Harrison's Ch 232: Bradyarrhythmias

Question 1

Bradycardia results from a failure of either…

Answer 1

#impulse initiation
#impulse conduction

Question 2

Failure of impulse initiation may be caused by…

Answer 2

…depressed automaticity.

Question 3

What are the 2 most common causes of pathologic bradycardia?

Answer 3

#SA node dysfunction
#AV conduction block

Question 4

SA node dysfunctions increases in frequency during what decades of life?

Answer 4

5th & 6th

Question 5

What are some signs & symptoms that should make the clinician suspect SA node dysfunction?

Answer 5

Patients with sinus bradycardia and...
#Fatigue
#Exercise intolerance
#Syncope

Question 6

There is one reliable therapy for symptomatic sinus bradycardia in the absence of extrinsic & reversible etiologies. What is it?

Answer 6

Permanent pacemaking!

Question 7

What are the 2 classifications of SA nodal dysfunction? Why are they important?

Answer 7

#Intrinsic
#Extrinsic

This is important because extrinsic etiologies are usually reversible & should be corrected before we go slapping a pacemaker in someone!

Question 8

1/3 to 1/2 of patients with SA node dysfunction develop SVT. What two types are most common?

Answer 8

#Atrial fibrillation
#Atrial flutter

Question 9

Why would a bradycardic patient show improvement in symptoms after transitioning into atrial fib?

Answer 9

Increase in average heart rate!

Question 10

What is the goal of therapy for SA node dysfunction?

Answer 10

Alleviation of symptoms

Question 11

Primary therapy for patients with symptomatic SA nodal dysfunction?

Answer 11

Pacemaker implantation!

Question 12

What drugs can cause SA node dysfunction, & should be discontinued before pacemaker implantation is considered?

Answer 12

#Beta blockers
#Calcium channel blockers
#Digoxin
#Antiarrhythmics (Classes I & III)
#Adenosine
#Clonidine (& other sympatholytics)
#Lithium carbonate
#Cimetidine
#Amitriptyline
#Phenothiazines
#Narcotics (including methadone)
#Pentamidine

Question 13

What are some conditions that may cause SA node dysfunction?

Answer 13

#Hypothyroidism
#Sleep apnea
#Endotracheal suctioning (vagal manuevers)
#Hypothermia
#Increased ICP

Question 14

Some things to remember when classifying AV conduction disturbances:

Answer 14

#Functional or structural
#Severity (from 1st to 3rd degree)
#Location of block

Question 15

Which type of AV conduction dysfunction tends to be more easily reversed: functional or structural?

Answer 15

Functional. These are autonomic, metabolic/endocrine, or drug-related causes.

Question 16

What do we mean by a “structural” cause of AV dysfunction?

Answer 16

Fibrosis, usually.

Question 17

What diseases really like to screw up the AV conduction system?

Answer 17

#Lyme disease (usually transient/reversible)
#Chagas' disease (common in Latin America; more permanent conduction problems)
#Syphilis (Also more permanent)
#SLE
#RA
#Scleroderma
#Amyloidosis
#Sarcoidosis
#Hemachromatosis

Question 18

One of the more common, degenerative causes of AV conduction block is…

Answer 18

…progressive idiopathic fibrosis of the conduction system.

Question 19

Coronary artery disease produces which one: transient or persistent AV block?

Answer 19

TRICK QUESTION! It can be either.
#Coronary spasm: pretty transient
#Acute MI: transient in 10-25% of pts

Question 20

Which has higher mortality rates: an AV block associated with an inferior MI or an anterior MI? Which one happens more often?

Answer 20

The anterior MI-associated AV block has a worse prognosis & higher mortality, but AV conduction disturbances tend to happen more often in inferior MI.

Question 21

What is the most reliable treatment for patients with symptomatic AV conduction disease?

Answer 21

Pacing, either temporary or permanent

Question 22

Essential considerations in management of the AV conduction disturbance patient:

Answer 22

#Exclusion of reversible causes
#Need for temporary heart rate support based on condition

Question 23

What is transcutaneous pacing?

Answer 23

Pacing with leads on the skin: over the cardiac apex anteriorly, & posteriorly between the spine & scapula OR above the right nipple.

Question 24

What are limitations to transcutaneous pacing?

Answer 24

#FREAKING DISCOMFORT OW! BZZZZZT!
#Long-term failure to capture the ventricle bc of changes in lead impedance

Question 25

If we’re gonna need to pace for more than a few minutes, what’s the alternative to transcutaneous temporary pacing?

Answer 25

Transvenous temporary pacing!

Question 26

Class I Guidelines for Pacemaker Implantation in SA Node Dysfunction

Answer 26

1. SA node dysfunction with symptomatic bradycardia or sinus pauses
2. Symptomatic SA dysfunction because of essential long-term drug therapy without acceptable alternatives
3. Symptomatic chronotropic incompetence
4. Atrial fibrillation with bradycardia & pauses > 5 seconds

Question 27

Class IIa Guidelines for Pacemaker Implantation in SA Node Dysfunction

Answer 27

1. SA dysfunction with heart rates < 40 bpm without a clear & consistent relationship between bradycardia & symptoms
2. Same as above, only due to long-term essential drug therapy without acceptable alternatives
3. Syncope of unknown origin when major abnormalities of SA node are discovered or provoked by EP testing.

Question 28

Class IIb Guidelines for Pacemaker Implantation in SA Node Dysfunction

Answer 28

Mildly symptomatic patients with chronic waking heart rate < 40 bpm

Question 29

Class III Guidelines for Pacemaker Implantation in SA Node Dysfunction

Answer 29

1. SA dysfunction in asymptomatic patients, even those with heart rates < 40 bpm
2. SA dysfunction in which symptoms suggestive of bradycardia are not associated with a slow heart rate
3. SA dysfunction with symptomatic bradycardia due to non-essential drug therapy

Question 30

There are no randomized trials that evaluate the efficacy of pacing in patients with AV block. Why is that, & why on earth are we okay with it?

Answer 30

Because that’s pretty much the only trick in our bag! There are no other reliable therapies for AV block & untreated, high-grade AV block can definitely kill ya.

Question 31

Class I Guidelines for Pacemaker Implantation in Acquired AV Block

Answer 31

1. 3º or high-grade AV block at any anatomic level with: symptomatic bradycardia, essential drug therapy producing it, periods of asystole > 3 sec or any escape rate < 40 bpm while awake, post-op AV block not gonna resolve, ablation of the AV junction (duh?!), neuromuscular diseases with an affinity for the conduction system
2. 2º AV block with symptomatic bradycardia
3. Type II 2º degree block with wide QRS (symptoms or no)
4. Exercise-induced 2º or 3º AV block without ischemia
5. Atrial fib with bradycardia & pauses > 5 sec

Question 32

Class IIa Guidelines for Pacemaker Implantation in Acquired AV Block

Answer 32

1. Asymptomatic 3º AV block regardless of level
2. Asymptomatic type II 2º with narrow QRS
3. Asymptomatic type II 2º block within or below the His at EP study
4. 1º or 2º AV block with symptoms similar to pacemaker syndrome

Question 33

Class IIb Guidelines for Pacemaker Implantation in Acquired AV Block

Answer 33

1. Asymptomatic 3º block regardless of level
2. Asymptomatic type II 2º block with narrow QRS
3. Asymptomatic type II 2º block within or below His
4. 1º or 2º block with symptoms similar to pacemaker syndrome
5. Marked 1º block (PR interval > 300 ms) in patients with LV dysfunction in whom shortening the AV delay would improve hemodynamics
6. Neuromuscular diseases with affinity for the conduction system, with any degree of AV block regardless of symptom presence

Question 34

Class III Guidelines for Pacemaker Implantation in Acquired AV Block

Answer 34

1. Asymptomatic 1º block
2. Asymptomatic type I 2º block at AV node level
3. AV block expected to resolve or unlikely to recur (i.e. Lyme disease, drug toxicity)

Question 35

What are the benefits of pacing mode that maintains AV synchrony?

Answer 35

Reduces complications of single-chamber pacing, like pacemaker syndrome & pacemaker-mediated tachycardia