Bradycardia

Bradycardia is defined as a heart rate below 60/min

Cardiac output = heart rate * stroke volume
Slow heart rate leads to low cardiac output

The tolerance of bradycardia worsens in patients with heart diseases who cannot compensate the bradycardia with increased stroke volume. Patients with advanced heart failure may require a higher heart rate than normal, and a “normal” heart rate might be excessively low for them.

Common causes of bradycardia

• Physiological (e.g. in athletes)
• Cardiac (myocardial infarction, sick sinus syndrome)
• Non-cardiac (vasovagal response, hypothermia, hypoglycemia, hypothyreosis, increased intracranial pressure)
• Drug toxicity (e.g. digoxine, beta-blockers, calcium channel blockers)

Classification of bradycardia

• Slow pacing by sinoatrial node (parasympathetic activation, sinus arrest, sick sinus syndrome)
• Atrioventricular blocks
  •  Ist degree (PR interval >200 msec)
  • 2nd degree Mobitz I (progressive PR prolongation with the dropped beat)
  • 2nd degree Mobitz II (repeated dropped beats, no change in PR interval)
  • 3rd degree (complete block between atria and ventricles)

Management of bradycardia

2021 ERC guidelines “Bradycardia” poster describes proper management.
Some of the specifics are highlighted in the text below.

• ABCDE approach
  Give oxygen if SpO2 <94 %, obtain IV access, Monitor ECG, blood pressure, SpO2
  Record 12-lead ECG if possible (it should not delay the treatment)
  Identify and treat reversible causes (e.g. electrolyte abnormalities, hypovolemia)

The drug of choice is atropine 0,5 mg IV (might be repeated, no effect of dose > 3 mg, doses > 3 mg might be useful in organophosphate intoxication, avoid doses < 0,5 mg IV because of risk of worse bradycardia, alternative: glycopyrrolate).

If repeated administration of atropine does not lead to a satisfactory response, continuous infusion of sympathomimetic drugs is used (isoprenaline, adrenaline). Other alternative drugs are aminophylline, dopamine and glucagon. Glucagon is used as an antidote in intoxication with beta-blockers or calcium channel blockers.

Failure of 2nd choice treatment requires transcutaneous pacing – adhesive pads are placed in an anterolateral position, and analgosedation is necessary. It is only a temporary measure, transvenous pacing or implantation of permanent pacemaker by consultant in intensive care or cardiology should follow.