EXAM2/CH18- Cardiac Electrical Pathophysiology Flashcards
____ % of the individuals who require pacemakers are over the age of 65 years
85%
85% of the individuals who require pacemakers are over the age of ____
65 years
____ pacemakers are implanted in the US each year
200,000
why is the number of pacemakers implanted growing?
because of the number of elderly people in the population
what 2 major factors increase need for a pacemaker
-CVD
-age
normal electrical conduction of the heart
SA node initiates the signal ->
signal passes through atria, stimulating contraction ->
AV node delays signal ->
bundle of His ferries the signal thru fibrous skeleton to interventricular septum ->
R+ L branches convey signal to apex ->
purkinje fibers carry signal thru ventricles, stimulating contraction from the bottom upward
what is the natural pacemaker where the heartbeat + depolarization is initiated
SA node
why does the AV delay occur
so that the ventricles cal fill
what does the apex do
separates R from L sides of the heart
sick sinus syndrome (SSS)
rhythm disorder involving the SA node
-individual has faulty SA node
-inability to generate a heartbeat or increase HR in response to the body’s changing circulation demands (if the SA node can’t generate a heartbeat, nothing else can happen)
sick sinus syndrome results in what 3 things
-bradycardia
-long pauses between heartbeats
-irregular heartbeats
symptoms of sick sinus syndrome
-heart palpitations
-angina
-fatigue
-light-headedness
-exercise intolerance
-syncope
syncope
brief loss of consciousness that occurs via fainting/passing out due to a sudden drop in blood flow to the brain
see slide 5 for SSS EKG
AV conduction block is also called
heart block
AV conduction block (heart block)
-loss of atrioventricular synchrony
-this is an issue with the AV node; SA node is working properly
-when the sa node is stimulated, it doesn’t pass the wave of stimulation to the AV node, so there is not an adequate contraction of the heart + the body does not get adequate bloodflow
AV conduction block or SSS is more life threatening
AV conduction block
symptoms of AV conduction block
similar to SSS
what is the body’s last ditch effort to generate a heart beat
junctional escape
-escape rhythms are not something you can survive off of past a few seconds/minutes
3 ultimate goals of pacemaker
-regular HR
-synchronize chambers of the heart (atrioventricular synchrony)
-defibrillate in case of arrhythmia
what 3 things make up the pacemaker (pulse generator)
-metal case (circuitry with battery)
-lithium batteries
-pacing leads (2 or 3)
where is the pacemaker implanted
just below the clavicle
-placed just below skin
-inferior to clavicle
how many pacing leads are in a pacemaker
2 or 3
pacemaker implantation
-fast, rather non-invasive
-can be done outpatient
describe the lithium batteries in a pacemaker
good because they last a long time (10+ years)
-given the time an individual has a pacemaker, we may need to go in to replace the battery
how does the pacemaker work
leads send sensory info to activity sensor that tells the pacemaker when to work
-where the leads get connected depends on what we are trying to fix with the pacemaker
3 types of pacemakers
-temporary external pacemakers
-permanent pacemakers
-AICD
temporary external pacemakers
-emergency
-ICU
-until permanent pacemaker placement
permanent pacemakers
the type of pacemaker we typically think of
AICD pacemakers
defibrillator
physiological pacing
sequence and timing of contractions between atria and ventricles to overcome CHRONOTROPIC INCOMPETENCE
-fixed rate vs. rate-responsive
chronotropic incompetence
when we don’t have the ability to generate a heartbeat
-pacemaker restores chronotropic competence
old school pacemakers were fixed rate or rate-responsive
only fixed rate
fixed rate pacemaker
pacemaker is limited to either lowering or increasing HR but doesn’t do both, only one or the other
-cardiologist will put a cap on the HR either on the lower or higher end
rate-responsive pacemaker
pacemaker can either increase or decrease HR when needed
-can go either direction
AV timing interval
signals ventricle to contract
optimal AV delay
how fast ventricle contracts
when is optimal AV delay
typically 150 ms from beginning of atrial depolarization
maximal tracking rate
highest pacing rate allowed
-pacemaker will not make HR go any higher than the value set for this
what is maximal tracking rate typically set at
110-150 bpm
pacemaker is programmed to account for what
delay between SA + AV node
if patient has problems with venous return, what would we change on pacemaker
AV delay
single chamber
-1 lead to RA
-for bradycardia WITHOUT AV block
dual chamber
-1 lead to RV
-1 lead to RA
-bradycardia WITH AV block
what does single chamber fix
SSS
what does dual chamber fix
heart block
there are up to ____ letters in a pacemaker code
5
pacemaker coding
how we set a pacemaker to work
-tells us what the pacemaker is programmed to do
how do we change the settings on a pacemaker
put wand over pacemaker which uses bluetooth to change the settings of the pacemaker
-more patient friendly option
pacemaker coding- A
atrial
pacemaker coding- V
ventricle
pacemaker coding- D
dual, both atrial + ventricle
pacemaker coding- o
none, off
pacemaker coding- T
trigger
-means increase
pacemaker coding- I
inhibit
-means decrease
pacemaker coding- D (for third)
dual, can either increase/decrease
-rate-responsive
first letter in pacemaker coding means
tells us what chamber is being paced
-aka the chamber being targeted by the pacemaker
options for first letter in pacemaker code
A, V, D, o
second letter in pacemaker coding means
tells us where the pacemaker is receiving sensory information from
-chamber sensed
options for second letter in pacemaker code
A, V, D, o
third letter in pacemaker coding means
how the pacemaker responds
options for third letter in pacemaker code
T, I, D, o
third letter in pacemaker code- if T or I is selected…
we have fixed rate
third letter in pacemaker code- if D is selected…
we have rate-responsive
fourth letter in pacemaker coding means
programmable features
options for fourth letter in pacemaker coding
P, M, R, o
fourth pacemaker letter- P
rate + output
fourth pacemaker letter- M
multiprogrammable
fourth pacemaker letter- R
rate-responsive
fourth pacemaker letter- o
none
fifth letter in pacemaker coding means
multisite pacing OR dual function
-some pacemakers can defibrilate the heart
options for fifth letter of pacemaker coding
P, S, D, o
fifth pacemaker letter- P
pacing
-actively pacing
fifth pacemaker letter- S
shock
-ONLY defibrillate, not pace
fifth pacemaker letter- D
dual (P + S)
-we want pacemaker to both pace the heart + defibrillate when necessary
-not all pacemakers have dual functioning
fifth pacemaker letter- o
none
exercise testing for pacemakers
-ensure appropriate rate response with exercise
-can determine need for a pacemaker
-provides info to adjust the pacemaker for optimal function in response to exercise (i.e., exercise capacity)
-determines anginal threshold
-helpful when we already have pacemaker implanted, to test if it is working properly
formal vs informal exercise testing for pacemaker
bruce protocol vs chronotropic assessment exercise protocol
**why is chronotropic assessment exercise protocol useful for pacemaker patients
intensity very minimally increases
-VERY SMALL CHANGES to safely assess ability of pacemaker to respond accordingly
ExRx special considerations- be familiar with the device
-fixed rate vs. rate-responsive features
-abrupt decreases in heart rates
-variation in heart rate responses based on the mode of activity + type of rate-responsive sensor in the pacemaker
ExRx special considerations- mode
all modes are acceptable, except for any activity that involves direct contact to the pacemaker (contact sports, lying prone on floor, etc.)
ExRx special considerations- communicate with patient’s physician
feedback about HR, BP, + symptopmatic responses to exercise
because we can’t rely on HR to determine intensity of exercise with pacemaker patients, what is our next best bet
RPE
**no 2 pacemaker patients are alike
**know Dr.Gardner’s take aways from other lectures for this
AICDs
automatic internal cardioverter defibrillators
who are AICDs prescribed for
HIGH-RISK CANDIDATES
-potential lethal ventricular tachycardias
-survived previous sudden death events
-high risk for recurrent cardiac arrest
-high risk for cardiac arrest; prior myocardial injury
why do high risk individuals need AICD (aka an implanted defibrillator)
because it delivers the same shock as defibrillator paddles do in the case that they need this on the sport
how do AICDs work
-implanted like a pacemaker
-battery-operated
-delivers shock when life-threatening arrhythmia is detected
can AICDs be combined with a pacemaker
YES
-we also have pacemakers that can do both pacing + defibrillating
AICD appearance
works + looks the exact same as a pacemaker
does an implanted defibrillator work 24/7
no, but it SENSES 24/7
-only delivers a shock when needed
major concern in AICD exercise
avoid reaching threshold HR that will cause the device to shock
training HR for someone with an AICD should stay ____ bpm below the present HR that produces a shock
20 bpm below
-the defibrillator can pick up on the speed of HR, but cannot differentiate if it is caused by exercise or TRUE tachycardia when they actually need the shock
-faulty shock is incredibly dangerous because if exercise induced it could put them into a life threatening condition
