Old Inferior Wall MI ECG: Key Signs and Guide: 1 Minute to Spot Old Inferior MI on an ECG

Identifying an old inferior wall myocardial infarction (MI) on an ECG is crucial for clinicians, especially when assessing cardiac history or planning future management. The classic features relate to changes in the inferior leads — II, III, and aVF. In old (as opposed to acute) MI, the ECG shows evidence of previous, resolved infarction rather than active injury.

Key Signs of Old Inferior Wall MI on ECG:

1. Pathological Q Waves: Deep, wide Q waves (duration > 0.04 s and depth >25% of the ensuing R wave)
2. Absent ST Elevation: Unlike acute MI, ST segment elevations are typically resolved
3. T Wave Changes: T waves may be inverted or normalized, depending on infarct age
4. Loss of R Wave amplitude: Diminished R waves in inferior leads
5. Reciprocal Changes: Occasional tall R waves in lateral leads (I, aVL) as reciprocal markers

When interpreting these findings, always correlate with patient history, symptoms, and prior ECGs. An old MI infers completed infarction and scarring — there are no signs of ongoing ischemia or new injury.

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Tips 1:

Always compare the current ECG with previous tracings if available — it helps confirm the "old" status of MI changes and distinguishes them from new onset.

FAQ

Q: What are the typical ECG changes in old inferior wall MI?

A: Deep Q waves in II, III, and aVF; absence of ST elevation; possible T wave inversion or normalization.

Q: How can I differentiate between old and acute inferior MI on ECG?

A: Acute MI usually shows ST elevation, hyperacute T waves, and evolving Q waves. Old MI lacks ST elevation and shows established Q waves.

Q: What causes Q waves in old MI?

A: Q waves represent myocardial scarring and loss of electrical activity in a region previously affected by infarction.

Q: Are T waves always inverted in old inferior MI?

A: No, T waves may normalize or remain inverted depending on the time since the infarct.

Q: Why is it important to recognize old inferior MI on ECG?

A: Accurate diagnosis can guide long-term treatment, risk stratification, and further cardiac workup for the patient.