[sidebar]ILLUSTRATION: Chris Whissen & shutterstock.com[/sidebar]
Have you ever thought of the cardiac conduction system as a night club—Club Ventricle? Who knows, you might have to stop yourself from busting a move the next time you’re assessing atrial fibrillation in your emergency department!
Atrial fibrillation has an atrial rate of 300–600 bpm. Picture it as 300–600 people trying to get into a club (ventricle). The atrioventricular (AV) node (bouncer) is only able to let 140–160 bpm (people) into the club at a time, and the rate is irregular. All beats (people) are going through the same point of entry, so all beats are the same width.
Wolff-Parkinson-White Syndrome (WPW)
In WPW, beats are being conducted by an accessory pathway (the side door of the club) and not going through the AV node (bouncer). The side door of Kent is farther from the dance floor, so the QRS complex is wider as the people travel farther and do a dance move called the Delta Wave. Travel distance and dance moves take time.
Atrial Fibrillation with Rapid Ventricular Response (RVR) After AV Nodal Blocking Agent
The AV node (bouncer) is inhibited. Now, fewer beats (people) will get into Club Ventricle because the bouncer is slower checking IDs and collecting a cover charges and cannot clear people as fast.
Atrial Fibrillation with RVR in a Patient with WPW
Some beats (people) are going through the main door with the AV node (bouncer). Those are the “straight and narrow” people, so the QRS complex will be narrower. Some beats (people) are going through the side door of Kent, and their path/QRS interval is wider. This sparks a dance competition in Club Ventricle with different QRS intervals (dance moves).
Atrial Fibrillation with RVR and WPW After an AV Nodal Blocking Agent Has Been Given
The AV node (bouncer) is inhibited by AV nodal blocking agents, so the beats (people) become impatient. Instead of waiting in line to go through the main door, they rush for the side door, which is now a faster point of entry. The club gets “turnt up” for a while but then gets shut down (ventricular fibrillation arrest).
Treatment Options for Atrial Fibrillation with RVR and WPW
- Procainamide acts like club security, running to the side door to slow down patrons from sneaking in. It prolongs the refractory period of the accessory pathway.
- Cardioversion acts as a strobe light that lowers the seizure threshold of the partygoers and resets them after a short post-ictal period, bringing order to the club.
- When dealing with atrial fibrillation, look closely at the widths of the QRS complexes. If they are different widths, then consider that an accessory pathway is being used in addition to the beats being transmitted through the AV node.
- Look at the rate of atrial fibrillation. If the rate is 200–300 bpm at times, then also consider an accessory pathway.
- Do not use AV nodal blocking agents in atrial fibrillation with RVR in the presence of WPW, as it allows the accessory pathway to take over.
- Use procainamide or consider cardioversion in patients with atrial fibrillation with RVR and WPW.
- The Delta Wave is an amazing dance move and can be used at most social events. Be cautious—you may get cardioverted!
Dr. Stephenson is an emergency physician with Integrative Emergency Services in Dallas.