PAROXYSMAL SUPRAVENTRICULAR TACHYCARDIAS


I. Features

  1. A group of arrhythmias characterized by sudden onset and termination
  2. Includes the former designations PAT and PJT
  3. Rhythm is usually absolutely regular

II. Etiology

  1. Etiology often unclear but includes pre-excitation syndromes (see below) and toxins/drugs
  2. Mechanism: 85% are due to reentry, (as opposed to automaticity)
  1. AVNRT (50%)
  2. Extranodal accessory tract (30-40%)
  3. SA node or atria (10%)

III. Differentiating among them:

  1. If it's a reentrant rhythm through AV node or accessory tract, see inverted p's in II, III, aVF
  2. If reentry occurs in sinus node or atria, get upright p waves
  3. In some AVNRT, atria & ventricles are depolarized simultaneously, and you don't see a p wave because it's hidden in the QRS complex!
  4. Accessory tract PSVT tends to be faster (up to 280/min, as opposed to 220 for others)

IV. Tx

  1. Vagal maneuvers: carotid massage (if no bruits or recent h/o CVA, ventricular arrhythmia, or MI); gagging, valsalva
  2. IV adenosine = drug of choice (6mg IV, then 9mg after 2-3min if necc.)
  3. IV verapamil (5-10mg over 1-3min; can repeat in 30min)-don't give in conjunction with beta-blockers, of if has CHF, or if pt has SSS, unless paced)
  4. IV beta-blockers (e.g. propanolol 1mg, repeat with 1mg-higher doses Q5min until conversion occurs or reach total dose of 0.1mg/kg)
  5. IV digoxin (0.5-0.75mg; wait 10-30min for results)-use with caution if EKG suggests antegrade conduction along accessory bypass tract (e.g., WPW), because can cause Vfib due to AV block and rapid conduction along bypass pathway.
  6. IV procainamide (100mg Q2min to total dose of 2g)
  7. Synchronized DC cardioversion usually works, use as 1st-line tx if pt unstable; not when dig is thought to be cause of arrhythmias!
  8. External atrial pacing may suppress arrhythmia
  9. RF transcatheter ablation can be used to eliminate accessory pathways or reentrant circuits