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newSchoolWorks.com › VoTechWorks › Health & Personal Services › EKG Technician › 12-Lead EKG Acquisition › Lesson 6
HLT-EKGT89-03 · Lesson 6 · 4 clock hours · theory

Paper Speed, Gain, and Filter Settings

Objective. Students will explain the effect of paper speed, gain, and filter settings on waveform appearance and select appropriate settings for standard adult clinical acquisition.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by a licensed clinician in the field or by a certification or approval body. It is a study draft and may contain errors. Do not use it to make decisions about any patient or medication. Always follow your instructor, your supervising professional, and current official references and regulations.

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Why Machine Settings Matter

A 12-lead EKG is only as useful as the tracing it produces. Before you press Acquire, three machine settings directly control what you see on paper: paper speed, gain (sensitivity), and filters. Choosing the wrong setting can make a normal rhythm look abnormal, hide a true abnormality, or produce a tracing so cluttered with noise that the interpreting clinician cannot read it. Understanding each setting—and knowing the standard values—is a core technician skill and a tested topic on the NHA CET exam.

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Paper Speed

Paper speed controls how fast the paper moves under the stylus (or how wide each time unit appears on a digital printout). It is measured in millimeters per second (mm/s).

Effect on appearance: Increasing speed from 25 to 50 mm/s stretches waveforms horizontally. The same P-QRS-T complex looks wider and easier to measure at 50 mm/s. However, fewer beats fit on a page, and every recording analyzed at a non-standard speed must be clearly labeled, or the reader may misinterpret interval durations. Never submit a 50 mm/s tracing without marking it as such.

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Gain (Sensitivity/Amplitude)

Gain—also called sensitivity—controls how tall the waveforms appear on paper relative to the actual voltage the heart produces. It is measured in millimeters per millivolt (mm/mV).

Effect on appearance: Doubling the gain doubles every waveform's height. Cutting gain in half shrinks every waveform by half. The rhythm and intervals are unchanged; only the visual size changes. Always note any non-standard gain on the printout and in your documentation so the reader knows the tracing has been scaled.

Safety point: A tracing acquired at double gain can falsely suggest ST elevation or voltage criteria for hypertrophy. A tracing at half gain can make true ST elevation appear normal. Always verify the calibration pulse before handing any tracing to a clinician.

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Filter Settings

Filters reduce electrical interference that appears as noise on the baseline. Two filters are commonly available:

Standard practice: Acquire the first tracing with the default factory filter settings (usually AC filter on, others off). If artifact persists after correcting technique, engage additional filters and document that you did so. Filters should supplement good technique, not replace it.

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Selecting Settings for Standard Adult Clinical Acquisition

For a routine adult 12-lead EKG, the correct starting settings are:

| Setting | Standard Value |

|---|---|

| Paper speed | 25 mm/s |

| Gain | 10 mm/mV |

| AC filter | On |

| Other filters | Off unless artifact persists |

Depart from these defaults only when there is a clinical reason. Document every non-standard setting directly on the tracing before it leaves your hands.

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Scope of Practice and Safety Reminders

Key terms8

Paper speedThe rate at which EKG paper moves, measured in mm/s; 25 mm/s is the standard adult setting and determines how wide each time interval appears on the tracing.
Gain (sensitivity)The amplification of the cardiac electrical signal expressed in mm/mV; standard is 10 mm/mV, meaning 1 mV produces a 10 mm deflection on paper.
Calibration pulseA standardized square wave printed at the start of a tracing to confirm that gain is set correctly; at 10 mm/mV, it should measure exactly 10 mm tall.
Baseline wanderA slow, rolling movement of the isoelectric line caused by respiration, poor electrode contact, or patient movement; addressed first by correcting technique, then by filter if needed.
AC (60 Hz) filterA filter that eliminates interference from alternating-current electrical equipment and power lines, reducing rapid regular noise on the tracing.
Muscle artifact filterA high-frequency filter that reduces noise caused by skeletal muscle activity such as shivering or tremor; may slightly alter true high-frequency waveform components.
Half standard (5 mm/mV)A gain setting that reduces waveform height by half, used when large-amplitude QRS complexes extend beyond the printable area of the grid.
Isoelectric lineThe flat baseline on an EKG representing the period when no net electrical activity is detected; wander or noise on this line can distort waveform measurement.

Worked examples4

1. A tracing is acquired at 25 mm/s. The QRS duration measures 5 small boxes wide. How many seconds does that represent, and how wide would the same QRS appear (in small boxes) if the speed were changed to 50 mm/s?
  1. At 25 mm/s, each small box = 0.04 seconds.
  2. QRS duration = 5 boxes × 0.04 s/box = 0.20 seconds.
  3. At 50 mm/s the paper moves twice as fast, so each small box still represents the same voltage but now covers half the time: each small box = 0.02 seconds.
  4. Same 0.20-second QRS at 50 mm/s: 0.20 s ÷ 0.02 s/box = 10 small boxes wide.
Answer: At 25 mm/s the QRS is 0.20 seconds (5 small boxes). At 50 mm/s the same QRS appears 10 small boxes wide because the paper moves twice as fast, stretching the waveform horizontally.
2. A calibration pulse measures 5 mm tall on a printout labeled with no special notation. What gain was the machine set to, and what is the standard gain the machine should have used?
  1. Standard gain: 10 mm/mV produces a 10 mm calibration pulse.
  2. The pulse measured 5 mm, which is exactly half of 10 mm.
  3. Half the standard deflection corresponds to half the standard gain: 5 mm/mV.
  4. The machine was set to 5 mm/mV (half standard) instead of 10 mm/mV.
Answer: The machine was set to 5 mm/mV (half standard gain). The correct standard setting is 10 mm/mV, which produces a 10 mm calibration pulse.
3. At standard gain (10 mm/mV), a patient's R wave in lead V5 measures 28 mm tall. If the technician switches to half gain (5 mm/mV) to prevent the complex from running off the grid, how tall will that same R wave appear on the new tracing?
  1. Original height at 10 mm/mV: 28 mm.
  2. Halving the gain to 5 mm/mV reduces every waveform's printed height by half.
  3. New printed height = 28 mm ÷ 2 = 14 mm.
  4. The actual cardiac voltage is unchanged; only the visual representation is scaled down.
Answer: At 5 mm/mV the R wave will appear 14 mm tall. The clinician must be informed of the non-standard gain so voltage measurements are not underestimated.
4. A technician needs to calculate what voltage a 22 mm deflection represents at standard gain (10 mm/mV). What is the voltage?
  1. At 10 mm/mV, 10 mm of deflection = 1 mV.
  2. Set up the proportion: 22 mm ÷ 10 mm/mV = 2.2 mV.
  3. The deflection represents 2.2 mV of cardiac electrical activity.
Answer: A 22 mm deflection at 10 mm/mV represents 2.2 mV.
In class: Examine printed tracing pairs showing the same rhythm recorded at 25 mm/s vs. 50 mm/s and at 5 mm/mV vs. 10 mm/mV gain, then write a brief explanation of how each change alters waveform appearance. · Complete a worksheet matching five clinical scenarios (large-amplitude QRS, tachycardia, baseline drift) to the recommended setting adjustment and clinical rationale. · Simulate a setting error in class—acquire a tracing at incorrect gain, identify the problem on the printout, correct the setting, and re-acquire, documenting both tracings with a note explaining the change.
Materials: Printed tracing comparison sets, EKG machine, settings worksheet, NHA CET exam content outline
Check: Settings scenario worksheet scored by instructor; students must correctly match settings to scenarios and provide rationale with ≥80% accuracy (4 of 5 scenarios correct).

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

EKG Acquisition and Instrumentation
1. What is the standard paper speed for a routine adult 12-lead EKG?
EKG Acquisition and Instrumentation
2. A technician acquires a tracing at 50 mm/s instead of the standard 25 mm/s. Compared with a standard-speed tracing of the same rhythm, the waveforms will appear:
EKG Acquisition and Instrumentation
3. A patient's QRS complexes are so tall they extend into adjacent lead rows and off the grid. The most appropriate adjustment is to change the gain to:
EKG Acquisition and Instrumentation
4. At standard gain (10 mm/mV), the calibration pulse on a freshly printed tracing measures 15 mm tall. This finding indicates:
EKG Acquisition and Instrumentation
5. A patient is shivering and the tracing shows rapid irregular noise throughout all leads. After repositioning and warming the patient does not resolve the artifact, which filter is most appropriate to engage next?
Patient Safety and EKG Quality
6. A technician documents a tracing was acquired at 5 mm/mV without writing this on the printout before giving it to the clinician. What is the primary concern?
EKG Acquisition and Instrumentation
7. A tracing shows a slowly rolling isoelectric baseline that rises and falls with each breath. The best first action is to:
EKG Acquisition and Instrumentation
8. An EKG technician is recording a 12-lead on a patient with a heart rate of 160 bpm and the clinician has requested easier interval measurement. Changing paper speed to 50 mm/s will:
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