ECG Review

Question 1

Sinus tachycardia

Answer 1

Over 100 bpm

Question 2

Sinus bradycardia

Answer 2

Under 60 bpm

Question 3

Normal axis range

Answer 3

-30 -> +100

Question 4

P-R interval definition

Answer 4

Atrial repolarization

End of P wave -> beginning of Q wave

Question 5

QT and QTc interval definition

Answer 5

Represents the time from beginning ventricle depolarization -> ventricle repolarization.

Usually measured in the lead showing the longest QT and QRS intervals (not always lead 2)

Question 6

Why does the P wave pause before it goes to the Q wave?

Answer 6

The pause after the P wave represents the slowing of depolarization through the AV node.

Allows time for the ventricle to fill with regurgitation “atrial kick”.

Question 7

1st heart block is defined as what?

Answer 7

AV node conduction is greater than 0.2 sec (200 ms)

Question 8

QRS interval definition and pathogenicity

Answer 8

Less than 0.12 sec (120 ms)

Longer = Left/right bundle branch blocks, left ventricular hypertrophy,

Question 9

What does a prolonged QRS usually mean?

Answer 9

Bundle branch block which would impair right/left bundle conduction.

Prolonged = greater than 0.12 sec (120ms)

Question 10

ST segments normal position and possible pathogenicity

Answer 10

Should be in line with the PR segment

Pathogenicity: Can be depressed or Elevated segments

• depressed = ischemia or poor blood flow
• elevated = dead tissue (this is worse)

Question 11

QRS complex and its waves definitions

Answer 11

The time frame where the ventricles are stimulated and depolarized

Q wave specific definition = initial negative deflection immediately preceding the PR interval

R wave specific definition = the first positive deflection in the QRS complex

S wave specific definition = the first negative deflection preceding an R wave.

• Some ECGs may not show all 3 waves*

Question 12

ST interval definition

Answer 12

Ending of ventricle depolarization -> end of ventricle repolarization

Question 13

P wave definition

Answer 13

Atrial depolarization

Question 14

T wave definition and pathogenicity

Answer 14

Ventricle repolarization

Usually 100ms- 250ms

• can be positive or negatively deflected, however the normal T wave will ALWAYS be ASYMMETRIC

Pathogenicity
- symmetric T waves = MI, hyperkalemia

Question 15

J point definition and pathogenicity

Answer 15

Beginning of the ST segment (right immediately after the S wave of QRS

Prolonged J point (called J waves) = signs of systemic hypothermia

• note: this can be elevated, which signals early repolarization NOT MI OR ISCHEMIC TISSUE*

Question 16

U wave

Answer 16

Final phase of ventricular repolarization right after the T wave
(may or may not be present is not considered pathogenic either way)

Question 17

TP segment

Answer 17

End of the T wave -> beginning of P wave

Electrical resting state and is used to determine the phase line reference for PR and ST pathogenicity

Question 18

RR intervals

Answer 18

Distance from the peak of the R wave on one QRS complex, subsequent QRS complexes R wave

*used as an alternative method to determine heart rate (60/RR (in seconds))

Question 19

What should the calibration rectangle look like on an ECG to tell you if the ECG is properly calibrated?

Answer 19

Should be 2 full boxes tall (10 small boxes) and 1 full box wide (5 small boxes)

Question 20

What is the conversion of mm -> mV in a standard calibrated ECG?

Answer 20

10 mm = 1 mV

Note 1 mm = 1 small box

Question 21

PR interval duration definition and pathogenicity

Answer 21

Is the time it takes for the stimulus from the SA node to spread through the atria and into the AV junction
- is required so that the ventricles can fill properly with the preload form the atria

Normal time = 120ms- 200ms

Pathogenicity

• prolonged (>200ms) = 1st degree heart block
• shorted (<120ms) = WPW, atrial fibrillation, atrial flutter

Question 22

Alterations to the QRS complex

Answer 22

QS wave =. One negative deflection preceding the PR interval

R wave = one positive deflection preceding the PR interval

QR wave = Large amplitude R wave w/ no negative deflection post R wave, but has one preceding the R wave.

Qr wave = small amplitude R wave w/ no negative deflection post R wave, but has one preceding the R wave.

rSR complex = one small amplitude Q wave positive reflection preceding a large negative reflection, w/ a large amplitude positive reflection after said large negative reflection
(reversed QRS complex)

Question 23

R prime and S prime waves definition

Answer 23

When a QRS complex occasionally contains more than 2-3 deflections they are called prime waves

• R prime = positive deflections
• S prime = negative deflections

Question 24

ST interval normal duration/position and pathogenicity

Answer 24

Normally isoelectric (w/ very slight elevation/depression being acceptable)

Normal time = 80ms

Pathogenicity
- depressed or elevated = MI and/or ischemic ventricular tissue

• elevation can also be left bundle branch block, left ventricular hypertrophy or acute pericarditis*

Question 25

QT and QTc duration and pathogenicity

Answer 25

Normal = 300 ms- 450ms after correction 
(QTc = QT(ms)+ 1.75(HR-60)) 

Pathogenicity =
- prolonged = hypokalemia, hypocalcemia, low potassium, torsades, BB drugs, hypothermia, channelopathy

Question 26

U wave duration and pathogenicity

Answer 26

There is no note worth time for normal U waves.

Normal U waves however should be no larger than the T wave and should have the same reflection

Pathogenicity:

• U wave > than T wave = hypokalemia
• opposite reflection of T wave = left ventricular hypertrophy or MI