Adenosine and WPW

When it comes to WPW syndrome, the classic associated supraventricular tachycardia is called AV re-entrant or reciprocating tachycardia (AVRT), and patients are usually treated due to symptomatic arrythmias. In the prehospital environment, treatment is usually reserved for patients with acute arrhythmias.

As you’ve alluded to, there are conflicting answers how to manage these patients, as standard therapies may actually worsen symptoms and lead to clinical deterioration in patients with a tachycardia involving an accessory pathway. Knowledge of the presence of an accessory pathway is critical in choosing the correct initial pharmacologic therapy.

In order to consider adenosine, patients need to be stable. If the patient is unstable, electrical cardioversion is the first line treatment. ACLS guidelines do not discriminate between PSVT and WPW.

In orthodromic AVRT, anterograde conduction is via the AV node, producing a regular narrow complex rhythm. In these patients, assuming patient hemodynamic stability, we take a stepwise approach. Try your vagal maneuvers first and escalate to medication as necessary. IV adenosine is effective for the acute termination of orthodromic AVRT. If your patient is unstable, then synchronized cardioversion is required.

In antidromic AVRT, anterograde conduction is via the accessory pathway (AP), producing a regular wide-complex rhythm. In patients with atrial fibrillation with preexcitation, we should not be administering adenosine, as AV nodal blocking drugs, since blocking the AV node will promote conduction down the accessory pathway and may sometimes directly enhance the rate of conduction over the accessory pathway, increasing the ventricular rate and potentially resulting in hemodynamic instability and can precipitate VF or VT. In fact, AV nodal blocking agents (adenosine, amiodarone, metoprolol, etc.) are also avoided. This is one reason why it is imperative that when treating with adenosine, paramedics apply the defibrillator pads.

Ultimately, the guidelines still suggest following tachydysrhythmia algorithm, but these rhythms can be difficult to distinguish from VT, and if there is any doubt, presume a diagnosis of VT.

At the hospital, the clinician who identifies WPW may choose to go directly to cardioversion or, if stable trial other medications first that are more appropriate (metoprolol, verapamil, sotalol, amiodarone, flecanide, procanamide).

Most WPW patients are diagnosed at birth or a younger age as it is a congenital heart defect, so usually, the patient is aware and would be able to tell you. Paramedics could patch for consultation with these cases and try modified Valsalva in the meantime. The patch consult would be to determine either transport, in some cases trial amiodarone, or cardioversion, if the patient is boarding unstable with prolonged transport times - especially in those patients with an identified Delta wave.