Two cases are described of cardioversion from stable supraventricular tachycardia after venepuncture. In both cases usual vagal manoeuvres at home and in the casualty department were unsuccessful. However, attempts to site intravenous cannulas by the attending medical staff terminated his supraventricular tachycardia. Venepuncture is probably the commonest vagal manoeuvre performed in hospital but has not previously been reported as a method of cardioversion.
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A 14 year old boy presented after two hours of sustained tachycardia. He was sweaty and tachypnoeic but had a normal blood pressure and normal capillary return. Clinical examination and electrocardiogram revealed a heart rate of 240 beats per minute and a narrow complex tachycardia. The young man was known to have Wolf-Parkinson-White syndrome and was awaiting radiofrequency ablation at a specialist centre. Previous episodes of tachycardia had been terminated with standard vagal manoeuvres—that is, unilateral carotid pressure or Valsalva. However, on this occasion these had not been successful, so he had attended the accident and emergency department with his mother.
The casualty officer and then the paediatric registrar continued attempts at vagal stimulation, first with one sided carotid body massage, then ice, and finally Valsalva. All were unsuccessful and so the first three standard doses of adenosine were prepared while the child had an 18G cannula inserted into his antecubital fossa. The first attempt at cannulation was unsuccessful resulting in three things: a cry of “ouch” from the patient (who had insisted on watching nervously), a small haematoma, and restoration of normal sinus rhythm with a rate of 75 beats per minute. The rhythm strip taken after cardioversion clearly demonstrated the delta wave phenomenon of Wolff-Parkinson-White syndrome (fig 1).
An 11 year old boy presented with sudden onset of a rapid heart rate after a physical education class at school. He had some mild central chest pain, but had no shortness of breath and no signs of cardiovascular compromise. Examination and electrocardiography confirmed a heart rate of 240 beats per minute with a narrow complex tachycardia. Valsalva manoeuvres and unilateral carotid sinus massage resulted in a transient but unsustained reduction in heart rate. Once again adenosine was drawn up and an intravenous cannula was sited. Cannulation resulted in successful sustained cardioversion and adenosine was not given.
Manoeuvres that increase vagal tone have been used to terminate paroxysmal supraventricular tachycardia since at least 1913 and have gained wide acceptance.1 Termination of tachycardia by an increase in vagal tone is not only immediate but also may be a specific test for paroxysmal supraventricular tachycardia.2 The APLS guidelines suggest unilateral carotid body massage, ice, or Valsalva.3 All of these were tried in our patient without success. More obscure methods of vagal stimulation as a treatment for paroxysmal supraventricular tachycardia have been reported in the medical literature in the past few years. These include sudden jolts along a bumpy road surface,4 the passing of a nasogastric tube,5 and the application of military antishock trousers.6 Vasovagal reactions are commonly seen after venepuncture in young patients.7 However, we could find no reports of successful cardioversion by venepuncture in the literature. Given our understanding of the physiology of vagal cardioversion and the high incidence of vasovagal reactions after venous cannulation in young adults we would like to recommend that medical staff wait until after cannulation before drawing up adenosine that may otherwise be wasted.
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