A 8 years old female with a known history of Wolff-Parkinson-White Pattern in her ECG presented to the emergency department due to palpitations and dizziness.
The previously known resting ECG is shown below:
Leg: short PR interval, delta wave positive in inferior leads.
Symptoms appeared suddenly during a walk in the park. It is the first time that the girl became symptomatic. The ECG showed the following:
Leg: 25mm/sec, HR around 290 bpm, narrow complex SVT, P waves most likely buried at the beginning of the ST segment.
Diagnosed as narrow complex tachycardia, highly likely atrioventricular reentry tachycardia (AVRT), the patient received adenosine (0.1 mg/kg iv push) to convert into sinus rhythm. However, instead of converting into sinus rhythm the following happened:
Leg: wide complex tachycardia with varying RR intervals - fast, broad & irregular (FBI)
In case of known WPW-pattern in the ECG one should remember that, given favorable conduction properties of the accessory pathway, adenosine may inflict atrial fibrillation which could eventually be conducted rapidly to the ventricles. It is important to know that accessory pathways (APs) may be able to conduct from ventricles to atria, atria to ventricles, or both ways. Furthermore, APs may have variable conduction properties. That is, while some APs may be able to conduct only in a relatively slow fashion (allowing for tachycardias of 200-220 bpm), others may be able to conduct quite rapidly (>250-300 bpm). In the rare case of atrial fibrillation (AF) caused by iv push of adenosine, AF may be conducted rather rapidly to the ventricles in case of an AP with rapid integrate conduction properties.
It is important to note that a WPW-pattern in the ECG (i.e. short PR interval, delta wave) gives away integrate conduction via the AP. However, it does not tell anything about how rapidly conduction might be possible. Thus, in case of known WPW-pattern in the ECG one should be prepared for FBI tachycardia when administering adenosine for treatment of a narrow complex tachycardia (apply defibrillator patches prior to adenosine administration).
Importanz note: Adenosine is not contraindicated in WPW patients, but should be administered carefully.