sinusrytm

Sinusrytm, or sinus rhythm, is the normal electrical rhythm of the heart produced by the sinoatrial (SA) node, the heart’s natural pacemaker. In sinus rhythm, impulses originate in the SA node, spread through the atrioventricular (AV) node and conduction pathways, and produce sequential atrial and then ventricular contractions with regular timing.

On electrocardiography, a normal sinus rhythm features a heart rate typically 60–100 beats per minute in adults at rest; a P wave before every QRS complex with a consistent shape; a PR interval of 120–200 ms; and a QRS duration of less than 120 ms. The rhythm is regular, though minor rate variation can occur with breathing or autonomic tone. Athletes may have resting bradycardia without harm.

Variants include sinus tachycardia (rate over 100 bpm), often from exercise, fever, pain, dehydration, or stimulants; and sinus bradycardia (rate under 60 bpm), which can be normal in athletes or caused by increased vagal tone or medications. Sinus arrhythmia is a benign, respiration-related variation in rate. Other rhythms with irregular or absent P waves require different diagnoses, such as atrial fibrillation.

Clinical relevance: Sinus rhythm is the standard baseline rhythm in healthy individuals. Changes in rate or regularity may reflect physiologic adaptation or underlying disease. Evaluation usually consists of ECG and clinical assessment; longer rhythm monitoring (Holter) or stress testing may be used when symptoms are intermittent or unexplained.