Torsades de pointes (TdP)

associated with sudden death
- pronunciation by Australians commonly associated with sudden death in native French speakers
ECG characteristics
- cyclical multiform ventricular ectopic complexes that vary about an isoelectric axis
  - due to 2 ventricular ectopic foci (a reciprocating tachycardia)
  - usual rate of 150-300/min
Other ECG features
- ectopy
- bradycardia
- high grade AV block

Risk factors

age: young children normally have a longer QTc without increased risk of TdP
gender: males usually have shorter QTc
ethnicity: higher risk in black skinned patients
causative agent
- amiodarone increases QTc but does not appear to increase the risk of TdP
rapid onset
- e.g. rapid infusion of a QT-prolonging drug
recent conversion from atrial fibrillation
- especially if a QT-prolonging drug has been used
congestive cardiac failure
digitalis therapy
rapid rate of intravenous infusion with a QT-prolonging drug
severe hypomagnesaemia
QTc prolongation
- caused by inhibition of the rapid component of the delayed rectifier potassium (IKR) channel
- risk not a linear function of the QT interval
- risk increases 6% (compound) for every 10% increase in QTc above 500 msec.

Antipsychotics	Antiarrhythmics	Tricyclics	Other antidepressants	Antihistamines	Others
Chlorpromazine	Quinidine	Amitriptyline	Citalopram	Diphenhydramine	Erythromycin
Haloperidol	Procainamide	Doxepin	Escitalopram	Loratadine	Clarithromycin
Droperidol	Disopyramide	Imipramine	Venlafaxine	Terfenadine	Quinine
Quetiapine	Flecainide	Desipramine	Bupropion		Chloroquine
Olanzapine	Sotalol				Hydroxychloroquine
Thioridazine	Amiodarone

Electrolyte abnormalities
- hypomagnesaemia
- hypocalcaemia
- hypokalaemia
  - does not actually cause prolonged QT syndrome
  - U wave of hypokalaemia is commonly misinterpreted as a T wave
Heart disease
- cardiomyopathy
- severe cardiac failure
- myocardial ischaemia
- complete heart block
- hypertension
Poisoning
- many drugs prolong the QTc to a minor degree, but rarely (if ever) cause TdP on their own
- type I, III anti-arrhythmics
  - quinine/quinidine
- antipsychotics
  - clozapine
  - haloperidol/droperidol (much lower risk)
  - quetiapine
  - olanzapine
  - risperidone
- TCADs
- carbamazepine
- methadone
- lithium
- organophosphates
- quinolones
  - erythromycin/clarithromycin/azithromycin
- ondansetron
- fluconazole/ketoconazole
Congenital
Other
- hypothyroidism
- SAH

cardioversion if pulseless or in extremis
- 200J
- may not synchronise, so asynchronous defibrillation may be required
MgSO₄
- 1-2 G of MgSO4 over 10 minutes if cardiac arrhythmia, torsades, seizures
- 1 G of MgSO4 in 100mL Normal Saline over 30 minutes for slow replacement
isoprenaline
atropine if organophosphates the cause
overdrive pacing
K⁺ replacement to 4.5 – 5 mmol/L
Calcium gluconate 1 G to replenish Calcium (normally go hand in hand)
Admission criteria for ECG monitoring
- QT interval above the QT Normogram