ECG Exercise 29- The QRS Complex

Last updated 11/8/26

Below is an ECG Exercise focused on the QRS complex (part of the Self-Study Curriculum) Consider reading the following ECG Topics before proceeding:

ECG 1

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What ECG findings define low voltage? Does this ECG qualify as low voltage?

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ECG 1497

ECG 2

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What is the 4th wide QRS complex in the rhythm lead?

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Does ECG qualify as low voltage?

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ECG 1498

ECG 3

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Does ECG qualify as low voltage?

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What is the cause of the abnormal voltage?

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Is this diagnostic of acute OMI?

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ECG 1499

LVH Diagnostic Criteria (Only need to fulfill one criteria)

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What is Seamens’ Sign?

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What is Sokolow Lyon criteria?

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What is Peguero Lo Presti?

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What are R wave findings in the limb leads that may suggest LVH?

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Click for basic LVH on ECG diagnostic algorithm

ECG 4

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Seamen’s Sign?

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S in V1 or V2 + R in V5/V6 ≥35mm?

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Peguero Lo Presti?

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Meets R wave criteria in limb leads?

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ECG 1500

ECG 5

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Seamen’s Sign?

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S in V1 or V2 + R in V5/V6 ≥35mm?

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Peguero Lo Presti?

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Meets R wave criteria in limb leads?

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ECG 1501

ECG 6

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Seamen’s Sign?

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S in V1 or V2 + R in V5/V6 ≥35 mm?

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Peguero Lo Presti?

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Meets R wave criteria in limb leads?

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1502

ECG 7

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Seamen’s Sign?

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S in V1 or V2 + R in V5/V6? ≥ 35mm

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Peguero Lo Presti?

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Meets R wave criteria in limb leads?

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ECG 1503

ECG 8

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Seamen’s Sign?

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S in V1 or V2 + R in V5/V6 ≥ 35mm?

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Peguero Lo Presti?

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Meets R wave criteria in limb leads?

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ECG-1504

ECG 9

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Seamen’s Sign?

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S in V1 or V2 + R in V5/V6 ≥ 35mm?

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Peguero Lo Presti?

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Meets R wave criteria in limb leads?

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ECG 1505

ECG 10

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What is the rhythm?

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Is atrial enlargement present?

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Which LVH criteria are met?

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What repolarization findings are present?

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How many chambers are enlarged?

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ECG 1509

ECG 11

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Is atrial enlargement present?

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Does this meet LVH criteria?

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The QRS complexes run off the paper. What can you do to measure them?

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ECG 1510

RVH and Tall R Waves in V1/V2

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What is the main ECG criterion for RVH?

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What is the differential for an increased R:S ratio in V1-V2?

ECG 12

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What finding suggests RVH?

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What do the T waves add?

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Is atrial enlargement present?

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ECG 1511

ECG 13

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Is the R:S ratio increased in V1 or V2?

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Run through the differential for a tall R in V1/V2. What is the most likely cause?

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What could the T waves represent?

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ECG 1512

QRS Duration

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What is a normal QRS duration, and how should you measure it?

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What causes a wide QRS (in decreasing order of mortality)?

ECG 14

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What is the rate? Are there P waves?

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What is the rhythm?

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Should you suppress these complexes with lidocaine or another antiarrhythmic?

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Is this LBBB, RBBB, or IVCD morphology?

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What is the most life-threatening cause of an IVCD? Do you wait for labs?

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ECG 1513

ECG 15

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What is the conduction abnormality?

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There appears to be ST elevation in III and aVF. Is this an inferior STEMI?

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ECG 1514

ECG 16

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The patient is awake and talking. What is the rhythm and how do you treat it?

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What must you also consider with very wide, bizarre complexes?

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ECG 1515

ECG 17

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What is the underlying rhythm?

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Why do the QRS morphologies change?

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Compare the R-R intervals of each morphology.

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ECG 1516

ECG 18

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In lead III, the third beat looks different from the beats before and after it. What is it?

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What follows the fusion beat?

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ECG 1517

Q Wave Significance

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When is a Q wave pathologic?

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What are examples of benign Q waves?

ECG 19

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Compare the Q waves in I and aVL. Why are Patient A's benign and Patient B's pathologic?

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In addition to pathologic Q waves, what other findings in Patient B suggest ischemia?

ECG 20

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What is a QS wave?

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Why is Patient A's QS wave benign and Patient B's pathologic?

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How old is Patient B's infarct? What else do you notice?

ECG 21

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Look at lead III rhythm strip. Why does the QRS amplitude vary from beat to beat?

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Is this electrical alternans? How do they differ?

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ECG 1518

ECG 22

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Identify the pathologic Q waves. What territory is involved?

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What abnormal findings do V1-V2 show and why does it matter?

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ECG 1519

ECG 23

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Identify the pathologic Q waves.

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Is there LVH?

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ECG 1520

ECG 24

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Identify the pathologic Q waves.

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Is this an old or acute infarct?

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ECG 1521

Transition Zone

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Where does the normal precordial transition occur? What are clockwise and counterclockwise rotation?

ECG 25

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Where is the transition? Is this normal, clockwise, or counterclockwise rotation?

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Is there atrial enlargement?

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Is the PR interval short, normal, or long?

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Does this qualify as low voltage?

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ECG 1522

ECG 26

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Where is the transition? Is this normal, clockwise, or counterclockwise rotation?

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What else do you notice?

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ECG 1523

ECG 27

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Where is the transition? Is this normal, clockwise, or counterclockwise rotation?

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Could this be RVH? What else is on the differential?

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Does this meet LVH criteria?

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ECG 1524

ECG 28

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Where is the transition? Is this normal, clockwise, or counterclockwise rotation?

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Why is posterior MI less likely than in ECG 27?

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What findings support RVH?

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What finding suggests the ST changes are non-ischemic?

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ECG 1525

QRS Notching vs Osborn Waves

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What is QRS notching and what does it suggest?

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What is an Osborn (J) wave and how does it differ from a notch?

ECG 29

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Look at the end of the QRS complexes. Is this finding concerning for ischemia?

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What other findings are present?

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What is the differential, and how do you tell them apart?

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ECG 1526

ECG 30

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Where are the QRS notches most prominent?

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What is the differential?

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ECG 1527

ECG 31

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There is a special type of QRS notching here. What emergency should you be concerned about?

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What other ECG findings of hypothermia are present?

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Look at the rhythm strip. Why does one P wave look different?

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ECG 1528

ECG 32

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Patient presents with AMS. Are you activating the cath lab?

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What causes the artifact on this ECG?

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What precaution should you take when moving this patient?

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ECG 1529

ECG 33

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What abnormal vital sign might this patient have?

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How does the third complex differ from the others?

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Which LVH criteria are met?

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This patient arrests. Will epinephrine work?

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ECG 1530

Sources

Garcia TB. 12-Lead ECG: The Art of Interpretation. 2nd ed. Burlington, MA: Jones & Bartlett Learning; 2015.

This post is for education and not medical advice.