Sinus rhythm

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Schematic representation of normal sinus rhythm showing standard waves, segments, and intervals

Sinus rhythm refers to any cardiac rhythm where the sinoatrial node is generating impulses within the cardiac muscle. The presence of sinus rhythm is necessary, but not sufficient, for normal electrical activity within the heart.

Sinus rhythms may be classified as either normal or abnormal. The term normal sinus rhythm denotes a sinus rhythm where the heart rate is regular and within normal limits, each impulse from the sinoatrial node generates a P wave of normal morphology on the electrocardiogram (ECG), and the impulse is further conducted normally through the rest of the electrical conduction system of the heart. This will give rise to the characteristic appearance of the normal ECG.

Abnormal sinus rhythms include sinus tachycardia, sinus bradycardia and sinus arrhythmia.

ECG characteristics of normal sinus rhythm[edit]

The characteristics of the ECG of a heart in normal sinus rhythm are, by definition, the characteristics of the normal ECG. Criteria for a normal sinus rhythm include:

  1. A normal heart rate (commonly defined as 60 to 100 beats per minute for an adult).
  2. Regular rhythm.
  3. The sinoatrial node should pace the heart – therefore, P waves must be present, round, upright, and before every QRS complex in a ratio of 1:1.
  4. PR interval is between 0.12 second and 0.20 second.
  5. QRS complex width should be less than 0.12 second.

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