Standard ECG Calibration Settings
The standard ECG calibration is 10 mm/mV (1 mV = 10 mm), which means each small box (1 mm) represents 0.1 mV and each large box (5 mm) represents 0.5 mV. 1
Technical Specifications
Amplitude Calibration
- Standard gain setting: 10 mm/mV is universally recommended for routine ECG recordings 1
- At this standardization, 1 mV produces a 10 mm deflection on the ECG paper 1
- Each small box (1 mm) = 0.1 mV 1
- Each large box (5 mm) = 0.5 mV 1
When to Adjust Calibration
- Half-standard (5 mm/mV): Use when QRS complexes are too tall and exceed the recording boundaries, preventing accurate measurement 1
- Double-standard (20 mm/mV): Use when QRS voltages are very low and difficult to measure accurately at standard calibration 1
- Always document when non-standard calibration is used, as this affects voltage-based diagnostic criteria (e.g., left ventricular hypertrophy) 1
Critical Technical Requirements
Frequency Response Settings
- High-frequency cutoff: minimum 150 Hz for adults and adolescents 1
- High-frequency cutoff: 250 Hz for infants and children to capture rapid deflections accurately 1
- Low-frequency cutoff: 0.05 Hz for routine filters, or relaxed to 0.67 Hz for linear digital filters with zero phase distortion 1
- Inadequate high-frequency response systematically underestimates QRS amplitude and smooths important features like Q waves 1
Digital Sampling Requirements
- Minimum sampling rate: 500 samples per second to allow accurate 150 Hz filtering and reduce amplitude measurement errors to <1% 1
- A/D conversion: minimum 12-bit precision for adequate signal resolution 1
- Higher sampling rates (1200 Hz) are preferred for capturing high-frequency components accurately 2
Common Pitfalls to Avoid
Calibration Errors
- Never use 40 Hz high-frequency cutoff for diagnostic ECGs—this invalidates all amplitude measurements used for diagnostic classification 1
- Electrocardiographs should automatically alert users when suboptimal settings are used 1
- Verify that voltage calibration is accurate to ±2% 1
Measurement Accuracy
- Use the largest-amplitude deflection in each lead as representative of that measurement, per ANSI/AAMI standards 1
- Noise levels should be reduced to <1 µV (root mean square) in the averaged signal for time-domain analysis 1
- Ensure proper electrode placement and skin preparation to minimize baseline wander and electrical interference 2
Documentation Requirements
- Always document if non-standard calibration (5 mm/mV or 20 mm/mV) is used 1
- Specify which diagnostic criteria are applied, as voltage-based criteria (e.g., Sokolow-Lyon, Cornell voltage for LVH) are calibration-dependent 1
- Computer interpretations require physician verification—automated systems still produce frequent errors 2
Age-Specific Considerations
- Adults >35 years: Standard 10 mm/mV calibration with 150 Hz high-frequency cutoff 1
- Adolescents (16-35 years): Standard calibration but recognize that voltage criteria for LVH have lower accuracy in this age group 1
- Children and infants: Standard 10 mm/mV calibration but require 250 Hz high-frequency cutoff to capture rapid deflections 1