Thursday, September 23, 2021

Cardiac Arrest at the airport, with an easy but important ECG for everyone to recognize

 Written by Pendell Meyers

Every once in a while we need to go back and cover some easy but important ECGs.

This will be far too easy for most readers of this blog, so please go find a learner and show them this case. Make sure they understand this case well, so that they will be able to learn from the harder versions of this case.

A middle aged female suffered sudden witnessed cardiac arrest at the airport, with quick bystander CPR.

EMS arrived and found her in VF. She was successfully defibrillated.

Her EMS ECG on the way to the ED was sent to us:

What do you think?

There is likely sinus tachycardia with a prolonged PR interval. Some learners might be worried about VT initially, if they do not recognize the QRS. Instead it is RBBB and LAFB. There is striking concordant STE in V2-V4 that is easy and unmistakable in this case, but often times is much harder to recognize when the J point is not quite as pronounced as it is in this case (see harder cases below).

This pattern is one of the highest risk OMI patterns recordable on an ECG: it is large proximal LAD occlusion until proven otherwise. The LAD supplies the anterior septum where the right bundle branch and left anterior fascicle are located. Acute proximal LAD occlusion can cause ischemia of these fascicles causing the combination of RBBB and LAFB. See below for review and references.

The cath lab was activated, and the patient fortunately suffered no further arrests. She was of course found to have an ostial LAD occlusion that was opened and stented.

The initial high sensitivity troponin I resulted elevated at 105 ng/L.

Here is her ECG the next morning:

The RBB and LAF have recovered. But there is significant loss of R waves anteriorly, with QS waves and some mild persistent STE. There has been a very large area of irreversible infarction.

The second troponin was around 16,000 ng/L, and no further troponins were ordered.

She survived the hospitalization.

Learning Points:

Like LBBB and many other abnormal QRS patterns, the formal "STEMI criteria" do not apply to RBBB with LAFB. There are no formal criteria for this situation, nor any "STEMI equivalent" criteria in the 4th universal diagnosis of MI. In standard 2021 practice, what generally happens is: if the STE is striking and clear like it is in this case, everyone understands it is "STEMI". If the STE is not as striking, or the J point is more obscured by the QRS pattern than in this case, it is often not recognized and missed. See the more difficult cases below.

Some of the most severe LAD or left main occlusions present with acute RBBB and LAFB, and these findings carry the highest risk for acute ventricular fibrillation, acute cardiogenic shock, and highest in-hospital mortality when studied by Widimsky et al. (in-hospital mortality was 18.8% for AMI with new RBBB alone). Additionally, the RBBB and LAFB make the recognition of the J-point and STE more difficult and more likely to be misinterpreted. Upon successful and timely reperfusion, the patient may regain function of the previously ischemic or stunned fascicles.

Widimsky PW, Rohác F, Stásek J, et al. Primary angioplasty in acute myocardial infarction with right bundle branch block: should new onset right bundle branch block be added to future guidelines as an indication for reperfusion therapy? Eur Heart J. 2012;33(1):86–95.

This pattern of LAD OMI with RBBB and LAFB is so high risk, I would estimate in my experience at least 20-50% of these patients suffer severe cardiogenic shock or arrest before emergent PCI can even be performed. 

See these examples below, almost all of which are more difficult than this case:

A woman in her 60s with 6 hours of chest pain, dyspnea, tachycardia, and hypoxemia

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