![]() Over half of patients will have persisting ST-elevation in precordial leads following anterior MI. Diagnosing acute OMI in the setting of prior MI The ECG morphology seen in this patient is more consistent with LAFB due to prior anterior MI. 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. Some authors advocate redefining QRS duration in LBBB to > 130-140ms given the prolonged conduction deficits seen in comparison to other causes of IVCD. Despite this, the 120ms cut-off point has persisted to today, often leading to an overdiagnosis of bundle branch block. At this time, other causes of QRS prolongation such as LAFB or LVH were not yet appreciated. 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. However, it is often leads with small QRS complexes that will manifest subtle concordant or excessively discordant ST-segment changes. 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”. Sequence of conduction in RBBB: 1) Left ventricular activation via the left bundle (black arrow) occurs normally. The diagnosis of occlusion myocardial infarction in intraventricular conduction delay (IVCD) can be challenging. The types of abnormalities are varied and include subtle straightening of the ST. Examples of ECG recordings showing incomplete right bundle branch block (RBBB) and anterior repolarization abnormalities in Patient 8 (A), incomplete right bundle branch block in Patient 52 (B. The changes may be seen in all or most of the leads (diffuse changes), or they may be present contiguous leads, such as the inferior, lateral, or anterior leads. Sgarbossa: smaller amplitude leads have higher diagnostic yield Nonspecific ST-T-wave changes are very common and may be seen in any lead of the electrocardiogram. ![]()
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