The Ultimate Shock-Block: How to Take Back “Charge” in Your ED

I recently had the following case:

52 year-old male presents to your ED from the cardiologist’s office complaining of shortness of breath and palpitations since this morning. This is the first episode. Vitals: BP 100/60, HR 135 – 148, RR 22, T 98, O₂ sat on RA 93%. On exam, the patient appears mildly uncomfortable and has mild crackles in his lung bases with an irregularly irregular heart rate on auscultation. No other significant exam findings are noted. An EKG is quickly obtained revealing atrial fibrillation with rapid ventricular response.

It was a gift from god. Well, maybe not for the patient—but for an ambitious EM resident like myself any chance at shocking a human heart is well received.

The criteria for D/C cardioversion were met, but no sooner than I could wipe away the dribble of saliva from my chin and tear through the plastic packaging of pacer pads like a child on Christmas (er, Hannukah) did the cardiologist arrive. “Hold on son, let’s just give cardizem 20” he said. And so we did. Grinch.

I got shock-blocked in my own ED, by an outside cardiologist no less! The implications of territorialism are beyond this entry, but for now let’s just discuss when to shock AFib.

If you answered: “when it is unstable”, you are correct! From what I’ve witnessed, however, there seems to be much confusion about what defines unstable atrial fibrillation (or tachydysrhythmia for that matter).  When in doubt you can use my mnemonic: “ACS”

A – is for ACS, anything from unstable angina to full blown MI

C – is for CHF. That is, acute exacerbation of old, or a new onset pulmonary edema

S – is for symptomatic hypotension

In the above case, the patient had acute pulmonary edema (no history of CHF), later confirmed by chest XR. And, lo and behold, he also threw a troponin of 0.5.

So why the fear and avoidance of cardioversion? It’s safe and actually carries less risk than pharmacologic cardioversion. And when any of three “ACS” criteria are met, it’s the right call. Still don’t believe me? Just follow the current guidelines from the AHA/ACC on management of atrial fibrillation.

Now that you’re convinced and excited about shocking your patient, here are some key points on successful cardioversion.

Sedation.

D/C cardioversion is painful—duh!—so use sedation.

"Check Pad Placement"

A nice go-to alternative to the classic versed/fentanyl combo (acceptable) is etomidate/fentanyl. Etomidate is advantageous due to its rapid onset/offset and stable cardiovascular profile. I use “half-dose” etomidate or 0.15 mg/kg. Remember, you’re not looking to intubate—only briefly sedate for a quick jolt. Scott Weingart describes sedating an unstable atrial fib patient in his EMCrit podcast.

Pad placement.

Optimal energy delivery to overcome the dense mass effect of fibrillating atria is best achieved with anterior-posterior pad configuration. Anterior-lateral is less successful. Rob Orman of ERcast discusses pad placement and cardioversion with an electrophysiologist in his podcast.

Device.

When available, opt for biphasic—it carries an overall higher success rate for cardioversion when compared to monophasic (94% vs 79%, respectively and 99.1% vs 92.4% in another study) and requires less energy. Less energy translates to less skin damage.

Energy.

Current recommendation is to start at 100 J on biphasic and 200 J in monophasic and titrating upward as needed every minute between shocks until cardioversion is achieved. Worried about causing myocardial damage? Evidence does not support clinically significant injury or troponin elevation in patients even when levels as high as 400 J are used.

For an amazingly brilliant 15 seconds of entertainment watch this: video

Anti-coagulation.

As we’ve all learned in medical school, prolonged periods of persistent fibrillation result in blood pooling and stasis in the atria leading to clot formation. Once cardioverted, any existing thrombus is at risk of dislodgement and embolization with the return of an atrial kick.

For patients known to be in fibrillation over 48 hours, the current guideline recommendation is to co-administer a heparin bolus (unless contraindicated) followed by drip when performing cardioversion in the ED. Coumadin is initiated thereafter on the floors once properly anticoagulated.

If fibrillation is acute (less than 48 hours), just shock.

Interested in more? Check out this in-depth review brought to you by the guys of Life in the Fast Lane. Oi Aussie!!