Ventricular Tachycardia and Fibrillation
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Direct answer
Ventricular tachycardia is a wide-complex rhythm originating in the ventricles at a rate of 100 per minute or more, and ventricular fibrillation is chaotic ventricular activity with no effective output that is fatal without immediate defibrillation. Any wide-complex tachycardia is treated as ventricular tachycardia until proven otherwise, with unstable patients needing synchronised cardioversion and pulseless patients needing immediate defibrillation.
What you must remember
- Brugada criteria: absence of RS complexes in all precordial leads favours VT; an RS interval longer than 100 ms in any precordial lead favours VT; atrioventricular dissociation is specific for VT.
- Morphology: morphological clues in V1, V2 and V6 help separate VT from aberrantly conducted supraventricular beats, and the default when in doubt is VT.
- Stable monomorphic VT: intravenous amiodarone is a common first choice, with procainamide or lidocaine as alternatives under specialist guidance.
- Unstable VT: synchronised cardioversion at the appropriate energy, with sedation as the patient's condition allows.
- Pulseless VT or VF: unsynchronised defibrillation immediately, cardiopulmonary resuscitation between shocks, and amiodarone after the shocks for refractory cases.
- Torsades de pointes: polymorphic VT with a prolonged QT interval; intravenous magnesium sulphate, withdrawal of offending drugs and overdrive pacing or isoprenaline.
- ICD indications: secondary prevention after sustained VT or aborted sudden cardiac death; primary prevention for ischaemic cardiomyopathy with ejection fraction 35 per cent or less at least 40 days after infarction or 90 days after revascularisation.
- Electrolytes: potassium and magnesium are corrected in every ventricular arrhythmia, and hyperkalaemia and sodium channel blocker overdose widen the QRS.
A stable patient with a broad-complex tachycardia
A 62-year-old man with prior anterior infarction presents with a regular broad-complex tachycardia at about 180 beats per minute. He is conscious, with blood pressure 105 over 70 mmHg. The first step is to treat the rhythm as VT and apply the Brugada criteria: absence of RS complexes across the precordial leads points strongly to VT, and atrioventricular dissociation, if present, confirms it. Potassium and magnesium are checked, and the trace is compared with previous ECGs.
Because the patient is stable, intravenous amiodarone is given under monitoring, with cardioversion held in reserve. If he becomes hypotensive or drowsy, synchronised cardioversion is performed immediately. After recovery, the team assesses the cause, which in this case is scar from the infarction, and measures ejection fraction. If it remains low after the recovery period, an ICD is considered for primary prevention, since sustained VT in ischaemic cardiomyopathy carries a high risk of sudden death.
Where the exam tries to catch you
Examiners set the sodium channel trap: tricyclic overdose produces a broad QRS and ventricular arrhythmias, and the correct treatment is intravenous sodium bicarbonate rather than the usual antiarrhythmics, which can worsen conduction. Another favourite is adenosine. It may terminate some regular narrow-complex tachycardias and help diagnosis, but it does not terminate sustained VT and should not be used to 'test' an unstable patient.
The third trap is the ICD timing rule. Primary prevention after myocardial infarction requires a waiting period, so recommending an ICD in the first weeks is wrong. Indian viva questions often ask what to do when a patient survives a cardiac arrest with no reversible cause; the answer is an ICD after assessment, with the reversible causes such as electrolyte disturbance and ischaemia excluded first.
Frequently asked questions
Which criterion first distinguishes ventricular tachycardia from aberrant supraventricular tachycardia?
Absence of RS complexes across all precordial leads is the first Brugada criterion and strongly favours ventricular tachycardia. An RS interval longer than 100 ms and atrioventricular dissociation further support the diagnosis.
What is the first-line drug for stable monomorphic ventricular tachycardia?
Intravenous amiodarone is a common first choice for stable monomorphic ventricular tachycardia, with procainamide or lidocaine as alternatives under specialist guidance. Synchronised cardioversion is reserved for patients who become unstable.
How is torsades de pointes treated?
Torsades de pointes is treated with intravenous magnesium sulphate, withdrawal of drugs that prolong the QT interval, and overdrive pacing or isoprenaline where needed. Correcting potassium and magnesium levels is part of the same treatment.
When is an ICD indicated for primary prevention after myocardial infarction?
An ICD is indicated when the ejection fraction is 35 per cent or less at least 40 days after infarction, or 90 days after revascularisation, with NYHA class II or III symptoms. The waiting period allows recovery of myocardial stunning before the decision is made.