Junior Doctor Notes 🩺

Ventricular Tachycardia

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  • The most common cause of VT is myocardial ischaemia or myocardial scarring following acute MI
  • A broad-complex SVT with aberrancy from ventricular pre-excitation (WPW) is treated the same as VT ⇒ Regard al broad complex tachycardia as VT until, or unless, proved otherwise
  • The identification of P waves dissociated from QRS complexes during broad complex tachycardia confirms VT
  • Accelerated idioventricular rhythm (idioventricular rhythm with a heart rate of 50-110 beats/min) is not categorised at VT and commonly occurs after successful thrombolysis or PCI (see ACS)

Differential Diagnosis of Wide Complex Tachycardias

  1. Ventricular tachycardia
  2. A supraventricular tachycardia with aberrant conduction (eg, supraventricular tachycardia with underlying bundle-branch block); often rate-related, appearing only with fast heart rates
  3. AV reciprocating tachycardia (antidromic tachycardia) in a patient with preexcitation (eg, WPW)
  4. Paced rhythms

Management

  • Unstable VT
    • No recordable BP and no palpable pulse (pVT)
      • Call for cardiac arrest trolley and proceed with ALS
      • Prioritise early defibrillation
    • VT with hypotension, angina, LVF or impaired mental status
      • Call for senior help
      • Apply high-flow oxygen by mask and gain IV access
      • Attach ECG monitor/defibrillator to the patient and confirm rhythm
      • Prepare procedural sedation such as propofol 200mg in 20mL IV and call an anaesthetist
      • Once senior assistence is present proceed with DC cardioversion (start with 120-150 J biphasic and repeat up to three times, with stepwise increase in joules)
  • Stable VT
    • Deterioration can be rapid, be prepared
    • Call for cardiac arrest equipment and senior assistance
    • Give the patient 100% by mask
    • Attach an ECG monitor to the patient
    • Make sure than IV line is in place
    • Obtain a 12-lead ECG and review QRS complexes and determine if it is monomorphic or polymorphic
      • Monomorphic: ECG shows a broad-complex QRS, regular rhythm, rate >100 beats/min with constant QRS
        • LV function unknown or impaired:
          • Give amiodarone 300 mg IV bolus over 20-60 minutes followed by infusion of 900 mg over 24 hours
        • LV function known to be normal:
          • Administer amiodarone as above
        • Prepare for synchronised cardioversion if amiodarone is unsuccessful or the condition deteriorates
        • Transfer to ICU/CCU for continuous ECG monitoring
        • Look for precipitating cause of the VT such as myocardial ischaemia, eletrolyte abnormality (hypokalaemia, hypomagnesaemia, hypocalcaemia) or drug toxicity (antiarrhythmic and other sodium-channel blocking drugs especially TCAs)
      • Polymorphic: ECG shows a braod-complex QRS, regular rhythm, rate >100 beats/min but with a variable and changing axis
        • Review the baseline 12-lead ECG
        • Normal baseline QT interval
          • Give amiodarone as for monomorphic VT
        • Baseline QT interval is prolonged leading to ‘torsades de pointes’
          • Causes include electrolyte abnormality (e.g. hypokalaemia, hypomagnesamia, tricyclic antidepressants) drug interactions or a congenital disorder
          • Give magnesium sulfate 2g (8mmol or 4mL of 49.3% solution) IV over 1-2 min
          • Correct any underlying metabolic disorder, particularly hypokalaemia
          • DC cardioversion is essential for critical hypotension but the torsades de points rhythym often recurs and may require several shocks
          • Avoid drugs that prolong QT interval (including amiodarone)

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