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…”

ECG Exigency 010


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

CPVT Catecholaminergic Polymorphic Ventricular Tachycardia
  • 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.


Cardiovascular curveball 700



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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