A 37 year-old Caucasian male presents to the emergency department with palpitations of two hours duration. A 12-lead EKG is recorded.
This 12-lead demonstrates an irregularly irregular, polymorphic wide complex tachycardia; this can only be atrial fibrillation with frequent conduction through a Wolf-Parkinson-White accessory pathway system.
The differential diagnosis for this presentation principally consists of polymorphic VT, RVR a-fib with ventricular conduction aberrancy, and a-fib with underlying WPW. The presence of multiple wide complex QRS morphologies excludes the diagnoses of a-fib with BBB, and, as Mattu and Brady have pointed out, polymorphic VT will typically hold a constant rate while this EKG shows significant variance between R-R intervals– from >450ms to <240ms. (Mattu, 2003, p.138)
RVR a-fib with aberrant conduction and gross ST-segment abnormalities but uniform QRS morphology. (EMS 12-Lead: http://ems12lead.com/2011/09/68-year-old-male-cc-chest-pain/)
Polymorphic VT of Torsades de Points in the setting of hypokalemia and prolonged QT; multiple QRS morphologies but uniform rate. (LITFL: http://lifeinthefastlane.com/ecg-library/tdp/)
Note that due to the fixed duration of the AV nodal refractory period, synchronized atrio-ventricular conduction is typically limited to below 200 impulses per minute. It is for this reason that RVR a-fib very rarely exceeds 180-200bpm. The bypass tract in WPW, however, has a dangerously short refractory period and thus can support re-entrant tachycardias well above this limit. As Chou has stated, “…the presence of the WPW syndrome can be suspected from the rhythm strip alone if the atrial fibrillation is accompanied by a ventricular rate greater than 200bpm. Such a rapid ventricular response would be highly unusual if the conduction is by way of the normal AV conduction system.” (Chou, 1996, p.480)
Antiarrhythmic agents which slow or block AV nodal conduction are contraindicated in this setting as they can enhance conduction through the accessory pathway and accelerate ventricular response. Procainamide and related sodium channel antagonists have therefore been used with favorable results.
Regarding amiodarone, although numerous case reports have tracked poor outcomes, it remains a popular treatment modality for this syndrome and may statistically be a safe alternative. In 2005, for example, Tijunellis and Herbert demonstrated a case-series of 10 patients in which amiodarone was malignantly proarhythmic; in half of these, the initial arrhythmia was v-fib. Nonetheless, case-series can be misleading and I do not know of definitive research in this area.
In light of this, judicious use of electrical therapy is often considered the safest and most reliable approach.
Mortality associated with the Wolf-Parkinson-White syndrome remains at <1% and is thought to result from rapid response a-fib degenerating into v-fib arrest (Ellis, 2011). This outcome can be fostered through inappropriate pharmacological management if the initial presentation is misunderstood. Fortunately, once this dramatic EKG signature has been appreciated, it is unlikely to go unrecognized.
Dr. Stephen Smith has discussed this syndrome and the treatment risks, and his insights can be found here. Among other remarks, he states, “Atrial fib with WPW is very recognizable: there are bizarre QRS with multiple morphologies, and very fast rhythms with short R-R intervals. If you can find any R-R interval shorter than 240 ms, then AV nodal blockers are definitely dangerous.” (Smith, 2011)
I wish also to excerpt Dr. Johnson Francis of Cardiophile MD who has addressed this topic directly. Dr. Francis states, “The shortest RR interval gives an estimate of the ventricular refractory period. If it is below 250 msec, it is ominous as the ventricular rates can go very high and it can degenerate into ventricular fibrillation.” (Francis, 2008) Note that in this particular case, the overall ventricular rate is not excessively fast and perhaps speaks to the relative clinical stability of the patient.
Additional case studies of WPW a-fib can be found in the Case Library.
Chou, T. and Knilans, T. (1996). Electrocardiography in Clinical Practice: Adult and Paediatric, 4th Ed. W.B. Saunders Co.
Ellis, C., et al. (2011). Wolff-Parkinson-White Syndrome. Medscape eMedicine. Retrieved from: http://emedicine.medscape.com/article/159222-overview
Mattu, A. and Brady, W. (2003). ECGs for the emergency physician, V.1. BMJ Publishing Group.
Tijunelis, M. and Herbert, M. (2005). Myth: Intravenous amiodarone is safe in patients with atrial fibrillation and Wolff-Parkinson-White syndrome in the emergency department. Canadian Journal of Emergency Medicine. (4): No.4, p262. Retrieved from: http://www.cjem-online.ca/v7/n4/p262