QT interval
description
Transcript of QT interval
QT interval
Lucy AdkinsonJuly 2013
What we are going to cover
• Reminder of ECGs and what is the QT interval• How to work out QTc• Why do we care?• What should we do or avoid?– Risk factors– Drugs– Methadone – General recommendations for practice
• Evidence
ECG
Corrected QT : QTc
• Adjust the QT for the heart rate• QTc : divide the QT interval by the square root of
the preceding R-R interval– QTc = QT /√RR
• Interpretation:QTc (msec) Male Female
Normal <430 <450
Borderline 430-450 450-470
Abnormal >450 >470
The significance of prolonged QTc
• Pro-arrhythmic state• Increased risk of ventricular arrythmia – Torsade de pointes
Long QT
• Inherited• Acquired:– Hypokalaemia/hypomagnesaemia– Drugs
• Cardiac disease – Bradycardia, LVH, Heart failure, recent
cardioversion from AF, ventricular arrhythmia
Drugs and torsades
• Potassium channel blockade• Modifies repolarisation and prolongs action
potential• 40 + drugs linked with QT and torsade– (not all that prolong QT, cause torsade)– Drug induced torsade is relatively rare – can be as
high as 2-3% with some (high risk) drugs
Drugs and Torsade
• Greatest with anti-arrhythmic drugs (class III)– Amiodarone, disopyramide, sotalol
• In some drugs, risk only present with:– High doses– IV – Drug interaction
• E.g. Ketoconazole inhibits CYP3A4 and impairs methadone metabolism
– Impaired metabolism • E.g. CYP2D6 poor metabolisms may have high plasma
concentrations of culprit drugs with normal doses• Hepatic or renal failure
Which drugs?Drugs available associated with prolonged QT and torsade de pointes
Anti-arrhythmics•Amiodarone•Disopyramide•Sotalol
Antimicrobials•Macrolides: clarithromycin, erythromycin,
Antimalarials•Chloroquine
Psychotropic drugs•Chlorporomazine•Droperidol•Haloperidol•Pimozide
Misc•Aresenic•Domperidone•Methadone •Saquniavir•Toremifine
www.azcert.org
http://www.azcert.org/medical-pros/drug-lists/list-01.cfm?sort=Generic_name
Methadone
• Prolongs QT – dose dependant and risk of torsade de pointes• Serious adverse events – more so than other opioids
– FDA, 59 reports, 1 confirmed death from torsade• For practice
– Role of ECG monitoring– Use in caution with:
• History of cardiac conduction abnormalities• Ischaemic heart disease• Liver disease• Family history of sudden death • Electrolyte abnormailites (or drugs which cause this e.g. Diuretics)• Concurrent treatment with other drugs which potentially prolong QT, inhibit
CYP3A4
Recommendations for practice• Be aware – polypharmacy in palliative care• But put in context
– 300 patients in specialist palliative care unit• 48 (16%) had prolonged QT• Only 2 severely prolonged - >500msec• They both had IHD
– Commonsense at end of life• If prescribing a drug:
– Understand the pharmacology, drug-drug interaction, impaired elimination– Avoid concurrent use of QT prolonging drugs– Use lowest dose effective
• If known prolonged QT avoid use of risk drugs• Cardiac disease (or other risk factors), avoid if possible
– If no alternative, monitor ECG before and after and ensure electrolytes monitored
• Report drugs which have prolonged QT to MHRA (yellow card)• Consider torsades as possible cause of palpitations, syncope, seizure like
activity
Summary
• Review cardiac history• Review drug history prior to any new drugs• Check out drugs in PCF/ online• Avoid multiple QT drugs• In particular haloperidol, methadone,
domperidone, macrolide antibiotics
References
• PCF – pages 727-733• www.azcert.org• European Medicines Agency
http://www.ema.europa.eu/ema/index.jsp?curl=pages/medicines/human/referrals/Domperidone-containing_medicines/human_referral_prac_000021.jsp&mid=WC0b01ac05805c516f