A young man with another episode of tachycardia. What is it? And why give adenosine in sinus rhythm?

Written by Bobby Nicholson MD and Pendell Meyers

A man in his 30s presented to the ED for evaluation of chest pain and palpitations. He described it as a "jackhammering" sensation, associated with palpitations, diaphoresis, and shortness of breath, and he stated it started soon after consuming an "energy drink" (product/contents unknown).

He stated these symptoms were the same as a prior episode which required cardioversion. He states that he has a heart condition which he does not know the name of and that he has felt his heart race like this once before and needed to be shocked. He was seen by a cardiologist in follow-up but was told he did not need routine follow-up.

Here is his triage ECG:

He had several more ECGs taken in the resuscitation bay over the next few minutes:

What do you think?

The ECGs show a wide complex, irregularly irregular tachycardia. The differential of wide complex irregularly irregular includes: polymorphic VT, atrial fibrillation with WPW, atrial fibrillation with other aberrancy. Closer examination shows polymorphic QRS complexes and multiple QRSs separated by 1 big box (200 msec) or even less. 

Thus, the patients rhythm is atrial fibrillation with WPW.

With that in mind, how would you proceed with treatment?

At this point, the patient had been symptomatic for almost 5 hours, appeared unwell with chest pain and diaphoresis. His blood pressure was 118/96. The team decided to start treatment with 1L of IV fluids, 4g of magnesium, and synchronized cardioversion. The following EKG was obtained after 200J cardioversion: 

What is your interpretation of this EKG? Does our initial diagnosis from the triage EKG appear consistent with our post-conversion diagnosis?

There is sinus rhythm with an abnormal (but monomorphic) QRS complex. In lead I, for example, the QRS onset occurs simultaneous with the end of the P wave, and there is a slightly slurred onset of the QRS complex. It could easily be mistaken for LBBB, if it were not diagnostic of WPW.

Cardiology was consulted at this point (now that the patient is in sinus rhythm) and assessed the patient at the bedside and expressed uncertainty between atrial fibrillation with LBBB versus atrial fibrillation with WPW when reviewing the ECGs of the presenting tachydysrhythmia. 

The logic at this point is somewhat unclear, but ultimately they decided to push 18 mg of adenosine (during sinus rhythm) in an attempt to either induce or exaggerate pre-excitation, if an accessory pathway exists. What do you think of the resultant rhythm strip?

Why did they give adenosine during sinus rhythm?

Smith comment: Normal WPW with a delta wave (pre-excitation through an accessory pathway) is a fusion beat between the accessory pathway and normal conduction.  If you eliminate normal conduction with adenosine, then the beat is VERY wide because it is ALL through the accessory pathway.  If there is an accessory pathway but it is not obvious, it is not obvious because its conduction is being competed with by the AV node.  This is what is often referred to as “concealed conduction,” in which there is no pre-excitation visible on the resting 12-lead.  Of course, in this case here, you CAN see the pre-excitation, if you recognize it. But if you give adenosine, it completely shuts down the AV node and all conduction is then through the accessory pathway and will be very wide.  

The therapeutic and diagnostic cardiac electrophysiological uses of adenosine

We can again see shortening of the PR interval and widening of the QRS complex with delta waves. This was believed to be consistent with the presence of an accessory pathway which was suspected on initial presentation and post-cardioversion ECG.

2 hrs later:

Still sinus with subtler WPW.

This patient was admitted to the hospital and taken to the EP lab the following day. An accessory pathway was identified and was ablated. The patient has not had any recurrent episodes of atrial fibrillation and has a narrow QRS complex without delta wave on his ECG post ablation. 

Post ablation:

This patient had a similar visit 4 years previously:

The patient had a prior admission 4 years ago for the same presentation. At that time, he presented via EMS and had received magnesium and lidocaine prehospital for concerns of ventricular tachycardia. On arrival to the ED, he was noted to be in a wide complex tachycardia with a rate in the 240s. He was treated with additional magnesium and amiodarone (which is contraindicated in atrial fibrillation with WPW). His systolic blood pressure declined from 130 to 90 and the emergency medicine team decided to proceed with cardioversion. The patient was admitted to the cardiology service with a plan for EP study, however the cardiologist during that visit thought that the ECG showed only LBBB, and thought that the patient's dysrhythmia was atrial fibrillation with LBBB, instead of atrial fibrillation with WPW. So he was simply discharged without EP study.

Learning Points:

Wide complex irregularly irregular tachycardias include PMVT, AF with WPW, and AF with aberrancy. 

AF with WPW can sometimes be differentiated from AF with aberrancy because AF with WPW may show polymorphic QRS complexes and very short R-R intervals (200 msec or less, but any R-R interval less than 240 ms -- 6 little boxes -- is likely to be AF with WPW).

WPW can simulate particular aberrancies such as LBBB, and confuse the reader into missing the diagnosis of WPW.

The way to differentiate Atrial fib with LBBB or other aberrancy from Atrial fib WPW is to look for polymorphic QRS complexes, as are clearly seen in the first ECG, and to look for the very short R-R intervals.