Lecture 14

Question 1

S-wave

Answer 1

-Negative deflection

-The base of the heart are last
to depolarize. Wave of
depolarization on R and L
is generally up

Question 2

ECG Leads

Answer 2

-12 Lead –> 3 frontal, 6 horizontal

1) Bipolar Limb Leads
- Lead I
- Lead II
- Lead III

2) Augmented (Unipolar) Limb Leads:
- aVL
- aVR
- aVF

3) Precordial Chest Leads
- V1 to V6

Question 3

ECG Leads

Answer 3

• 12 Lead (pair of electrodes) –> 3 frontal, 6 horizontal
• Each lead view QRS depolarization from different angles/electrodes

1) Bipolar Limb Leads (+ and - terminal)
- Lead I –> Right arm - and left arm +
- Lead II –> Right arm - and left leg +
- Lead III –> Left arm - and left leg +

2) Augmented (Unipolar) Limb Leads: (Frontal plane)
- aVL
- aVR
- aVF

3) Precordial Chest Leads (Transverse plane)
- V1 to V6

Question 4

Bipolar Limb Leads:

Answer 4

1) Lead 1
-Mean QRS vector (→) is directed
down and towards left side of heart

-QRS Complex: Largely upward

2) Lead 2
- QRS complex is upward

-depolarization moving towards
the +ve electrode on LL

-QRS complex is a relatively large
upward deflection since most of
the QRS vector (→) is in direction
of Lead II

3) Lead 3
-QRS vector is now nearly
perpendicular to the recording axis
(LA to LL). LL is the +ve electrode

-QRS complex is biphasic with
significant downward and upward
deflections giving a net deflection of
practically zero

-This type of QRS complex is called the “isoelectric” complex.

-Mean QRS vector (→) nearly perpendicular to
recording axis of Lead III.

Question 5

Augmented Limb Leads

Answer 5

-Only have a positive pull (Electrode)

1) aVR (R=right)
- LA and LL electrodes

2) aVL (L=left)
- RA and LL electrodes

3) aVF (F=Foot)
- LA and RA electrodes

Question 6

Augmented Limb Leads

Answer 6

-Only have a positive pull (Electrode)

1) aVR (R=right)
- RA and a “V” lead made by connecting LA and LL electrodes

2) aVL (L=left)
- LA and a “V” lead made by connecting RA and LL electrodes

3) aVF (F=Foot)
- LL and a “V” lead made by connecting LA and RA electrodes

Question 7

Augmented Limb Leads

Answer 7

-Only have a positive pull (Electrode)

1) aVR (R=right) –> Net negative
- RA and a “V” lead made by connecting LA and LL electrodes (Records electrical activity between RA and V=indifferent electrode)

-QRS vector is in the opposite direction to lead aVR = QRS negative and downward deflection

2) aVL (L=left) –> Net positive
- LA and a “V” lead made by connecting RA and LL electrodes (Records electrical activity between LA and “V” = indifferent electrode)

-QRS vector is biphasic with usually a net
upward deflection (Somewhat in same direction)

3) aVF (F=Foot)
- LL and a “V” lead made by connecting LA and RA electrodes (Records electrical activity between LL and “V” = indifferent electrode)

-QRS vector is largely upward (Mostly in same direction)

Question 8

Precordial Chest Leads: Transverse (Horizontal) Plane

Answer 8

-All positive electrodes
V1/2 “looks at” RV
V3/4 “looks at” septum
V5/6 “looks at” LV

Note change in QRS complex:
V1/2 downward
V3 equiphasic
V4-6 upward