Certified Medical Assistant (CMA AAMA)Procedures, Examinations and DiagnosticsHard
During EKG standardization, the machine is set so that 1 millivolt (mV) of electrical activity produces a deflection of 10 mm on the graph paper. If a patient's QRS complex measures 15 mm in height, what is the approximate voltage represented?
- A1.5 mV
- B0.5 mV
- C2.0 mV
- D1.0 mV
Show answer & explanationAnswer & explanation
Correct answer: A. 1.5 mV
Standard calibration is 10 mm = 1 mV, so each millimeter represents 0.1 mV. A 15 mm deflection equals 15 x 0.1 mV = 1.5 mV.
Why the other options are wrong
- B. This would correspond to only 5 mm of deflection, not 15 mm.
- C. This would require 20 mm of deflection, more than stated.
- D. This would correspond to exactly 10 mm, not the 15 mm given.
EKG Standardization Calculation
Standard EKG calibration is 10 mm = 1 mV, meaning each millimeter of deflection equals 0.1 mV of electrical voltage.
- Standard calibration: 10 mm = 1 mV
- Each mm = 0.1 mV
- Used to verify accurate machine calibration and voltage measurement
Memory trick: Ten millimeters, one millivolt—divide by ten for each mm.