Nursing & health sciences · Study page
ECG vs EKG: leads, waves and intervals
ECG and EKG are the same thing. Here are the 12-lead layout, where precordial leads V1 to V6 sit in the textbook, what the P wave, QRS complex and T wave mean, the listed durations, and side-by-side comparisons, then 12 practice questions with every answer explained. Free, and for study only.
- ECG = EKG
- 6 chest-lead landmarks
- 12 practice questions
- No sign-up needed
CollegeCompass360 is an independent education resource. We are not a school, a testing company or a government agency.
1 · The name
ECG vs EKG: the same thing
Short answer first: they are two abbreviations for one electrocardiogram.
- ECG stands for electrocardiogram: the tracing of the heart’s electrical signal, recorded with electrodes placed on the skin.
- EKG is the same thing. The K comes from the German term for cardiology, so ECG and EKG are two spellings of one abbreviation, not two different tests or tracings.
- The instrument that makes the tracing is the electrocardiograph; the tracing itself is the electrocardiogram.
- A standard electrocardiograph uses 3, 5 or 12 leads, and the more leads it uses, the more information the tracing gives.
- The word “lead” can mean the cable from an electrode to the recorder, but it usually describes the voltage difference between two electrodes.
3 leads
The smallest standard set-up.
5 leads
A middle set-up.
12 leads
Uses 10 electrodes: six on the chest and four on the limbs.
2 · The 12 leads
Precordial leads V1 to V6
The 12-lead printout is laid out as limb leads, augmented limb leads and the six precordial (chest) leads. Pick a chest lead to see its textbook landmark.
Limb leads
I, II, III
Augmented limb leads
aVR, aVL, aVF
Precordial (chest) leads
V1 to V6
V1
Fourth intercostal space on the right sternal border.
Starts the row, right of the breastbone.
- V1Fourth intercostal space on the right sternal border
- V2Fourth intercostal space at the left sternal border
- V3Midway between the placement of V2 and V4
- V4Fifth intercostal space at the midclavicular line
- V5Left anterior axillary line, on the same horizontal level as V4
- V6Mid-axillary line, on the same horizontal level as V4 and V5
Landmarks as listed in an open nursing-skills textbook, for study. Your own course text and lab instructor come first.
3 · Waves and intervals
What each wave means
Three prominent features on a normal tracing: the P wave, the QRS complex and the T wave.
P wave
Depolarization of the atria. The atria begin contracting about 25 ms after the start of the P wave.
QRS complex
Depolarization of the ventricles. It is the largest because the ventricular muscle is bigger and needs a stronger electrical signal. The ventricles begin to contract as the QRS reaches the peak of the R wave.
T wave
Repolarization of the ventricles.
Atrial repolarization happens during the QRS complex, so the QRS hides it on the tracing.
Segment versus interval
Segment
The region between two waves.
The PR segment runs from the end of the P wave to the start of the QRS complex.
Interval
One segment plus one or more waves.
The PR interval runs from the start of the P wave to the start of the QRS complex.
Durations listed in the textbook
| Feature | Listed normal |
|---|---|
| PR interval | 0.12 to 0.20 seconds |
| QRS complex | 0.06 to 0.12 seconds |
| QT interval | 0.36 to 0.44 seconds |
- One small box (thin lines, 1 mm apart) is 0.04 seconds.
- One large box (thick lines, 5 mm apart) is 0.2 seconds.
4 · Comparisons
VT vs VF, left vs right bundle branch
Textbook comparisons for study. They describe what the books say about each pattern, not how to read any person’s tracing.
Ventricular tachycardia vs ventricular fibrillation
Ventricular tachycardia
- QRS complexes
- Wide, and the shape of the QRS complex is abnormal; no visible P and T waves.
- Rate
- The ventricular rate is often over 120 beats per minute.
Ventricular fibrillation
- QRS complexes
- None to measure: there is just a fibrillatory line with no normal electrical activity.
- Rate
- The textbook gives no numeric rate; the ventricles are quivering with no effective contractions.
- Pattern
- No pattern to the waveforms. The fibrillatory waves can be coarse or fine, and coarse waves are taller than fine.
OpenStax describes ventricular fibrillation as a medical emergency in its textbook, because the ventricles are not effectively pumping blood.
Left vs right bundle branch block
- Name and place: left versus right bundle branch block is named for the branch where the conduction is blocked.
- What they share: a generic bundle branch block is characterized by a widened QRS complex, wider than 0.12 seconds (the normal QRS is 0.06 to 0.12 seconds).
- Telling left from right on a 12-lead tracing is beyond the two textbooks used here, so this page does not describe it; use your course text for the lead-by-lead pattern.
The three degrees of heart block
First-degree block (partial)
A delay in conduction between the SA and AV nodes, which shows as an abnormally long PR interval.
Second-degree block (incomplete)
Some impulses from the SA node reach the AV node and continue, others do not: some P waves are not followed by a QRS complex, while others look normal.
Third-degree block (complete)
No correlation between atrial activity (the P wave) and ventricular activity (the QRS complex).
Pacing rates of the conduction system
The rate slows from the SA node to the Purkinje fibers when each fires on its own.
- SA node (the pacemaker): about 80 to 100 impulses a minute
- AV node: 40 to 60 a minute
- Atrioventricular bundle: about 30 to 40 a minute
- Bundle branches: 20 to 30 a minute
- Purkinje fibers: 15 to 20 a minute
5 · Practice questions
12 practice questions
Names, lead counts, chest-lead landmarks, the waves and intervals and the comparisons above, multiple choice, one at a time. Every answer is explained, and your score is free: no sign-up needed.
Question 1 of 12
What is the relationship between ECG and EKG?
Bonus · unlocks with your email
The printable one-page EKG sheet and 12 more questions
- A one-page sheet you can print: ECG vs EKG, the 12-lead layout, the six chest-lead landmarks, what each wave means, the listed durations and the paper grid, and the VT vs VF and heart block comparisons.
- 12 more practice questions, every answer explained: the paper grid, the listed durations, the lead groups, the heart blocks, bundle branches and pacing rates.
Enter your email in the box above and the bonus opens right here, and stays open on this browser.
More free study tools
Next on the same shelf
Sources
Where the facts come from
Every fact on this page is reworded from these two free open textbooks. Check anything important against your course materials.
Questions
Common questions
None. ECG is the abbreviation of electrocardiogram; EKG is the same word abbreviated with a K, which comes from the German term for cardiology. Both mean the tracing of the heart’s electrical signal recorded from electrodes on the skin.
Ten: six on the chest and four on the limbs. They produce the 12 leads, which print as the limb leads (I, II, III), the augmented limb leads (aVR, aVL, aVF) and the precordial leads (V1 to V6).
The textbook landmarks are: V1, fourth intercostal space on the right sternal border; V2, fourth intercostal space at the left sternal border; V3, midway between the placement of V2 and V4; V4, fifth intercostal space at the midclavicular line; V5, left anterior axillary line, on the same horizontal level as V4; V6, mid-axillary line, on the same horizontal level as V4 and V5.
The P wave is depolarization of the atria, the QRS complex is depolarization of the ventricles, and the T wave is repolarization of the ventricles. Atrial repolarization happens during the QRS complex, which hides it.
Ventricular tachycardia is described as wide QRS complexes without visible P and T waves, at a rate often over 120 a minute. Ventricular fibrillation has no pattern to the waveforms and nothing that can be measured, just a fibrillatory line.
No. It is a study page that repeats what two open textbooks say. It does not read, interpret or diagnose anything, and it is not for use with a real person’s tracing. Your textbook and your instructor come first.
The whole reference and the 12 practice questions with your score are free with no sign-up. An email unlocks the bonus: a printable one-page sheet and more practice questions.