Torsades de pointes - Ventricular arrhythmias

Torsades de pointes

Definition

Torsades de pointes or ‘twisting of the points’ is a condition in which there is episodic tachycardia and a prolonged Q–T interval when in sinus rhythm.

Aetiology

It arises when ventricular repolarisation is prolonged due to congenital cause, hypokalaemia, hypocalcaemia, anti-arrhythmic drugs, tricyclic antidepressants or bradycardia from the sick sinus syndrome. It may also occur in overdose of drugs that prolong the Q–T interval.

Pathophysiology

It is thought that the long Q–T interval allows adjacent cells, which are repolarising at slightly different rates, to trigger one another in a knockon effect. The Q–T interval is prolonged by biochemical abnormalities and drugs, and is also prolonged in bradycardic states.

Clinical features

It typically recurs in frequent short attacks, causing pre-syncope, syncope or heart failure.

Investigations

Repetitive bursts of rapid regular, polymorphic, QRS complexes, the axis of which undergoes cyclical change. During periods of sinus rhythm a prolonged Q–T interval is seen.

Complications

The major risk of torsades de pointes is progression to ventricular fibrillation.

Management

Any underlying cause should be identified and corrected. Overdrive pacing at 90–100 bpm may terminate the arrhythmia and is the best method for preventing recurrences, alternatively an infusion of isoprenaline may be used. If cardiac output is compromised synchronised DC cardioversion is used.