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20 Cards in this Set
- Front
- Back
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What is meant by "unstable" bradycardia? |
Unstable bradycardia refers to bradycardia associated with signs and symptoms suggestive of inadequate perfusion:
Hypotension
Altered mental status
Ongoing ischemic chest pain
Evidence of acute pulmonary edema |
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What are the different types of AV block? |
There are four:
First degree (conduction delay rather than a true block)
Second degree - Mobitz type I
Second degree type - Mobitz type II
Third degree
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What is first degree AV block? How does it appear on EKG? |
First degree AV block refers to a consistent DELAY in conduction through the AV node.
There is complete AV association: each atrial impulse is conducted through the AV node and His-Purkinje system to the ventricles. As such, first degree "block" is not a true block at all but rather consistently delayed or slowed conduction through the AV node.
EKG:
Uniform prolongation of the PR interval (>0.20s)
P-P interval: regular
R-R interval: REGULAR (complete AV association results in REGULAR ventricular rhythm) |
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What defines second degree AV block? |
Second degree AV block is defined by the presence of INTERMITTENT COMPLETE BLOCK in conduction between the atria and ventricles.
There are two types: Mobitz type I and Mobitz type II.
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What defines Mobitz type I second degree block?
How does it appear on EKG? |
Mobitz type I is defined by progressively decremental (decreasing) conduction through the AV node that eventually culminates in a completely blocked impulse.
Physiologically, there is progressive slowing of each subsequent impulse through the AV node until finally an impulse arrives at a time when the node is absolutely refractory.
In Mobitz type I, the lesion lies within the AV node itself.
On EKG:
Progressive lengthening of the PR interval until a normally ocurring P wave is not followed by a QRS complex.
There is only ONE non-conducted P wave. This completely blocked P wave is on time and all PP intervals are equal.
P-P interval: regular
R-R interval: IRREGULAR
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What defines Mobitz type II second degree block?
How does it appear on EKG? |
Mobitz type II is defined by episodic/unpredictable intermittent complete block.
The lesion lies further down the conduction pathway in the His-Purkinje or both bundle branches ("infranodal block").
Mobitz type II has a higher risk of complete heart block than type I and is usually an indication for pacemaker.
On EKG:
Unpredictably non-conducted P wave not followed by a QRS. The failed conduction is NOT preceded by a change in the PR interval.
P-P interval: regular
R-R interval: IRREGULAR (variable conduction) |
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What defines third degree AV block?
How does it appear on EKG? |
Third degree block is defined by complete AV dissociation: there is complete failure of the AV node to conduct any impulses from the atria to the ventricles.
An escape rhythm develops that is either junctional or ventricular.
On EKG:
AV dissociation:
P-P interval regular
R-R interval REGULAR (as a result of a junctional or ventricular escape rhythm) |
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What is the PR interval?
Physiologically, what does the PR interval represent?
What is the normal length of the PR interval? |
PR interval = time between BEGINNING of P wave to the beginning of the QRS complex
Represents time between the onset of atrial depolarization and onset of ventricular depolarization. The isoelectric PR SEGMENT represents delayed condutin within the AV node.
Normal duration = 0.12 - 0.20 seconds
3-5 small boxes
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What is the typical rate of a junctional escape rhythm?
What is the typical rate of a ventricular escape rhythm? |
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Describe an approach to determining the type of heart block. |
1) Are there P waves? Is the sinus node blocked?
2) If there is sinus nod activity, assess the regularity of the ventricular impulses (R-R interval).
3) If the ventricular rhythm is REGULAR (regular R-R interval), the block is either first degree or third degree. Assess for AV dissociation.
In first degree "block" the ventricular rhythm is regular because there is no block: each atrial impulse is consistently conducted to the ventricles.
In third degree block the ventricular rhythm is regular because the block is complete: each atrial impulse is consistently blocked and a regular junctional or ventricular escape rhythm develops.
4) If the ventricular rhythm is irregular, a second-degree block is present (second degree block defined by variable conduction).
Check the pattern of conduction: progressively decremental conduction = Mobitz type I, episodic block = Mobitz type II
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Describe the ACLS algorithm for bradycardia. |
1) Assess the appropriateness of the heart rate for the patient's clinical condition (HR usually <50 if bradyarrhythmia)
2) Primary survey and intervention: ABCs with associated adjuncts and interventions
Clinical assessment of airway, oxygenation, ventilation, and circulation
Adjunctive tools in the primary assessment: oximetry, blood pressure, cardiac monitoring, 12-lead EKG.
Provide primary interventions: airway management, oxygen, assisted ventilation, IV access and fluids
3) Identify and treat the underlying cause
4) If the patient is unstable (signs/symptoms of hypoperfusion):
Give atropine and re-assess
If atropine fails, prepare for transcutaneous pacing and (?or) vasopressor infusion |
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What is the dose of atropine for unstable bradycardia? |
0.5 mg IV bolus
May be repeated every 3-5 minutes
Maximum 3 mg (6 doses) |
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Describe the technique of initiating transcutaneous pacing in a patient with unstable bradycardia. |
... |
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What vasopressors does ACLS recommend in the management of unstable bradycardia? |
Dopamine
Epinephrine |
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What is the dose of dopamine in the management of unstable bradycardia (as per ACLS guidelines): |
Note that dopamine is dosed as mg/kg
Start at 2 mcg/kg/minute and titrate up as needed
Maximum dose: 10 mck/kg/minute |
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What is the dose of epinephrine in the management of unstable bradycardia (as per ACLS guidelines): |
2-10 mcg/minute
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What are the potential causes of heart block? |
Drugs and disease...
Drugs: digitalis, calcium-channel blockers, beta-blockers, antiarrhythmic drugs
Disease: acute and chronic
Acute:
Acute cardiac ischemia, esp...
Hyperkalemia
Chronic: hyperthyroidism, sequela of old ischemia, cardiomyoptathy, myocarditis (classically Lyme, SLE), familial AV conduction block, "idiopathic progressive cardiac conduction disease" (fibrosis and sclerosis of the conduction system) |
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What is considered the first-line, antidotal treatment for beta-blocker poisoning? |
Glucagon |
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What is considered the first-line, antidotal treatment for calcium-channel blocker poisoning? |
Glucagon |
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What is the antidote for digoxin? |
Digi-bind |
