Exam1Lec5CardiacElectroPhysiology Flashcards
The heart is an ____ driven ____ cycle ____
electrically, two, pump
two cycles=2phases=filling and ejectitng intermittent pump
What is the dynamic range of heart rate?
20-250 bpm
250 is not effective b/c it is not allowing enough blood to refill and perfuse
180 is the maxium “effective” heart rate especially during exercise
What is the intrinsic heart rate?
intrinsic=no neural input; heart beats on its own
100 bpm
w/ no autonomic neural input
What does the electrocardigram measure?
records electroactivity of the heart in real time and can show abnormalities in CO
What does a normal adult 12-lead ECG show?
each one shows electroactivity of different points of the heart. Waveforms of leads differ b/c you are looking at diff spot in the heart with every lead, so you get diff waves of depolariation
What is a wave of depolorization?
Cardiac action potential that spreads across the heart during each heartbeat and cardiac cycle.
looking at each wave can tell us if theres abnormalities of the heart (ex: multiple p waves of the heart, av node delay shortened or lengthened, etc)
What is the p wave?
It comes after the SA node fires (pacemaker) and it represent atrial action potential that results in atria depolarozation
What is the QRS complex?
This represent the ventricualr action potential and where you see ventricles depolorize. This complex is longer in duration compoared to p-wave
What are the atrial components of the conduction system of the heart?
- SA node
- Atrial internodal pathways
- Bachman’s Bundle
- Atrial-Ventricular node
What is the SA node?
initial pacemaker region
origin of the cardiac action potential
this gives heart intrinis activity (heart can beat on its own)
What is the Atrial internodal pathway?
carries SA node AP to the A-V node (mitral and tri-cuspid) and spreads AP across the atrium
b/w SA node and AV node
What is Bachman’s Bundle?
Passage of the right atrial AP to the left atrial AP
allows electrical coupling b/w L and R atria, and for signal to spread across myocardiumq
What is the atrial ventricular node?
Passage of atrial AP to ventricular AP
Conductance slowed, enables atrium time to contract and fill ventricles
What are the ventricular components of the heart?
- AV bundle (Bundle of his)
- Left and right bundle branches
- Purkinje fibers
What is the A-V bundle (bundle of his)?
AV node: secondary pacemaker region
Passage of atrial AP to ventricles
What are the left and right bundle branches?
conducts A-V node AP thorugh cardiac septum along left and right ventricular pathways (L and R ventricles)
What are purkinje fibers?
conducts AP throughout thje ventricular myocardial tissue (ventricular myocytes). Tertiary pacemaker site
Action potential conduction velocities vary, why?
b/c not a single wire, there are different conductive properties in each part of the heart.
ap varies at different location within the heart
List the conduction velocities of each region of the heart as fast or slow from SA node to ventricular myocardium
- SA node (slow)
- Internodal atrial fibers (fast)
- Atrial myocardium
- Junction (slow)
- AV node (slow)
- Bundle of his
- Purkinke fibers (fast)
- Ventricular myocardium
purkinje fibers are fast to ensure all myocytes conduct together
There is a gap in conduction velocity between junction and AV node, why?
It provides time for blood to fill and pump, it also shows timing on ECG
The heart is an electrical ____ that functions as a ____.
Syncytium, unit
How does electrical current flow?
Cell to cell via low resistance patheyas, triggering all or non action potentials.
What factors affect current flow?
- # of cell to cell gap jxns
- Cell diameter
- Cell alignment
How does the number of cell to cell gap jxns affect current flow?
High permeability, low resistance, fast velocity
intercalated disks is the jxn from myocyte to myocyte, it contains gap jxns that allows electrons to move from one cell to another. The more of this, the faster the conduction to the other site
How does cell diameter affect current flow?
Purkinje fibers are very thick compared to AV nodes so they have lower resistancr and faster conduction velocity.
Think of a thin copper wire vs a thick copper wire. The thick one can conduct more current, faster.
How does cell alignment affect current flow?
Purkinje fibers have more alignment/organization than SA node so it is faster.
What is the importance of a desmosome?
It provides mechanical strength to prevent cells from tearing apart during contraction and relaxation.
What protein is gap jxns made of?
Connexons
connexins> form hexamer> connexon
What does the sa node represent in this picture?
Before atrial depolarization, before p wave
What occurs before ventricular myocardial depolarization?
Bundle of his, bundle branches, purkinje network
What is the rr interval?
Time from r wave to r wave. I/RR is the heart rate.
What is the PR interval?
Start of atrial dep to start of ventricular dep
What is ST segment?
Time b/w ventricular depolarization and repolarization
What is QRS duration and QT interval?
QRS DURATION: ventricular myocyte depolarization
QT INTERVAL: time interval b/w dep of ventricles and rep of ventricles
If you have a longer/wider of any interval does the heart rate incr or decr?:
heart rare dcr
if you have a shorter or skinner curce hr incr
Does the pacemaker cells (SA node and Atrioventricular node) have fast or slow action potential?
SLOW it takes longer to dep bc slow action potential
Do conducting cells (atrial muscle, bundle branch, purkinje fibers, ventricular muscle) have fast or slow action potential and do the waves look the same
They have faster action potential an no they waves are diff bv because of differences in expressed ion channels and their affect on “shaping” the AP waveform.
diffferences in wave shape bc of diff ion channels being expresses
Fast action potentials in ventricular cells
Phase 0
Phase 1
Phase 2
Phase 3
Phase 4
Phase 0: depolarization
phase 1: early repolarization
phase 2: plateau
phase 3: final rep
phase 4: diastolic “resting potential
Inward current is mediated by channel(s)?
Na+ and Ca+
dep
Outward current is mediated by?
K+
rep/hyper
What are the 3 functional states of voltage gated Na+channels?
Closed: no ions flow through
Open: (dep) ions flow through (in or out)
Inactivated state: no ions flow through
Transitions b/w closed and open inactivates states are ____ dependent
time and voltage
the rates of transition and their voltage dependence varies amond diff voltage gates ion channels
voltage change causes conformational change
What is the structure of voltage gated K+ channels?
These channels are formed by 4 subunits each with 6 transmembrane domains. S4 senses voltage changes
What is the structure of voltage gated Na+ and Ca+ channels?
1 subunit (polypeptide) with 24 transmembrane domains divded into 4 domains
What channels are open/closed/inactivated during phase 0 dep phase?
open: Inward flux of Ina and Ica
What channels are open/closed/inactivated in phase 1 early repolarization?
Open: outward flux Ito 1 and 2
inactivated: Na channels
“transient outward”
What channels are open/closed/inactivated in phase 2 plataeu?
Open: inward ICa and outward IKr IKs (delayed rectifier channels)
inward Ca flux and outward K flux counteract each other
What channels are open/closed/inactivated in phase 3 final repolarization?
Open: IK1, IKr IKs=outward K flux
Inactive: Ca+ channels
k1=inward rectifier K channels (goes outward tho)
What channels are open/closed/inactivated in phase 4 diastolic “ resting” potential”?
open: K1
Ik1=inward rectifier K channels (goes outward tho)
Which has a faster dep nerve cell or a cardiac myocyte?
Nerve cell. Cardiac myocytes are much slower b/c need time to refill ventricles and push blood out, hence why we see so many phases. We see an extended refractory period that gives us enough time for the heart chambers to fill with blood, bc you can’t fire another ap i this phase.
both cardiac and neurins fire overshooting all or none action potentials
What is effective/absolute refractory period?
Cells cant fire another action potentials between phase 0 and 2
caused by the inactivation state of na and/or ca channels, NOT CLOSED STATE
What is relative refractory period?
Cell can fire another action potential, but amplitude is reduced (b/w phase 3 and 4)
caused by the inactivation state of na and/or ca channels, NOT CLOSED state
Compade and contrast ventricular and pacemaker action potentials
Pacemaker cells has slower phase 0 (dep)
Pacemaker cells doesnt have a phase 1 (early rep)
Pacemaker cells doesnt have a phase 2 (plateau)
In pacemaker cells, Phase 4 is slowly dep while in ventricles it is completely in its resting state
What is the dominant pacemaker cell and if there is a dysfxn what occurs?
Dominant pacemaker=SA node
with sa node dysfunction the AV node can become the dominant pacemaker ( a little slower), and if that fails, purkinje cells can act as dom pacemaker (slowest)
SA, AV, and purkinje all have automacticity in which they can fire AP on their own.
All pacemaker cells express what type of channel?
I(f) funny chhannel also called HCN channel for “hyperpol activated channel” This opens up when it senses hyperpol and it resposible for the automaciticty
automaticity: initiates heartbeat
rhythmicity: regualr pacemaking activity
Explain the phases of ionic currents mediating “slow” pacemaker cells.
Phase 0 dep: Ica activated (slowr bc Ca+ slower than Na+)
Phase 3 final rep: IK activated
Phase 4 (slight, slow dep-resting state): IF “funny” cyclic gated nucleotide gated Na channel NECESSARY FOR AUTOMATICITY (bc activated by hyperpol)
nodal cells: only Ca channels, na channels not involved
What are 3 ways you can alter the automaticity and firing frequency (heart -rate) of SA nodes?
- Change slope of phase 4 (incr slope, incr HR)
- Hyperpol during Phase 4 ( incr time to dep, lower hr)
- A change in threshold for firing (lower the threshold, incr hr)
How is the heart rate regualated by the autonomic ns?
Innervated by parasymp (vagus) and symp. Innervation of nodal regions are mostly by parasymp
resting heart rate is reduced by what?
Basal parasympathetic tone
constatly firing (why some athelties have lower hr)
Exercise redues ____ tone and incr ____ tone causing incr hr.
parasymp, symp
modulation of ion channel fxn by neurotransof ANS and their pathway
Sympathetic signaling pathway
- NE is releases and binds to and activates Beta-1 adrenergic receptor
- Receptor is coupled to Gs which activated ad cyclasse to produce cAMP.
- cAMP activated PKA and PKA phosphorylates calcium incr Ca channel current (ICa)
funny channels are also incr bc of lower rep time leading to incr HR
modulation of ion channel fxn by neurotransof ANS and their pathway
Parasymp signaling pathway
- Vagus nerve releases ACh which binds to and activates muscuranic M2 receptor
- This receptor is couples to Gi and this inhibits ad cyclase whihc then inhibits cAMP, lowering activation of Ca2+ channel..
- This leads to direct G-protein interaction where we see incr in G-protein Kir current (IK(ACh)
ACh is activated, K+ channel, hyperol, lower HR
Explain how parasymp can slow heart rate in terms ion channel activity
You see
1. Der IF and ICa (decr cAMP, decr IF)
2. Incr IK(ACh), more hyperpol
Explain how symp can incr heart rate in terms ion channel activity
You see
1. Incr IF (incr cAMP), ICa (Incr PKA phosp), and Ik (rep faster)
incr cAMP, incr slope, more IF open.
