Chapter 5 Flashcards
Why is there a delay in the electrical impulse?
Allows the atria to contract and complete filling of ventricles before the next ventricular contraction
Job of the Bundle of His?
Connects AV node with bundle branches
Has pacemaker cells capable of discharging at a rhythmic rate of 40-60bpm
When would the AV junction assume responsibility for pacing the heart? Why?
The AV junction will assume responsibility when the SA node fails to discharge (sinus arrest)
SA node impulse is generated but blocked as it exists the SA node (SA block)
The rate of discharge of the SA node is slower than that of the AV junction (sinus bradycardia or the slower phase of the sinus arrhythmia)
An impulse from the SA node is generated and is conducted through the atria but is not conducted to the ventricles (AV block)
In what direction does the electrical impulse travel to activate the atria?
If the AV junction paces the heart, the electrical impulse must travel in a backward (retrograde) direction to activate the atria
Sinus arrest
Missing beat - SA node not firing properly - after missing beat, next one is late
AV junction (P waves)
- With a sinus rhythm, the P wave is positive (upright) because the wave of depolarization is moving toward the positive electrode
- P wave associated with a junctional beat may be inverted (retrograde) and appear before the QRS
- P wave may be hidden by the QRS
- P wave can appear after the QRS
Premature Junctional Complexes (PJC)
Occurs when an irritable site within the AV node junction fires before the next expected sinus beat
QRS will usually measure 0.11sec or less (narrow QRS - supraventricular)
Often followed by a noncompensatory (incomplete) pause
May occur in patterns
How to recognize PJCs?
Rhythm: irregular because of the premature beats
Rate: usually within normal range but depends on underlying rhythm
P waves: may occur before, during or after the QRS; if visible, the P wave is inverted in leads II, III, and aVF
PR interval: if a P wave occurs before the QRS, the PR interval will usually be 0.12 sec or less; if no P wave occurs before the QRS, there will be no PR interval
QRS duration: 0.11sec or less unless abnormally conducted
What causes PJCs?
- Acute coronary syndromes
- Digitalis toxicity
- Electrolyte imbalance
- Heart failure
- Mental and physical fatigue
- Rheumatic heart disease
- Stimulants (caffeine, tobacco, cocaine)
- Sympathomimetics
9.valvular heart disease
What to do about PJCs?
Most individuals with PJCs are asymptomatic
PJCs may lead to symptoms of palpitations or the feeling of skipped beats
Lightheadedness, dizziness, and other signs of decreased cardiac output can occur if PJCs are frequent
If PJCs occur because of the ingestion of stimulants or digitalis toxicity, these substances should be withheld.
Junctional Escape Beats
Junctional escape beat originates in the AV junction and appears LATE (after the next expected beat of the underlying rhythm
A JEB is protective - preventing cardiac standstill
Characteristics of a Junctional escape beat
Rhythm: irregular because of the late beat
Rate: depends on rhythm
P waves: inverted before or after QRS or absent
PR interval: 0.12-0.20sec and constant
QRS duration: 0.11sec or less (narrow)
Junctional Escape Rhythm
When you have 3 JEB in a row, it is called a junctional escape rhythm
Several sequential junctional escape beats
Intristic rate of the AV junction is 40-60bpm
If the AV junction paces the heart at a rate slower than 40bpm, the resulting rhythm is called junctional bradycardia
How to recognize junctional rhythm?
Rhythm: regular
Rate: 40-60bpm
P waves: may occur before, during or after the QRS; if visible, the P wave is inverted in leads II, III, and aVF
PR interval: if P wave occurs before QRS, the PR interval will usually be 0.12sec or less; if no P wave occurs, there will be no PR interval
QRS duration: 0.11sec or less unless abnormally conducted (narrow)
Causes of junctional rhythm
- Acute coronary syndrome (notably inferior wall MI)
- Effects of medications including amiodarone, beta blockers, calcium channel blockers, digitalis
- Hypokalemia
- Immediately after cardiac surgery
- Increased parasympathetic tone
- Obstructive sleep apnea
- Rheumatic heart disease
- SA node disease
- valvular disease
What to do about junctional rhythm? (asymptomatic)
Patient may be asymptomatic or may experience signs and symptoms associated with the slow heart rate and decreased cardiac output
If the patient is experiencing symptoms, try to determine their frequency, timing, duration, severity, longevity, circumstances, triggers, and alleviating factors
What to do about junctional rhythm? (Signs and symptoms related to slow heart rate)
- Apply a pulse oximeter
- Administer supplemental oxygen, if indicated
- Establish intravenous (IV) access
- Obtain a 12 lead ECG
- Administer IV atropine
- Reassess the patient; continue monitoring
Accelerated Junctional Rhythm
An ectopic rhythm caused by abnormal automaticity of the bundle of his
Results in regular ventricular response at rate of 60-100bpm
How to recognize atrial junctional rhythm?
Rhythm: regular
Rate: 60-100bpm
P waves: may occurs before, during or after the QRS; if visible, the P wave is inverted in leads II, III, and aVF (retrograde P waves)
PR intervals: if a P wave occurs before the QRS, the PR interval will usually be 0.12sec or less; if no P wave occurs before the QRS, no PRI
QRS duration: 0.11sec or less unless abnormally conducted (narrow)
What causes AJR?
- Acute myocardial infraction
- Cardiac surgery
- Chronic obstructive pulmonary disease
- Digitalis toxicity
- Hypokalemia
- Rheumatic fever
What to do about AJR?
Patient may be asymptomatic but monitor closely
If the rhythm is caused by digitalis toxicity, this medication should be withheld
Junctional tachycardia
Ectopic rhythm that begins in the bundle of his
Exists when three or more sequential PJCs occur at a rate more than 100bpm
How to recognize junctional tachycardia?
Rhythm: ventricular rhythm usually regular, but may be irregular
Rate: 101-220bpm
P waves: may occur before, during or after the QRS; if visible the P wave is inverted in leads II, III, aVF (retrograde P waves - before QRS)
PR interval: none
QRS duration: 0.11sec or less - narrow QRS
Nonparoxysmal (gradual onset) junctional tachycardia
Benign dysrhythmia that is usually associated with a gradual increase in rate
Rarely exceeds 120bpm
Paroxysmal junctional tachycardia
Starts and ends suddenly
Often precipitated by a PJC
Ventricular rate is generally faster, at a rate of 140bpm or more
What causes junctional tachycardia?
Disorder of impulse formation (automaticity)
Uncommon in adults but may occur because of
-acute coronary syndromes
-digitalis toxicity
-heart failure
-theophylline administration
What to do about junctional tachycardia?
Patient may be asymptomatic
With sustained ventricular rates of 150bpm or more, the patient may complain of fatigue, palpitations or chest discomfort or may experience syncope
Decreased cardiac output may result because of the fast ventricular rate
Depending on severity of the symptoms
Observe patient and if symptomatic:
-apply pulse oximeter, administer oxygen
-establish IV access
-obtain 12 lead ECG
-Vagal maneuvers, adenosine
-Possible beta blocker, calcium channel blocker, if no contraindications exist
-synchronized cardioversion is not indicated
Select the correct statements about PJCs
A. A noncompensatory (incomplete) pause often follows a PJC
B. Unlike premature atrial complexes, PJCs do not occur in patters
C. If seen, the P wave of a PJC is negative and may appear before or after the QRS complex
D. A PJC begins within the AV junction and appears earlier than the next expected beat of the underlying rhythm
A, C, D
A PJC occurs when an irritable site within the AV junction fires before the next essay no impulse is ready to fire, interrupting the underlying rhythm. PJCs may occur as single beats or patterns (couplets, bigeminy, trigeminy, quadrigeminy). Noncompensable (incomplete) often follows a PJC. This pause represents the delay during which the essay note resets its rhythm for the next beat. When the P wave of a PJC is seen, it is a negative and may appear before or after the QRS complex
An accelerated junctional rhythm is identified by a regular ventricular response occurring at the rate of:
A. 20 to 40bpm
B. 40 to 60bpm
C. 61 to 100bpm
D. 101 to 180bpm
C
An accelerated junctional rhythm is dysrhythmia originating in the AV bundle with a ventricular rate between 61 and 100 Bpm
The term junctional bradycardia is used to describe a rhythm that is junctional in origin with:
A. An atrial rate of 40 to 60bpm
B. An atrial rate slower than 60bpm
C. A ventricular rate of 40 to 60bpm
D. A ventricular rate slower than 40bpm
D
If the AV junction paces the heart at a rate slower than 40bpm, the resulting rhythm is called junctional bradycardia. This wording may seem confusing because the AV junctions normal pacing rate (40 to 60bpm) is Bradycardic. However, the term junctional bradycardia refers to a rate slower than normal for the AV junction.
When viewing a junctional rhythm in lead II, where is the P wave location on the ECG if ventricular depolarization precedes atrial depolarization?
A. Before the QRS complex
B. During the QRS complex
C. After the QRS complex
C
If the AV junction paces the heart, the electrical impulse must travel in a backward (retrograde) direction to activate the atria. If a P wave is seen, it will be converted in leads II, III, and aVF because the impulse is traveling away from the positive electrode. If the atria depolarize before the ventricles, an inverted P will be seen before the QRS complex, and the PR interval will usually measure 0.12 seconds or less. The interval is shorter than usual because an impulse that begins in the AV junction does not have to travel as far to stimulate the ventricles. The atria ventricles depolarize at the same time, a P wave will not be visible because it will be hidden in the QRS complex. When the atria are depolarized the ventricles, the P typically distorts the end of the QRS complex and an inverted P wave will appear after the QRS
In rhythms originating from the AV junction, the QRS duration is typically _________ or less unless an intraventricular conduction delay exists
A. 0.04sec
B. 0.11sec
C. 0.14sec
D. 0.20sec
B
The QRS duration associated with a rhythm that begins in the AV junction measures 0.11 second or less if conduction through the bundle branches, Purkinje fiber, and ventricles is normal
Select the correct statements regarding junctional dysrhythmias
A. The intrinsic rate of the AV junction is 40 to 60bpm
B. Junctional dysrhythmias may be seen in acute coronary syndromes
C. An accelerated junctional rhythm is a potentially life threatening dysrhythmia
D. The ventricular rhythm associated with junctional dysrhythmias is usually very regular
A, B, D
The patient with an accelerated junctional rhythm is usually a symptomatic because the ventricular rate is 61 to 100 bpm which is the same rate as sinus rhythm
The primary waveform used to differentiate PJCs from PACs is the
A. P wave
B. Q wave
C. R wave
D. T wave
A
You can usually tell the difference between a PAC and a PJC by the P wave. A PAC typically has an upright P way before the QRS complex in Leads II, III, aVF. A P we may or may not be present with a PJC. If a P is present, it is inverted (retrograde) and may precede or follow the QRS. PJCs can be misdiagnosed when the P wave of a PAC is buried in the proceeding T wave
A 63 year old man is complaining of dizziness that began about 45min ago while cleaning his garage. Because the patients oxygen level on room air was 88%, supplemental oxygen is being administered. The cardiac monitor has been applied, revealing the rhythm in Fig. 5.10. A coworker is attempting to establish intravenous access.
Which of the following statements are true about this patients cardiac rhythm?
A. The atrial rhythm is regular
B. The QRS complex is narrow
C. ST segment elevation is present
D. The ventricular rhythm is regular
E. There are more P waves than QRS complexes
B, D
In this rhythm strip the atrial rate and rhythm cannot be determined because P waves are not visible. The ventricular rhythm is regular and the QRS is narrow, measuring 0.08 seconds
A 63 year old man is complaining of dizziness that began about 45min ago while cleaning his garage. Because the patients oxygen level on room air was 88%, supplemental oxygen is being administered. The cardiac monitor has been applied, revealing the rhythm in Fig. 5.10. A coworker is attempting to establish intravenous access.
The rhythm shown on the cardiac monitor is
A. Sinus bradycardia
B. Junctional bradycardia
C. Junctional escape rhythm
D. Accelerated junctional rhythm
B
The cardiac monitor shows junctional bradycardia at 32 bpm with ST segment depression and inverted T waves
A 63 year old man is complaining of dizziness that began about 45min ago while cleaning his garage. Because the patients oxygen level on room air was 88%, supplemental oxygen is being administered. The cardiac monitor has been applied, revealing the rhythm in Fig. 5.10. A coworker is attempting to establish intravenous access.
The patients blood pressure is 82/50mm hg. Ventilation is 16. He states his normal blood pressure is about 130/80mm hg. The patient denies chest discomfort and states that he takes no prescription medication. His skin is cool, pink and moist, and his breath sounds are clear. Intravenous access has been successfully established. Based on the information provided, which of the following states is true regarding this patient situation?
A. Because the patient is symptomatic with this rhythm, a vagal maneuver should be attempted
B. The patient is symptomatic with this rhythm. Obtain a 12 lead ECG then administer atropine IV
C. Therapeutic interventions are not indicated because there is no evidence of ST segment elevation on the cardiac monitor
D. Although the patient is complaining of dizziness, this symptom does not warrant any further intervention other than cardiac monitoring at this time
B
Although there is no evidence of ST segment elevation on the cardiac monitor , this patient is symptomatic with his heart rate, evidenced by his dizziness and hypertension. Treatment of symptomatic bradycardia should include applying a pulse oximeter, administering supplemental oxygen (if indicated), and establishing IV access, which has already been done. Obtain a 12 lead ECG and then administer atropine IV. Reassess the patient response to your interventions and continue monitoring. Because vagal maneuvers are used to attempt to slow the heart rate of some tachycardia, and this patient is bradycardic, vagal maneuvers are contraindicated in the situation
