Preexcitation was defined by Durrer et al in 1970 with the following statement, “Preexcitation exists, if in relation to atrial events, the whole or some part of the ventricular muscle is activated earlier by the impulse originating from the atrium than would be expected if the impulse reached the ventricles by way of the normal specific conduction system only.”1 In preexcitation, atrial impulses bypass the typical electrical pathway that conducts via the atrioventricular node and activates the ventricular myocardium directly via an accessory pathway. Of the various preexcitation syndromes, the most common is Wolff-Parkinson-White (WPW) syndrome. Emergency departments should be familiar with this syndrome and the proper treatment of its associated dysrhythmias to minimize morbidity and mortality.
For a CME activity, see Heart Healthy: Preventive Medicine 2008.
Accessory pathways or connections between the atrium and ventricle are the result of anomalous embryonic development of myocardial tissue bridging the fibrous tissues that separate the two chambers. This allows for electrical conduction between the atria and ventricles at sites other than the atrioventricular node (AVN). Passage through accessory pathways circumvent the usual conduction delay between the atria and ventricles, which normally occurs at the AVN and predisposes the patient to develop tachydysrhythmias.
Although dozens of locations for bypass tracts can exist in preexcitation, including atriofascicular, fasciculoventricular, intranodal, or nodoventricular, the most common bypass tract is an accessory atrioventricular (AV) pathway otherwise known as a Kent bundle. This is the anomaly seen in WPW syndrome. Conduction through a Kent bundle can be anterograde, retrograde, or both. Another common preexcitation syndrome, Lown-Ganong-Levine (LGL), also has an accessory pathway (the James fibers), which connect the atria serially to the His bundle. The end result is the same, preexcitation and a predisposition to the development of tachydysrhythmias. Fortunately, the treatment of LGL parallels that of WPW, and they are discussed together.
WPW syndrome affects approximately 0.15-0.2% of the general population. Of these individuals, 60-70% have no other evidence of heart disease.
Death from WPW syndrome occurs secondary to the associated dysrhythmias or from mistreatment of these dysrhythmias with inappropriate medications. Little data are available regarding the mortality rate of such dysrhythmias, but most studies report the incidence of sudden death in the 0-4% range.
Men (60-70% cases) are affected more often than women. Typically, those affected are young, otherwise healthy individuals.
Although this disease affects people of all ages, it is most commonly recognized in children and young adults presenting to the ED with a dysrhythmia. Conduction speed in the accessory pathway appears to attenuate with age.
Patients with Wolff-Parkinson-White syndrome may present with anything from mild chest discomfort or palpitations with or without syncope to severe cardiopulmonary compromise or cardiac arrest.
Occasionally, electrocardiographic evidence of disease is discovered on routine electrocardiography (ECG), independent of a concurrent tachydysrhythmia.
Patients commonly present with rapid heart rates in the 250 beats per minute (bpm) range, often with associated hypotension.
Many patients are not aware of their underlying condition.
WPW has no specific examination features except for those that may accompany symptomatic dysrhythmias.
Many young patients appear minimally symptomatic (eg, palpitations, weakness, mild dizziness) despite exceedingly fast heart rates.
On physical examination, the patient may be cool, diaphoretic, and hypotensive.
Crackles in the lungs are common, as the rapid heart rate may cause pulmonary vascular congestion due congestive heart failure.