Ventricular tachycardia - Torsades de pointes Flashcards
what is ventricular tachycardia?
potentially life-threatening arrhythmia
originates in cardiac ventricles
what causes ventricular tachycardia?
cardiac scars conduction disorders drugs long-QT syndrome - congenital or acquired electrolyte imbalances ischaemic stroke intracranial haemorrhage endocrine disorders nutritional disorders can rarely occur in healthy individuals
what cardiac scars can cause ventricular tachycardia?
cardiomyopathy
myocardial infarction
iatrogenic
post-op
conduction disorders
e.g. cardiomyopathy
disruption of conduction pathways
what drugs cause ventricular tachycardia?
antiarrhythmics antibiotics antidepressants antipsychotics anticonvulsants
which antiarrhythmics cause VT?
class Ia - quinidine and disopyramide class III - sotalol, amiodarone
which antibiotics cause VT?
macrolides
fluoroquinolones
which antidepressants cause VT?
most tricyclic and tetracyclic antidepressants
lithium
which antipsychotics cause VT?
haloperidol
which anticonvulsants cause VT?
felbamate
fosphenytoin
what electrolyte imbalances cause VT?
hypokalemia
hypomagnesemia
hypocalcemia
what is the most ECG abnormality after ischaemic stroke or intracranial haemorrhage?
QT prolongation
what endocrine disorders cause VT?
hypothyroidism
what nutritional disorders cause VT?
anorexia nervosa
pathophysiology of VT
monomorphic VT
polymorphic VT
decreased cardiac output
monomorphic VT
all QRS complexes look similar
increased automaticity
re-entry circuit
what is a re-entry circuit?
myocardial scarring creates an area of poor electrical conduction so the impulse travels around the scar
polymorphic VT
dissimilar QRS complexes
caused by abnormal ventricular repolarisation
e.g. long QT syndrome, drug toxicity and electrolyte abnormalities
decreased cardiac output
asynchronous atrial and ventricular beats
rapid ventricular rhythm
decreased blood flow into the ventricle during diastole
decreased CO
haemodynamic compromise
what are the clinical features of VT
often asymptomatic - especially if non-sustained
symptoms if sustained
clinical features of sustained VT
palpitations hypotension syncope severe cases: chest pain/pressure - in conjunction with MI cardiogenic shock loss of consciousness progression to ventricular fibrillation sudden cardiac death
what are the subtypes/variants of VF
torsades de pointes
what is torsades de pointes?
polymorphic ventricular tachycardia with QRS complexes that appear to twist around the isoelectric line
can progress to life-threatening ventricular arrhythmia
what causes torsades de pointes?
prolonged QT interval caused by congenital disease, electrolyte abnormalities and drugs
treatment for torsades de pointes
defibrillation if haemodynamically unstable
IV magnesium sulfate if haemodynamically stable
diagnosis of ventricular tachycardia
ECG - main
holter monitor
patient-activated event recorder
echocardiography
ECG VT findings
3 or more consecutive premature ventricular beats - widened QRS
>120bpm = HR
ECG findings sustained vs nonsustained
nonsustained = <30seconds sustained = >30 seconds
ECG findings - morphology
monomorphic = all QRS complexes look similar polymorphic = QRS complexes are different
other possible ECG findings
AV dissociation
Fusion complex
capture beats
AV dissociation
no relationship between P waves and QRS complexes
ventricular rhythm is often faster than atrial rhythm
Fusion complex
atrial and ventricular impulses occur simultaneously
Capture beats
supraventricular impulse may reach AV node and produce a subsequent ventricular beat
holter monitor
24-48 hour ambulatory monitor
useful for diagnosing intermittent VT which may not be present on a single ECG
patient-activated event recorder
device to evaluate patient’s heart rhythm during symptomatic episodes - can be manually initiated or automatic
echocardiography
provides information about possible causes of VT
common differential diagnosis
supraventricular tachycardia with aberrancy - RBBB, LBBB or wolff-parkinson-white
signs and symptoms that suggest VT rather than SVT
over 35 year olds
history of structural heart defects or past MI
AV dissociation, fusion beats and capture beats
signs and symptoms that suggest SVT with aberrancy rather than VT
BBB on prior ECG
history of SVT
evidence of wolff-parkinson-white
what is SVT with aberrancy?
group of tachyarrhythmias that originate in the atria or AVN
wide QRS complex
due to conduction defects
can be irregular or regular
what is wolff-parkinson-white?
congenital condition
intermittent tachycardia and ventricular pre-excitation pattern on ECG
due to bundle of kent which connects the atria and ventricles, bypassing the AVN - delta wave and shortened PR interval
treatment of VT
initial therapy and long-term therapy
initial therapy for VT
different depending on whether patient is haemodynamically unstable or stable
initial therapy is patient is hemodynamically unstable
VT with pulse = cardioversion
VT without pulse = defibrillation
advanced cardiac life support
look for and address possible causes = electrolyte abnormalities and correct, medication induced QT prolongation
initial therapy is patient is hemodynamically stable
antiarrhythmics
cardioversion if medical therapy fails
look for and address possible causes = electrolyte abnormalities, metabolic-induced QT prolongation
which antiarrhythmics can be used to treat VT?
lidocaine
procainamide
amiodarone
what electrolyte abnormalities cause VT?
hypokalaemia
correct as part of treatment
medication-induced QT prolongation
remove any causative medication
use digoxin immune fragment antigen binding for digoxin toxicity
long-term therapy for VT
intracardiac devices
catheter ablation
antiarrhythmics
intracardiac devices
most effective treatment for reducing mortality from VT - used when VT doesn’t respond to therapy
catheter ablation
used when intracardiac devices cannot be tolerated or often receive intracardiac device shocks because of repeated VT
