PHYSIO-LEC: Cardiac Electrophysiology Flashcards
what is the functional connection between cardiac muscle cells
intercalated discs
compare the striations of cardiac to skeletal
cardiac are arranged in series = irregular striations
what is the significance of mitochondria
heart requires a lot of energy = plenty mitochondria
why is there no room for anaerobic metabolism
if anaerobic angina sets in and may lead to cardiac arrest; always aerobic
slow response AP is exhibited by
SA, AV and junctional areas
explain the ionic exchange during slow response AP
prepotential: caused by transient opening of Ca channels; goes towards depol
spike potential: after it reaches firing level; more Ca opens = AP
Overshoot: goes over 0 as more Ca enters; as it reached the peak Ca closes
K channels open to start repol and closes after repol
Funny current: initiates prepotential; stimulates opening of transient Ca; Na leaks into pacemaker cell
cycle repeats
what are the phases of slow response AP
0: depol
3: repol
4: back to RMP; prepotential
fast response AP is exhibited by
atrial/ventricular muscles, fiber tracts, purkinje fibers
this refers to the standard cardiac potential
fast response ap
what is the RMP of fast response AP
-90 mV
what is the RMP of slow response AP
-50 to -65 mV
explain the phases of fast response AP
0: influx of Na; causes a spike potential - overshoot once firing level is reached
1: upon reaching peak Na channels close and K open; initial repol
2: opening of Ca overwhelms Ka = plateau
3: final repol bc of continuous opening Ka channels; close as repol is reached
4: going back to RMP due to Na-K pump
explain the genesis of plateau
influx of Ca is counterbalanced by K = plateau; influx of Ca is involved in excitation-contraction coupling
explain the restorations of ionic concentrations
via Na-K pumps; 3 Na in - 1 Ca out
how much ATP does the heart require
1 ATP for power stroke and 3 ATP for restorations of ionic conce; 4 ATP
it is the notch in phase 1 - peak
cardiac notch
tetrodotoxin in fast response AP
once introduced it makes fast response into slow; if transmission slows down hr decs = less CO = heart failure
compare slow vs fast response AP
slow: sa node, 0,3,4; no NA
fast: purjinke; 0-4; NA is involved
ap will alwayd precede …
muscle twitch
what does absolute RP do
prevents re entry of AP for steady hr
when does absolute RP occur
onset of depol to 1/3 phase 3
what does relative RP do
allows a stronger stimulus to initiate AP; hr gets faster
where can the supranormal period be found
just after relative refractory period in fast graph
what is the supranormal period mean
stimulus less than thresholds elicit AP; must be avoided when using defibrilator bc v tach/fib will occur
it is the remnant of sinus venosus
SA node
true pacemaker
SA node
where can the SA node be found
junct of RA and SVC
conducting system of heart from SA to AV node
from SA node to internodal pathway of bachmann, wenckebach. thorel; these will connect the atrium and converge towards the AV node
from AV node
from AV into bundle of his divide into left and right bundle branches
right bundle branches vs left bundle branches
right bundle - right ventricle - purkinje
left - left ventricle - left anterior/posterior fascicles - purkinje
describe the ECG
P wave - atrial depolarization which is in line with atrial muscle depolarization
QRS - ventricular depolarization which is in line with fast response AP in ventricles
T wave - ventricular repolarization which is in line with phase 3 of fast response
U wave - ventricular filling; found in diastole
why is the SA node the true pacemaker
frequency of impulse production is faster
greater rhythmicity depresses the rhythmicity of other potential pacemakers
1st grade heart block
AV junction - 40-55 bpm - bawal exercise
principle of overdrive suppresion
SA node has the fastest firing, therefore all the other pacemakers will be inhibited which also include the aberrant pacemaker
2nd deg heart block
purkinje - 25-40 bpm - transplant/int pacemaker
what are aberrant pacemakers
causes palpitations, arrythmia
what are the factors that determine pacemaker discharge frequency
Rate or slope of depolarization during phase 4
Level of threshold potential which must be attained
Magnitude of resting potential
what happens when you decrease the slope of pacemaker
tp will be reached slower; overshoot will be at later time
what happens if u have a higher TP
threshold potential will be reached at a very later time before we reach the firing level and produce an overshoot, causing the heart rate to decrease, causing further bradycardia
what factors affect pacemaker activity
ach nd vagal influence
sympathetic activity
temperature
ions
how does ach nd vagal influence affect pacemaker activity
brady - decreases phase 4 slope - inc K conductance vua M2 MUSCARINIC
sinus arrest - vagal massage
how does sympathetic activity affect pacemaker activity
inc hr - inc slope phase 4 - lower RMP - NE binds to beta1 - inc depol
how does sympathetic activity affect pacemaker activity
inc hr - inc slope phase 4 - lower RMP - NE binds to beta1 - inc depol
temp affect pacemaker activity
cool - dec hr - depressing slope phase 3
severe cooling - metabolism stops
heating - same as NE
ions affect pacemaker activity
dec K - inc hr
hyperkalemia - RMP lowered - unexcitable
stops in diastole
where do internodal tracts go to
Anterior Tract of Bachman o goes to (L) atrium
- Middle Tract of Wenckebach
- Posterior Tract of Thorel o Spread of excitation from atria to ventricles o converge to the AV Node
has slowest conduction velocity out of all cardiac tissues
AV node
why is it that AV node is always at anterograde
Safety feature to prevent arrythmia
where is the AV node found
beneath the endocardium on the (R) side of the atrial septum
significance of AV nodal delay
ensures that the atria have ejected their blood into the ventricles first before the ventricles contract. - ventricular filling
bundle of kent
15% of popu; fibers that bypass his - aberrant
has fastest conduction velo
purkinje; 4 m/s
relate diastole nd inc hr
hr inc - diastole dec - low sv - low co - hr goes higher - cardiac arrest
