Cardiac Electrophysiology Flashcards
What is commotio cardis?
sudden blunt impact to the chest that causes sudden cardiac arrest
What is the intrinsic heart rate?
no neural input: 100 bpm
What is the meximum effective heart heart?
180 bpm
What is the bpm for tachycardia?
greater than 100
What is the bpm for bradycardia?
less than 60
What is the dynamic range?
20 - 250 bpm
What does an ECG measure?
cardiac action potential; events happen quickly
What occurs during a P wave?
atria depolarize
What happens during a QRS wave?
ventricles depolarize
What happens during the T wave?
ventricles repolarize
Does ventricular or atrial AP last longer?
ventricular has longer duration
What waves are considered ventricular AP?
QRS and T wave
What waves are considered atrial AP?
P wave
What are the atrial components?
- sino-atrial node
- arterial internodal pathways
- atrial ventricular node
- Bachman’s bundle
What is the sinal-atrial node?
- initial packemaker region
- origin of cardiac AP
What are the atrial internodal pathways?
Carries sino-atrial node to AV node and spreads AP across the atrial myocardium
What is the atrial ventricular node?
- passage of atrial AP to ventricular AP
- conductance slowed; enables atrium time to contract and fill ventricles
What is Bachman’s bundle?
passage of right atrial AP to left atrial AP
What are the ventricular components?
- AV bundle of HIS
- left and right bundle branches
- Purkinje fibers
What is the AV bundle?
secondary pacemaker region
What is the function of the left and right bundle branches?
- conducts AV node AP through cardiac septum along left and right branches
- separate left and right ventricular pathways
What in the purpose of Purkinje fibers?
- conducts AP throughout ventricular myocardial tissue
- tertiary packemaker site
What is the path of AP conduction velocities?
SA node -> internodal atrial fibers -> atrial myocardium -> junction ->AV node -> bundle of HIS -> Purkinje fibers ->ventricular myocardium
What are the factors that affect current flow?
- # of cell-cell gap junctions
- cell diameter: small= small conduction velocity; large= large conuction velocity
- cell alignment
What is the RR intervak in cardiac excitation?
time from one R wave to the next
inverse= heart rate
What is the RR interval in cardiac excitation?
time from one R wave to the next
inverse= heart rate
What is the PR interval in cardiac excitation?
start of atrial depolarization to ventricular depolarization
What is the QRS interval in cardiac excitation?
time ventricular depolarization occurs
What is the ST segment in cardiac excitation?
time after ventricular polarization
What is the QT interval in cardiac excitation?
start of deplarization to end of repolarization
What has a fast AP and is considered a conducting cell??
- atrial muscle
- ventricular muscle
- bundle branch
- Purkinje fibers
What has slow AP and is considered a pacemaker cell?
- SA node pacemaker
- atrioventricular node
What is the affect on ion channels during depolarization?
inward Na and Ca currents
What is the affect on ion channels during repolarization/hyperpolarization?
outward K currents
What happens in phase 0 of ion channels?
- depolarization
- activation of fast voltage gated Na and Ca channels
- inward Na (Ina) and Ca (Ica) flux
What happens in phase 1 of ion channels?
- early repolarization
- activation of a transient outward voltage gated K channel
- outward K flux (Ito)
- inactivation of Na channels
What happens in phase 2 of ion channels?
- plateau
- activation of voltage gated Ca channels
- activation of delayed rectifier K channels (Ikr and Iks)
- inward Ca flux and outward K flux counteract each other
What happens in phase 3 of ion channels?
- late repolarization
- activation of voltage gated Ca current
- activation of delayed rectifier K channels
- inward rectifier K channels (Ik1)
- outward K flux
What happens in phase 4 of ion channels?
- diastolic resting potential
- activated inward rectifier K channels
- outward K influx (Ik1)
What are the 3 states of voltage gated channels?
- closed: NO ions flow through the channel pore
- open (depolarization): ions flow through the channel pore based on electrochemical force
- inactivated: NO ions flow through the channel pore
How many subunits do voltage gated K channels have?
4 subunits with 6 transmembrane domains in each
Where does ion selectivity occur?
in the pore, only allowing K to pass
The transmembrane region has what sensor in what specific region?
voltage sensor in S4 region
Outward currents include what channels?
voltage gated K channels and inward rectifier K channels
How many subunits are required to form the ion channel in outward currents?
4 subunits
Inward currents include what channels?
Na and voltage gated Ca channels
How many subunits are required to form the ion channel in inward currents?
1 alpha subunit with 4 domains
Inward currents are produced by what?
single polypeptide chain
What is a pore region in inward currents?
one specifically allows Na to come through and another allows Ca to come through
What is the similarity between cardiac and neuronal AP?
both fire overshooting all-or-none AP
What is the difference between cardiac and neuronal AP?
- duration of cardiac AP is longer than neuronal AP
What is a refractory period?
period that causes enough time for heart to fill with blood before the next contraction
What is the effective refractory period?
when the cell CANNOT fire another AP
What is the relative refractory period?
cell CAN fire another AP but amplitude is reduced
Both the effective and relative refractory periods are caused by what?
inactivation state of voltage gated Na or Ca channels
What differerntiates pacemaker cells from ventricular cells?
pacemaker cells have:
* slower riding phase in phase 0
* no early repolarization pahse 1
* no plateau phas in phase 2
* slower depolarize in phase 4
* resting potential is more depolarized
All cells express what specific channel?
If (funny)
What is automaticity?
initiates heart beat
What is rhythmicity?
regular pacemaking activity
What is the dominant packemaker?
SA node
AV node is the backup
What happens in phase 0 of slow pacemakers?
Ica: Ca current voltage dependent Ca channel
What happens in phase 3 of slow pacemakers?
Ik: K current voltage-dependent K channel
What happens in phase 4 of slow pacemakers?
If: pacemaker cureent cyclic-nucleotide gated Na channel
needed for automaticity
What is the threshold potential?
membrane potential for triggering all or nothing AP
What are the steps for altering automaticity and firing frequency?
- change in slope of phase 4
- hyperpolarization during phase 4
- change in threshold for firing
What is the resting heart rate reduced by?
basal parasympathetic tone
Innervation of nodal regions are predominantly what?
parasympathetic
How does exercise affect the heart rate regulated by the autonomic nervous system?
- reduces parasympathetic tone
- increases sympathetic tone
- increases HR and force of myocardial contraction
How does sympathetic stimulation affect ion channels?
increase If, Ica, and Ik
How does parasympathetic stimulation affect ion channels?
- decrease If and Ica
- increase Ik (Ach)
