From the Guidelines
ST elevation criteria for diagnosing myocardial infarction requires elevation of at least 1 mm (1 small square) in at least two contiguous leads, except in leads V2-V3 where different thresholds apply, as stated in the 2018 European Society of Cardiology guidelines 1.
Key Criteria
- In leads V2-V3, ST elevation should be ≥ 2 mm (2 small squares) in men ≥ 40 years, ≥ 2.5 mm (2.5 small squares) in men < 40 years, and ≥ 1.5 mm (1.5 small squares) in women.
- Each small square on an ECG represents 0.1 mV vertically, so 1 mm elevation equals 0.1 mV.
- The elevation is measured at the J point, where the QRS complex meets the ST segment.
Rationale
These criteria help distinguish pathological ST elevation from normal variants like early repolarization. The different thresholds for V2-V3 exist because these leads normally have some ST elevation, particularly in young men. Accurate measurement is crucial for timely diagnosis and treatment of ST-elevation myocardial infarction (STEMI), as this determines eligibility for immediate reperfusion therapy.
Clinical Context
The 2018 guidelines 1 emphasize the importance of initiating ECG monitoring as soon as possible in all patients with suspected STEMI to detect life-threatening arrhythmias and allow prompt defibrillation if indicated. If the ECG is equivocal or does not show evidence to support the clinical suspicion of MI, ECGs should be repeated and, when possible, compared with previous recordings.
Additional Considerations
In patients with inferior MI, it is recommended to record right precordial leads (V3R and V4R) seeking ST-segment elevation, to identify concomitant right ventricular (RV) infarction, as noted in the 2018 guidelines 1. Likewise, ST-segment depression in leads V1 –V3 suggests myocardial ischemia, especially when the terminal T-wave is positive (ST-segment elevation equivalent).
From the Research
ST Elevation Criteria
The provided studies do not directly address the question of the number of small squares for ST elevation criteria.
- The studies focus on the diagnosis and treatment of ST-segment elevation myocardial infarction (STEMI) 2, 3, 4, as well as the differential diagnosis of ST-segment elevation 2, 5.
- None of the studies provide information on the specific number of small squares for ST elevation criteria on an electrocardiogram (ECG).
- The studies discuss the importance of prompt diagnosis and treatment of STEMI 2, 3, 4, as well as the differential diagnosis of ST-segment elevation 2, 5.
- However, they do not provide the specific criteria for measuring ST elevation in terms of small squares on an ECG.
Relevant Information
- The studies provide information on the diagnosis and treatment of STEMI, including the use of P2Y12 inhibitors 3, 4.
- They also discuss the differential diagnosis of ST-segment elevation, including early repolarization, pericarditis, and ST elevation secondary to an abnormality of the QRS complex 5.
- However, the specific question of the number of small squares for ST elevation criteria is not addressed in the provided studies.