Download Chapter02_Detailed_Answers

Chapter 2
Detailed Answers to Assess Your Understanding
1.
a:
An electrocardiogram is a graphic record of the heart’s electrical activity. The device
that measures and records the ECG is called an electrocardiograph.
2.
b:
The electrocardiograph can be used to detect cardiac dysrhythmias, identify the
presence of myocardial ischemia and/or infarction, and evaluate the function of artificial implanted
pacemakers. The electrocardiograph cannot be used to determine cardiac output.
3.
a:
Electrodes positioned on the patient’s skin detect the heart’s electrical activity. The ECG
machine determines which electrode is positive, negative, or ground based on the lead selected.
4.
d:
Impulses that travel toward a positive electrode and away from a negative electrode are
recorded on the electrocardiogram as upward, upright, or positive deflections. Impulses traveling
toward a negative electrode and away from a positive electrode are recorded as downward deflections.
5.
d:
The lead most commonly used for continuous cardiac monitoring is lead II.
6.
a:
With lead II the positive electrode is placed on the left leg. This is labeled as II. Because
depolarization of the heart flows in the same path as the negative to positive layout of the ECG
electrodes the waveforms should appear upright or in a positive direction.
7.
c:
Bipolar leads require two electrodes of opposite polarity. Bipolar leads have a third (and
often a fourth) electrode called a ground. The ground is used to help prevent electrical interference
from appearing on the ECG and has zero electrical potential when compared with the positive and
negative electrodes. There are three bilateral leads; I, II and III.
8.
a:
activity.
The frontal plane provides an anterior and posterior view of the heart’s electrical
9.
a:
The limb leads are obtained by placing electrodes on the right arm (RA), left arm (LA),
and left leg (LL).
10.
c:
An ECG printout provides a more accurate picture of the ST segments than does the
oscilloscope. It is a static view of the heart’s electrical activity.
11.
b:
duration.
Each small square on the ECG paper running horizontally represents 0.04 seconds in
12.
c:
The larger box on the ECG paper which is made up of five small squares represents 0.20
seconds in duration.
13.
b:
Vertical markings on the top or bottom of the ECG paper represent 3-second intervals.
14.
a:
Each small square on the ECG paper running vertically represents 1 mm or 0.1 mV. Four
small squares represent amplitude of four mm or 0.4 mV.
15.
a:
The reference point used to identify the changing electrical amplitude on the ECG is
called the isoelectric line.
16.
True: A calibration mark serves as a reference point on the ECG tracing from which you can
assess the height of the P waves, QRS complexes, and T waves.
17.
c:
Artifact may be caused by the patient moving, shivering or experiencing muscle tremors,
worn out lead wires, a malfunctioning ECG machine, or the presence of 60-cycle current interference.
18.
b:
The ECG only measures electrical activity which we call the heart rate on the monitor.
The pulse is the actual palpated beat of the heart felt at the wrist or other pressure point. It must be
correlated with the ECG to ensure that every complex seen on the monitor results in a pulse. The blood
pressure can only be measured using a blood pressure cuff that detects the mechanical pulse of the
heart. Cardiac output can only be measured using a special device called an echocardiogram that
measures the stroke volume of the contraction. Stroke volume is then multiplied by heart rate to obtain
cardiac output.
19.
d: Regardless of the patient’s stroke volume, if the heart rate decreases significantly the cardiac
output will diminish to the point the brain does not receive adequate perfusion resulting in a loss of
consciousness.
20.
c: The Vagus nerve supplies parasympathetic tone to the heart. When it fires the heartbeat
slows. When it stops firing the heart beats more quickly.