---
title: "Pacemaker Potentials, Conduction and Reading an ECG"
description: "Heart cells that drift towards threshold on their own set the rhythm, and the wave they start spreads through the muscle by a fixed route with a deliberate delay. The trace recorded at the skin is the"
canonical: https://lightmysky.com/learn/science/pacemaker-potentials-conduction-and-reading-an-ecg-mt_D-WKFc7BZm
source: https://lightmysky.com/learn/science/pacemaker-potentials-conduction-and-reading-an-ecg-mt_D-WKFc7BZm.md
retrieved: 2026-09-12
---

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# Pacemaker Potentials, Conduction and Reading an ECG

Heart cells that drift towards threshold on their own set the rhythm, and the wave they start spreads through the muscle by a fixed route with a deliberate delay. The trace recorded at the skin is the sum of those events, so each deflection can be named.

Subject: Science · Area: The Human Body · Ages 19 to 20
Page: https://lightmysky.com/learn/science/pacemaker-potentials-conduction-and-reading-an-ecg-mt_D-WKFc7BZm

## Ready when they can

- Names each deflection of the trace and the electrical event behind it.
- Explains why the delay at the atrioventricular node is useful rather than a flaw.
- Reads a rate and a rhythm irregularity from a trace.

## Lesson: Reading the heartbeat line

Picture the beat starting by itself inside you. Special cells leak inward until they hit threshold and fire, and the top node fires first. The wave crosses the upper chambers, then holds briefly at the gate before running down to the lowers. That hold is deliberate: it tops up the load.

Now you can translate the wiggly line. The first small bump marks the upper chambers squeezing, the sharp tall spike marks the lower chambers squeezing, and the last bump marks the lowers resetting. What you see on the skin is the sum of those events underneath.

**Example.** Try reading a strip yourself. Count the large squares between two tall peaks and divide 300 by that number to get beats per minute. Then check whether the gaps stay even: even gaps mean a steady rhythm and wandering gaps mean an uneven one. A wiggly line becomes a readout of wiring.

**Tip.** One practical warning before you trust any strip. Each chest sensor must sit on its exact landmark with clean skin contact and a still patient. Wrong spots or poor contact blur the signal and can fake abnormalities that are not there.

**Recap.** You match each wiggle to its event and read spacing for rate and rhythm.

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Channel Kinetics and the Ionic Basis of the Spike](https://lightmysky.com/learn/science/channel-kinetics-and-the-ionic-basis-of-the-spike-mt_47-LDzgcKp)
- [The Cardiac Cycle and Pressure in the Heart](https://lightmysky.com/learn/science/the-cardiac-cycle-and-pressure-in-the-heart-mt_iOSVyoV3Pj)

## Opens up

- [Preload, Afterload and the Frank-Starling Relationship](https://lightmysky.com/learn/science/preload-afterload-and-the-frank-starling-relationship-mt_WK8o6OPZ-O)