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Tachcardia

 

Definition of tachycardia

  • Cardiac arrhythmia with a rate >100 beats per minute (bpm)

 

Types of tachycardia

  • Narrow complex tachycardias
    • Regular (supraventricular tachycardia [SVT])
      • Sinus tachycardia
        • Physiological response to insult. Impulse originates from sino-atrial (SA) node.
      • Atrial tachycardia
        • Aberrant atrial focus producing impulse independent of SA node
      • Atrioventricular nodal re-entry tachycardia (AVNRT)
        • Re-entry circuit within or near AV node
      • AV re-entry tachycardia (AVRT)
        • Re-entry circuit conducted from atria to ventricles via abnormal accessory pathway; usually due to Wolff-Parkinson-White (WPW) syndrome
      • Atrial flutter with regular AV block (eg 2:1, 3:1)
        • Re-entry circuit within the atria
    • Irregular
      • Atrial fibrillation (AF)
        • Atria twitch instead of beating in a coordinated manner
  • Broad complex tachycardias
    • Regular
      • Ventricular tachycardia (VT)
        • Generated by a single ventricular focus
      • SVT with bundle branch block (BBB)
        • This is rare. Any broad complex tachycardia should be treated as VT unless there the patient has an old ECG with clear previous bundle branch block of unchanged morphology.
    • Irregular
      • Polymorphic VT (Torsades de pointes)
        • Sinusoidal morphology usually due to abnormal ventricular repolarisation (long QT)
      • AF with bundle branch block

 

 Aetiology of tachyarrhythmias (pathological as opposed to physiological)

  • Cardiac
    • Post-cardiac arrest
    • Post-myocardial infarction (MI)
    • Long QT syndrome
    • Valvular heart disease
    • Cardiomyopathy
  • Non-cardiac
    • Hypoxia
    • Hypovolaemia
    • Electrolyte abnormalities
      • Especially hypo/hyper-kalaemia, -calcaemia or -magnesaemia
    • Hypoglycaemia
    • Hypo/hyperthermia
    • Hypo/hyperthyroidism
    • Sepsis
  • Drug-induced
    • Cocaine
    • Amphetamines
    • Tricyclic antidepressants
    • Beta blockers
    • Digoxin
    • Amiodarone

 

 Clinical features of tachycardias

  • Adverse features
    • Shock
      • Hypotension, diaphoresis, pallor, increased capillary refill time (CRT)
    • Syncope
      • Transient loss of consciousness
    • Myocardial ischaemia
      • Ischaemic chest pain and/or ischaemic electrocardiogram (ECG) changes
    • Cardiac failure
      • Orthopnoea, paroxysmal nocturnal dyspnoea (PND), bibasal crepitations, raised jugular venous pressure (JVP)
  • Non-adverse features
    • Palpitations
    • Dyspnoea
    • Anxiety

 

 Initial investigation of tachycardia

  • Bloods
    • Full blood count
    • Urea & electrolytes
    • Magnesium
    • Bone profile (particularly noting calcium and phosphate)
    • Thyroid function tests
    • Other: liver function (useful pre-medication); coagulation (may need anticoagulation)
  • Chest radiograph (CXR)

 

Further investigation of tachycardia

  • Echocardiogram (echo)

 

Initial management of tachycardia

  • Assess patient from an ABCDE perspective
  • Maintain a patent airway
    • Use manoeuvres, adjuncts, supraglottic or definitive airways as indicated
  • Controlled oxygen
    • Maintain saturations (SpO2) 94-98%
  • Attach monitoring
    • Pulse oximetry
    • Non-invasive blood pressure
    • Three-lead cardiac monitoring
    • Defibrillator pads
  • 12 lead ECG
  • Obtain intravenous (IV) access and take bloods
  • Give IV fluid challenge if appropriate and repeat as necessary
  • Identify and treat any reversible causes e.g. electrolyte abnormalities on initial VBG
  • If adverse features are present [shock, syncope, myocardial ischaemia, heart failure], prepare for emergency synchronised DC cardioversion under general anaesthesia or conscious sedation
    • Once ready, warn all those nearby to stand clear and remove any oxygen delivery device whilst the defibrillator is set to synchronised mode and charged to 120 J
    • Once the defibrillator is charged and all are clear, deliver the shock
    • Should this fail, two subsequent shocks at increasing increments may be tried
    • Should this fail, give a loading dose of amiodarone 300 mg IV over 10-20 minutes and repeat DC cardioversion followed by amiodarone 900 mg IV over 24 hours
  • If adverse features are not present, assess the rhythm:
  • Narrow complex tachycardias (QRS duration <0.12 s)
    • Regular: likely SVT
      • Attempt vagal manoeuvres
        • Valsalva (ask patient to blow into syringe); carotid sinus massage.
          • If this fails then:
      • Adenosine 6 mg IV
        • Rapid bolus ideally into a large-bore cannula in the antecubital fossa
        • Warn patients of transient unpleasant side effects: flushing, nausea and chest tightness, ‘feeling of impending doom’
        • Avoid in patients with asthma, WPW syndrome, and denervated hearts
        • Caution in taking theophylline, dipyridamole or carbamazepine
        • If 6mg unsuccessful:
      • Adenosine 12 mg IV
        • If first 12mg unsuccessful:
      • Further adenosine 12 mg IV
      • If adenosine is contraindicated, consider verapamil 2.5-5.0 mg IV, or flecainide 2 mg/kg IVI over 20-30 min if no evidence of structural heart disease
    • Irregular: likely AF
      • Onset <48 hours
        • Aim for rhythm control
          • Flecainide 2 mg/kg IVI over 20-30 min if no evidence of structural heart disease or amiodarone 300 mg IV over 20-30 min and 900 mg over 24 hours if flecainide contraindicated
          • Anticoagulate with enoxaparin 1.5 mg/kg subcutaneous (SC) prior to this
      • Onset >48 hours
        • Aim for rate control
          •  Metoprolol 5 mg IV OR bisoprolol 5 mg orally (PO) OR verapamil 5 mg IV
            • If signs of heart failure try digoxin 0.5 mg IVI over 30-60 min
            • Digoxin can be added to the above if beta-blockade unsuccessful
          • Anticoagulate with enoxaparin 1.5 mg/kg subcutaneous (SC) prior to this
  • Broad complex tachycardias (QRS duration >0.12 s)
    • Regular
      • If likely monomorphic VT
        • Give amiodarone 300 mg IVI over 20-30 min followed by amiodarone 900 mg IVI over 24 hours
        • Any broad complex tachycardia should be treated as VT unless there the patient has an old ECG with clear previous bundle branch block of unchanged morphology.
      • If definitely SVT with BBB
        • Try adenosine as for regular narrow complex tachycardias
    • Irregular
      • If likely AF with BBB
        •  Treat as for irregular narrow complex tachycardias
      • If likely polymorphic VT (Torsades de pointes)
        • Magnesium 2 g IV over 10 min
        • Stop any medications which prolong the QT interval
        • Correct any electrolyte abnormalities if not already done so, and give

 

Further management of tachycardia

  • Request 12 lead ECG once back in sinus rhythm
    • Look specifically for ischaemic changes (ST elevation, ST depression and T wave inversion), prolonged QT interval (QTc >440 ms) and signs of WPW syndrome (shortened PR interval, delta wave and broad QRS complex)
  • Identify and correct any underlying cause if not already done so
  • Call cardiologist
    • Arrange for an implantable cardioverter defibrillator (ICD) if appropriate

 

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