is an interesting use of the terms rate and rhythm. The atrial rhythm and the ventricular rhythm are both irregular in atrial fibrillation (AF). The atria contract at a rate of 400-600 bpm in AF, so the atrial rate is always rapid in AF.
The ventricular rate in AF can be
- within the normal range ("controlled AF")
- faster than normal ("uncontrolled AF")
RAF is short-hand for AF with a faster than normal ventricular rate.