ECG Case 122

• Sinus tachycardia, rate ~100 bpm
• QRS is widened at ~120ms, and on first glance this may appear to be left bundle branch block. However, given the lack of notched R waves in lateral leads, this is more likely intraventricular conduction delay (IVCD) due to left anterior fascicular block (LAFB)
• QS complexes in leads V1-4, with hyperacute T waves in leads V2-4
• ST elevation in V2-4 appears appropriately discordant, with ST elevation measuring < 25% of the depth of the preceding S wave in V3
• Concordant ST elevation ~1mm in V5

What is the diagnosis?

What is your interpretation?

Reveal answer

Parasternal short axis (PSAX) view at the level of apex

• There is regional wall motion abnormality evident, with hypokinesis of the anterior wall consistent with an anterior territory infarct

PSAX (apical level):

1. Anterior LV wall
2. Lateral
3. Inferior
4. Septal

Based on these findings, the patient was taken for emergent angiography, where he was found to have a 99% sub-total occlusion of his mid-level LAD with TIMI-1 flow, as well as severe triple vessel disease. Successful PCI was performed to his LAD with resultant TIMI-3 flow.

His initial high-sensitivity troponin taken at 3.5 hours post onset of pain later returned a negative result.

Sgarbossa: smaller amplitude leads have higher diagnostic yield

The diagnosis of occlusion myocardial infarction in intraventricular conduction delay (IVCD) can be challenging. We are often drawn to leads with large QRS complexes, such as V2-3 in this patient, to determine if the degree of ST-elevation seen is “acceptable”. However, it is often leads with small QRS complexes that will manifest subtle concordant or excessively discordant ST-segment changes.

LBBB v LAFB: improving definitions

The threshold of 120ms in defining LBBB was established in 1941 via animal model experimentation limited to limb leads, and not by objective measurements in humans. At this time, other causes of QRS prolongation such as LAFB or LVH were not yet appreciated. Despite this, the 120ms cut-off point has persisted to today, often leading to an overdiagnosis of bundle branch block. Some authors advocate redefining QRS duration in LBBB to > 130-140ms given the prolonged conduction deficits seen in comparison to other causes of IVCD.

The American Heart Association recommendations include “notched or slurred R wave in leads I, aVL, V5 and V6” as part of diagnostic criteria for LBBB, largely absent in this case. The ECG morphology seen in this patient is more consistent with LAFB due to prior anterior MI.

Diagnosing acute OMI in the setting of prior MI

Over half of patients will have persisting ST-elevation in precordial leads following anterior MI. This so-called LV aneurysm morphology is associated with a small T-wave amplitude:

Differentiating LV aneurysm morphology from OMI can be difficult, and relies on clinical suspicion, reciprocal changes, and as discussed above, T wave amplitude relative to the QRS complex. Such reciprocal changes can be more difficult to ascertain in the context of IVCD. “Pseudonormalisation” of previously inverted T waves (such as V3 in the above example) can mask hyperacute T waves — previous ECGs are important in diagnosing OMI in these settings.

Summary

The subtlety of ECG findings in this patient, combined with his negative initial high sensitivity troponin and pain-free status on arrival, could have lead to a misdiagnosis of “unstable angina” and caused significant delays in potentially life-saving intervention.