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Ventricular Arrhythmias

Sustained ventricular tachycardia (VT) (>30 seconds)

  • Can result in dizziness, syncope, hypotension, cardiac arrest
  • 120-220 bpm

Etiology

  • Occurs in the setting of acute MI, coronary artery disease, cardiomyopathy
  • Happens when there is extensive left ventricular (LV) dysfunction

Pathogenesis

  • Caused by abnormal automaticity/triggered activity (in ischemic tissue) or re-entry (in scarred ventricular tissue), extra systoles
  • VT can cause haemodynamic compromise and can degenerate into ventricular fibrillation

Clinical features

  • Palpitations, dizziness, dyspnoea, syncope

ECG

  • Rapid ventricular rhythm with broad, abnormal QRS complexes
  • Features of AV dissociation – results in a fusion beat (see pic)
    • relationship between P waves and QRS is lost as ventricles contract independently of atria

Management

  • DC cardioversion – to restore sinus rhythm
  • IV amiodarone [200mg t.i.d]
  • Correct hypokalaemia, hypomagnesaemia, acidosis
  • BB – to reduce ventricular automaticity
  • ICD – for patients at high risk of arrhythmic death

Ventricular fibrillation (VF)

  • Very rapid and irregular ventricular activation with no mechanical effect
  • VF is usually provoked by a ventricular ectopic beat (see below)
  • Patient is pulseless and becomes rapidly unconscious; respiration ceases
  • ECG – shapeless, rapid oscillations with no organised complexes
  • Tx – ALS, electric defibrillation. ICD to manage later risk of sudden death

Brugada syndrome

  • Inherited condition – idiopathic VF in pts who have no evidence of structural heart disease
  • Associated with loss of sodium channel function due to a mutation in the SCN5A gene
  • Can present with sudden death during sleep
  • Dx is by seeing ECG changes
    • Ajmaline/flecainide (Class I AA) are administrated to induce arrhythmia in a pt suspected to have Brugada
    • ECG shows – RBBB with coved STE in V1-V3
  • ICD is only successful tx

Long QT syndrome

  • Describes an ECG where the ventricular repolarisation (QT Interval) is prolonged

Congenital QT Syndrome

  • Mutations in cardiac potassium and sodium channel genes
  • 3 main types of congenital long QT (LQT)
    • LQT1 – KCNQ1 gene mutation, affects K channel
      • Provoked by exercise
    • LQT2 – KCNH2 mutation, affects K channel
      • Provoked by emotion or loud sounds
    • LQT3 – SCN5A mutation, affects Na channel
      • Occur at rest or during sleep

Acquired QTS – most commonly due to bradycardia (see box)

Clinical features

  • Syncope and palpitations due to torsades de pointes (a polymorphic ventricular tachycardia)
  • Normally terminate spontaneously but can result in VF/sudden death

Diagnosis

  • ECG – torsades de pointes seen as rapid, irregular, sharp complexes that continuously change from upright to inverted position

Treatment

  • Acquired acute LQT
    • Correct electrolyte disturbance (Mg, Ca, K), stop causative drugs
    • Maintain HR
    • Magnesium sulphate [8mmol]
  • Long term management
    • BB – for LQT1
    • Na channel blockers – for LQT3
    • Pacemaker
    • ICD

Ventricular ectopic beat (VEB)

Etiology

  • anxiety, hypokalaemia, hypomagnesaemia, digoxin toxicity, excessive caffeine

Pathogenesis

  • VEB is an electrical stimulus of the ventricles which occurs in the ventricles themselves – not from the atria
  • Originate from an ectopic location in the ventricles
  • Caused by groups of pacemaker cells throughout the conducting system that start to operate independently of the normal stimulation. Classified as
    • Unifocal – every VEB appears identical (arise from the same ectopic location)
    • Multifocal – different VEB morphologies (multiple ectopic sites)
  • Following a premature beat there is usually a complete compensatory pause

Clinical features

  • Pts complain of extra, missed or heavy beats
  • palpitations
  • Irregular pulse due to the premature beats

Diagnosis

  • ECG
    • Absence of P waves before QRS
    • Wide, tall QRS >120ms

Treatment

  • Tx for otherwise healthy pts not needed
  • In VEB pts with troubling symptoms or other heart disease
    • Beta blockers
    • Catheter ablation

 

Narrow complex (adenosine)

SVA, multifocal ectopic, AF

Wide complex (lidocaine)

VA, WPW

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