The Sinus Rhythms

Sinus Rhythm

HR = 75bpm
  • Normal rhythm and rate
  • P Waves present- originating in SA node.

Sinus Tachycardia

HR = 150bpm
  • Sinus Rhythm, >100bpm
    • Expected with exercise
    • Expected with fear/ pain
    • Normal in children
  • Can be caused by:
    • Hypoxia
    • Hypercarbia
    • Pulmonary Embolism
    • ß- Agonists
  • Can occur without obvious stimuli. (More common in young females)
  • Tachycardia at rest suggests a pathology
  • Could represent atrial tachycardia or atrial flutter

Sinus Bradycardia

HR = 35bpm
  • Sinus rhythm, <60bpm
    • Normal during sleep
    • Normal in athletes
  •  Can be caused by:
    • Sinus Node disease
    • Anorexia nervosa (pictured)
    • Hypothermia
    • ß- Blockers
    • Hypothyroidism
    • Hyperkalaemia
  • Can be mistaken for Sinoatrial Block Type II

Sinus Arrhythmia

Varied RR interval. HR varies from 57 – 100bpm
  • Sinus Rhythm, varying HR
    • Normal in young individuals
  • RR interval increases and decreases with respiratory cycle
    • SA node firing rate is increased
  • Constant PR interval
    • Excludes Mobitz I

Sinus Arrest

  • A pause >3s

Sinoatrial Block Type I

  • Lengthened impulse generation/ transmission interval. Results in transmission failure
  • P waves pushed closer together
  • PP interval gets progressively shorter
    • PQRS complex is then absent

Sinoatrial Block Type II

  • Sporadic dropped P waves. Interval between atrial depolarisation and prior impulse generation
  • Fragmentary ‘dropping out’ of P waves from rhythm.
    • Followed by regular P wave


Luthra, A. (2007) ECG Made Easy. Third edition. Tunbridge Wells: Anshan




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