Pacemaker Potentials, Conduction and Reading an ECG · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Reading the heartbeat line

Science · The Human Body · ages 19-20
Name ______________________   Date ____________
  1. Why does the signal pause briefly on its way down?

    • It lets the lower chambers finish filling
    • It stops all blood flow
    • It skips the upper chambers
  2. What event makes the sharp tall spike on the trace?

    • Upper chambers reset
    • Lower chambers squeeze hard
    • Nothing happens
  3. Every wiggle on the trace maps to one electrical event in the muscle.

    Circle one:   True   False

  4. You count 5 large squares between two tall peaks. What is the rate per minute?

    Answer: ______________

  5. What is the normal path of excitation through the pump?

    • Lower chambers first, then upper
    • Middle wall first
    • Top pacemaker, across uppers, pause, then lowers
  6. The gaps between beats keep changing length. What do you read?

    • An uneven rhythm
    • A perfectly steady rhythm
    • A faster paper speed
  7. A friend says the sharp spike marks the upper chambers. Is that right?

    • Yes, spikes always mean upper chambers
    • Yes, placement never matters
    • No, that spike belongs to the lower chambers
  8. The pause vanishes so lowers squeeze too early. What happens to output?

    • Output rises
    • Output falls for lack of filling
    • Nothing changes
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Reading the heartbeat line W1-mt_D-WKFc7BZm-s1

  1. It lets the lower chambers finish filling · The deliberate hold tops up volume before the big squeeze.
  2. Lower chambers squeeze hard · The sharp spike is the surface sum of the lower chambers contracting.
  3. True · Each wiggle is the skin level sum of one electrical event underneath.
  4. 60 · Rate is 300 divided by the squares between tall peaks, so 300 split 5 ways is 60.
  5. Top pacemaker, across uppers, pause, then lowers · The top node leads, the wave crosses the upper chambers, holds, then runs down.
  6. An uneven rhythm · Rhythm comes from regularity, so uneven gaps spell an uneven beat.
  7. No, that spike belongs to the lower chambers · The first small bump is the upper chambers. The sharp spike is the lowers.
  8. Output falls for lack of filling · Without the hold the lower chambers squeeze early on a smaller load.
Worksheet · LightMySky