DSA: Cardiac physiology and the electrocardiogram - Steve

Question 1

What does the P wave reflect?

Answer 1

Depolarization of the right and left atrial muscle.

Question 2

What does the QRS complex represent?

Answer 2

Depolarization of ventricular muscle

Question 3

what does the T wave represent?

Answer 3

Repolarization of both ventricles

Question 4

what does the U wave represent?

Answer 4

May reflect repolarization of papillary muscle.

is rarely seen

Question 5

What do the six limb leads define?

Answer 5

The frontal plane

Question 6

What do the six precordial leads define?

Answer 6

A perpindicular transverse plane

Question 7

What does the ECG recording from a single lead show?

Answer 7

How that lead views the time-dependent changes in voltage of the heart.

Question 8

Describe the three initial limb leads and the axis they define.

Answer 8

I (positive connection to left arm, negative connection to right arm). This lead defines an axis in the
frontal plane at 0 degrees

II (positive to left leg, negative to right arm). This lead defines an axis in the frontal plane at 60 degrees.

III (positive to left leg, negative to left arm). This lead defines an axis in the frontal plane at 120 degrees.

Question 9

An electronic reconstruction of the three limb connection defines an electrical reference point in the middle of
the heart that constitutes the negative connection for the augmented “unipolar” limb leads and for
the chest leads. The three augmented unipolar limb leads compare one limb electrode to the average of the other
two. What are these?

Answer 9

aVR
aVL
aVF

Question 10

Describe the aVR lead. What axis and plane are described?

Where is the negative connection defined?

Answer 10

(positive connection to right arm, negative connection is electronically defined in the middle of the
heart). The axis defined by this limb lead in the frontal plane is −150 degrees (Fig. 21-9B). The a stands for
augmented, and the V represents unipolar.

Question 11

Describe the aVL lead. What axis and plane are described?

Where is the negative connection defined?

Answer 11

(positive to left arm, negative is middle of the heart). The axis defined by this limb lead in the frontal
plane is −30 degrees.

Question 12

Describe the aVF lead. What axis and plane are described?

Where is the negative connection defined?

Answer 12

(positive to left leg [foot], negative is middle of the heart). The axis defined by this limb lead in the
frontal plane is +90 degrees.

Question 13

Describe the precordial leads.

Answer 13

These leads lie in the transverse plane, perpendicular to the plane of the frontal leads. The positive connection is
one of six different locations on the chest wall (Fig. 21-8B), and the negative connection is electronically
defined in the middle of the heart by averaging of the three limb electrodes. The resultant leads are named V1 to
V6, where the V stands for unipolar:

Question 14

Where is the V1 lead placed?

Answer 14

fourth intercostal space to the right of the sternum

Question 15

Where is the V2 lead placed?

Answer 15

fourth intercostal space to the left of the sternum

Question 16

Where is the V3 lead placed?

Answer 16

halfway between V2 and V4

Question 17

Where is the V4 lead placed?

Answer 17

fifth intercostal space at the midclavicular line

Question 18

Where is the V5 lead placed?

Answer 18

halfway between V4 and V6

Question 19

Where is the V6 lead placed?

Answer 19

fifth intercostal space at the midaxillary line

Question 20

How are special leads obtained? What are two examples of special leads?

Answer 20

by employing the same negative connection used
for the unipolar limb and precordial leads and a positive “probe” connection. Special leads that are used include
esophageal leads and an intracardiac lead (e.g., that used to obtain a recording from the His bundle).

Question 21

The normal pacemaker is the SA node; the signal then
propagates through the AV node and activates the ventricles. When the heart follows this pathway at a normal
rate and in this sequence, the rhythm is called a…

Answer 21

normal sinus rythm

Question 22

What does the P wave duration indicate?

Answer 22

How long atrial depolarization takes.

Question 23

What does the PR interval reveal?

Answer 23

The PR interval indicates how long it takes the action potential to conduct through the AV node before
activating the ventricles.

Question 24

What does the QRS duration indicate?

Answer 24

The QRS duration reveals how long it takes for the wave of depolarization to spread
throughout the ventricles.

Question 25

What does the QT interval show?

Answer 25

how long the ventricles remain depolarized and is thus a rough measure of the duration of the overall “ventricular” action potential