ECG Criteria for STEMI and Reperfusion Therapy Candidacy
Both statements in the question are false (answer d). The correct ECG criteria for STEMI requiring reperfusion therapy are: ST-segment elevation of at least 1 mm in two contiguous limb leads OR at least 2 mm in two contiguous precordial leads 1.
Correct STEMI Diagnostic Criteria
The question contains critical errors in both the magnitude and lead requirements:
Statement a is incorrect: While 1 mm ST elevation is accurate, it must be present in two contiguous precordial leads (not just any two precordial leads), and the threshold is actually 2 mm for precordial leads 1
Statement b is incorrect: ST elevation of 2 mm in one limb lead is insufficient. The requirement is 1 mm in at least two contiguous limb leads 1
Accurate ECG Thresholds for Reperfusion
For limb leads: ST-segment elevation ≥1 mm in two or more contiguous limb leads indicates STEMI and warrants reperfusion therapy 1
For precordial leads: ST-segment elevation ≥2 mm in two or more contiguous precordial leads (V1-V6) indicates STEMI and warrants reperfusion therapy 1
High-risk anterior MI definition: The ACC/AHA specifically defines high-risk features as anterior MI with ≥2 mm ST-segment elevation in 2 ECG leads 1
Critical Timing Requirements
The 12-lead ECG must be performed and interpreted within 10 minutes of first medical contact or emergency department arrival 1, 2. This is a Class I recommendation that should never be delayed 2.
Reperfusion decisions must not wait for cardiac biomarker results 1, 2. For patients with ST elevation meeting criteria, the diagnosis of STEMI is secure and treatment should begin immediately 1.
Additional ECG Findings Warranting Reperfusion
Beyond the standard criteria, these ECG findings also indicate need for reperfusion:
- New or presumed new left bundle branch block with clinical presentation consistent with STEMI 1
- Posterior MI patterns: ST-segment depression ≥2 mm in anterior leads (V1-V3) with tall R waves may represent posterior STEMI 1
- Right ventricular infarction: ST elevation ≥1 mm in right-sided lead V4R in the setting of inferior STEMI 1
Common Pitfall to Avoid
The most dangerous error is requiring ST elevation in only one lead or using incorrect millimeter thresholds. Contiguity matters: the ST elevation must appear in anatomically adjacent leads to confirm a regional infarction pattern 1. Serial ECGs at 5-10 minute intervals should be performed if initial ECG is non-diagnostic but clinical suspicion remains high 1.