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Tachyarrhythmias
 
 

Ventricular Tachycardia

 
 
 
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Monomorphic Ventricular Tachycardia

  • Monomorphic VT is a focal or reentrant ventricular rhythm that requires rapid assessment and management, due to its risk of haemodynamic instability and collapse.
    • Look For

    • Heart rate >100bpm
    • Regular rhythm (RR interval)
    • Broad QRS complexes >120ms
    • Monomorphic Ventricular Tachycardia
       
  • A left bundle branch morphology classically suggests a right ventricular focus of VT, while a right bundle morphology pattern suggests a left ventricular focus. A septal focus may manifest as either a left or right bundle branch morphology.
  • To find out how to distinguish VT from SVT with aberrancy, read the section called ‘distinguishing VT and SVT with aberrancy'.
    • Classification

    • Nonsustained VT - three or more ventricular beats at a rate of >100bpm, lasting less than 30 seconds, without haemodynamic instability
    • Sustained VT - a ventricular rhythm at a rate of >100bpm, lasting at least 30 seconds or with haemodynamic instability
    • Mechanisms

    • Monomorphic VT occurs most commonly in the context of a macro-reentrant pathway in a structurally abnormal heart. The rhythm may also be caused by a focal arrhythmogenic ventricular focus.
    • Causes of Monomorphic Ventricular Tachycardia

    • Myocardial infarction
    • Cardiomyopathy
    • Congestive cardiac failure

Polymorphic Ventricular Tachycardia

  • Polymorphic VT is a wide complex tachycardia with multiple QRS complex morphologies. This most commonly refers to torsade de pointes, however PVT also present in patients with acute myocardial infarction.
    • Look For

    • Heart rate >100bpm
    • Irregular rhythm
    • Broad QRS complexes of varying amplitude and morphology
    • Causes of Polymorphic Ventricular Tachycardia

    • Torsade de pointes - due to prolonged QT
    • Non-torsades polymorphic VT - most commonly due to coronary ischaemia / infarction
  • Polymorphic VT other than torsade de pointes will have a normal QTc once reverted to sinus rhythm.

Torsade de Pointes

  • Torsades is a polymorphic VT that occurs as a result of a prolonged QT interval.
    • Look For

    • Polymorphic ventricular tachycardia with ‘twisting’ around the isoelectric line
    • Prolonged QT interval once reverted to sinus rhythm
    • Torsade de Pointes
       
    • Causes of Prolonged QT

    • Congenital

    • LQTS1 (triggered by exercise)
    • LQTS2 (triggered by stress and loud noises)
    • LQTS3 (triggered by sleep)
    • Others - LQTS4-6, Jervell and Lange-Nielsen syndrome
    • Drugs

    • Antiarrhythmics - amiodarone, sotalol, procainamide, quinidine
    • Antidepressants - amitryptiline, dothiepine, citalopram, escitalopram
    • Antipsychotics - risperidone, haloperidol, clozapine, droperidol, chlorpromazine
    • Antiemetics - ondansetron, domperidone
    • Macrolides - azithromycin, clarithromycin, erythromycin
    • Quinolones - ciprofloxacin, moxifloxacin
    • Antifungals - fluconazole, ketoconazole
    • Antimalarials - chloroquine, mefloquine
    • Anaesthetic gases – halothane, sevoflurane
    • Methadone
    • Others

    • Hypokalaemia
    • Hypomagnesaemia
    • Hypocalcaemia
    • Severe hypothermia
    • Severe bradycardia - sick sinus syndrome, complete heart block
    • Cardiovascular disease - tako-tsubo cardiomyopathy, MI, CCF
    • Cerebrovascular disease - intracranial / subarachnoid haemorrhage, stroke
    • Hypothyroidism
 
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