TOC | Cardiology   
WPW Preexcitation Syndrome (Wolff-Parkinson-White)

It is associated with AV bypass tracts; has paroxysmal tachycardia.

ECG changes: short PR interval <0.12 seconds, a slurred upstroke of the QRS complex (delta wave), a wide QRS complex.

During the PSVT in WPW, the impulse is usually conducted antegradely over the normal AV system & retrogradely through the bypass tract.

Atrial flutter & Atrial Fib. also occur commonly in pts with WPW synd. The ventricular responses may be unusually rapid and may cause ventricular fibrillation.

Acute Rx of episodes of PSVT in WPW syndrome is similar to that of PSVT in pts with concealed bypass tracts.

  1. Vagal maneuvers (if no hypotension) as carotid sinus massage, can terminate the arrhythmia in 80% of cases.
  2. If hypotension is present, raising the BP by the cautious use of IV phynylephrine in 0.1 mg increments may terminate the arrhythmia lone or in combination with carotid sinus pressure. if thse Rx are unsuccessful, then
  3. IV adenosine 6-12 mg (or ?? verapamil 2.5-10 mg.) - agent of first choice.
  4. IV propranolol 0.05-0.2 mg/kg to slow or terminate the tachycardia - agent of second choice. digoxin has a lower onset of action & should not be used for acute Rx.
  5. Prevention of AV nodal reentry: digoxin, B-blocker, calcium channel blockers, quinidine, flecainide, amiodarone.
  6. Radiofrequency catheter modification of AV nodal function for those who require chronic med. Rx..

In pts with WPW synd, Atrial fib. with rapid vent. response may be treated with direct current cardioversion if it is life-threatening. Alternatively, lidocaine 3-5 mg/kg or procainamide 15 mg/kg IV over 15-20 min will usually slow the ventricular response.

* Caution should be employed when using digoxin, or IV verapamil in pts with the WPW synd & Atrial fib., since these drugs can shorten the refractory period of the accessory pathway and can increase the ventricular rate, thereby placing the pt at increased risk for vent. fibrillation.

Chronic PO verapamil is not associated with this risk.

Propranolol are of no utility in controlling the vent. response during AF when conduction proceeds over the bypass tract.

Although atrial or ventricular pacing can almost always terminate PSVT in pts with WPW synd, they can induce AF. As such, chronic pacemaker Rx is to be discouraged.

Surgical or radiofrequency catheter ablation of the bypass tracts are possible in >90% of cases & offer a permanent cure of SVT & most AF associated with SVT.

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