“THIS IS MEDIC 2915 REQUESTING STAT MEDICAL COMMAND! OVER.” You hear the EMS radio call out. You and your charge nurse Shannon hustle over to the radio to see what’s going on.
“Go ahead Medic 2915, this is the hospital”
“Hey Doc, we need some help out here. We’re about 30 minutes from your location, we’re out in the middle of nowhere today with questionable radio signal. We have a 65 year old male who felt weak and dizzy all morning. He finally put his smart watch on and it started alarming for tachycardia. Told him his heart rate was in the 200s. He called 9-1-1 and we found him in SVT. We’ve tried adenosine twice, first 6 mg then 12 mg with no response. His BP is falling a bit, we were at 100/65, now mid 80s systolic. Probably getting close to time to shock him, I think. Looking for some help with what to do next. Sending his ECG to you now take a look:”
Rate: Fast. Around 250-280
Rhythm: Not sinus
Axis: Left Axis
Intervals: no PR interval, narrow QRS complexes
Morphology: ST Elevation in aVR, Diffuse depressions
Final Read: This is consistent with SVT with extremely fast rates. This ECG also shows signs of strain with elevations in aVR and diffuse depressions
“Medic 2915, it sure looks like SVT to me, what happens when you push the adenosine?” you ask.
“Doc, I’ve never seen anything like it. I give the adenosine, he converts back to sinus rhythm for about 10-20 seconds and then BAM, back into SVT. Rates 250 and higher. Shit. Hold on a second. Sir .. Sir! SIR!!”
“What’s going on guys? Talk to us??” Shannon calls out over the radio. It’s far away and the radio is cutting in and out but you’re pretty sure you hear the familiar hum of the defibrillator charging.
You and Shannon look at each other. “That’s not a good sign” you say.
“DOC! This is medic 2915, he lost consciousness, systolic dropped to 50 but still had a pulse. We synchronized cardioverted him once with no response. Second time seemed to work though. He’s in sinus rhythm now but his ECG looks really weird. Sending it to you now.”
Rate: 90
Rhythm: Sinus
Axis: Normal
Intervals: very short PR interval, widening of the QRS right at the beginning of the complex
Morphology: There is a delta wave present
Final read: This ECG shows a delta wave consistent with WPW.
See the enlarged figure below for a closer look at the delta wave and the loss of the PR interval:
“Medic 2915, does the patient have a history of Wolff-Parkinson-White or WPW?” you ask.
“Negative sir. Only history is hypertension and high cholesterol. He said he has had palpitations on and off for years but never got them checked out since they always just seemed to go away”
“Got it. Ok Medic 2915, this is very important, you must avoid AV nodal blocking medications in this patient if he goes into a wide complex tachycardia.”
“…” The radio goes dead.
“MEDIC 2915! Do you copy? Did you get my last transmission?”
“…” Nothing.
“Shannon, get dispatch on the phone. We need to see where Medic 2915 is and get back in touch with them. We’ve lost contact and this patient is very sick.”
“No problem, Doc. Hey, the ECG machine is dinging.”
It’s tough to tell off a single lead rhythm strip, but given the known WPW, this is likely WPW and antidromic conduction. This is very bad.
“THIS IS …. Click . .. MEDIC …. 15. ..” the radio chirps
“MEDIC 2915 do you copy? You must not give AV blocking drugs. Cardiovert this patient!”
“…. Static …. ACLS… Amiodarone … more static…”
“No, do not give amiodarone. I repeat, DO NOT GIVE AMIODARONE” you say into radio with no response.
“[no words come across but you hear the charging of the defibrillator again]”
**While we wait for medic 2915 to regain signal and get back in touch with us, let’s recap WPW quickly. **
The hallmark of WPW is an accessory pathway (called the Bundle of Kent) that connects the atria and ventricles but is not subject to AV nodal control. Somewhere, there is a rogue strand of myocardium that links the two. Sometimes, you’ll get a PVC or a PAC that hits at just the wrong time that launches the heart into SVT.
The accessory pathway is not unidirectional, so electrical impulses can go down the native conduction system and up the accessory pathway, called orthodromic conduction and producing a narrow complex tachydysrhythmia or going down the accessory pathway and up the native conduction pathway, called antidromic conduction and producing a wide complex tachydysrhythmia (pictured below):
Cite: EKG Teaching Rounds. Springer 2022. https://link.springer.com/book/10.1007/978-3-031-06028-1
“THIS IS MEDIC 2915, DO YOU COPY?”
“Go ahead Medic 2915”
“Lost you for a bit there, Doc, sorry about that. We’re still about 7 minutes out. Weirdest thing happened. The patient went into VTach! We tried to shock him but couldn’t get him out of VTach. We had no coms and his blood pressure was still ok, so, following ACLS protocol for stable VTach, we pushed amiodarone. About 5 minutes later he went into a VFib arrest. We defibrillated him immmediately and started CPR. After 4 rounds of compressions and ACLS, we got ROSC. He’s currently sedated and intubated.”
“Medic 2915, do not give anymore amiodarone. Repeat, do not give amiodarone to this patient. Continue to monitor and transport. We’ll review the case with you upon arrival, go over why ACLS may have led you astray here, and talk about WPW. If you see any more episodes of VTach, attempt cardioversion and call back. Please call back for any changes or questions.”
“Copy, Doc. See you in 5.”
Case Wrap Up:
AHA guidelines are really useful for some cases and can, unfortunately, can lead you astray on other cases, especially in complex patients, like those with WPW and clinical instability. Here are the guidelines referenced that the medic’s protocols would have likely been based on:
For the initial ECG when the patient was in SVT and stable:
And then once medications didn’t work and the blood pressure started to fall:
And when he went into a hemodynamically stable wide complex tachycardia:
For more information, see the full guidelines, here. I’d really take a look at the recommendation-specific supportive text under each of these boxes. There’s a ton of great information there.
Recap:
- WPW can be seen on an ECG as a shortened PR interval and Delta Wave.
- The two major types of tachydysrhythmias seen with WPW are SVT with orthodromic or antidromic conduction:
- Orthodromic is a narrow complex tachycardia where conduction goes down the native conduction pathway and back up the accessory pathway.
- Antidromic is a wide complex tachycardia where conduction goes down the accessory pathway and back up the native conduction pathway.
- Treatment differs for each of these:
- For orthodromic, adenosine, beta blockers, and calcium channel blockers are usually considered safe with adenosine as first line treatment to get back into sinus rhythm.
- For antidromic, AV nodal blockers must be avoided as they can precipitate the patient degrading into ventricular fibrillation:
- If you must give drugs, consider procainamide or ibutilide (neither of which are routinely carried on an EMS rig).
- Be careful with WPW, this is one condition where ACLS can mislead you.
- Welcome to all of the new interns starting today! And congratulations to all the residents graduating!
- Make sure to keep your email address up to date as you graduate to keep getting ECG Teaching Cases emails!
Hit me up with any questions,
Lloyd
**Looking for a dynamic guest lecture on Emergency Cardiology for your Grand Rounds? Reach out here for a lecture request by Dr. Tannenbaum. If you have reached out already, I have emailed you back. If you haven’t gotten it, please message me directly on Substack or just reply to this email.**
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Lloyd Tannenbaum, MD
