CARDIAC MONITORING

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CHAPTER 9 CARDIAC MONITORING

PRETEST QUESTIONS

Answer the pretest questions before studying the chapter. This will help you determine your strong and weak areas in the material covered.

1. Which statement about the P wave on an ECG is FALSE?

A. It represents atrial depolarization.
B. It is a positive wave on the graph.
C. Normal duration time is 0.06 to 0.10 s.
D. It represents ventricular repolarization.

2. Artifacts found on an ECG may be caused by which of the following?

1. Electrical interference at the bedside.
2. Poor electrode contact with the skin.
3. Excessive movement of the patient.
A. 1 only
B. 2 only
C. 1 and 3 only
D. 1, 2, and 3

3. In which of the following cardiac arrhythmias is the QRS complex abnormally shaped as well as wider than normal?

A. Sinus tachycardia
B. Premature ventricular contractions (PVCs)
C. Atrial fibrillation
D. Premature atrial contractions (PACs)

4. A patient with a blood pressure of 110/50 mm Hg and a pulse rate of 75 beats/min has which of the following pulse pressures?

A. 40 mm Hg
B. 50 mm Hg
C. 60 mm Hg
D. 70 mm Hg

5. A weak pulse is detected distal to the arterial catheter in a patient. This is indicative of which of the following?

A. Infection
B. Hemorrhage
C. Thrombosis
D. Tachycardia

6. Which of the following conditions results in a decreased central venous pressure (CVP) reading?

1. Hypovolemia
2. Vasoconstriction
3. Air bubbles in the CVP line
A. 1 only
B. 2 only
C. 1 and 2 only
D. 1 and 3 only

See answers and rationales at the back of the text.

REVIEW

I. ELECTROCARDIOGRAPHY

CRT Exam Content Matrix: IA8a, IB9a, IB10a, IIA17-18

RRT Exam Content Matrix: IA8a, IB9a, IB10a

A. Electrical Conduction of the Heart
1. The sinoatrial (SA) node is the pacemaker of the heart; it usually initiates about 75 impulses/min.
2. Once an impulse has been initiated by the SA node, the impulse travels down to the AV node.
3. From the AV node, the impulse travels on to the bundle of His, located in the interventricular septum.
4. The bundle of His divides into the right and left bundle branches, which deliver the impulses to the right and left sides of the heart.
5. The bundle branches divide even further into the Purkinje fibers, which send the impulse to individual muscle fibers of the ventricles, which causes ventricular contraction.
6. Once the SA node sends an impulse, the conduction system depolarizes, sending the impulse through the conduction system to the heart muscle, which depolarizes and contracts. After contraction, repolarization occurs, and the heart is in a resting state, called diastole. The term used for the heart in contraction is systole.
B. ECG Leads. Through the use of various numbers of electrodes (leads) placed on the patient’s body, the electrical activity of the heart can be monitored. The device to which the electrodes are attached is the electrocardiograph. The electrical activity of the heart recorded on graph paper is called the electrocardiogram and may be displayed continuously on an ECG monitor, called an oscilloscope.
C. Standard 12-Lead ECG Has Three-Lead Systems
1. Standard limb leads (three leads) (+, positive pole; −, negative pole)
a. The leads are placed on the right arm, left arm, and left leg.
b. Limb lead I measures the electrical potential between the right arm (−) and left arm (+).
c. Limb lead II measures the electrical potential between the right arm (−) and left leg (+).
d. Limb lead III measures the electrical potential between the left arm (−) and the left leg (+).
e. A ground is placed on the right leg.
2. Augmented leads (three leads)
a. The same electrodes used in the standard leads are used for augmented lead composition but in different combinations.
b. Lead aVR: Leads are connected to right arm (+), left arm, and left leg. The right arm is the positive electrode and records electrical activity from the direction of the right arm.
c. Lead aVL: Leads are connected to left arm (+), right arm, and left leg. The left arm is the positive electrode and views the electrical activity from the direction of the left arm.
d. Lead aVF: Leads are connected to left leg (+), right arm, and left arm. The left leg is the positive electrode and views the electrical activity from the direction of the bottom of the heart.
3. Precordial (chest) leads (six leads)
a. Lead 1 (V1): positioned at the fourth intercostal space at the right border of the sternum
b. Lead 2 (V2): positioned at the fourth intercostal space at the left border of the sternum
c. Lead 3 (V3): positioned in a straight line between lead 2 and lead 4
d. Lead 4 (V4): positioned at the midclavicular line and at the fifth intercostal space
e. Lead 5 (V5): positioned at the anterior axillary line, level with lead 4 horizontally
f. Lead 6 (V6): positioned at the midaxillary line, level with lead 4 and 5 horizontally
image

FIGURE 9-1 Precordial (chest) leads.

image Exam Note

The 12-lead ECG is not normally used for long-term ECG monitoring, such as that seen in the intensive care unit (ICU) or coronary care unit (CCU).

D. Long-Term ECG Monitoring
1. Lead placements (three leads)
a. The first electrode is placed on the upper right side of the chest (−).
b. The second electrode is placed on the lower left side of the chest (+).
c. The third electrode is used as a ground and may be attached to any location that is convenient.
2. To obtain a clear ECG reading, there must be good skin contact with the electrode; otherwise, artifacts will appear. An electrode gel is used to improve conduction. Hair should be shaved from the chest if an electrode is to be attached in that area. Other causes of artifacts are electrical interference and excessive movement of the patient.
E. ECG Graph Paper
image

FIGURE 9-2 Normal electrocardiographic (ECG) pattern.

From Davis D: Differential diagnosis of arrhythmias, ed 2, Philadelphia, 1997, Saunders.

1. The ECG paper is made up of very small squares, which represent 0.04 s horizontally and 0.5 mV vertically (voltage axis).
2. So that counting time is easier, there is a darkened line at every fifth small square; from one darkened line to the next is 0.20 s (0.04 s × 5 squares).
3. Most ECG paper has short vertical lines at the top to designate 3-s intervals, which makes it easier to calculate the heart rate.
F. Normal ECG Pattern: The ECG strip shows a baseline and positive and negative deflections from it.
image

FIGURE 9-3 One cardiac cycle.

From Davis D: Differential diagnosis of arrhythmias, ed 2, Philadelphia, 1997, Saunders.

G. ECG Waves: One cardiac cycle consists of a series of waves, represented by the letters P, Q, R, S, and T.
1. P wave
a. Positive wave
b. Represents atrial depolarization (contraction)
c. Duration: 0.06 to 0.10 s
2. Q wave
a. Negative wave that follows the P wave
b. May be absent even in healthy people
3. R wave
a. Positive wave that follows the Q wave
4. S wave
a. Negative wave that follows the R wave
5. QRS complex
a. Represents ventricular depolarization (contraction). Atrial repolarization occurs during the QRS complex and therefore is not seen on the ECG.
b. Duration: 0.06 to 0.12 s
c. Widened QRS seen in right bundle-branch block
image

FIGURE 9-4 Electrocardiographic (ECG) tracing showing the widened QRS complex.

From Levitsky MG, Cairo JN, Hall SM: Introduction to respiratory care, Philadelphia, 1990, Saunders.

6. T wave
a. Positive wave
b. Represents ventricular repolarization
c. Inverted (negative wave) T waves indicate the presence of coronary artery disease.
7. PR interval
a. Measured from the beginning of the P wave to the beginning of the Q wave.
b. Represents the time it takes for the impulse to travel from the SA node through the AV node.
c. Duration: 0.12 to 0.20 s
d. May be prolonged in first- and second-degree heart block
image

FIGURE 9-5 Electrocardiographic (ECG) tracing showing a prolonged PR interval.

From Davis D: Differential diagnosis of arrhythmias, ed 2, Philadelphia, 1997, Saunders.

8. ST segment
a. Measured from the end of the S wave to the beginning of the T wave
b. Measures the time that is required for ventricular repolarization to begin
c. The ST segment may be elevated above the baseline or depressed below the baseline. This is an indication of cardiac ischemia. Cardiac ischemia results from a decreased amount of oxygenated blood delivered to the left ventricle because of narrowed coronary arteries. If the blood supply is not restored, ventricular muscle may die; this is called infarction. ST segment elevation or depression is a sign of coronary artery disease.
image

FIGURE 9-6 Electrocardiographic (ECG) tracing showing ST segment depression.

From Davis D: Differential diagnosis of arrhythmias, ed 2, Philadelphia, 1997, Saunders.

H. Normal Heart Rhythm
image

FIGURE 9-7 Normal heart rhythm.

From Davis D: Differential diagnosis of arrhythmias, ed 2, Philadelphia, 1997, Saunders.

1. Atrial depolarization (contraction) is represented on the ECG as the P wave.

image Blood supply to the heart is supplied by two main arteries: the right and left coronary arteries, which originate from the aorta. The right coronary artery extends down to feed the right ventricle and then separates into several branches. The left coronary artery divides into two major branches: the circumflex branch, which feeds the upper lateral wall of the left atrium and left ventricle, and the left anterior descending branch (anterior interventricular artery), which feeds the anterior portion of the heart.

image

FIGURE 9-8 Primary and secondary arteries in the heart.

From O’Toole M, editor: Miller-Keane encyclopedia and dictionary of medicine, nursing, and allied health, revised revision, Philadelphia, 2005, Saunders.

2. Cardiac impulse travels to the AV node, bundle of His, and the Purkinje fibers, which are represented on the ECG as the PR interval.
3. Cardiac impulse reaches muscles in the ventricles, causing ventricular depolarization (contraction), which is represented on the ECG as the QRS complex.
4. Ventricular repolarization is represented on the ECG as the ST segment and T wave.
I. Basic Steps to ECG Interpretation
1. Calculate heart rate
a. As mentioned, most ECG paper has 3-s intervals marked off at the top of the paper. Count the number of R waves in a 6-s period and multiply by 10 to obtain the number of beats/minute.
b. Normal rate: 60 to 100 beats/min
c. Bradycardia: less than 60 beats/min
d. Tachycardia: more than 100 beats/min
2. Determine regularity of the rhythm
a. Using calipers, measure the distance between a pair of R waves. Leave the calipers at that distance, and measure the next pair of R waves to determine whether the distance is the same.
b. Continue measuring the distance between successive pairs of R waves to determine whether it is constant. If the distances remain constant, the rhythm is regular.
3. Observe P waves and PR interval
a. Make sure that there is a P wave before every QRS complex and that they are of the same shape.
b. Using calipers, measure several PR intervals to determine whether they are consistent.
c. As stated earlier, the normal PR interval is 0.12 to 0.20 s. If the PR interval is longer than 0.20 s, first-degree heart block is present.
4. Determine length of the QRS complex
a. Remember, the QRS complex represents the time it takes for ventricular depolarization to occur. The normal QRS complex takes 0.06 to 0.12 s; any longer duration would indicate heart block.

image Exam Note

If all the above observations are within normal limits, the ECG shows normal sinus rhythm.

J. Cardiac Arrhythmias: most often encountered by RCPs
1. Sinus bradycardia
image

FIGURE 9-9 Sinus bradycardia.

From Davis D: Differential diagnosis of arrhythmias, ed 2, Philadelphia, 1997, Saunders.

a. Rate: less than 60 beats/min
b. Rhythm: regular
c. Wave pattern abnormalities: none
d. Cause: stimulation of vagus nerve (e.g., during tracheal suctioning), hypothermia, increased ICP; sinus bradycardia may be normal in well-conditioned athletes.
e. Treatment: If accompanied by shortness of breath, hypotension, or abnormal beats, atropine is used; a pacemaker may also be indicated.
2. Sinus tachycardia
image

FIGURE 9-10 Sinus tachycardia.

From Davis D: Differential diagnosis of arrhythmias, ed 2, Philadelphia, 1997, Saunders.

a. Rate: 100 to 160 beats/min
b. Rhythm: regular
c. Wave pattern abnormalities: none
d. Cause: hypoxemia, increased sympathetic nervous system stimulation (e.g., fear, anxiety), medication
e. Treatment: stop underlying cause; administration of digitalis or beta blockers
3. Sinus arrhythmia
image

FIGURE 9-11 Sinus arrhythmia.

From Davis D: Differential diagnosis of arrhythmias, ed 2, Philadelphia, 1997, Saunders.

a. Rate: 60 to 100 beats/min
b. Rhythm: irregular
c. Wave pattern abnormalities: R to R cycles vary more than 0.16 s. In Figure 9-11, note how the distance between the R wave of the QRS complex varies and is inconsistent.
d. Cause: none; normal in young, healthy individuals; heart rate may increase during inspiration and decrease during expiration.
e. Treatment: none necessary
4. Premature Atrial Contraction
image

FIGURE 9-12 Premature atrial contraction (PAC).

From Davis D: Differential diagnosis of arrhythmias, ed 2, Philadelphia, 1997, Saunders.

a. Rate: 60 to 100 beats/min. Less than 6 PACs per minute is considered a minor arrhythmia; more than 6 PACs per minute is considered major arrhythmia.
b. Rhythm: regular, except for PAC
c. Wave pattern abnormalities: the premature P wave looks different than the sinus P wave; the PAC occurs sooner than the next beat would be expected.
d. Cause: atrial irritability caused by organic heart disease, CNS disturbances, sympathomimetic drugs, tobacco, caffeine
e. Treatment: if more than 6 PACs per minute, lidocaine may be used
5. Premature Ventricular Contraction
image

FIGURE 9-13 Premature ventricular contraction (PVC).

From Davis D: Differential diagnosis of arrhythmias, ed 2, Philadelphia, 1997, Saunders.

a. Rate: 60 to 100 beats/min; less than 6 PVCs per minute is considered minor and more than 6 PVCs per minute is considered major.
b. Rhythm: regular, except for PVCs

image Exam Note

When every other beat is a PVC, the arrhythmia is termed bigeminy, which is considered a dangerous arrhythmia.

c. Wave pattern abnormalities: the shape of the QRS complex is abnormal and wider than 0.12 s.
d. Cause: ventricular irritability caused by hypoxia, acid–base disturbances, electrolyte abnormalities, excessive dose of digitalis, CHF, myocardial inflammation, coronary artery disease
e. Treatment: lidocaine IV or other antiarrhythmia drugs, such as procainamide or propranolol if more than 6 PVCs per minute
6. Atrial fibrillation
image

FIGURE 9-14 Atrial fibrillation.

From Davis D: Differential diagnosis of arrhythmias, ed 2, Philadelphia, 1997, Saunders.

a. Rate: variable; atrial rate greater than 350 beats/min
b. Rhythm: irregular
c. Wave pattern abnormalities: P waves cannot be distinguished and have an uneven baseline; PR interval is also indistinguishable.
d. Cause: hypoxia, arteriosclerotic heart disease, mitral stenosis, valvular heart disease
e. Treatment: cardioversion, propranolol, digitalis

image Exam Note

Atrial fibrillation is considered to be a major arrhythmia, whereby the atria fail to pump blood adequately to the ventricles, which results in a significant decrease in cardiac output.

7. Atrial flutter
image

FIGURE 9-15 Atrial flutter.

From Davis D: Differential diagnosis of arrhythmias, ed 2, Philadelphia, 1997, Saunders.

a. Rate: atrial, 200 to 400 beats/min; ventricular, 60 to 150 beats/min
b. Rhythm: regular or irregular
c. Wave pattern abnormalities: P waves have a characteristic sawtooth pattern and thus are often referred to as “F” waves
d. Cause: hypoxia, arteriosclerotic heart disease, MI, rheumatic heart disease
e. Treatment: cardioversion, carotid artery massage, procainamide, digitalis, tranquilizers
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