Download Chapter17_Detailed_Answers

Chapter 17
Detailed Answers to Assess Your Understanding
1.
c:
With lead I, the LA lead wire is the positive electrode, the RA lead is the negative electrode, and
the LL and RL leads are the ground and there to complete the circuit. With lead II, the LL lead is the
positive electrode, the RA lead is the negative electrode, and the LA and RL leads are ground and there
to complete the circuit. With lead III, the LL lead is the positive electrode, the LA lead is the negative
electrode, and the RA and RL leads are ground.
2.
b:
With the aVF lead, the positive electrode is positioned in/on the left leg. In lead aVR, the RA lead
is the positive electrode and in lead aVL , the LA lead serves as the positive electrode.
3.
c:
4.
b:
The horizontal plane gives us a/an superior and inferior view of the heart’s electrical activity. It is
a transverse (upper and lower) cut through the middle of the heart. The leads arranged along this plane
give us an anterior, lateral, and posterior (back) view of the heart.
5.
a:
Leads V1, V2, V3, V4, V5, and V6 view the heart on the horizontal plane.
6.
a:
leg.
The limb leads are obtained by placing electrodes on the right arm, left arm, left leg and right
7.
a:
Leads I, II, and III are referred to as the standard limb leads.
8.
Leads V1, V2, V3, V4, V5, and V6 are referred to as the precordial leads. They are also called V leads, or
chest leads.
9.
ECG leads with the correct description: a. V1 and V2: - septal leads; b. V3 and V4 - anterior leads; c. II, III,
and aVF - inferior leads; d. V1, V2, V3, and V4 - anteroseptal leads; e. I, aVL, V5, and V6 - lateral leads.
10.
b:
11.
b:
The currents produced by depolarization and repolarization of the cardiac cells are called
instantaneous vectors.
12.
d:
The electrical axis is depicted as a single large arrow.
13.
a:
Axis is defined in the frontal plane only.
14.
c: The QRS axis is the most important and also the most frequently determined axis.
15.
c: Completion of right ventricle depolarization occurs during completion of left ventricle depolarization.
Bipolar leads require two electrodes of opposite polarity and include leads I, II and III.
Contiguous ECG leads include any two leads that are anatomically next to one another.
16.
b: (False) The left ventricular vectors are larger and persist longer than those of the right ventricle.
17.
b: The sum of all the small vectors of ventricular depolarization is called the mean QRS vector.
18.
a: The center of the circle used to determine the axis of the mean QRS vector is the AV node.
19.
c: The circle used to determine the axis of the mean QRS vector is divided into equal, 30-degree
segments.
20.
d: On the circle used to determine the axis of the mean QRS vector lead I starts at 0 degrees and is
located at the 3 o’clock position.
21.
c: The mean QRS axis normally points downward and to the patient’s left, between 0 and 90 degrees.
22.
Axis deviations with the correct degrees. d: Right axis deviation: + 90 degrees and ± 180 degrees b: left
axis deviation: 0 and -90 degrees c: extreme axis deviation: ±180 and -90 degrees
23.
If the QRS complex is positive in leads I and aVF, the QRS axis must be normal. If the QRS complex is
upright in lead I and negative in lead aVF then left axis deviation exists. If the QRS complex is negative in
lead I and positive in lead aVF then right axis deviation exists. If the QRS complex is negative in both leads
extreme right axis deviation exists.
24.
Positive or upright.
25.
Left half is negative, right half is positive.
26.
Top half is negative, bottom half is positive.
27.
a:
Referring to the scenario at the beginning of this chapter As the mass of the left ventricle
increases, the sum of the electrical forces is greater from the left side of the heart causing the axis to
shift toward the left ventricle that is toward the left of normal.
28.
b: As the mass of the left ventricle increases, the sum of the electrical forces is greater from the left side
of the heart causing the axis to shift toward the left ventricle that is toward the left of normal.
29.
a:
(True) Infarcted tissue cannot depolarize and therefore has no vectors. The vectors from the
other side are unopposed vectors because of this, so the mean QRS vector tends to point away from the
infarct.