Lecture 10: Bradyarrhythmia

Question 1

Normal PR interval (ms) and traveling path

Answer 1

200 ms; SA node –> AV node –> bundle of His

Question 2

Three big differences between sinus node APs and normal cardiac APs

Answer 2

1. Higher resting potential; 2. Spontaneous resolving phase 4 due to If current; 3. Phase 0 upslope is mediated by Ca2+ currents

Question 3

Why is the SA node the “pacemaker” of the heart? (2)

Answer 3

Because it’s the fastest pacemaker cell and it suppresses the other latent pacemaker cells

Question 4

What is an escape beat? What does this look like on the EKG?

Answer 4

When the predominant pacemaker cell doesn’t fire (SA node), and another latent pacemaker takes over; missed P wave before QRS complex

Question 5

Describe the intrinsic rate of pacemaker cells moving down the conduction system

Answer 5

The rate decreases: sinus node > AVN > His-Purkinje > Ventricular myocardium

Question 6

Define bradyarrhythmia

Answer 6

ABNORMAL heart rate from any cause

Question 7

Why would you get a bradyarrhythmia? (3)

Answer 7

Decreased rate of automaticity, slow conduction, or conduction block

Question 8

Another name for sinus node dysfunction

Answer 8

Sick sinus syndrome

Question 9

Who typically gets sinus node dysfunction? Describe the pathophysiology

Answer 9

Older people: idiopathic fibrosis in the sinus node

Question 10

What are some acquired ways someone could get sick sinus syndrome (4 common, 2 rare)

Answer 10

Ablation (surgery), inflammatory disorders, infiltrative disease (amyloidosis), hypothyroidism; Na+ channel mutations, muscular dystrophy

Question 11

List some presentations of sick sinus syndrome and presentation

Answer 11

1. Sinus bradycardia = fatigue, dizziness, dyspnea; 2. Sinus pauses/arrest = internittent dizziness, syncope; 3. Chronotropic incompetence: inadequate response of sinus node –> physiological needs = dyspnea/fatigue w/ exertion; 4. Tachy-brady –> tachycardia w/ intermittent sinus pauses = intermittent lightheadedness

Question 12

Is sick sinus syndrome deadly?

Answer 12

Rarely

Question 13

When do you treat sick sinus syndrome? If there is an emergency, what would you treat with? What about longterm solution?

Answer 13

If symptoms are present; anticholinergics (atropine) or beta adrenergic agonists (isoproterenol); pacemaker

Question 14

Atrioventricular block (def). Where can it occur?

Answer 14

Any abnormality in conduction b/t sinus node and ventricle; atria, AVN, or His Purkinje system

Question 15

First degree AV block: how do you define and definition. Where? Treat?

Answer 15

Defined electrocardiographically; PR interval > 200 ms w/ preserved 1:1 conduction ratio; generally within AVN; rarely causes symptoms/does not need treatment

Question 16

Second degree AV block

Answer 16

Block between atrium and ventricle in which a single impulse is not conducted to the ventricle; occurs in a FIXED ratio

Question 17

What is important to know about with second degree AV block?

Answer 17

Where is it occurring?

Question 18

An athlete w/ second degree block is likely to be blocked…

Answer 18

At the AV node because it is sensitive to the high vagal tone of being an athlete

Question 19

If the QRS complex is wide, where is the block, generally?

Answer 19

Below the AV node

Question 20

What is decremental conduction?

Answer 20

As you input to AV node faster, slower the output of AV node

Question 21

Type 1 second degree AVB: define as what is seen on the EKG and give other name

Answer 21

Progressive prolongation of the PR interval followed by a single non-conducted p-wave, then reset; Wenckebach block

Question 22

Describe type 1 second degree AVB

Answer 22

Asymptomatic, occurs at rest, often due to high vagal tone, common, only treat if symptomatic (rare)

Question 23

Is type 1 second degree AVB ever physiologic?

Answer 23

Yes, can be a normal finding for athletes/young people at rest

Question 24

Does the conduction from the His bundle –> ventricles have decremental conduction?

Answer 24

No: stays the same

Question 25

Type 2 second degree AVB: where is it what what you see on the EKG

Answer 25

Below AVN, no progressive prolongation, but just a dropped QRS after a p wave

Question 26

What’s difficult about a second degree AV block in a 2:1 ratio? What do you look for here?

Answer 26

Type of block cannot be determined as easily because you can’t look back for progressive prolongations; use other information: is QRS wide? are there symptoms? then likely Type 2

Question 27

High degree AV block (def)

Answer 27

More than one consecutive atrial impulse that is not conducted

Question 28

Complete heart block (def)

Answer 28

No conduction b/t atrium and ventricle

Question 29

Where do complete/high degree blocks usually occur, broadly?

Answer 29

Below AVN

Question 30

Treatment for second degree type 2 –> CHB is what? Etiologies of these pathologies (5).

Answer 30

Pacemaker; >50% due to idiopathic fibrosis; amyloidosis/sarcoidosis; trauma; genetic disease/muscular dystrophy; neonatal lupus (very rare)

Question 31

Bundle branch block is a…Where is it found? What does this result in as seen in the EKG?

Answer 31

Conduction abnormality; block in either one of the two bundles; widened QRS because one ventricle must depolarize via mycoardium

Question 32

Right bundle branch block EKG

Answer 32

QRS > 120 ms; second portion of QRS is rightward and anterior; positive in V1

Question 33

Are right bundle branch blocks common? Are they dangerous?

Answer 33

Yes; not necessarily

Question 34

Left bundle branch block EKG

Answer 34

QRS > 120 ms; second portion of QRS is leftward and posterior; negative in V1

Question 35

Left bundle branches are typically associated with some sort of ______, give examples (4)

Answer 35

Disease; myocardial, valvular, coronary artery, or significant conduction disease (e.g. fibrosis)

Question 36

What is aberrancy? How many ways can this happen?

Answer 36

When a healthy person gets a transient bundle branch block; two

Question 37

What HR does rate-related aberrancy occur at? Describe physiology and other name

Answer 37

Occurs at faster heart rates; impulse encounters cells prior to full repolarization (phase 3)

Question 38

Why does deceleration/phase 4 block happen? Disease/not disease?

Answer 38

Slow loss of resting membrane potential during a prolonged phase 4; usually occurs w/ diseased tissue

Question 39

What medications treat bradyarrhythmias? When?

Answer 39

Sympathetic agonists/anticholinergics –> ST tx of bradyarrhythmias for above AVN blocks

Question 40

When are pacemakers indicated? (3)

Answer 40

Persistent bradyarrhythmias, patients who require medications that cause arrhythmias that cause arrhythmias, any block below AVN w/out reversible cause

Question 41

How do pacemakers work?

Answer 41

Senses if the atria fires (arial sense) and if the ventricle contracts (ventricle sense) and if either needs to be “paced” (atrial/ventricle pace)