From the Guidelines
False inferior myocardial infarction patterns on an EKG can be caused by various conditions, including early repolarization syndrome, left ventricular hypertrophy, ventricular aneurysms, pericarditis, hyperkalemia, pulmonary embolism, and bundle branch blocks, as well as technical factors and normal variant patterns. According to the most recent and highest quality study 1, these conditions can mimic the ST elevations and Q waves typically seen in true inferior myocardial infarctions, making accurate diagnosis challenging.
Some key points to consider when interpreting EKGs for inferior MI include:
- Early repolarization syndrome can produce benign ST elevations that can be mistaken for ischemic changes 1
- Left ventricular hypertrophy can alter the electrical vectors of the heart, leading to false inferior MI patterns 1
- Ventricular aneurysms from previous infarctions can create persistent ST changes that may be misinterpreted as acute MI 1
- Pericarditis can produce diffuse ST elevations that may be mistaken for inferior MI 1
- Hyperkalemia can flatten T waves and widen QRS complexes, leading to false MI patterns 1
- Pulmonary embolism may cause right heart strain patterns that can be misinterpreted as inferior MI 1
- Bundle branch blocks, particularly right bundle branch block, can alter ventricular depolarization and lead to false MI patterns 1
It is essential to consider the clinical context, compare with previous EKGs, and sometimes use additional diagnostic tools like echocardiography or cardiac biomarkers to distinguish true infarctions from mimics 1. Technical factors such as lead misplacement or reversed limb leads can also create false patterns, and certain medications like digoxin can affect ST segments, making accurate interpretation even more challenging 1.
In patients with suspected inferior MI, it is crucial to record posterior leads at the fifth intercostal space (V7-V9) 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, and the specificity is increased at a cut-point >0.1 mV ST elevation, which should be used in men <40 years old 1.
Overall, accurate interpretation of EKGs for inferior MI requires a comprehensive approach, considering multiple factors and using additional diagnostic tools when necessary to minimize false positives and ensure timely and appropriate treatment.
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 PR interval can mimic pseudo-diaphragmatic (inferior) myocardial infarction 2
- The WPW pattern on EKG can mask ischemic changes and may also increase the risk of arrhythmia and subsequent mortality 4
- Pseudo-infarct patterns due to WPW syndrome can mask underlying true infarct patterns, especially in the presence of coronary artery disease risk factors 5
- The mechanism of false inferior MI in WPW syndrome is due to the abnormal myocardial activation by the accessory pathway, which can cause prominent repolarization changes and Q-waves in inferior limb leads 6, 3
Specific Accessory Pathways and False Inferior MI
- Posteroseptal accessory pathways can direct the ventricular depolarization vector superiorly, giving rise to prominent Q-waves in inferior limb leads and simulating inferior myocardial infarction 3
- Left lateral accessory pathways can cause Q-waves in lateral limb-leads, simulating high lateral myocardial infarction, but not typically false inferior MI 3
- Right lateral accessory pathways can simulate anterior infarction, but not typically false inferior MI 3