Back on the Block - Heart Blocks Part 2

Case 1

A 43-year-old male with no significant medical history presents to the emergency department via EMS with an episode of pre-syncope. The episode occurred 30 minutes ago after getting out of a hot shower, and he is currently asymptomatic. Vitals per EMS were BP 130/88, HR 59, RR 20, O2 sat 99%, T 97.5, and BS 99. He currently appears comfortable and he is in no acute distress.

You are handed this EKG:

Figure 1. Irregular rhythm with 2nd degree heart block.

Figure 1. Irregular rhythm with 2nd degree heart block.

What is the conduction abnormality?

2nd degree Mobitz type 1, Wenckebach

Based on this patient’s EKG alone, does he require admission?

In isolation, a patient with a 1st degree AV block or 2nd degree Mobitz type 1 block can be discharged with follow-up. [2] These blocks are essentially benign but should be managed by the patients PCP

  • 1st degree AV block does not cause hemodynamic instability and requires no specific treatment [2]
  • 2nd degree Mobitz Type 1 can cause a minimal hemodynamic disturbance and rarely progresses to a 3rd degree AV block
  • High grade 2nd degree AV block, 2nd degree Mobitz type 2 block and 3rd degree AV block have a high risk of hemodynamic compromise, syncope, ventricular standstill and sudden cardiac death. These blocks require admission for further work-up, cardiac monitoring, backup temporary pacing, permanent pacemaker evaluation and possible placement [2]
  • LAFB and LPFB do not require admission, although disposition ultimately depends on patients symptoms and clinical context [2]
  • Trifascicular block is always pathologic and requires admission for further evaluation of underlying cause and likely pacemaker placement [2]

Case 2

76-year-old female with a history of CAD, HTN and DM presents to the ED with dyspnea. Vitals are BP 110/76, HR 42, RR 22, O2 sat 94%, T 98.4, and BS 140. She appears uncomfortable and diaphoretic, but is otherwise in no acute distress.

Here’s her EKG Doc:

Figure 2.

Figure 2.

What is the conduction abnormality?

3rd degree AV block

The patient now complains of chest pain and starts feeling light-headed, she appears increasingly lethargic and her vitals are now deteriorating, BP 85/44 HR 32 RR 24 O2 sat 94%. How would you manage this patient?

  • ABC’s, IV/O2/Monitor (if not already done) and place transcutaneous pacer pads. Per AHA/ACLS guidelines, Atropine, transcutaneous pacing, Epinephrine and Dopamine are used in symptomatic/unstable bradycardia, although Dopamine is less commonly used
  • Atropine unlikely to treat a High grade AV block since the block is likely below the AV node, but can be used as a temporizing measure while pacer pads are placed and/or transvenous pacemaker is set-up 1
  • Epinephrine is effective in a broader range of patients and provides a greater amount of hemodynamic support when compared to Atropine [3]
  • A reasonable strategy is to attempt both electrical and medical therapy simultaneously, as it is unpredictable which therapy will work for which patient [3]
  • If electrical and medical therapy fail, prepare for transvenous pacing and obtain expert consultation.
  • Check out this great blog post by Dr. Mike Bohanske on transvenous pacemaker placement
  • Assess for reversible causes, EKG to assess for STEMI or new ischemic changes and continue work-up. Disposition will be admission for the underlying cause, pacemaker evaluation and placement

Case 3

62-year-old male with a history of HTN, Hyperlipidemia, DM and 1 PPD smoker presents to the ED with chest pain that started 20 minutes ago while mowing his lawn. He is visiting from out of town. Vitals are BP 130/92, HR 96, RR 18, O2 sat 95%, T 98.3 and BS 95. He appears comfortable and in no acute distress.

You are handed this EKG (he has no old EKG):

Figure 3.

Figure 3.

What is the conduction abnormality?

Left Bundle Branch Block (LBBB)

Would you activate the cardiac cath lab? Why or Why Not?


  • A new LBBB is no longer a STEMI equivalent according to ACC guidelines. [4] According to current guidelines, a LBBB that is new or presumed new and an old LBBB are to be assessed equally [4]
  • When evaluating a patient that has a LBBB on EKG, first assess for hemodynamic stability, if unstable and there is suspicion for MI, activate the cardiac cath lab for emergent reperfusion or fibrinolysis [4]
  • If the patient is stable, interpret the EKG and use the modified Sgarbossa’s criteria [4] Sgarbossa Criteria:
  • Concordant ST elevation > 1mm in leads with a positive QRS complex (score 5)
  • Concordant ST depression > 1 mm in V1-V3 (score 3)
  • Excessively discordant ST elevation > 5 mm in leads with a negative QRS complex (score 2)
  • Score of greater than or equal to 3 is significant for STEMI Modified Sgarbossa Criteria:
  • No longer uses a scoring system
  • Concordant ST elevation > 1mm in leads with a positive QRS complex
  • Concordant ST depression > 1 mm in V1-V3
  • ST-elevation is “excessively discordant” when the ST-elevation (measured at the J-point) is > 0.25 or 25% the depth of the S-wave.
  • ST-depression is “excessively discordant” when the ST-depression (measured at the J-point) is > 0.3 or 30% the height of the R-wave.

What is the disposition for this patient?

With a moderately suspicious presentation and negative cardiac markers, this patient has a heart score of at least 5. He requires admission for serial cardiac markers, serial EKG’s, echocardiogram, risk stratification and possible angiography.

Figure 4.

Figure 4.

What is the conduction abnormality

2:1 2nd degree AV Block

Is this a Wenckebach or type 2 AV block?

  • This can be tricky, but in general, there are a couple of things you can look for to distinguish the two:
  • PR interval tends to be prolonged in a type 1 block, whereas a wide QRS complex tends to make a type 2 block more likely [5]
  • Vagal maneuver can also help, by having the patient perform a vagal maneuver this increases parasympathetic activity to the AV node and increases inhibition, if this leads to a high grade block such as a 3:1 or 4:1 block, a Mobitz type 1 is more likely [5]
  • If vagal maneuver creates a 1:1 ratio or no change, a Mobitz type 2 is more likely [5]. If you are unable to determine if the block is a Mobitz type 1 or type 2, assume type 2 and admit the patient. Ultimately, evaluation to determine whether the patient has a Mobitz type 1 or 2 AV block is done by an electrophysiologist
Figure 5.

Figure 5.

What is the conduction abnormality?

  • Complete trifascicular block: RBBB + LAD + 3rd degree heart block
  • A trifascicular block is always pathologic, it requires admission for further evaluation and pacemaker evaluation and/or placement.


  1. Yealy, D. M., Kosowsky, J. M. (2014). Dysrhythmias. In Rosen's Emergency Medicine: Concepts and Clinical Practice 8th edition (pp. 1034-1046). Philadelphia, PA: Elsevier Saunders.
  2. Nickson, C. (2015, April 22). Heart Block and Conduction Abnormalities. Retrieved November 12, 2017, from
  3. Farkas, J. (2017, February 13). PulmCrit- Epinephrine vs. atropine for bradycardic periarrest.
  4. Wilner, B., De Lemos, J. A., Neeland, I. J. (2017, February 28). LBBB in Patients With Suspected MI: An Evolving Paradigm. Retrieved November 12, 2017, from
  5. Dubin, D. (2000, October 15), Rhythm, Part II: Blocks. In Rapid Interpretation of EKG’s 6th Edition (pp. 173-191). Cover Pub Co.

Author: Diego Iparraguirre, MD, PGY-1

Peer Review: Nicholas Ludmer, PGY-4, Jeffery Hill, MD MEd

Posting: Jeffery Hill, MD MEd