Lecture 10: Bradyarrhythmia Flashcards
Normal PR interval (ms) and traveling path
200 ms; SA node –> AV node –> bundle of His
Three big differences between sinus node APs and normal cardiac APs
- Higher resting potential; 2. Spontaneous resolving phase 4 due to If current; 3. Phase 0 upslope is mediated by Ca2+ currents
Why is the SA node the “pacemaker” of the heart? (2)
Because it’s the fastest pacemaker cell and it suppresses the other latent pacemaker cells
What is an escape beat? What does this look like on the EKG?
When the predominant pacemaker cell doesn’t fire (SA node), and another latent pacemaker takes over; missed P wave before QRS complex
Describe the intrinsic rate of pacemaker cells moving down the conduction system
The rate decreases: sinus node > AVN > His-Purkinje > Ventricular myocardium
Define bradyarrhythmia
ABNORMAL heart rate from any cause
Why would you get a bradyarrhythmia? (3)
Decreased rate of automaticity, slow conduction, or conduction block
Another name for sinus node dysfunction
Sick sinus syndrome
Who typically gets sinus node dysfunction? Describe the pathophysiology
Older people: idiopathic fibrosis in the sinus node
What are some acquired ways someone could get sick sinus syndrome (4 common, 2 rare)
Ablation (surgery), inflammatory disorders, infiltrative disease (amyloidosis), hypothyroidism; Na+ channel mutations, muscular dystrophy
List some presentations of sick sinus syndrome and presentation
- 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
Is sick sinus syndrome deadly?
Rarely
When do you treat sick sinus syndrome? If there is an emergency, what would you treat with? What about longterm solution?
If symptoms are present; anticholinergics (atropine) or beta adrenergic agonists (isoproterenol); pacemaker
Atrioventricular block (def). Where can it occur?
Any abnormality in conduction b/t sinus node and ventricle; atria, AVN, or His Purkinje system
First degree AV block: how do you define and definition. Where? Treat?
Defined electrocardiographically; PR interval > 200 ms w/ preserved 1:1 conduction ratio; generally within AVN; rarely causes symptoms/does not need treatment
Second degree AV block
Block between atrium and ventricle in which a single impulse is not conducted to the ventricle; occurs in a FIXED ratio
What is important to know about with second degree AV block?
Where is it occurring?
An athlete w/ second degree block is likely to be blocked…
At the AV node because it is sensitive to the high vagal tone of being an athlete
If the QRS complex is wide, where is the block, generally?
Below the AV node
What is decremental conduction?
As you input to AV node faster, slower the output of AV node
Type 1 second degree AVB: define as what is seen on the EKG and give other name
Progressive prolongation of the PR interval followed by a single non-conducted p-wave, then reset; Wenckebach block
Describe type 1 second degree AVB
Asymptomatic, occurs at rest, often due to high vagal tone, common, only treat if symptomatic (rare)
Is type 1 second degree AVB ever physiologic?
Yes, can be a normal finding for athletes/young people at rest
Does the conduction from the His bundle –> ventricles have decremental conduction?
No: stays the same
Type 2 second degree AVB: where is it what what you see on the EKG
Below AVN, no progressive prolongation, but just a dropped QRS after a p wave
What’s difficult about a second degree AV block in a 2:1 ratio? What do you look for here?
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
High degree AV block (def)
More than one consecutive atrial impulse that is not conducted
Complete heart block (def)
No conduction b/t atrium and ventricle
Where do complete/high degree blocks usually occur, broadly?
Below AVN
Treatment for second degree type 2 –> CHB is what? Etiologies of these pathologies (5).
Pacemaker; >50% due to idiopathic fibrosis; amyloidosis/sarcoidosis; trauma; genetic disease/muscular dystrophy; neonatal lupus (very rare)
Bundle branch block is a…Where is it found? What does this result in as seen in the EKG?
Conduction abnormality; block in either one of the two bundles; widened QRS because one ventricle must depolarize via mycoardium
Right bundle branch block EKG
QRS > 120 ms; second portion of QRS is rightward and anterior; positive in V1
Are right bundle branch blocks common? Are they dangerous?
Yes; not necessarily
Left bundle branch block EKG
QRS > 120 ms; second portion of QRS is leftward and posterior; negative in V1
Left bundle branches are typically associated with some sort of ______, give examples (4)
Disease; myocardial, valvular, coronary artery, or significant conduction disease (e.g. fibrosis)
What is aberrancy? How many ways can this happen?
When a healthy person gets a transient bundle branch block; two
What HR does rate-related aberrancy occur at? Describe physiology and other name
Occurs at faster heart rates; impulse encounters cells prior to full repolarization (phase 3)
Why does deceleration/phase 4 block happen? Disease/not disease?
Slow loss of resting membrane potential during a prolonged phase 4; usually occurs w/ diseased tissue
What medications treat bradyarrhythmias? When?
Sympathetic agonists/anticholinergics –> ST tx of bradyarrhythmias for above AVN blocks
When are pacemakers indicated? (3)
Persistent bradyarrhythmias, patients who require medications that cause arrhythmias that cause arrhythmias, any block below AVN w/out reversible cause
How do pacemakers work?
Senses if the atria fires (arial sense) and if the ventricle contracts (ventricle sense) and if either needs to be “paced” (atrial/ventricle pace)
