Troubling Tachycardia

aka ECG Exigency 010

Another crazy night in the ED… One of the nurses hands you this ECG. “Can you take a look at this guy? He doesn’t look so well…”


Q1. What is the name of this rhythm?

Answer and Interpretation

This is an example of bidirectional ventricular tachycardia with

  • Regular broad complex tachycardia
  • The frontal-plane axis swings 180 degrees from left to right with each alternate beat

Q2. What are the two main causes of this dysrhythmia?

Answer and Interpretation
  • Severe digoxin toxicity
  • Familial Catecholaminergic Polymorphic Ventricular Tachycardia (CPVT)

Q3. What are the clinical and ECG features of Digoxin toxicity?

Answer and Interpretation

Digoxin toxicity

Clinical features

  • GIT: Nausea, vomiting, anorexia, diarrhoea
  • Visual: Blurred vision, yellow/green discolouration, haloes
  • CVS: Palpitations, syncope, dyspnoea
  • CNS: Confusion, dizziness, delirium, fatigue

Electrocardiographic Features

  • Digoxin can cause a multitude of dysrhythmias, due to increased automaticity (increased intracellular calcium) and decreased AV conduction (increased vagal effects at the AV node)
  • The classic dysrhythmia associated with digoxin toxicity is the combination of a supraventricular tachycardia (due to increased automaticity) with a slow ventricular response (due to decreased AV conduction), e.g.  ‘atrial tachycardia with block’.

Other arrhythmias associated with digoxin toxicity are:

  • Frequent VEBs (the most common abnormality), including ventricular bigeminy and trigeminy
  • Sinus bradycardia or slow AF
  • Any type of AV block (1st degree, 2nd degree & 3rd degree)
  • Regularised AF = AF with complete heart block and a junctional or ventricular escape rhythm
  • Ventricular tachycardia, including polymorphic and bidirectional VT

Examples of digoxin toxicity:

Q4. What are the clinical and ECG features of CPVT?

Answer and Interpretation

Clinical features

  • An inherited arrhythmogenic disease characterised by episodic palpitations, syncope or cardiac arrest precipitated by exercise or acute emotion (i.e. catecholamine-triggered ventricular dysrhythmias)
  • Onset during childhood (mean age: 7-9 years old)
  • Family history of sudden cardiac death
  • Ventricular arrhythmias reproducible on exercise stress testing

Electrocardiographic Features

  • Bidirectional VT
  • Polymorphic VT
  • Ventricular fibrillation

CPVT Example

  • Exercise stress test in a patient with CPVT.
  • Progressively worsening ventricular arrhythmias are observed during exercise.
  • Typical bidirectional VT develops after 1 minute of exercise with a sinus heart rate of approximately 120 beats per minute.
  • Arrhythmias rapidly recede during recovery.

Q5. How are these conditions treated?

Answer and Interpretation


  • The antidote for acute or chronic digoxin toxicity is digoxin-specific immune Fab (‘Digibind’)
  • Initial empiric dosing of Digibind is 5 ampoules for acute overdose, 2 ampoules for chronic toxicity and up to 20 ampoules for cardiac arrest
  • AV block may respond to atropine 0.6 mg IV bolus, repeated to a maxium of 1.8 mg (20 mcg/kg in children)
  • Dysrhythmias may be treated with IV lignocaine 1mg/kg (max 100mg) over 2 minutes
  • Hyperkalaemia is treated in the usual way with insulin and dextrose, sodium bicarbonate… however, IV calcium is (traditionally) contraindicated!
  • DC cardioversion is unlikely to be successful in digoxin poisoning. Patients in cardiac arrest may require continuous CPR until Digibind can be sourced and administered.

Catecholaminergic Polymorphic Ventricular Tachycardia

  • Beta blockers (e.g. propranolol) are used for suppression of catecholamine-triggered ventricular tachydysrhythmias.
  • Electrical cardioversion / defibrillation may be required for haemodynamically unstable VT/VF, although patients often spontaneously revert to sinus rhythm.
  • Implantable cardioverter-defibrillator (ICD) insertion is considered for primary or secondary prevention of cardiac arrest.




Emergency Physician in Prehospital and Retrieval Medicine in Sydney, Australia. He has a passion for ECG interpretation and medical education | ECG Library |

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