An 85 year old male arrives at your ED at Canadian Janus General Hospital by ambulance. EMS was called to the scene because the patient had a fluctuating level of consciousness. At handover they state that the patient has been rousable, GCS 13-15. Vitals are: Temp 36.5, RR 16, O2 sat 96% on room air, BP 95/55, HR of 16! EMS has established IV access and attempted two doses of atropine 0.5 mg without any results. There is no pre-arrival ECG available.
The patient appears pale and a little drowsy. He easily responds to his name, and is able to answer any and all questions. He denies chest pain and dyspnea. He does however feel week and dizzy and hasn’t had the energy to get out of bed today. Medications have been taken as instructed though today he hasn’t taken his morning doses. Until today he has been well.
PHx: hypertension, dyslipidemia, BPH
Meds: bisoprolol, perindopril, crestor, tamsulosin
You re-check his vitals: Temp 36.7, RR 16, O2 sat 96% on room air, BP 90-110 systolic, HR still 12-18!
Pupils are equal and reactive. On auscultation his chest is clear. JVP is flat and heart sounds are normal. There are no other signs of CHF such as hepatomegaly or peripheral edema.
Of course the first necessary test is the ECG, and here it is:
I like Amal Mattu’s approach to AV Blocks:
1) What is the atrium doing?
2) What is the ventricle doing?
3) What is the relationship between atrium and ventricle (ie look at the PR interval)?
Interpretation: Upright P-waves in the limb leads suggest the atrial rate is sinus rhythm with a regular rate of about 80 bpm. The ventricles are conducting at a rate of about 18 bpm. This is consistent with an ventricular escape. There is complete dissociation between atria and ventricles, as the PR intervals vary. Of note, the T-waves are pretty enormous. There are no obvious signs of ischemia. You determine that this is 3rd degree (complete) heart block with a ventricular escape rhythm at 18 bpm.
You’re feeling good about your interpretation. Don’t forget to treat the patient!
You recall the latest ACLS Guidelines and think about your options in the patient with unstable bradycardia:
- Unstable = acutely altered mental status, ischemic chest discomfort, acute heart failure, hypotension, or other signs of shock that persist despite adequate airway and breathing
- First try atropine (0.5mg IV q3-5min) (Class IIa, LOE B); if unresponsive to atropine, IV of dopamine or epinephrine (2-10 mcg/min) or transcutaneous pacing can be effective (Class IIa, LOE B)
- Immediate transcutaneous pacing showed no hospital survival benefit over IV infusion of dopamine in this trial. Epinephrine was not assessed as an alternative.
- Avoid relying on atropine if high grade AV block (Mobitz II or 3rd Degree heart block)
- Isoproterenol, a beta 1&2 agonist with chronotropic and vasodilatory effects, can also be considered as an alternative to dopamine or epinephrine, with an infusion rate of 2-10 mcg/min. Some data suggest it may provoke arrhythmias however.
- The above measures should be temporizing while preparing for transvenous pacing if the unstable bradycardia cannot be reversed
- Identify and treat the cause!
Despite his severe bradycardia, the patient is not having CP, SOB or CHF. He is mentating quite well though a bit drowsy. His SBP remains in the 90-110 range with good peripheral pulses and warm extremities. Labs have been sent off, including troponin, CBC, lytes/BUN/Cr, lactate. A chest x-ray is pending.
You decide to start your patient on epinephrine 5 mcg/min via 18G antecubital peripheral IV (Are peripheral pressors safe? See EMCrit Episode 107 for more), instead of starting with transcutaneous pacing. Minutes later his HR is 22 and BP 115/60. You increase to 8 mcg/min and call your cardiologist on call. The HR comes up to 32 with a BP of 125/60. The patient perks up and regains his colour.
Finally your labs come back: Normal CBC. Creatinine 105 micromol/L, K+ 6.5, lactate 2.4. Troponin is negative.
For the hyperkalemia, you administer two amps of calcium gluconate (But doesn’t calcium chloride work faster/better than calcium gluconate?), 10 units of IV insulin (with an amp of D50W), and place the patient on nebulized salbutamol. You also give 500cc of normal saline. Cardiology asks for 30 grams of oral kayexelate (does it work?).
A repeat ECG shows the following:
Unfortunately the quality isn’t great. This repeat ECG is a little less clear. Is this is 2nd degree Mobitz II or 3rd degree heart block? Atrial rhythm is sinus at about 100 bpm. Ventricles are beating at a rate of about 33. The PR intervals for each apparently conducted P-wave appear consistent, suggesting Mobitz II block with 3:1 conduction. T-waves are less prominent. If you disagree, feel free to leave your interpretation in the comments!
Cardiology arrives and tries to wean the epinephrine off and cannot. The patient is transferred to CCU. A repeat K+ drawn two hours later is 4.4 yet the patient remains dependent on epinephrine infusion, suggesting that the potassium was not the sole factor in the patient’s bradycardia. Ultimately a transvenous pacer is placed. Repeat troponin is negative and the next day he undergoes successful implantation of a permanent pacemaker. His ECG at discharge is below.
Electronic ventricular pacemaker, paced rhythm at 70 bpm.
Take home points from this case:
First line management of unstable bradycardia, according to ACLS Guidelines, is either transcutaneous pacing or epinephrine or dopamine infusion. Prepare for transvenous pacing.
Identify the cause of the bradycardia and target your treatment.
When determining the level of heart block, look at the atrial rate, the ventricular rate, and if they are related (check the PR interval).
Useful videos on approach to Bradycardia and AV Blocks:
EKG of the week April 24 2012 http://ekgumem.tumblr.com/post/21717157267/rhythm-interpretation-and-diagnosis-of-av
EKG of the week September 17 2012 http://ekgumem.tumblr.com/post/31726238627/3-step-approach-to-diagnosing-av
EKG of the week September 16 2013 http://ekgumem.tumblr.com/post/61407503619/unstable-bradycardia-episode-107-september-16
2010 ACLS Guidelines. Circulation. 2010; 122: S729-S767 http://circ.ahajournals.org/content/122/18_suppl_3/S729.full
Morrison et al. A randomized controlled feasibility trial comparing safety and effectiveness of prehospital pacing versus conventional treatment: ‘PrePACE.’ Resuscitation. 2008;76:341–349 http://www.resuscitationjournal.com/article/S0300-9572(07)00441-8/abstract
EM:RAP – July 2013 – Kayexalate Myths http://www.emrap.org/episode/2013/july/kayexalatemyths
Academic Life in Emergency Medicine – July 2, 2013 – Does calcium gluconate raise serum calcium as quickly as calcium chloride? http://academiclifeinem.com/calcium-gluconate-vs-calcium-chloride-myth-busted/