Emergency Medicine

CARDIAC ARRHYTHMIAS

General Medical Emergencies 63

(iv) Narrow-complex supraventricular tachycardia (SVT)
When regular this may be one of the re-entry tachycardias or
atrial flutter with regular AV conduction (usually 2 to 1 block if
the rate is about 150/min)
(a) proceed directly to synchronized DC cardioversion if the
patient is shocked, unstable or deteriorating, starting at
70–120 J biphasic or 100 J monophasic, after a senior doctor
with airway experience has given a short-acting anaesthetic
(b) use a vagal stimulus such as carotid sinus massage (CSM) if
patient is stable and young with no carotid bruit, or prior transient
ischaemic attack (TIA) or cerebrovascular accident (CVA)

• press firmly at the upper border of the thyroid cartilage
  against the vertebral process with a circular motion


• or get the patient to perform Valsalva’s manoeuvre
  (c) give adenosine 6 mg rapidly over 2–5 s i.v. if CSM fails,
  followed by 12 mg i.v. rapidly after 1–2 min, then a further
  12 mg i.v. rapidly once more if still no response


• make sure to warn the patient to expect transient facial
  flushing, headache, dyspnoea, chest discomfort and nausea
  from the adenosine
  (d) alternatively, give verapamil 5 mg i.v. as a bolus over 30 s to
  2 min. Verapamil may cause hypotension and bradycardia,
  particularly in elderly patients, who may be pre-treated with
  calcium gluconate 10 mL given slowly i.v. to prevent these
  (e) never use verapamil after a -blocker, when digitalis toxicity
  is suspected, or if the patient has a wide complex tachycardia.
  (v) Irregular narrow-complex tachycardia or AF
  Irregularly irregular narrow-complex tachycardia is usually AF or
  less frequently atrial flutter with variable AV block
  (a) proceed directly to synchronized DC cardioversion starting
  at 120–150 J biphasic or 200 J monophasic, if the patient is
  shocked, unstable or deteriorating. In patients on digoxin
  therapy, temporary transcutaneous pacing may be required
  as asystole may follow DC reversion
  (b) otherwise try rhythm control, if the patient has been in the
  AF for less than 48 h, with amiodarone 5 mg/kg i.v. over
  20–60 min, followed by an infusion of amiodarone 900 mg
  over 24 h
  (c) however, when the patient has been in AF for over 48 h,
  or the time duration is unclear, rhythm control with drugs
  or elective DC reversion is contraindicated prior to full
  anticoagulation, due to the risk of clot embolization:


• attempt rate control only using an oral or i.v. -blocker,
  digoxin, diltiazem or magnesium. Seek senior ED doctor
  advice