Sinus rhythm
A sinus rhythm is any
The term normal sinus rhythm (NSR) is sometimes used to denote a specific type of sinus rhythm where all other measurements on the ECG also fall within designated normal limits, giving rise to the characteristic appearance of the ECG when the
Other types of sinus rhythm that can be normal include
Characteristics
In humans, for an ECG to be described as showing a sinus rhythm, the shape of the P wave in each of the 12 standard ECG leads should be consistent with a "typical P vector" of +50° to +80°.[2] This means that the P wave should be:
- always positive in lead I, lead II, and aVF
- always negative in lead aVR
- any of biphasic (-/+), positive or negative in lead aVL
- positive in all chest leads, except for V1 which may be biphasic (+/-)[2]
If the P waves do not meet these criteria, they must be originating from an abnormal site elsewhere in the atria and not from the sinus node; the ECG cannot, therefore, be classed as showing a sinus rhythm.[2]
In general, each P wave in a sinus rhythm is followed by a QRS complex, and the sinus rhythm therefore gives rise to the whole heart's depolarization. Exceptions to this include
Characteristics of normal sinus rhythm
By convention, the term "normal sinus rhythm" is taken to imply that not only are the P waves (reflecting activity of the sinus node itself) normal in morphology but that all other ECG measurements are also normal.[3][5] Criteria therefore include:
- Normal heart rate (classically 60 to 100 beats per minute for an adult).
- Regular rhythm, with less than 0.16-second variation in the shortest and longest durations between successive P waves
- The sinus node should pace the heart – therefore, P waves must be round, all the same shape, and present before every QRS complex in a ratio of 1:1.
- Normal P wave axis (0 to +75 degrees)
- Normal PR interval, QRS complex and QT interval.
- QRS complex positive in leads I, II, aVF and V3–V6, and negative in lead aVR.[3]
References
- ISBN 9780702046421.
- ^ OCLC 942900796.
- ^ ISBN 9780323019057.
- ISBN 9780803620353.
- PMID 26702344.
External links
- "Normal Sinus Rhythm". Archived from the original on 15 December 2012.