From the Guidelines
Inferior myocardial infarction is best detected on ECG using leads II, III, and aVF, as these leads view the inferior wall of the left ventricle, which is supplied by the right coronary artery in most people. When an inferior infarction occurs, these leads will typically show ST-segment elevation, pathological Q waves, and T-wave inversions during the evolution of the infarction. Lead III usually shows the most prominent ST elevation among these three leads. It's essential to examine all three inferior leads together for diagnostic accuracy, as ST elevation in a single lead may not be sufficient for diagnosis. Additionally, when evaluating for inferior MI, one should also check leads V1 and V4R for right ventricular involvement, and leads I and aVL for reciprocal ST depression, which often accompanies inferior infarctions, as recommended by the American Heart Association and the European Society of Cardiology 1. This pattern occurs because the electrical forces from the damaged inferior wall create opposite changes in the high lateral leads, providing further diagnostic confirmation. The most recent guidelines from the European Society of Cardiology, published in 2018, emphasize the importance of recording right precordial leads (V3R and V4R) in patients with inferior MI to identify concomitant right ventricular infarction 1.
Some key points to consider when evaluating inferior MI on ECG include:
- ST-segment elevation in leads II, III, and aVF is suggestive of inferior wall ischemia/infarction
- Lead III usually shows the most prominent ST elevation among these three leads
- Right ventricular involvement should be evaluated using leads V1 and V4R
- Reciprocal ST depression in leads I and aVL often accompanies inferior infarctions
- The spatial vector of the ST segment can help distinguish between right coronary artery and left circumflex coronary artery occlusion, as recommended by the American Heart Association 1.
It is crucial to note that the diagnosis of inferior MI should be made in the context of the patient's clinical presentation and other diagnostic tests, as the ECG findings alone may not be sufficient for a definitive diagnosis. The European Society of Cardiology guidelines recommend that a working diagnosis of STEMI should be made based on symptoms consistent with myocardial ischemia and signs on the 12-lead ECG, and that reperfusion therapy should be initiated as soon as possible in patients with a clinical suspicion of myocardial ischemia and ST-segment elevation 1.
From the Research
Inferior Infarction on ECG
The leads that show inferior infarction on an ECG include:
- Lead III
- Lead aVF
- Sometimes, lead II may also be involved
Characteristics of Inferior Infarction
Inferior infarction is often characterized by:
- ST-segment elevation in leads III and aVF
- ST-segment depression in leads I and aVL
- Q waves in leads III and aVF, indicating myocardial necrosis
- T wave inversion in leads III and aVF, indicating myocardial ischemia
Clinical Significance
Inferior infarction can be associated with a higher risk of complications, such as:
- Heart failure, as seen in patients with maximal precordial ST-segment depression in leads V4-V6 2
- Cardiogenic shock, which can be ameliorated with aggressive interventional strategies, including emergency angioplasty of the right coronary artery 2
- Recurrent cardiovascular events, despite advances in treatment strategies 3
Diagnostic Approaches
The diagnosis of inferior infarction is typically made using: