What are the appropriate settings for an electrocardiogram (ECG)?

Standard ECG Technical Settings

The standard ECG should be recorded at 10 mm/mV calibration (where 1 mV produces a 10 mm deflection), with a paper speed of 25 mm/second, using a high-frequency cutoff of at least 150 Hz for adults and adolescents, and 250 Hz for infants and children. 1

Core Calibration Parameters

Amplitude (Gain) Settings

• Standard calibration is 10 mm/mV universally, meaning each small box (1 mm) represents 0.1 mV and each large box (5 mm) represents 0.5 mV 1
• Alternative gain settings (5 mm/mV for high-amplitude complexes or 20 mm/mV for low-amplitude complexes) may be used but must be clearly documented on the tracing, as this fundamentally alters voltage-based diagnostic criteria 1

Frequency Response Requirements

For Adults and Adolescents (>16 years):

• High-frequency cutoff: minimum 150 Hz to accurately capture rapid QRS upstrokes and small deflections 2, 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

For Infants and Children:

• High-frequency cutoff: 250 Hz required to capture the more rapid deflections characteristic of pediatric ECGs 2, 1
• This higher bandwidth prevents amplitude underestimation and missed small deflections 2

Digital Sampling Specifications

• 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
• Noise levels should be reduced to <1 µV (root mean square) in the averaged signal 1

Equipment and Recording Standards

Electrocardiographic System Requirements

• The system must meet American Heart Association specifications for frequency response and signal fidelity 2
• Silver-silver chloride electrodes are recommended as most dependable for minimizing motion artifact 2
• Continuous oscilloscopic monitoring of minimum 3 leads is recommended, though 12-lead printed capability is highly recommended for accurate interpretation 2

Critical Technical Considerations

• Use the largest-amplitude deflection in each lead as representative of that measurement, per ANSI/AAMI standards 1
• Digital electrocardiographs should form "templates" from averaged beats to reduce beat-to-beat variability, which significantly improves measurement reproducibility compared to single-beat analysis 2
• Electrocardiographs should automatically alert users when suboptimal high-frequency cutoff (such as 40 Hz) is used, as this invalidates amplitude measurements 2

Environmental Conditions

Room Temperature and Humidity

• Maintain temperature range of 20°C to 22°C (68°F to 71.6°F) for optimal patient comfort and stable cardiovascular responses 2
• Keep humidity below 60% to prevent variable cardiovascular responses and maintain maximum performance 2
• Use circulating fans to assist temperature control and ventilation 2

Barometric Considerations

• If performing gas exchange measurements concurrently, measure barometric pressure and temperature, as gases expand with heat/low pressure and contract with cold/high pressure 2
• Most automated cardiopulmonary testing systems adjust for ambient conditions automatically 2

Common Pitfalls to Avoid

Setting high-frequency cutoff to 40 Hz to reduce noise will invalidate all amplitude measurements used for diagnostic classification, rendering voltage criteria for left ventricular hypertrophy and other diagnoses unreliable 2

Inadequate skin preparation is a frequent source of poor signal quality regardless of electrode type—extra time spent on preparation results in more stable recordings 2

Using Mason-Likar limb lead placement without obtaining a standard 12-lead ECG first may alter inferior lead complexes to either mimic or hide previous Q waves 2

Failing to document non-standard calibration when using 5 mm/mV or 20 mm/mV settings makes the tracing uninterpretable for voltage-based criteria 1

Interpretation Requirements

All computer ECG interpretations must be verified by a qualified physician, particularly interpretations of rhythm disturbances, ischemia, or infarction 2

Computer programs can provide accurate heart rate, intervals, and electrical axes, but a skilled physician must integrate clinical data, compare with previous tracings, and recognize that identical ECG patterns may occur in different pathophysiologic states 2