Sinus Rhythm: Normal Sinus Heart Rate, Sinus Pause, Sinus Arrhythmia, Sinus Bradycardia and Sinus Tachycardia

It is the characteristic rhythm of the healthy human heart, and its rate is usually regular, but it will vary depending on the autonomic inputs in the sinus node.

There may be an irregularity in sinus frequency, and when this occurs, it is called ” sinus arrhythmia. ” A sinus rhythm faster than the normal range is sinus tachycardia, while a slower rhythm is sinus bradycardia.

Due to its small mass, the sinoatrial node does not have a visible manifestation in the electrocardiogram (ECG). Therefore, the behavior of the sinoatrial node must be inferred from the atrial response.

The right upper atrium is depolarized first, followed by simultaneous depolarization of the rest of the right and some of the left atrium, and finally by depolarization of the left atrial appendage.

Normal Sinus Heart Rate

The average heart rate has been considered to be between 60 and 100 beats per minute, although there is some disagreement concerning the intermediate frequency in adults.

The range (defined by percentiles 1 and 99) is between 43 and 102 beats per minute in men and between 47 and 103 beats per minute in women.

There is also significant variability in age in young children. The average heart rate is 110 to 150 beats per minute in babies, gradually decreasing during the first six years of life.


A normal sinus rhythm refers to an average heart rate and a rhythm.

The shape of the electrocardiogram (ECG) tracing will show specific vital attributes that will be considered normal, as explained below. With normal sinus rhythms, the electrical impulse of the heartbeat originates in the sinoatrial node.

The P waves are vertical, appear before each QRS, and have the same shape. The intervals between P waves are regular, although some variations with breathing may occur. Sinus rhythms are classified as:

Normal Sinus Rhythm

This is the normal rhythm of the heart. The electrical impulse originates within the sinoatrial node and travels through the atria. After a short delay, the impulse travels through the branches of the bundle.

Average heart rate in children

Expressed in beats per minute (bpm):

  • Newborns: 110 – 150 bpm.
  • Two years: 85 – 125 pm.
  • Four years: 75 – 115 pm.
  • Six years: 60 – 100 pm.

Average heart rate in adults

Normal sinus rhythm in a healthy adult of 18 years:

  • Regular rhythm at 84 beats per minute.
  • The morphology and the axis of the standard P wave.
  • Narrow QRS complexes.
  • A QRS complex follows each P wave.
  • The PR interval is constant.

Factors that can alter Normal Sinus Rhythm

  • Stimulation (for example, pain)
  • Lower myocardial infarction.
  • The disease of the Sinus node.
  • Hypothyroidism
  • Hypothermia.
  • Anorexia nervosa.
  • Electrolyte abnormalities; hyperkalemia, hypermagnesemia.
  • Hernia of the brainstem (the Cushing reflex).
  • Myocarditis.


  • Beta-blockers.
  • Blockers of calcium channels (Verapamil and Diltiazem).
  • Digoxin
  • Central agonists alpha-2 (Clonidine and Dexmedetomidine).
  • Amiodarone
  • Opiates
  • GABA-ergic agents (Barbiturates, Benzodiazepines, Baclofen).
  • Poisoning by organophosphates.

Sinus pause

The sinus pause includes stop and blockade of sinus output. Sinus arrest is caused by the failure of the sinus node to create an impulse. An interruption in regularity can be observed; with the blockade of sinus output, the node generates an inspiration but is blocked before being transmitted through the cardiac atria.

Sinus arrhythmia

Sinus arrhythmia seems normal, except for slight irregularities. A frequent cause of sinus arrhythmia may be rhythm variations caused by breathing.

The PP range varies widely from 1.04 seconds (heart rate ~ 57 bpm) to 0.60 seconds (heart rate ~ 100 bpm), a variability of more than 400ms.

Sinus Bradycardia

Sinus bradycardia is a rhythm with a frequency of 40-60 beats per minute.

Sinus Tachycardia

Sinus tachycardia is a regular rhythm with more than 100 bpm heart rate. It is a normal response to exercise, excitement, and some diseases.