Chapter 2 Flashcards
(99 cards)
1
Q
What is antrioventricular (AV) bundle also called?
A
Bundle of His
2
Q
What are the two types of cardiac cells?
A
- Myocardial cells
- Pacemaker cells
3
Q
Myocardial cells
A
- Working or mechanical cells
- Responsible for contraction
- Muscle cell
4
Q
Pacemaker cells
A
- Specialized cells of electrical conduction system that are able to form electrical impulses spontaneously and to alter the speed of electrical conduction
- Start spark (creating impulse)
5
Q
What are the 4 properties of cardiac cells?
A
- Automaticity
- Excitability
- Conductivity
- Contractility
6
Q
Automaticity (cardiac cells)
A
Ability of pacemaker cells to initiate an electrical impulse without being stimulated from another source
Able to create impulse on its own
7
Q
Excitability (cardiac cells)
A
Ability of cardiac muscle cells to respond to an outside stimulus
Sensitive to stimulation and will contract
8
Q
Conductivity (cardiac cells)
A
Ability of a cardiac cell to receive an electrical stimulus and conduct that impulse to an adjacent cardiac cell
Ability to pass the electrical stimulus to other cardiac cells
9
Q
Contractility (cardiac cells)
A
Contract and create pressure
10
Q
What does the P wave represent?
A
Atrial depolarization
11
Q
What does the QRS wave represent?
A
Ventricular depolarization
12
Q
What does the ST segment and ST wave represent?
A
Ventricular REpolarization (mechanical)
13
Q
Refractoriness
A
Recovery time cells need after being discharged before they are able to respond to stimulus
14
Q
Effective refractory period (ERP)
A
Absolute refractory period - nothing happens - no way cells can do anything
15
Q
Relative refractory period (RRP)
A
Chance the cells can conduct again
Some cardiac cells have repolarized to their threshold potential and thus can be stimulated to depolarize to a stronger than normal stimulus
16
Q
Sinoatrial (SA) Node
A
- Primary pacemaker
- Supplied by RIGHT coronary artery in most people
- Rate: 60-100 beats / minute
Creates and starts all stimulus
Located right atrium right below superior vena cava
17
Q
What is the secondary pacemaker site?
A
Includes atrialventricular (AV) node, junction, and purkinje fiber’s cells
18
Q
In what situations does the secondary pacemaker sites assume responsibility?
A
- SA nodes fires too slowly due to suppression of medications
- SA node fails to generate impulse because of disease, surgical removal, suppression by meds.
- SA node is blocked by action potential
- Firing rate of ectopic site becomes faster than that of the SA node
19
Q
Bundle of His
A
Connects AV node with bundle branches
Conducts impulse to right and left bundle branches
Beats 40 to 60 beats / minute
20
Q
Accessory pathway
A
When an atypical pathway bypasses the AV node and bundle
21
Q
Atrialventricular (AV) node
A
-right of the tricuspid valve
1. Works as a gatekeeper
2. Once right atrium starts to contract, the AV node does a physiological delay to give time for right ventricle to be ready for contraction
22
Q
Purkinje Fibers
A
- Receive impulse from bundle branches
- Relay it to ventricular myocardium
- Intrinsic pacemaker rate of 20-40 beats / minute
23
Q
What are some of the uses of a electrocardiographicmonitoring (ECG)?
A
- Recognize sudden cardiac arrest and improve time to defribilation
- Recognize deteriorating conditions that may lead to life threatening, sustained dysrhythmias
- To assist in the diagnosis of dysrhythmias or causes of symptoms and guide appropriate management
- Monitor patients heart rate
24
Q
What information can the ECG provide?
A
- Orientation of the heart in the chest
- Conduction disturbances
- Electrical effects of medications and electrolytes
- Mass of cardiac muscles
- Presence of ischemic damage
25
What does the ECG NOT do?
1. Does not provide information about the mechanical (contractile) condition of the myocardium)
2. Mechanical activity is evaluated by assessment of pulse and blood pressure
26
Where are the electrodes applied?
Electrodes are applied at specific locations on the chest wall and extremities to view the hearts electrical activity from different angles and planes
27
What areas do leads allow for viewing?
Allow for viewing the heart’s electrical activity in the frontal and horizontal (transverse) planes
28
Standard limb leads
Leads I, II, and III (right arm electrode is always negative. Left leg electrodes are always positive)
Einthoven’s triangle
Six leads view the heart in the frontal plane
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Lead I
Records difference in electrical potential between left arm (+) and right arm (-) electrodes
Views lateral wall of left ventricle
30
Lead II
Records difference between in electrical potential between left leg (+) and right arm (-) electrodes
Viewed inferior surface of left ventricle
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Lead III
Records difference in electrical potential between left leg (+) and left arm (-) electrodes
Views inferior surface of left ventricle
32
Augmented Limb Leads
Leads aVR, aVL, aVF
-a = augmented
-V = voltage
-R = right arm
-L = left arm
- F = Foot (usually of the left leg)
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Lead aVR
Views the heart from the right shoulder
Waveforms are typically negative
34
Lead aVL
Viewed the heart from the left arm
Oriented to the lateral wall of the left ventricle
35
Lead aVF
Views the heart from the left foot (leg)
Views the inferior surface of the left ventricle
36
Lead aVF
Views the heart from the left foot (leg)
Views the inferior surface of the left ventricle
37
Right chest leads
Right chest lead placement is identical to the placement of the stand chest leads except that it is done on the right side of the chest
If time does not permit obtaining all the right chest leads, the lead of the choice is V4R
38
Posterior chest leads
Lead V7 is placed at the posterior axillary line
Lead V8 is placed at the angle of the scapula
Lead V9 is placed over the left border of the spine
39
What are some uses for the ambulatory cardiac monitoring (AECG) system?
1. Determine association between patients symptoms and cardiac rhythm disturbances
2. Detect myocardial ischemia and to evaluate the efficacy of anti-ischemic medications in patients with coronary artery disease
3. Assess the patients risk of dysrhythmias after myocardial infraction
4. Assess the efficacy of medications on the cardiac conduction system, the patients cardiac rhythm, or both
5. Aid in correlating patients symptoms with dysrhythmias and evaluating symptomatic patients for pacemaker implantation
6. Assess the function of implanted devices such as a pacemaker or implantable cardioverter-defibrillator
7. Assess the efficacy of ablation procedures
40
Different types of monitors
1. Holter monitor
2. Event monitor
3. External loop recorder
4. External patch recorder
5. Implantable loop recorders
6. Portable handheld ECG monitors
41
What does each axis represent on the ECG paper?
Vertical - voltage/amplitude (how high is the electricity
Horizontal - duration (time - each square is 1mm {0.04sec} bigger square is 5mm {0.20sec})
42
Horizontal axis
Time:
Small box - 0.04sec
Bigger box - 0.20 sec
43
Vertical axis
Size or amplitude of waveform is measured in millivolts (voltage) or millimeters (amplitude)
Small square - 0.1mV
Bigger square - 0.5mV
44
Baseline (isoelectric line)
A straight line recorded when electrical activity is not detected
45
Waveform
Movement away from the baseline in either a positive or negative direction
46
Segment
A line between waveforms; named by the waveform that precedes or follows it
47
Complex
Several waveforms
48
Normal P wave characteristics?
1. Smooth and rounded
2. No more than 2.5mm in height (0.25mV)
3. No more than 0.12sec in duration (3 squares)
4. Positive in leads I, II, III, aVL, aVF, and V2 through V6
5. May be biphasic in V1
49
P, QRS wave
P wave - atrial depolarization
QRS wave - ventricular depolarization
50
Normal QRS complex
1. Measure the QRS complex with the longest duration and clearest onset and end
2. Normal duration of 0.075 to 0.11 sec in adults
3. QRS amplitude varies among leads
SN - always try to find the ones that are clear
51
T wave
Represents ventricular repolarization
Normal T waves:
-slightly symmetric
-negative in aVR, may be positive or negative in leads aVL, III, and V1
-Normally upright in leads I, II, and V3 through V6
-Usually 0.5mm or more in height in leads I and II
-usually 5mm or less in height in any limb lead or 10mm or less in any chest lead
52
U wave
1. Represents late repolarization of the purkinje fibers
2. Normally small, round, symmetric
3. Most easily seen when the heart rate is slow
4. Usually appear in the same direction as the T wave that precedes it
53
Segment
Line between waveforms
Named by waveform that precedes or follows it
54
What are some important segments?
PR segment
ST segment
TP segment
55
J point
The junction where the QRS complex and the ST segment meet is the J point
To assess ST elevation or depression
-identify the onset of the QRS
-locate the J point
-compare ST segment with reference point
56
PR interval
P wave + PR segment = PR interval
Normally measures 0.12 to 0.20 sec in adults; may be shorter in children and longer in older adults
Reflects total supraventricular activity
57
Abnormal PR interval
Long PR interval (greater than 0.20 sec) - indicates the impulse was delayed as it passed through the atria, AV node, or AV bundle
Short PR interval (less than 0.12 sec) - may be seen when the impulse originates in the atria close to the AV node or the AV bundle
0.12 - 0.20 = normal
58
Artifact
Distortion of an ECG tracing by electrical activity that is noncardiac in origin
Can mimic various cardiac dysrhythmias, including ventricular fibrillation
Patient evaluation is essential before initiating any medical intervention
59
Systematic rhythm interpretation
1. Assess regularity (atrial and ventricular)
2. Assess rate (atrial and ventricular)
3. Identify and examine waveforms
4. Assess intervals (e.g. PR, QRS, QT) and examine ST segments
5. Interpret the rhythm and assess its clinical significance
60
Regularity
1. Ventricular - compare R-R intervals
2. Atrial - compare P-P intervals
3. If the rhythm is regular, the intervals will be equal (measure the same)
4. If the intervals are unequal, the rhythm is considered irregular
61
Six-second method
Ventricular rate
1. Count the number of complete QRS complexes within a period of 6 second
2. Multiply number by 10 to determine the number of QRS complexes in 1min
62
Large box method
Count the number of large boxes between two consecutive waveforms (R-R interval or P-P interval) and divide into 300
Best used if the rhythm is regular
Alternatively, select an R wave that falls on a dark verticals line
Number the next 6 consecutive dark verticals lines as follows: 300, 150, 100, 75, 60, and 50
Note where the next R wave falls in relation to the six dark verticals lines already marked. This is the heart rate
63
Small box method
Count the number of small boxes between two consecutive waveforms (R-R interval or P-P interval) and divide into 1500
Time consuming, but accurate
64
When an ECG machine is properly calibrated, a 1-millivolt (mV) electrical signal will produce a deflection measuring exactly _______ tall?
A. 1mm
B. 5mm
C. 10mm
D. 20mm
C
An ECG machines sensitivity must be calibrated so that a 1mV electrical signal will produce a deflection measuring exactly 10mm tall. When properly calibrated, a small box is 1mm high (0.1mV) and a large box (equal to five small boxes) is 5mm high (0.5mV)
65
Fifteen large boxes equal an interval of _________ on ECG paper?
A. 1 sec
B. 3 sec
C. 6 sec
D. 10sec
B
Five large boxes, each consisting of five small boxes, represent 1 second. 15 large boxes equal 3 sec. Thirty large boxes represent 6sec.
66
The QRS complex ____________
A. Normally follows each P wave
B. Represents ventricular depolarization
C. Normally measures 0.20sec or less
D. Generally represents right ventricular electrical activity
A, B
A QRS complex normally follows each P wave. The QRS complex represents ventricular depolarization. Ventricular repolarization is recorded on ECG as the ST segment and T wave. In adults, the normal duration of the QRS complex is 0.11 sec or less. If an electrical impulse does not follow the normal ventricular conduction pathway, it will take longer to depolarize the myocardium. This delay in conduction through the ventricles produces a wider QRS complex. Because of its greater muscle mass, the QRS complex generally represents the left ventricles electrical activity
67
The SA node _______
A. Is normally the hearts primary pacemaker
B. Is supplied by sympathetic and parasympathetic nerve fibers
C. Generates electrical impulses at a rate of 40-60 beats/min
D. Is located at the junction of the superior vena cava and right atrium
A, B, D
The SA node is the hearts primary pacemaker because it has the fastest firing rate of the heats pacemaker sites. Sympathetic and parasympathetic nerve fibers richly supply the SA node. The SA node is specialized conducting tissue located in the upper posterior part of the right atrium where the superior vena cava and the right atrium meet. The SA node generates electrical impulses at a rate of 60 to 100bpm
68
Which of the following surfaces of the heart are not directly viewed when using a standard 12-lead ECG?
A. Right ventricle
B. Lateral surface of the left ventricle
C. Inferior surface of the left ventricle
D. Anterior surface of the left ventricle
E. Posterior surface of the left ventricle
A, E
The right ventricle and posterior surface of the left ventricle are not directly viewed when using a standard 12 lead ECG. Right chest leads and posterior chest leads, respectively, are used for this purpose
69
On the ECG, total supraventricular activity is reflected by the:
A. TP segment
B. PR interval (PRI)
C. QT interval
D. QRS duration
B
The P wave plus the PR segment equals the PRI; thus, the PRI reflects total supraventricular activity. The QT interval (which includes the QRS complex, ST segment, and T wave) represents total ventricular activity; this is the time from ventricular depolarization (activation) to repolarization (recovery)
70
Which of the following are disorders of impulse formation?
A. Reentry
B. Triggered activity
C. Conduction blocks
D. Altered automaticity
B, D
Altered automaticity and triggered activity are disorders of impulse formation. Conduction blocks and reentry are disorders of impulse conduction.
71
U Waves:
A. Represent repolarization of the purkinje fibers
B. Are most easily seen when the heart rate is slow
C. Are often associated with elevated potassium levels
D. Usually appear in the opposite direction as the T waves that precede them
A, B
A U wave is a small waveform that, when seen, follows the T wave. U waves usually appear in the same direction as the T waves that preced them. The U wave is thought to represent the late repolarization of the purkinje fibers. However, some cardiologist believe that U waves are simply two part T waves resulting from a longer action potential duration in some ventricular myocardial cells. U waves are most easily seen when the heart rate is slow and are difficult to identify when the rate exceeds 95bpm. Possible causes of prominent U waves include central nervous system disease, electrolyte imbalance (hypokalemia), hyperthyroidism, long QT syndrome, and medications
72
You are caring for a 64 year old man complaining of chest pain that he rates a 9/10. He says his symptoms began 20min ago while moving boxes in his garage.
You are applying ECG leads to this patient and will be using lead V1 for continuous monitoring. This lead is an example of a(n):
A. Chest lead
B. Horizontal lead
C. Standard limb lead
D. Augmented limb lead
A
Lead V1 is a chest lead and views the heart in the horizontal plane
73
You are caring for a 64 year old man complaining of chest pain that he rates a 9/10. He says his symptoms began 20min ago while moving boxes in his garage
Lead V1 views the
A. Right ventricle
B. Interventricular septum
C. Lateral surface of the left ventricle
D. Posterior surface of the left ventricle
B
Leads V1 and V2 view the interventricular septum
74
You are caring for a 64 year old man complaining of chest pain that he rates a 9/10. He says his symptoms began 20min ago while moving boxes in his garage
When analyzing this patients ECG rhythm, the first areas of the rhythm strip that should be assessed are:
A. Rate
B. P waves
C. Intervals
D. Regularity
E. Segments
F. QRS complexes
A, D
When analyzing a rhythm strip, begin by assessing regularity (atrial and ventricular) and rate (atrial and ventricular)
75
You are caring for a 64 year old man complaining of chest pain that he rates a 9/10. He says his symptoms began 20min ago while moving boxes in his garage
The patients ECG shows four large squares between two consecutive R waves. Based on this information, you calculate the patient’s heart rate to be _________beats/min:
A.50
B.75
C.100
D.150
B
Using the large box (rule of 300) method to calculate heart rate, four large boxes between two consecutive R waves equals a heart rate of 75bpm (300/4)
76
You are caring for a 64 year old man complaining of chest pain that he rates a 9/10. He says his symptoms began 20min ago while moving boxes in his garage
When analyzing the leads facing the affected area of the heart, ECG evidence of myocardial injury is displayed as:
A. Inverted P waves
B. ST segment elevations
C. Prolonged PRIs
D. ST segment depression
B
In a patient experiencing an acute coronary syndrome, ECG evidence of myocardial injury is displayed as ST segment elevation in the leads facing the hearts affected area
77
You are caring for a 64 year old man complaining of chest pain that he rates a 9/10. He says his symptoms began 20min ago while moving boxes in his garage
Which of the following statements is true regarding analysis of the ST segment on the patients ECG?
A. ST segment displacement should be measured at a point 0.12sec after the J point.
B. ST segment elevation viewed in lead II would be considered clinically significant if also seen in lead III or aVF
C. Based on this patients age, ST segment elevation seen in lead II would be considered clinically significant if elevated more than 0.5mm
D. Use the PRI as the baseline from which to evaluate the degree of ST segment displacement from the isoelectric line
B
The onset of the QRS complex is used as the reference point from which to evaluate the degree of displacement of the ST segment from the isoelectric line. If ST segment displacement is present, note the number of millimeters of deviation (at the J point) from the reference point. When ECG changes of myocardial ischemia, injury or infarction occur, they are not found in every ECG lead. Findings are considered significant if viewed in two or more leads looking at the same or adjacent heart area. If these findings are seen in leads that look directly at the affected area, they are called indicative changes. Indicative changes are significant when they are seen in two anatomically contiguous leads. Two leads are contiguous if the look at the same or adjacent area of the heart or they are numerically consequitive chest leads. Remember that leads DII, DIII, and aVF views the inferior wall of the left ventricle. Therefore, in this patient situation, ST segment changes viewed in lead DII would be considered clinically significant if elevated more than 1mm and also seen in lead DIII and aVF
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Interval
A waveform and a segment
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In adults, what is the normal duration of the QRS complex?
0.11sec or less
80
The amplitude of a waveform is measured in __________
Millimeters
81
What waveform is always negative?
Q wave
82
Waveform
Movement away from the baseline in either a positive or negative direction
83
What is the normal duration of the PRI?
0.12sec to 0.20sec
84
What waveform is always positive?
R wave
85
On ECG paper, each horizontal 1mm box represents _________
0.04sec
86
Segment
A line between waveforms
87
How much do 15 large boxes represent on ECG paper?
3 seconds
88
What is the area called where the QRS complex and the ST segment meet?
J point
89
Complex
Several waveforms
90
What type of action potential occurs in the SA and AV nodes?
Slow response
91
Wave depolarization
A chain reaction that occurs from cell to cell in the hearts electrical conduction system until all the cells have been stimulated
92
Repolarization
The movement of charged particles across a cell membrane in which the inside of the cell is restored to its negative charge
93
What are some examples of anti arrhythmias that block sodium channels?
Procainamide and lidocaine
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Action Potential
The rapid sequence of voltage changes that occur across the cell membrane during the electrical cardiac cycle
95
What type of action potential occurs in normal atrial and ventricular myocardial cells and in the His-Purkinje fibers?
Fast response
96
Depolarization
The movement of ions across a cell membrane causing the inside of the cell to become more positive
97
What are some examples of anti arrhythmias that slow the rate at which calcium passes through the cells?
Verapamil and diltiazem
98
List uses for ECG monitoring
1. To immediate recognize sudden cardiac arrest and improve time to defibrillation
2. To recognize deteriorating conditions that may lead to life threatening dysrhythmias
3. To assess in the diagnosis of dysrhythmias or causes of symptoms and guide appropriate management
4. To monitor a patients heart rate
5. To evaluate the effects of disease or injury on heart function
6. To evaluate for signs of myocardial ischemia, injury and infraction
7. To evaluate pacemaker function
8. To evaluate a patients response to medication
9. To obtain recordings before, during and after medical procedure
99
List, in order, the first steps used in ECG rhythm analysis
1. Assess regularity (atrial and ventricular)
2. Assess rate (atrial and ventricular)
3. Identify and examine waveforms
4. Assess intervals (e.g. PR, QRS, QT) and examine ST segments
5. Interpret the rhythm and assess its clinical significance
