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Bradycardia and Pacing
Sinus brady
• Fit
• Cold
• Drugs- β-blockers, CCBs, digoxin
Sick-sinus syndrome
Heart blocks
1 degree
– Prolonged PR interval >0.2s
2 degree
– Mobitz I (Wenkebach)
• Progressive PR prolongation until a beat is dropped
– Mobitz II
• PR interval is constant, dropped beat randomly
3 degree (complete)
– Complete dissociation between P waves and QRS complexes
Mobitz II
 Is the patient compromised?
o Chest pain
o Altered LOC
o Hypotension
 Atropine 0.5mg-1.5mg IV q 15 minutes
 Pacing
 If pacing not available consider
o Isoprenaline 10-20mcg IV followed by infusion (may exacerbate hypotension)
o Adrenaline 10-20mcg IV
 Associated with MI
o In inferior MI is usually transient
o In anterior MI is usually permanent and a poor prognostic indicator- need pacing
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%
QRS widening rx= sodium bicarbonate
QT prolongation rx= magnesium, isoprenaline, overdrive pacing
Westmead JMO After-hours STAR Program
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
o Charcoal if within 1 hour of ingestion for standard preparations, or 4 hours for extended release
o Whole bowel irrigation after charcoal in extended release preparations
o Calcium chloride 10% 20ml or calcium gluconate 10% 60ml
o Atropine is temporising
o 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
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 freagments) – suggested resource – “Tox Handbook” (Elesevier). Tox Reg (Page 8333)
o Acute HD stable = 5 vials
o Acute HD unstable = 10 vials
o Acute cardiac arrest = 20 vials
o Chronic = 2 vials
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.
Transcutaneous Pacing
o bradycardia unresponsive to drug therapy
o 3rd degree heart block
o Mobitz type II second-degree heart block when haemodynamically unstable or operation planned
o overdrive pacing for Torsades (due to prolonged QT)
o not likely to be effective in asystole (can trial if clear reversible cause)
Set intial 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
Westmead JMO After-hours STAR Program