Standard ECG Calibration Settings
The standard 12-lead ECG must be recorded at a paper speed of 25 mm/s and a vertical gain (amplitude) of 10 mm/mV (1 mV = 10 mm deflection). 1
Paper Speed (Horizontal Calibration)
- Standard paper speed is 25 mm/s, which means each small box (1 mm) represents 0.04 seconds (40 milliseconds) and each large box (5 mm) represents 0.2 seconds 1
- This standardized speed allows for accurate measurement of intervals (PR, QRS, QT) and is essential for temporal alignment of waveforms across different leads 2
Vertical Gain (Amplitude Calibration)
- Standard vertical gain is 10 mm/mV, meaning a 1 millivolt electrical signal produces a 10 millimeter deflection on the ECG paper 1
- This calibration is critical for accurate measurement of ST-segment elevation and depression, where thresholds are defined in millimeters (e.g., 2 mm ST elevation in V2-V3 equals 0.2 mV) 3
- The standard calibration pulse should produce a 10 mm vertical deflection to verify proper calibration 1
Clinical Importance of Standardization
- These standardized settings enable consistent interpretation of diagnostic criteria across different machines and institutions 3
- ST-segment elevation thresholds for acute myocardial infarction are defined based on standard calibration: ≥2 mm (0.2 mV) in leads V1-V3 for men ≥40 years, and ≥1 mm (0.1 mV) in other leads 3
- Without standard calibration, voltage-based diagnostic criteria (such as those for left ventricular hypertrophy or ST-segment changes) become unreliable 3
Common Pitfalls
- Always verify the calibration mark on the ECG tracing before interpretation - if the calibration pulse is not 10 mm high, all voltage measurements will be inaccurate 1
- Some machines allow adjustment of gain (e.g., half-standard at 5 mm/mV or double-standard at 20 mm/mV) for very large or very small amplitude complexes, but this must be clearly marked on the tracing 4
- Digital electrocardiographs must maintain temporal alignment of multiple leads to within 10 ms maximum misalignment to allow accurate spatial-temporal interpretation 2