ECG Exercise 28 - Rhythm Refresher

Last updated 8/30/26

Consider these five questions on every ECG before opening any toggle:

1. What is the rate - atrial vs. ventricular?
2. Are there P waves? One per QRS? Same morphology within each lead? Correct axis (up in II/III/aVF, down in aVR)?
3. Is the PR interval fixed, progressively prolonging, or varying without pattern?
4. Is the QRS narrow or wide?
5. Is the rhythm regular, irregular, or grouped?

ECG 1

ECG 2

ECG 3

ECG 4

Questions

ECG 5

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Most likely diagnosis?

• AVNRT or orthodromic AVRT. From an ED standpoint, telling the two apart will not usually change management
• What is the most likely diagnosis if this is the patient's prior ECG?

• Short PR and a delta wave — Wolff-Parkinson-White — which makes orthodromic AVRT the likely mechanism
• Both are reentry tachycardias

ECG 6

ECG 7

ECG 8

ECG 9

ECG 10

ECG 11

ECG 12

ECG 13

ECG 14

ECG 15

ECG 16

ECG 17

ECG 18

ECG 19

ECG 20

ECG 21

ECG 22

ECG 23

ECG 24

ECG 25

ECG 26

ECG 27

ECG 28

ECG 29

ECG 30

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What is the rhythm?

• Polymorphic VT, specifically Torsades de Pointes, rate 150 to 200 or more
• Irregular wide complex tachycardia with QRS complexes that vary in morphology — the hallmark of polymorphic VT
• The complexes appear to twist around the baseline, amplitudes rising and falling cyclically. Look at the V1 and V2 rhythm leads
• The rhythm terminated shortly after starting magnesium; K came back at 2.7 mEq/L. A repeat ECG is below — what is the QTc?

This post is for education and not medical advice.