Wolff-Parkinson-White syndrome

From Dog

Wolff-Parkinson-White syndrome (WPW) is a rare cardiac disorder of dogs characterized by ventricular pre-excitation and intermittent paroxysmal ventricular tachycardia.

Causes include:

Ventricular pre-excitation occurs as a result of impulses originating in the sinoatrial node or atrium, which lead to a portion of the ventricles to contract through an accessory pathway without going through the sinoatrial node, while the remainder of the ventricle contracts through normal sinoatrial initiation.

This disorder is associated with normal ECG heart rhythm and conduction, but widened QRS complexes, often with slurring or notching of the upstroke R wave (delta wave)[1]. The P waves are usually normal, with shortened P-R intervals and there is usually a frank ventricular tachycardia (often > 400 beats per minute), making P waves difficult to recognize[2].

Clinical signs include exercise intolerance, weakness and syncope.

A differential diagnosis would include anemia, hyperthyroidism, atrial fibrillation and ventricular tachycardia.

In dogs with ventricular pre-excitation without ventricular tachycardia do not require treatment, but WPW syndrome usually necessitates cardioconversion with defibrillation, or ocular or carotid sinus pressure, followed by intravenous lidocaine to normalize ventricular activity.


  1. Nagasaka M et al (1991) Detection of myocardial infarction in the presence of Wolff-Parkinson-White syndrome by QRST isoarea map in dogs. Am Heart J 121(3):763-769
  2. Ichihara Y et al (1993) Estimation of anterior infarct size with body surface QRST integral maps in the presence of abnormal ventricular activation sequence in dogs. Am Heart J 125(2):291-300