ECG

Question 1

What is the QRS complex?

Answer 1

Depolarization of ventricle

Q↓ R↑ S↓ after R

Question 2

What does the T represents on an ECG?

Answer 2

The repolarization

Question 3

What does the P represents on an ECG? When is it abnormal?

Answer 3

The P wave represents depolarization of the right atrium followed quickly by depolarization of the left atrium (superimposed). They are seen in lead II and V1

Question 4

What is the ST interval ?

Answer 4

The line between the QRS complex and the T wave, it is normally isoelectric (at the same level as the “baseline”). It may move up or down when the heart is lacking oxygen:

• Upward = MI
• Downward = Ischemia

Question 5

What is the PR interval ?

Answer 5

Time from the start of the P wave to the start of the QRS complex

NORMAL = 0.12-0.20 sec.

Question 6

What is the QT interval?

Answer 6

Time from the start of the QRS complex to the end of the T wave, represents the time for ventricular depolarization and repolarization. This interval changes according to the heart rate and is not constant.

You calculate it with Bazett’s formula (QTc ≤ 0.44 for men and 0.46 for women) or the rapid rule with normal heart rate: if the QT interval is less than ½ the R-R interval, then the QT is within normal range.

Question 7

What are the 12 leads recorded by an ECG?

Answer 7

• 6 “LIMB LEADS” record the depolarization currents in the FRONTAL PLANE
  ​By overlaying the vectors of the 6 limb leads, an Axial Reference System is established.
• 6 “PRECORDIAL” LEADS record depolarization currents in the TRANSVERSE PLANE

Question 8

What are the bipolar leads?

Answer 8

• I : RA (-) to LA (+)
• II: RA (-) to LL (+)
• III: LA (-) to LL (+)

Question 9

What are the unipolar leads?

Answer 9

• aVR: CT (-) to RA (+)
• aVL: CT (-) to LA (+)
• aVF: CT (-) to LL

Question 10

What are the corresponding lead references on the electric circuit of the heart ?

Answer 10

Avant P : SA node

P: du SA node au AV node

Après P: AV node

QRS: ventricules

T: repolarization des ventricules

Question 11

The normal rhythm initiated by depolarization of the sinus node is known as “Sinus rhythm”. Sinus rhythm is presented how on an ECG?

Answer 11

Criteria:

1. Each P wave is followed by a QRS
2. Rach QRS is preceded by a P wave
3. The P wave is upright in leads I, II, and III
4. The PR interval is greater than 0.12 seconds (3 small boxes)

• Normal sinus rhythm = Heart rate between 60 and 100 beats/min
• Sinus bradycardia = Sinus rhythm with heart rate < 60 beats/min
• Sinus tachycardia = Sinus rhythm with heart rate > 100 beats/min

Question 12

How do we calculate heart rate ?

Answer 12

• Method 1: count number of small boxes between QRS complexes. Very good method for fast heart beat
  1500
  23
• Method 1: Count-off method from QRS peaks. You memorize the sequence: 300-150-75-60-50
• Method 3: ECG recording paper often indicates 3-sec time markers N beats x 20.

Question 13

What is mean axis and its 4 classification?

Answer 13

“AXIS” refers to the angle of this average vector in the frontal plane. In a normal individual, the normal axis vector lies between -30° - +90°. The orientation of your heart in your chest will deviate your axis. Axis is classified into one of 4 categories:

• NORMAL (lead I and II positive)
• LEFT AXIS DEVIATION (lead I positive lead II negative)
• RIGHT AXIS DEVIATION (lead I negative lead II positive)
• EXTREME AXIS DEVIATION (lead I negative lead II negative)

Question 14

When do we suspect a Right ventricular hypertrophy?

Answer 14

• R > S in V₁
• Right axis deviation

Question 15

When do we suspect a Left ventricular hypertrophy?

Answer 15

• S in V1 plus R in V5 or V6 > 35 mm
• R in aVL > 11 mm or R in lead I > 15 mm

Question 16

Where is the pathological Q wave in an anteroseptal Myocardial Infarction?

Answer 16

V₁ and V₂

Question 17

Where is the pathological Q wave in an Anterolateral Myocardial Infarction?

Answer 17

I, aVL, V₅, V₆

Question 18

Where is the pathological Q wave in an Inferior Myocardial Infarction?

Answer 18

II, III, aVF

Question 19

Where is the pathological Q wave in an Anteroapical Myocardial Infarction ?

Answer 19

V₃, V₄

Question 20

Where is the pathological Q wave in an Posterior Myocardial Infarction ?

Answer 20

TRICK QUESTION: WE GET TALL R NOT Q WAVE IN V1, V2

Question 21

What do we see in Transient Myocardial Ischemia?

Answer 21

T wave inversion or ST depression

Question 22

What do we see in acute MI if the blockage is complete?

Answer 22

ST elevation

Question 23

What do we see in acute MI if the blockage in not complete (the thrombus is only partially occlusive)?

Answer 23

NO Q waves as typically only the sub-endocardium is involved

Question 24

What are the criteria of a right bundle branch?

Answer 24

• Wide QRS
• Rabbit ears in V1
• Big S in V6

Question 25

What are the criteria of a left bundle branch?

Answer 25

• Wide QRS
• Big R in V6
• Big S + no R in V1