- A group of arrhythmias characterized by sudden onset and termination
- Includes the former designations PAT and PJT
- Rhythm is usually absolutely regular
- Etiology often unclear but includes pre-excitation syndromes (see below) and toxins/drugs
- Mechanism: 85% are due to reentry, (as opposed to automaticity)
- AVNRT (50%)
- Extranodal accessory tract (30-40%)
- SA node or atria (10%)
III. Differentiating among them:
- If it's a reentrant rhythm through AV node or accessory tract, see inverted p's in II, III, aVF
- If reentry occurs in sinus node or atria, get upright p waves
- In some AVNRT, atria & ventricles are depolarized simultaneously, and you don't see a p wave because it's hidden in the QRS complex!
- Accessory tract PSVT tends to be faster (up to 280/min, as opposed to 220 for others)
- Vagal maneuvers: carotid massage (if no bruits or recent h/o CVA, ventricular arrhythmia, or MI); gagging, valsalva
- IV adenosine = drug of choice (6mg IV, then 9mg after 2-3min if necc.)
- 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)
- IV beta-blockers (e.g. propanolol 1mg, repeat with 1mg-higher doses Q5min until conversion occurs or reach total dose of 0.1mg/kg)
- 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.
- IV procainamide (100mg Q2min to total dose of 2g)
- Synchronized DC cardioversion usually works, use as 1st-line tx if pt unstable; not when dig is thought to be cause of arrhythmias!
- External atrial pacing may suppress arrhythmia
- RF transcatheter ablation can be used to eliminate accessory pathways or reentrant circuits