Cardiac Electrophysiology Flashcards
Slowly and automatically depolarize to the threshold potential at which they fire an all or none action potential
Pacemaker cells
Cells involved in developing force during each contraction of the heart— they fire action potential when stimulated
Non-pacemaker
Pacemaker cells are specialized myocardial cells that are located in the
SA and AV nodes
Pacemakers cells are authorhythmic?
Yep, the spontaneously generate action potential
Pacemaker potential- phase 4
Depolarization- membrane potential slowly rises to threshold in SA and AV nodes
Step 2 is when
Action potential begins to fire once threshold is reached
Step 3 is when
There is a repolarization to resting potential
_____ response action potential
Slow
Funny current
Inward slow flux of Na+ through non-specific ion channels
Phase 4 depolarization involves 3 voltage gated membrane currents
- Decrease in outward flux of K+
- Funny current
- Gradual inlfux of Ca2+ as threshold is approached
Depolarization results from opening of voltage gated
L-type Ca2+ channels
Repolarization results from opening of voltage gated
K+ channels
The primary pacemaker in the intact heart with an intrinsic rhythm at rest of 60-100 depolarizations per minute
SA node
Depolarizers at a slower intrinsic rhythm and typically receives its signal from the SA node. It acts as a secondary pacemaker that can take over regulation of the heart if the SA node is damaged
AV node
Conducting network in the ventricles has an even slower intrinsic rhythm and could act as pacemakers only of the SA and AV nodes fail
His-purkinje fibers
All pacemakers share the same ionic mechanism of autorhythmicity
Yep
What happens when there is a parasympathetic action?
- Voltage gated K+ channels close more slowly- hyper polarizes resting potential
- Decreased funny current- reduces slope of phase 4 depolarizations
- Decrease in Ca2+ channels in late phase
This all leads to a slow heart rate
Parasympathetic innervation and mediator
Vagus n. And releases acetyl choline to SA node
Action of sympathetic intervention on heart
- Increased funny current in nodes and Ca2+ channels in all myocardial cells
- Alters threshold toward more negative voltage
- this increases heart rate and increases force of contraction owing to increasing intracellular Ca2+ leading to a +/- inotropic effect
Sympathetic innervation and mediator
Innervation is the cardiac plexus and releases Norepinephrine to SA and AV nodes and myocardium
Non pacemaker cells true resting potential of
-90 mV
Non pacemaker cells are excited by
APs from adjacent cells
Phase 0
Rapid influx of Na+ through voltage gated channels leading to a depolarization towards ENa+
Phase 1
Inactivation of Na+ channels plus opening of a transiently outward K+ channel
Phase 2
Plateau phase involve an inward flux of Ca2+ through L-type. (Long lasting) voltage gated channels, balanced by a slow outward K+ current and Iks - voltage stays close to 0
Phase 4
Small fluxes of Na+ and K+ maintain the resting potential
Phase 3
Repolarization when Ca2+ channels close and potassium effluent, returns the membrane to resting potnetial
Non pacemakers cells have a rapid depolarization thus they are referred to as
Fast response
Period comprising phases0,1,2, and part of 3, during which a new action potential cannot be elicited
Effective or absolute refractory period
Are Na+ channels inactivated during refractory period?
Yep
Duration of ERP (effective refractory period) can be 100-250 msec; _____ times for atrial muscle and _____ for ventricular
Shorter times for atrial muscle and longer for ventricular
Significance of ERP
Limits the frequency AP and prevents the heart from summing twitches or tetanizing thus allowing time for ventricular filling between beats
In atrial and ventricular myocardium conduction of AP is primarily by cell-cell contact through
Gap junctions
Gap junctions contain ______ resistance ion channels that allow depolarizing currents to spread from one cell to adjacent cells
Low
Explain to me the sequence of the activation of the heart
- SA node fires AP
- Signal is conducted through the atrial muscle cell to cell
- Signal reaches the AV node which is the only conducting pathway from the atria into the ventricles
- Small diameter fibers within the AV node delay conduction of the impulse into the ventricular muscles
5/ fibers leaving the AV node expand and enter the ventricles at the base of the septum= bundle of His - Bundle of His divides into right and left brindle branches that ratify down the Endo cardinal surfaces of the septum spreading laterally
- Bundle branch fibers divide into purkinhe fibers that spread the impulse into the ventricular myocardium to individual myocytes which then conduct via gap junction
Junctions fibers are slow or fast acting fibers?
Slow that is why we see a delay in conduction into the ventricular muscle
Spread of impulse
Septum—> apex—> base and endo—> epicardium
Duration of APs is longer in _____ and ________ myocytes than in _______ myocytes
In bundle branches and subendocardial are longer than in subepicardial
Who are the last to depolarize but are the first to repolarize
Subepicardial myocytes
Ventricular depolarizations spreads _______ over the pathway of depolarization
Backwards
Dipoles measure and record electrical changes on the
Outside fo the muscle strip
Dipoles exist when there is a
Separation of charge along the muscle strip
If the tissue is uniformly charge— isoelectric— how are the dipoles?
No dipoles exist
When a dipole vector indicating depolarization it points toward the positive electrode the signal is
positive
When a dipole vector indicating repolarization points toward the positive electrode, the signal is
Negative
Electrodes placed perpendicularly to a dipole vector it shows
No deflection
