Pacing and Bradycardia Quick Summary

Posted on by Andrew Coggins

Bradycardia and Pacing

SHOW NOTES

Sinus bradycardia – 5 causes

  • Fit
  • Cold
  • Drugs- β-blockers, CCBs, digoxin
  • Sick-sinus syndrome
  • Hypothyroidism

Types of Heart block

  • 1st degree
    • Prolonged PR interval >0.2s
  • 2nd degree
    • Mobitz I (Wenkebach)
      • Progressive PR prolongation until a beat is dropped
    • Mobitz II
      • PR interval is constant, dropped beat randomly
    • 3rd degree (complete)
      • Complete dissociation between P waves and QRS complexes
    • Pacing
      • Mobitz II
      • Complete

Emergency Approach

  • Signs of life? – DRABC
    • No – Start CPR
  • Yes
    • Decide if the patient is ‘compromised’?
      • Chest pain, Syncope
      • Hypotension, Poor perfusion
      • Altered LOC
      • CCF
    • Follow Bradycardia Algorithm – CLICK HERE ARC Bradycardia
  • Overview of steps:
    • Atropine 0.5mg-1.5mg IV q15 minutes (Westmead has 600mcg vials)
    • Transcutaneous Pacing
    • If pacing not immediately available or deemed inappropriate consider
      • Isoprenaline 10-20mcg IV followed by infusion (may exacerbate hypotension)
      • Adrenaline infusion +/- 10-20mcg IV
    • Associated with MI
      • In inferior MI is usually transient
      • In anterior MI is usually permanent and a poor prognostic indicator- need pacing

Pacing Guideline (ARC)

Patients who fail to respond to pharmacotherapy, or who are at high risk of asystole, may require electrical pacing (via either an internal or external route). The potential risk of asystole is indicated by the presence of any of the following:

  • recent asystole;
  • Mobitz II atrioventricular (A V) block;
  • complete AV block (3rd degree heart block) (especially with broad QRS or initial heart rate < 40/min);
  • ventricular standstill of > 3 sec.

Many defibrillators now have the capacity to provide external pacing via the defibrillation paddles or adhesive pads. External pacing stimulates skeletal muscle as well as cardiac muscle and may produce discomfort to the patient.

The pacing is usually set to demand (as required) at 70-80 beats per minute starting low (eg. 30 mA) and increasing until electrical capture with established output occurs. In some settings (such as pre-hospital) where there is a concern that electrical artifact may inhibit pacing in the demand mode, it is reasonable to use a fixed (asynchronous) mode.

 

Indications for Pacing

  • Asystole (see above)
  • Recurrent long sinus pauses (see above)
  • Prolonged QT interval (to prevent torsades de pointes) – overdrive pacing
  • Hemodynamically unstable bradycardia
  • Bifascicular block (or trifascicular)
  • Mobitz type 2 second degree heart block
  • Selectively for other arrhythmias – seek expert help

Contraindications to Pacing

  • All relative – patient’s often do not pacing tolerate due to pain

Transcutaneous Pacing – QiSummary Steps

  • Set initial milliamps (mA) and desired rate to 70
  • Start pacing and increase the mA looking for electrical capture and then feeling for mechanical capture
  • Once captured set mA 5-10 above the capture threshold
  • Troubleshoot and consider analgesia/sedation/intubation as appropriate

 

Life-Threatening Drug Toxicities

β-blockers Overdose

  • Highest risk with propranolol (widens QRS and seizures) and sotalol (prolongs QT)
  • PR prolongation may be the earliest sign
  • May have associated hypoglycaemia
  • Atropine is only temporising
  • Rx= high dose insulin euglycaemic therapy (1u/kg IV insulin followed by 1-2u/kg/hr infusion with 10% dextrose)
  • QRS widening rx= sodium bicarbonate
  • QT prolongation rx= magnesium, isoprenaline, overdrive pacing
  • Glucagon is no longer commonly used

Calcium channel blocker Overdose

  • Highest risk with verapamil and diltiazem
  • May be associated with hyperglycaemia
  • Decontamination is a priority
    • Charcoal if within 1 hour of ingestion for standard preparations, or 4 hours for extended release preparations
    • Whole bowel irrigation after charcoal in extended release preparations
  • Rx
    • Calcium chloride 10% 20ml or calcium gluconate 10% 60ml
    • Atropine is temporising
    • High dose insulin euglycaemic therapy

Digoxin Toxicity

  • Differentiate acute (supratherapeutic ingestion) v chronic (normal doses in patients with dehydration/ renal or hepatic impairment)
  • Levels are more useful in chronic than acute toxicity (although a level over 15 predicts lethality in acute ingestions)
  • Predictors of lethality in acute ingestion
    • ingested dose (more than 10 mg in adults, more than 4 mg in children)
    • cardiac arrest
    • potassium concentration above 5.0 mmol/L
    • life-threatening ventricular arrhythmias
    • decompensation (hypotension) from bradyarrhythmias
  • Atropine is temporising, pacing is rarely effective, and tachyarrhythmias often resistant to cardioversion
  • Rx= Digibind (Fab fragments) – suggested resource – “Tox Handbook” (Elsevier).
  • Tox Reg at WMH or Poisons Centre = Call 131126
    • Acute HD stable = 5 vials
    • Acute HD unstable = 10 vials
    • Acute cardiac arrest = 20 vials
    • Chronic = 2 vials
  • Haemodialysis
  • Treat hyperkalaemia aggressively with insulin-dextrose and sodium bicarbonate. There is a theoretical risk of “stone heart syndrome” with calcium administration but this is not based on more than case reports