Cardiac Electrophysiology Flashcards
When is the cardiac membrane most permeable to potassium?
At rest
What happens in a cardiac cell when the Sodium Potassium Pump is inhibited?
RMP becomes less negative
Cell hyperpolarizes
Cell becomes more excitable
What are the four phases of a normal cardiac action potential?
Phase 4 - RMP
Phase 0 - Rapid Upstroke
Phase 1 - Partial Repolarization
Phase 2 - Plateau
Phase 3 - Repolarization
Phase 4 - RMP
What happens to fast sodium channels during phase 1 of the cardiac musclr action potential?
They inactivate
When is the cardiac muscle membrane most permeable to Sodium?
Phase 0
When is the cardiac muscle membrane most permeable to Calcium?
Phase 0
What is the pathway of a Fast Na+ Channel?
Voltage of the membrane increases
Activation gate is activated and opens Fast Na+ channel
Na+ Enters channel
High membrane voltage triggers inactivation gate
Channel closes
What happens to the action potential of a cardiac muscle given tetrodotoxin?
Phase 0 is eventually lost and the Fast Na+ channel is blocked
How does Diltiazem affect cardiac muscle?
It blocks L=Type Ca2+ channels and shortens phase 2
Lacl of Ca2+ causes contraction to weaken
What is important for contraction during phase 2?
influx of Ca2+ ions
What is the purpose of the ARP?
Long ARP protects the cardiac muscle from tetanus because it prevents another AP from firing
In cardiac muscle, what occurs first, Mechanical activity or Electrical activity?
Electrical activity proceeds mechanical activity
Which parts of the cardiovascular system experience fast response?
Atrium
Ventricle
Purkinje FIbers
Which parts of the cardiovascular system experience slow response?
SA Node
AV Node
Why is the atrium AP different fron the ventricle and purkinje AP?
Atrium generates less force and ha a shorter phase 2
Which node is the typical pacemaker?
SA Node
What happens if the SA Node cannot function properly as the pacemaker?
The AV Node will take over
Where is the SA Node located?
Between the Super Vena Cave and Atrium
Where is the AV Node located?
Between the Atrium and Ventricle
What is the difference between fast response and slow response tissues?
Fast Response Tissues have Fast Na+ Channels
Slow responsse do not
Why is the SA Node the dominate pacemaker?
The SA Node has the highest rate of depolarization
What causes Phase 0 in SA Nodal cells?
Increase in Ca2+ permeability
What do If channels do in SA Nodal Cells?
Conduct Na+ at rest
Na+ leaks in
Ca2+ leaks out
What causes the action potential in SA Nodal Cells?
SA Nodal Cells spontaneously move toward threshold and fire AP
How does Sympathetic Stimulation from the SNS affect Cardiac Muscle?
SNS releases NE
NE binds B1 receptors
K+ permeability decreases
Na+/Ca2+ permeability increase
Heart Rate increases
How does Parasympathetic Stimulation from the PSNS affect Cardiac Muscle?
PSNS releases ACh
ACh binds M1 receptors
K+ permeability increases
Na+/Ca2+ permeability decrease
Heart Rate decreases
Which branch of the ANS causes cardiac muscle to reach threshold more quickly?
SNS
Which ANS system dominates at rest?
PSNS
What happens if you cut all ANS innervation from the heart?
Heart Rate increases
What happens to heart rate when the PSNS is stimuated?
Heart Rate Decreases
What happens to Heart Rate when the SNS is stimulated?
Heart Rate Increases
What happens when sympathetic innervation to the heart is cut?
Heart rate decreases
Whatr happens when parasympathetic innervation to the heart is cut?
Heart Rate Increases
What is the normal sequence of activation for cardiac muscle electrical activity?
SA Node -> Atrial Myocardium -> AV Node -> AV Bundle -> Bundle Branches -> Purkinje Network -> Ventricular Myocardium
Which node has the slowest conduction velocity?
AV Node
What are the requirements for reentry?
Unidirectional Block
The absolute refractory period of the reentered tissue must be shorter tan the propagation time around the reentry loop
Why is Ca2+ important in the heart?
The heart is highly dependent on extracellular Ca2+ for contractile function
Why would tetanus be bad in the heart?
No blood could be pumped during tetanus
Which refractory period prevents any stimulus, no matter how strong, from generating an action potential?
ARP
How does the RRP affect the action potential?
It would have a lower amplitude than normal and a reduced rate of rise due to the fast Na+ channels not being completely reset and the gradients fully reestablished
What in is responsible for the pacemaker activity in SA Nodal cells?
The unstable resting membrane potential of the cells
What causes the prepotential in SA Nodal Cells?
The cells are more permeable to Na+ at rest (RMP) and they exhbit a gradual decline in the K+ conductance through their cell memrbanes
What factors produce the SA Nodal prepotential?
Increased Na+ conductance at rest
Gradually decreasing K+ conductanc
Slow Ca2+ influx
How do you slow the pacemaker discharge?
Decrease rate of depolarization
Hyperpolarize the cell
Change threshold potential
What are the components of the conduction system?
SA Node
Atrial internodal pathways
AV Node
Bundle of His or AV Bundle
Bundle Branches
Purkinje System
Ventricualr Muscle
How does the SA Node spread impulses?
Impulses move out of the SA node through the internodal pathways to the AV Node
Where does the main delay of SA Node impulses occur?
In the AN Zone of the AV Node
How does the sympathetic nervous system affect the AV node?
Increases conduction velocity
How does the parasympathetic system affect the AV Node?
Decreases conduction velocityin AV Node
Why is the AV Node a critical region for heart block development?
Under normal conditions, it is the only region where impulses from the atria can get to the ventricles
Sumarizes the process of Excitation-contraction coupling and uncoupling…
- Voltage-depedent calcium influx
- Calcium release from SR
- Removal of calcium from cytosol
- b-receptor activation (catecholamines)
- Action of cardiac glycosides (digitalis)
- Excitation-contraction uncoupling
What are the mechanisms of calcium release in cardiac cells?
Ca induced Ca release
Charge movement coupled Ca release
IP3 induced Ca release
Which of the following statements regarding the autonomic nervous system is correct:
A. Parasympathetic activity increases the membrane permeability to K+
B. Sympathetic innervation decreases the slope of the pacemaker potential
C. Sympathetic innervation decreases the membrane permeability to Na+ and Ca2+
D. The heart will stop beating if it is denervated
E. The heart rate will decrease significantly if the heart is denervated
A. Parasympathetic activity increases the membrane permeability to K+
Which of the following is MOST responsible for phase 0 of the SA Nodal Phase:
A. Pacemaker Channels
B. Voltage-gated Ca2+ channels
C. Tetrodotoxin-sensitive Na+ channels
D. K+ leak Channels
Cl- Channels
B. Voltage-gated Ca2+ channels
Which one of the following would increase the rate of phase 4 depolarization in an SA nodal cell?
A. An increase in SA Nodal K+ conductance
B. Stimulation of cardiac muscarinic receptors
C. Stimulation of the vagus nerve
D. Increasing levels of circulating epinephrine
D. Increasing levels of circulating epinephrine
In the normal heart, premature re-excitation of myocytes is prevented by:
A. Gating properties of the gap junctions within the intercalated disks
B. Offsetting multiple reentry mechanisms
C. The ARP of the myocardial cells
D. Rapid re-setting (h-gates open; m-gates close) of the voltage-gated, fast sodium channels
E. Overdrive Suppression of secondary pacemakers
C. The ARP of the myocardial cells
During Atrial Fibrillation, the rate of ventricular depolarization depends on …
A. The firing ate of the SA node
B. The refractory period of cells in the AV node
C. The conduction velocity in the atrial internosal tracts
D. The conduction velocity of the Purkinje Gibers
E. None of the above
B. The refractory period of cells in the AV node
