Vagal manoeuvres, then adenosine, then rate control
Expansion
First: are there adverse features? Shock, syncope, myocardial ischaemia or heart failure mean immediate synchronised DC cardioversion under sedation.
If stable, work through the steps
- Vagal manoeuvres - the modified Valsalva is markedly more effective than the standard: blow into a syringe for 15 seconds while sitting, then lie flat with the legs raised passively
- Adenosine 6 mg rapid intravenous bolus into a large proximal vein with a flush, then 12 mg, then 12 mg again
- If unsuccessful, verapamil or a beta blocker, then expert help
Warn the patient before adenosine: it causes a brief but very unpleasant sense of chest tightness and impending doom, and a few seconds of asystole on the monitor.
Adenosine cautions: avoid in asthma (use verapamil), in Wolff-Parkinson-White with atrial fibrillation (it can accelerate conduction down the accessory pathway), and note that dipyridamole potentiates it while theophylline blocks it.
Adenosine is both diagnostic and therapeutic: it terminates a re-entrant tachycardia involving the atrioventricular node, and in atrial flutter it transiently blocks the node to reveal the flutter waves.