Sinus rhythm
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Image:SinusRhythmLabels.png Sinus rhythm is a term used in medicine to describe the normal beating of the heart, as measured by an electrocardiogram (ECG).
Sinus rhythm is the ECG trace obtained from an individual with a normal heart. It has certain generic features that serve as hallmarks for comparison with normal ECGs. There are typically four distinct waves (identified by the letters P, Q, R, S, and T) in a single beat of the heart in sinus rhythm, and they occur in a specific order, over specific periods of time, with specific relative sizes. While there is a significant range within which variations in rhythm are considered normal, anything that deviates from sinus rhythm by more than a certain amount may be indicative of heart disease.
In normal sinus rhythm, electrical impulses from the SA node travel to the AV node with successful contraction of the two atria. The electrical impulses from the AV node successfully contract the ventricles. On the ECG, there are normal PQRST elements with no evidence of arrhythmia, tachycardia, or bradycardia.