: Interpretation of Electrocardiogram Tracings

MULTIPLE CHOICE

1. Why is it important for a respiratory therapist (RT) to be able to identify cardiac dysrhythmias?

a.
It is likely that the RT will observe the onset of the initial event.
b.
The RT is primarily responsible for management of the dysrhythmia.
c.
The RT must be able to confirm the physician’s initial diagnosis.
d.
RTs are always the first responders for complaints of a cardiac nature.

ANS: A

Given the hands-on nature of respiratory care, the likelihood that an RT may observe a patient during the acute onset of an ischemic cardiac event or a lethal dysrhythmia is high. Thus, it is vital for RTs to have basic knowledge in electrocardiogram (ECG) interpretation.

REF: pg. 235 OBJ: 1

2. Why is an ECG tracing so useful?

a.
It reflects the heart’s pumping ability.
b.
It can identify structural abnormalities in the heart.
c.
It can be used to diagnose malfunctioning valves.
d.
It can aid in the diagnosis of cardiac tissue ischemia.

ANS: D

If a patient presents with dyspnea and chest discomfort, an ECG can aid in the diagnosis of an ischemic cardiac event. It is important to note that the ECG tracing does not measure the pumping ability of the heart. It is not unusual for a patient with low cardiac output to have a normal ECG tracing. This is because the ECG does not directly depict abnormalities in cardiac structure such as defects in the heart valves or the interventricular septum.

REF: pg. 235 OBJ: 1 | 2

3. Which of the following symptoms is least suggestive of the need for an ECG?

a.
Fever
b.
Orthopnea
c.
Chest pain
d.
Fainting spells

ANS: A

Orthopnea, chest pain, and fainting spells all are clinical findings that suggest the need for an ECG; fever is not (see Box 11-1, pg. 236).

REF: pg. 236 OBJ: 3

4. Which chamber of the heart initially receives deoxygenated blood from the vena cava?

a.
Left atrium
b.
Left ventricle
c.
Right atrium
d.
Right ventricle

ANS: C

The right atrium receives deoxygenated blood from the vena cava and directs the blood into the right ventricle.

REF: pg. 236 OBJ: 3

5. Which chamber is responsible for pumping blood into the pulmonary circulation?

a.
Left atrium
b.
Left ventricle
c.
Right atrium
d.
Right ventricle

ANS: D

Right ventricular contraction ejects blood into the pulmonary artery, which carries blood to the lungs for oxygenation.

REF: pg. 236 OBJ: 3

6. Which chamber normally has the largest muscle mass?

a.
Left atrium
b.
Left ventricle
c.
Right atrium
d.
Right ventricle

ANS: B

Because the left side of the heart pumps blood throughout the entire body, it normally has a significantly larger muscle mass than the right side.

REF: pg. 236 OBJ: 3

7. Where does the normal electrical impulse originate for each heartbeat?

a.
Atrioventricular (AV) node
b.
Sinoatrial (SA) node
c.
Bundle of His
d.
Right bundle branch

ANS: B

Normally, the electrical activity of the heart is initiated in the sinus or sinoatrial (SA) node, which is located in the right atrium (see Figure 11-2, pg. 236).

REF: pg. 236 OBJ: 5

8. What term describes heart cells that have the ability to spontaneously depolarize?

a.
Systole
b.
Purkinje
c.
Automaticity
d.
Myocardiocity

ANS: C

Cells that have the ability to generate electrical activity spontaneously are said to exhibit automaticity.

REF: pg. 236 OBJ: 5

9. Why is the electrical signal delayed slightly at the AV node?

1. To allow better filling of the ventricles

2. To protect the ventricles against excessively rapid atrial rates

3. To provide time for atrial contraction prior to ventricular systole

4. To prevent premature atrial beats from reaching the ventricles

a.
1, 3
b.
2, 4
c.
1, 2
d.
1, 2, 3, 4

ANS: C

Once the electrical impulse reaches the AV node, it is delayed for approximately 0.1 second before it passes on into the bundle of His. The delay is believed to serve the purpose of allowing more complete filling of the ventricles before ventricular contraction, which occurs as the result of atrial contraction. In addition, the AV node can protect the ventricles from excessively rapid atrial rates that the ventricles could not tolerate.

REF: pg. 237 OBJ: 5

10. What is the ventricular heart rate when the AV node paces the heart?

a.
20 to 40 beats/min
b.
40 to 60 beats/min
c.
60 to 80 beats/min
d.
80 to 100 beats/min

ANS: B

If the SA node fails to function properly and does not pace the heart, the AV junction can serve as the pacemaker for the ventricles. When this occurs, the ventricular rate is usually between 40 and 60 beats/min and the ECG reveals a distinct pattern, as is described later in this chapter (see Figure 11-3, pg. 237).

REF: pg. 237 OBJ: 5

11. What term applies to any heartbeat that originates outside the SA node?

a.
Ectopic impulse
b.
Aberrant impulse
c.
Eccentric impulse
d.
Recurrent impulse

ANS: A

Any impulse that originates outside the SA node is called an ectopic impulse, and the site from which the ectopic impulse originates is called the focus.

REF: pg. 239 OBJ: 5

12. Which of the following physiologic effects is associated with myocardial infarction?

a.
Arterial hypertension
b.
Increased cardiac output
c.
Good blood flow to the brain
d.
Backup of blood into the lungs

ANS: D

Infarction of a major portion of the left ventricle is likely to cause significant arterial hypotension, an abnormal sensorium, and a backup of blood into the pulmonary circulation.

REF: pg. 239 OBJ: 11

13. Which of the following are associated with the onset of dysrhythmias?

1. Hypoxia

2. Electrolyte imbalances

3. Sympathetic stimulation

4. Pulmonary hypertension

a.
1, 2
b.
3, 4
c.
2, 4
d.
1, 2, 3

ANS: D

Dysrhythmias can be caused by hypoxia, ischemia, sympathetic stimulation, drugs, electrolyte imbalances, abnormal heart rate, and abnormally stretched or dilated cardiac chambers.

REF: pg. 239 OBJ: 9

14. What term describes the sudden loss of the negative charge inside the myocardial cells?

a.
Repolarization
b.
Depolarization
c.
Automaticity
d.
Conductivity

ANS: B

Depolarization occurs when a polarized cell is stimulated. Polarized cells carry an electrical charge on their surface, the inside of the cell being more negatively charged than the outside of the cell. The sudden loss of the negative charge within the cell is called depolarization.

REF: pg. 240 OBJ: 4

15. What is represented by the P wave on the ECG tracing?

a.
Repolarization of the atria
b.
Depolarization of the atria
c.
Repolarization of the ventricles
d.
Depolarization of the ventricles

ANS: B

Depolarization of the atria creates the initial wave of electrical activity detected on the ECG tracing, known as the P wave (see Figure 11-5, pg. 240). Because the atria usually are small, they generate less voltage than the ventricles, and the resulting P wave is small.

REF: pg. 240 OBJ: 6

16. What does the QRS complex represent?

a.
Depolarization of the atria
b.
Repolarization of the atria
c.
Depolarization of the ventricles
d.
Repolarization of the ventricles

ANS: C

Depolarization of the ventricles is represented by the QRS complex. Because the ventricular muscle mass is larger than the atria and produces more voltage during depolarization, the QRS complex normally is taller than the P wave in most cases (see Figure 11-5, pg. 241).

REF: pg. 241 OBJ: 6

17. At what speed does the paper travel through the ECG machine?

a.
25 mm/sec
b.
30 mm/sec
c.
40 mm/sec
d.
50 mm/sec

ANS: A

Time is measured on the horizontal axis of the ECG paper. The ECG paper moves through the electrocardiograph at a speed of 25 mm/sec.

REF: pg. 242 OBJ: 8

18. How much time is represented on the horizontal axis of the ECG paper by five large boxes?

a.
0.5 second
b.
1 second
c.
3 seconds
d.
5 seconds

ANS: B

Each small square (1 mm) represents 0.04 second, and each larger square (5 mm) represents 0.2 second. Five large boxes represent 1 second.

REF: pg. 242 OBJ: 6

19. What is the upper limit in height of the normal P wave?

a.
1 mm
b.
2.5 mm
c.
3.5 mm
d.
5 mm

ANS: B

The normal P wave is less than 2.5 mm in height and is not more than 0.10 second in length.

REF: pg. 242 OBJ: 6

20. What is the normal range for the PR interval?

a.
0.05 to 0.1 second
b.
0.12 to 0.2 second
c.
0.2 to 0.35 second
d.
0.25 to 0.5 second

ANS: B

The normal PR interval is between 0.12 and 0.2 second (three to five small boxes).

REF: pg. 242 OBJ: 6

21. The normal QRS complex does not exceed what time on the horizontal axis?

a.
0.05 second
b.
0.10 second
c.
0.5 second
d.
1 second

ANS: B

Normally, the QRS interval does not exceed 0.12 second (three small boxes).

REF: pg. 248 OBJ: 7

22. What is the heart rate if the RR interval is five large boxes apart?

a.
40 beats/min
b.
60 beats/min
c.
90 beats/min
d.
120 beats/min

ANS: B

The RR interval is useful in identifying the rate and regularity of ventricular contraction. The distance in millimeters is determined from one R wave to the next in successive QRS complexes. This is done for several different RR intervals. The average of the measurements is determined and converted to time. Remember that each large box is equal to 0.2 second and five large boxes equal 1 second. If the RR interval is 1 second, the heart rate is 60 beats/min.

REF: pg. 243 OBJ: 8

23. In the terminology for three of the limb leads—aVR, aVL, and aVF—what does the letter “A” stand for?

a.
Atrial
b.
Assisted
c.
Ambient
d.
Augmented

ANS: D

The three limb leads—aVR, aVL, and aVF—are called augmented leads because the ECG machine must amplify the tracings to get an adequate recording.

REF: pg. 244 OBJ: 8

24. What part of the heart is best viewed by the chest leads V5 and V6?

a.
Left atrium
b.
Right atrium
c.
Left ventricle
d.
Right ventricle

ANS: C

V5 and V6 lie over the left ventricle.

REF: pg. 245 OBJ: 7

25. What is considered to be the normal position of the axis in a healthy patient’s heart?

a.
0 to –90 degrees
b.
0 to 90 degrees
c.
60 to 120 degrees
d.
120 to 180 degrees

ANS: B

Normally, the mean QRS axis (vector) points leftward (patient’s left) and downward, somewhere between 0 and +90 degrees in the frontal plane previously described (see Figure 11-12, pg. 245).

REF: pg. 245 OBJ: 8

26. What axis change is common in patients with chronic pulmonary hypertension?

a.
Left axis deviation
b.
Right axis deviation
c.
Inverted axis deviation
d.
Extreme left axis deviation

ANS: B

Right axis deviation is important to recognize early in the care of the patient because it often indicates significant chronic pulmonary hypertension. This most often is related to chronic hypoxemia from chronic obstructive pulmonary disease.

REF: pg. 246 OBJ: 10

27. What problem is indicated by elevation of the ST segment?

a.
Heart block
b.
Myocardial ischemia
c.
Elevation of serum potassium
d.
Depletion of serum potassium

ANS: B

Inspect the ST segment in all leads. ST segment elevation may indicate myocardial injury, whereas ST segment depression may indicate myocardial ischemia.

REF: pg. 258 OBJ: 9

28. What is the upper limit of normal for the width of a normal Q wave?

a.
0.08 second
b.
0.04 second
c.
1.2 seconds
d.
1.4 seconds

ANS: B

Evaluate the Q wave. A Q wave is considered normal (or physiologic) if it is less than 0.04 second (40 msec) wide and less than one-third the amplitude of the R wave. Q waves that exceed either of these values are considered pathologic and indicate a new or possibly old infarction.

REF: pg. 248 OBJ: 8

29. What is indicated by high-voltage R waves in the QRS complex?

a.
Axis deviation
b.
Atrial enlargement
c.
Myocardial ischemia
d.
Ventricular enlargement

ANS: D

Look for signs of chamber enlargement. High-voltage R waves in the precordial leads indicate ventricular hypertrophy.

REF: pg. 248 OBJ: 8

30. Which of the following are common causes of tachycardia?

1. Pain

2. Fever

3. Hypoxemia

4. Hypothyroidism

a.
1, 3
b.
2, 4
c.
1, 2, 3
d.
1, 2, 3, 4

ANS: C

Fever, pain, hypoxemia, hypovolemia, hypotension, sepsis, and heart failure are causes of sinus tachycardia.

REF: pg. 249 OBJ: 9

31. What dysrhythmia is characterized by a sawtooth pattern of waves between normal QRS complexes on the ECG tracing?

a.
Atrial flutter
b.
Atrial fibrillation
c.
Ventricular flutter
d.
Ventricular fibrillation

ANS: A

Atrial flutter is a dysrhythmia that produces a very distinctive ECG pattern, usually caused by a rapidly firing ectopic site in the atria that presents as a characteristic sawtooth pattern between normal-appearing QRS complexes.

REF: pg. 250 OBJ: 9

32. Which of the following would describe the ECG of a patient with atrial fibrillation?

a.
Regular ventricular response
b.
Large bizarre QRS complexes
c.
Chaotic baseline between QRS complexes
d.
No identifiable QRS complexes

ANS: C

In atrial fibrillation, the electrical activity of the atria is completely chaotic and lacks coordination because it is arising from multiple ectopic sites within the atria. The ECG tracing shows a chaotic baseline between QRS complexes, with no regular pattern or organization.

REF: pg. 251 OBJ: 9

33. Which of the following is a hallmark of a premature ventricular contraction (PVC)?

a.
The QRS complex is early but normal in appearance.
b.
The QRS complex is wider than normal.
c.
There is a P wave in front of the QRS complex.
d.
The T wave moves in the same direction as the QRS complex.

ANS: B

No P wave is associated with a PVC. The QRS complex comes early, exceeds 0.12 second in width, and has abnormal configuration. The T wave following the PVC is deflected in a direction opposite to that of the QRS complex.

REF: pg. 253 OBJ: 9

34. What dysrhythmia often follows sustained ventricular tachycardia?

a.
Heart block
b.
Atrial fibrillation
c.
Elevated ST segments
d.
Ventricular fibrillation

ANS: D

Sustained ventricular tachycardia may lead to ventricular fibrillation, particularly if untreated.

REF: pg. 253 OBJ: 9

35. Which of the following dysrhythmias is associated with the lowest cardiac output?

a.
AV block
b.
Atrial fibrillation
c.
Ventricular flutter
d.
Ventricular fibrillation

ANS: D

In ventricular fibrillation, the heart cannot pump blood, the cardiac output drops to zero, and the patient becomes unconscious immediately.

REF: pg. 253 OBJ: 9

36. Which of the following dysrhythmias represents a dissociation of the mechanical and electrical activities of the heart?

a.
Asystole
b.
AV block
c.
Bradycardia
d.
Pulseless electrical activity (PEA)

ANS: D

PEA is not a discrete dysrhythmia but rather an electromechanical condition that can be diagnosed clinically. As the name implies, there is a dissociation of the electrical and mechanical activity of the heart. In other words, the pattern that appears on the ECG monitor does not generate a pulse.

REF: pg. 254 OBJ: 9

37. Which of the following is a characteristic of third-degree heart block?

a.
There is a lengthening PR interval.
b.
There is often a 2:1 ratio between P waves and QRS complexes.
c.
The atrial rate is the same as the ventricular rate.
d.
There is no relationship between the P waves and the QRS complexes.

ANS: D

This block does not allow any conduction of stimuli from the atria to the ventricles. In this situation, the ventricles and the atria beat independently of one another. Thus no pattern is distinguishable between the atria and the ventricles.

REF: pg. 256 OBJ: 9

38. What is the normal progression of abnormalities seen on the ECG for a patient who is having a myocardial infarction?

a.
ST elevation followed by large Q waves
b.
ST depression followed by large Q waves
c.
Large Q waves, ST elevation, followed by ST depression
d.
ST depression, large Q waves, and then ST segment elevation

ANS: A

The typical pattern of acute myocardial injury is ST segment elevation in the leads that reflect electrical activity of the corresponding injured heart tissue (see Figure 11-32, pg. 258). In general, the degree of damage to the heart caused by the ischemia determines the degree of ST segment elevation. The ST segment abnormality usually resolves when perfusion is restored. At some point after myocardial infarction, significant Q waves (0.04 second in length) are seen on the ECG in the corresponding leads. Q waves may develop within hours of an infarction but may not evolve for several days in some patients. They persist for the remainder of the patient’s life.

REF: pg. 258 OBJ: 11

39. Which of the following would be a typical ECG finding in a patient with emphysema?

a.
Reduced voltage in the limb leads
b.
Left axis deviation
c.
Smaller-than-normal P waves
d.
Prominent QRS complexes, particularly in leads V5 and V6

ANS: A

Hyperinflation of the lungs, as occurs with emphysema, impairs passage of the electrical activity of the heart through the lung. This causes reduced voltage to be seen in the limb leads.

REF: pg. 259 OBJ: 10

40. A patient who has atrial fibrillation is at risk for which of the following pulmonary conditions?

a.
Chronic obstructive pulmonary disease (COPD)
b.
Pneumothorax
c.
Pleural effusion
d.
Pulmonary emboli

ANS: D

Similar to atrial flutter, patients with atrial fibrillation are at greater risk for mural thrombi formation and embolization due to blood stagnation in the atria. As a result, RT’s and other clinicians should be on the alert for pulmonary emboli and stroke in such patients.

REF: pg. 251 OBJ: 10

41. A patient complaining of chest pain that has not been relieved by nitroglycerin should be treated with all of the following except:

a.
oxygen therapy
b.
thrombolytic therapy
c.
stress testing
d.
surgical intervention

ANS: C

The AHA recommends that for chest pain or associated symptoms not relieved by nitroglycerin, a myocardial infarction should be suspected until proven otherwise. Remember that “time is muscle,” and treatment interventions, such as thrombolytic therapy or surgical intervention, should be implemented quickly to minimize damage to the myocardium.

REF: pg. 259 OBJ: 12