Sinuatrial Block: Symptoms, Complaints, Signs

The following symptoms and complaints may indicate sinuatrial block (SA block):

  • 1st-degree SA block
    • No symptoms
  • SA block 2nd degree
    • Mobitz type I (Wenckebach block)
      • Heart rate usually rhythmic with sudden pause, thus often bradycardia (heartbeat too slow: < 60 beats per minute)
    • Mobitz type II (Mobitz block).
      • Heart rate is arhythmic (occasional failure of an entire electrical cardiac excitation (e.g., following a 2:1 or 3:1 periodicity))
  • SA block 3rd degree (asystole/ arrest of electrical and mechanical cardiac action if no replacement rhythm occurs!).
    • Secondary replacement rhythm (AV node): heart rate about 40-50/min.
    • Tertiary replacement rhythm (HIS bundle or Tawara thigh): heart rate about 20-30/min.

Accompanying symptoms depending on

  • Length of the break
    • Nausea (sickness)
    • Paleness
    • Vertigo (dizziness)
    • Cardiogenic shock (form of shock caused by weakened pumping action of the heart).
  • Speed of replacement rhythm
    • Bradycardia < 40 beats per minute → cerebral underperfusion/inferior brain supply (easy fatigability, dizziness, apathy (listlessness), cognitive impairment), heart failure (cardiac insufficiency), dyspnea (shortness of breath)

If the heart is pre-damaged, the replacement rhythm of the AV node may be absent, which may lead to prolonged cardiac arrest with immediate unconsciousness.