This ECG is from a 66-year-old woman who called 911 for a complaint of chest pain for the past four hours. She also complained of nausea, vomiting, and diarrhea for that time. She was pale and diaphoretic, and her BP was 77/43 sitting up, improving to 90/54 reclining. She denied “cardiac” history. Her medications included: aspirin, an SSRI, cilostazol, amlodipine, umeclidinium and vilanterol inhaler, atorvastatin, levothyroid, and metoprolol. We don’t have a previous ECG. The EMS crew followed their chest pain protocol and delivered the patient to a facility with an interventional cath lab, but they did not designate a “STEMI Alert” because of the wide QRS. It is their protocol to use the term “STEMI Alert” only when no M.I. mimics, such as left bundle branch block, are present.
What does this ECG show? There is an underlying sinus rhythm at 75 bpm. There is AV dissociation, with regular, wide QRS complexes at a rate of 44 bpm. This meets the criteria for complete heart block (third-degree AV block). The morphology of the QRS complexes meets the criteria for left bundle branch block (wide, upright in Leads I and V6, negative in V1). At a rate of 44 bpm, several options for this escape rhythm are possible: 1) junctional escape with LBBB, 2) junctional escape with intraventricular conduction delay due to AMI, and 3) idioventricular escape rhythm. Also, in the presence of IWMI, AV node ischemia is very likely, resulting in AV blocks at the level of the AV node. CHB at the AV node would result in junctional escape rhythm, and CHB below that, in the fascicles of the bundle branches, would result in idioventricular escape. The issue for this patient, and ANY patient, is cardiac output, and we see several reasons for cardiac output to be lower:
· Wide QRS
· Slow rate
· Lack of P waves preceding every QRS (loss of atrial kick).
In the EMS setting, it really doesn’t matter if the escape rhythm is junctional with wide QRS or ventricular. The patient's hemodynamic status is the important consideration.
Even more alarming, this ECG shows signs of acute inferior wall M.I. It can be difficult to ascertain when STEMI is present in the presence of wide-complex rhythms. That is because most wide-complex rhythms have discordant ST and T wave changes. That is, whenever the wide QRS is positive, there is ST depression and T wave inversion, and whenever the wide QRS is negative, there is ST elevation and upright T waves.
This ECG shows excessively elevated discordant ST segments in the inferior leads (II, III, and aVF.) We also see excessively discordant ST elevation in V3, and V4. The change from ST depression to ST elevation between V2 and V3 is very abrupt, with the obvious ST depression in V1 and V2 indicating reciprocal views of ST elevation on the posterior wall. In LBBB without STEMI, there is normally ST elevation in V1 a V3.
Sgarbossa and Smith In 1996, Sgarbossa, et al proposed a univariate scoring system for determining acute M.I. in the presence of LBBB. Sgarbossa’s Criteria has been used for with some success both in the presence of LBBB and ventricular paced rhythms. These criteria were formulated before results could be confirmed with cath lab results. In this decade, Dr. Steven Smith and his colleagues have proposed some modifications to Sgarbossa’s Criteria which take into account the ratio of ST alteration to R wave. In Smith’s Modification, excessive discordance is measured as discordant ST elevation when the j point is > 0.25, or 25% the depth of the S wave. His results have been, and continue to be, measured against cath lab findings, and are more accurate than the original criteria. For an excellent discussion of LBBB, Sgarbossa’s Criteria, and Smith’s modified Sgarbossa criteria, we recommend Tom’s Bouthillet’s excellent three-part series on the topic.
With the exception of right bundle branch block, most wide-QRS conditions are considered “mimics” of acute M.I., and can both disguise the presence of an M.I. and masquerade as M.I. Unfortunately, the mimics do not prevent the patient from having an M.I.
How did this patient do? The infero-lateral M.I. was recognized in the emergency department, and the patient’s hypotension was treated with pacing and fluids. She was sent immediately to the cath lab, where it was found that she had a single-vessel lesion in the proximal to mid right coronary artery. There was 100% occlusion with TIMI-0 flow. She underwent angioplasty and stent placement, with excellent TIMI-III results. The RCA was dominant, and much larger than the LCA. The second ECG shows the excellent results of the angioplasty - QRS is narrow, the rhythm is sinus, and ST segments returning to normal. The tiny Q wave in Lead III eventually disappeared, probably because it was due to right ventricular M.I.
This crew felt they were following their protocol in not calling this a “STEMI Alert”, but fortunately they were able to transport the patient to a full-service cardiac hospital, where she received angioplasty very quickly.
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