Electrophysiology

Question 1

SA node

Answer 1

primary pacemaker of the heart
has highest rate of reaching threshold (70-80 APs/min)

failure–>bradycardia (because AV node would take over and it is slower)

Question 2

Bachmann’s bundle

Answer 2

interatrial tracts that spread depolarization from RA to LA

Question 3

AV node

Answer 3

allows signal to pass from atria to ventricles (only bridge b/w the two)

AN region: transitional zone, longer conduction path
N: midpoint of AV node, slower conduction velocity
NH: transition to bundle of His
—>delay before signal goes to ventricles
**allows for adequate ventricular filling

Question 4

Wolff Parkinson White (WPW) syndrome

Answer 4

some individuals have alternate pathway for atrial–>ventricle conduction

faster AV nodal pathway
slower ventricular depolarization
—> can cause signal to conduct back up the normal pathway–>tachycardia

Question 5

Purkinje fibers

Answer 5

arranged linearly like myocytes: have sarcomeres in the R and L ventricles
**larger diameter= increased conduction velocity

activated endocardial–>epicardial
apex–>Base

Question 6

Functional Syncytium

Answer 6

cells contract in synchrony as a result of gap junction connections

if one cell depolarizes, the rest will follow suit

Question 7

Extracellular Ca and Cardiac contraction

Answer 7

influx of EC Ca is required for additional Ca release from SR
**activates RYR

Question 8

Relaxation

Answer 8

removeal of Ca

• 3Na1Ca antiporter–>ECF
• ATP Ca++ pump—>ECF (against ECF)
• SERCA back to sarcolemma

Question 9

Pacemaker cell RMP

Answer 9

NO resting membrane potential

maximum diastolic potential only (slow depolarization)

Question 10

Non-pacemaker cell RMP

Answer 10

RMP around -90mv (true RMP)

same ion distribution as normal AP

Question 11

Hypernatremia

Answer 11

increased ECF Na increases CG during depolarization–>increased amplitude of AP depolarization

Question 12

Slow response fibers

Answer 12

No RMP, lower threshold potential (-40mV)

• smaller amplitude depolarization
• Slower conduction velocity

slower upstroke (phase 0)

Question 13

Fast response

Answer 13

have RMP, which is more negative threshold (-70mV), higher amplitude depolarization

very fast upstroke (phase 0)

Question 14

Na current

Answer 14

phase 0 (rapid depol) in fast AP cells

Rapidly activate when membrane depolarizes
IG gates close at +30mV–>phase 1
but some channels remain open and prolongs plateau

Na current–.increased conduction velocity

Question 15

Ca current

Answer 15

depolarization (phase 0) in slow AP channels
Small role in pacemaker phase (phase 4)
plateau in fast response cells
triggers contraction in all cardiomyocytes

*Slower conduction velocity due to smaller Ca current

Question 16

K current

Answer 16

repolarization in all cardiomyocytes

In SA/AV K current decreased negative diastolic voltage to assist with pacemaker activity (phase 4)

Question 17

pacemaker funny current

Answer 17

responsible for slow depolarization in SA and AV
-mostly Na influx–> pacemaker potential
Phase 4

Question 18

Purkinje fiber

Answer 18

Normally a fast response fiber
but can also become pacemaker cells (very slow)
can have funny current

Question 19

Conduction velocity

Answer 19

depends on

1) amplitude of AP (affected by Na ECF)
- -> increase amplitude= increase ability to depolarize adjacent membrane
2) Slope of depolarization

Question 20

Hyperkalemia and conduction velocity

Answer 20

Small persistent depolarization (to -50)–> closes IG gates on may Na channels–> fewer channels able to respond–> smaller amplitude AP–> decrease conduction velocity

can be caused by CAD/MI ischemia–> decrease Na+K+ ATPase–> exs ECF Na and Exs ECF K–>rhythm disruption
-MI also releases K+

Question 21

effective refractory period

Answer 21

aka absolute refractory

• IG gates closed after fast response depolarization
• phase 0–> midPhase 3

reopen after repolarization

Question 22

relative refractory

Answer 22

can initiate another AP
mid-phase 3–> end phase 3

if a subsequent AP comes in, the later in the RP= greater amplitude of its upstroke

can limit ectopic beats

Question 23

Ectopic foci

Answer 23

abnormal impulse that takes a different conduction path and setup its own pacemaker rhythm –> arrhythmias and fibrillation (circus movements)

ex: WPW syndrome

Question 24

Long QT syndrome

Answer 24

prolonged action potential
still in some degree of refractory when another AP comes in–>causes oscillation of moderate depolarization/repolarization

Question 25

Early afterdepolarization (EAD)

Answer 25

low slope, low amplitude
abnormal depolarization in late phase 2 or in phase 3
Long QT
more abnormal

Question 26

Reentry

Answer 26

set up a new circuit that it completely out of order

generate APs that do not follow normal pathways (out of order)
cause premature contractions
–>prolonged QRS (PVCs)

Question 27

Factors promoting reentry

Answer 27

***—>increase likelihood that you comeback to node by the time the cell has recovered

1) lengthened conduction pathway: dilated heart chambers, atrial enlargement etc
2) decrease conduction velocity: hyperkalemia, ischemia, Purkinje block
3) Shorten refractory period (drugs, epi)

Question 28

Funny current

Answer 28

opens at more negative (hyperpolarized voltages)

causes Na influx

Question 29

Hyperkalmeia and HR

Answer 29

slowes HR by affecting driving force for K efflux

–> slows phase 4 repolarization–>delay in reaching hyperpolarization