From the Guidelines
False inferior infarction patterns on an EKG can be caused by several conditions, including early repolarization syndrome, left ventricular hypertrophy, ventricular pacing, acute pericarditis, hyperkalemia, pulmonary embolism, and Wolff-Parkinson-White syndrome, as well as technical factors such as lead misplacement or reversed limb leads, and normal variant patterns in some individuals. When evaluating suspected false inferior infarction patterns, clinicians should consider the patient's clinical presentation, cardiac biomarkers, and previous EKGs for comparison 1. Some of the key conditions that can mimic inferior myocardial infarction include:
- Early repolarization syndrome, which produces benign ST elevations that can be mistaken for ischemic changes
- Left ventricular hypertrophy, which alters the electrical vectors of the heart
- Ventricular pacing, which distorts normal ventricular depolarization
- Acute pericarditis, which produces diffuse ST elevations
- Hyperkalemia, which can flatten T waves and widen QRS complexes
- Pulmonary embolism, which may cause right heart strain patterns
- Wolff-Parkinson-White syndrome, with its characteristic delta waves Certain medications like digoxin can also affect repolarization and create ST-segment changes 1. It is essential to note that a completely normal ECG in a patient with chest pain does not exclude the possibility of acute coronary syndrome (ACS), as 1% to 6% of such patients may eventually be proven to have had a myocardial infarction (MI) 1. The diagnosis of MI is more difficult in the presence of left bundle branch block (LBBB) or right bundle branch block (RBBB), but concordant ST-segment elevation or a previous ECG may be helpful to determine the presence of acute MI in these settings 1. In patients with high clinical suspicion for acute circumflex occlusion, recording of posterior leads at the fifth intercostal space (V7-V9) is strongly recommended to capture electrocardiographic evidence of myocardial ischemia in the distribution of a left circumflex artery 1. A cut-point of 0.05 mV ST elevation is recommended in leads V7-V9, with increased specificity at a cut-point >0.1 mV ST elevation, particularly in men <40 years old 1. When evaluating EKGs, it is crucial to consider the patient's clinical context, including symptoms, medical history, and other diagnostic test results, to accurately diagnose and manage potential myocardial infarctions.
From the Research
Causes of False Inferior Myocardial Infarction on an EKG
- Wolff-Parkinson-White (WPW) syndrome can cause false inferior myocardial infarction (MI) on an electrocardiogram (EKG) due to the altered sequence of ventricular activation 2, 3
- The presence of a delta wave and a short P-R interval can mimic pseudo-diaphragmatic (inferior) myocardial infarction 2
- The mechanism of WPW syndrome involves a reentry phenomenon via anomalous and normal atrioventricular (A-V) pathways, which can lead to pseudo-infarct patterns on the EKG 2, 4
- The location of the accessory pathway in WPW syndrome can also affect the appearance of the EKG, with posteroseptal accessory pathways potentially simulating inferior myocardial infarction 3
- In some cases, the pseudo-infarct pattern caused by WPW syndrome can mask a true underlying infarct, making diagnosis more challenging 4, 5
Key Factors to Consider
- Recognition of a delta wave is a crucial diagnostic criterion for WPW syndrome 2
- The presence of a short P-R interval and broad QRS complex may not always be present in WPW syndrome 2
- The use of EKG criteria alone may not be sufficient to diagnose myocardial infarction in patients with WPW syndrome, and additional diagnostic tests such as 2D echocardiogram and nuclear stress test may be necessary 4