cardiac physiology and conduction disorders Flashcards
three types of cardiac cells
pacemaker
conducting
contracting
conducting cells
carry signals to the muscle wall
contracting cells
do the contracting
where are pacemaker cells found (5)
SA node –> superior part of the R atrium
AV node–> in the atrioventricular septum
bundle of his
left and right branches
purkinje fibers
what specific subset of pacemakers cells set the rhythm of the heart
SA node in the superior part of the right atrium
pacemaker cells in the AV node respond to
signals sent from the SA node and then fire impulses that are conducted in the ventricle
what is the bundle of his
bundle of fibers that rub within the ventricular septum and when they get to the apex of the heart the fibers loop around and extend up the wall of the ventricles as the L and R bb
describe the three types of channel states
open allows for the flow of ions
closed inhibits the flow of ions and
inactivated is where the flux is inhibited by a gate function of a part of the protein called the inactivation gate
describe how the inactivation gate works
when the voltage gets to a certain point the flux of ions is so great that the inactivation gate closes which inhibits the flow of ions then the membrane has to reset that electrical charge back to normal so that the channel can reset to normal posture
close–>open–>inactivated–>closed
what does the term threshold mean with respects to voltage gating
the membrane potential where predominance of a given channel is open
three types of channels in cardiac cells
fast
slow
and
potassium
how do pacemakers cells differ from regular muscle
closer to the threshold because of more positive resting potential
and have a innate permeability to sodium which pushes the cell charge up
this permeability is what give the cell it’s rhymic nature because it is always climbing toward threshold
falling phase of pacemaker cells happens as a result of what
K channels opening
phases of pacemaker cells
0 - upstroke d/t opening of voltage gated sodium/calcium channels
3- repolarization d/t inactivation of sodium/calcium channels and opening of potassium channels
4 - resting, d/t slow leak of sodium into cell
how do contracting cells differ from pacemaker cells physiologically speaking
0 = fast Na+ channels (as opposed to slow acting) 1 = K+
Potassium channels starting to open and membrane potential starting to reset but then calcium channels start to open
2 = Ca++
3 = K+
60-100 bpm pace is seen where
a. SA node
40-55 bpm seen at what pacemakers
AV node
25-40 bpm seen in what pacemakers
Purkinje cells
which area of pacemakers set the heart rate usually?
SA node unless there is an issue in which case you might see a much lower heart rate
what is normal sinus rhthym
Normal basically means that the contraction or electrical spike is generated from the atrium. If it is not generated in the atrium, then it is not normal
- If b/w 60-100bpm and there is a p wave for every QRS complex, then you can call it NSR
45 yo man w/ chest pain. If he is shown to have a block at the SA node due to infarction, what would his HR be if all other areas are normal?
The AV node provides the next faster pace; that is probably going to give you the heart rate of 40-55 bpm
P wave
= atrial contraction
depolarization of atria
Q wave
= ventricular contraction
Gap b/w p wave and QRS complex is represented by what in a EKG
delay in AV node
Atrial repolarization results in what EKG marker
loss in QRS spike
sinus bradycardia
coming from the sinus node seen as P waves but less than 60 bpm
what is a respiratory sinus arrhythmia
Arrhythmia (first 2 spikes are farther apart, next 3 are closer together and last 2 are further apart í so pace is speeding up and slowing down which corresponds with respiration
i. Atrial flutter
flutter waves which occur at a very rapid rate (>200 bpm) but ventricular rate remains regular b/c only so many atrial contractions get transmitted to the ventricle
atrial flutter is characterized by what in EKG
flutter waves
Atrial fibrillation
í disco-ordinated contraction; wave but not as crisp as you would see in flutter
Atrial fibrillation seen as
Disorganized atrial activity
PAT
rapid rate, P for every QRS but at the onset you see it accelerate dramatically
Sudden onset, occurs in phases of very rapid rate triggered by the atria
Premature atrial contractions
abnormally short interval between contractions before the atrium fires another P wave
First-degree block
elongation of normal interval b/w P wave and R wave.
Two parties are growing apart
what are heart blocks
disorders at the AV node
Second degree block
sometimes you have a P wave w/ no QRST complex
One of the parties doesn’t come home
third degree block
total disconnect; no real relationship between atrial activity (p wave) and the ventricular activity
PVC
ventricle spontaneously contracts (sometimes electrical abnormality and sometimes a volume problem)
Ventricular tachycardia
rapid rate triggered by ventricle; the spike gets very wide
Ventricular fibrillation
disorganized electrical activity
polarization is when there are more ____ ions on the outside of the cell than are on the inside
positive ions on the outside=polarization
what is the membrane potential
it is the difference between the positive charge we see outside the cell and the less positive charge we see in side the cell
membrane potential decreasing in multiple cells is known as a
depolarization wave
auto iirrhytmic pacemaker cells
self generate ap and trigger each other
describe the depolarization wave seen in pacemaker and myocytes
fast in pacemaker connects atria through bundle branches and will be see traveling slow in myoctes leads to the contraction of the atria
depolarization wave will travel from the SA node to the AV node and conduction velocity will change here because
the AV node cells have very small diameters which increases resistance to electrical flow
and they use slower opening Ca ion channels rather than the faster opening Na channels
pacemaker cell phases
4 0 3 4
