5000 Electrical Conduction System

the electrical roadmap was first described by ____ _____ _________ in 1845

J.E. Von Purkinje

electrical roadmap

1. SA node

2. internodal pathways

3. Bachmann’s bundle

4. AV node

5. bundle of His

6. bundle branches

7. purkinje fibers

internodal pathways

1. anterior

2. posterior

3. middle

4. interatrial/Bachman’s Bundle

SA node: 1) it has a _________/________ location in the “_____” of the RA at the junction of the _____, _____, and ________ _________ (which cannot be seen ________), 2) it is set ___________ (about ___mm ______ the surface) within the __________ _________ (thus if an ablation occurs __________, it will require more _______)

posterior/superior; roof; SVC; RAA; sulcus terminalis; grossly; subepicardially; 1; below; sulcus terminalis; endocardially; energy

SA node: 1) it is a small, ________, ________ strip of specialized cells (___mm wide, ___mm long, ___mm thick, ___-___um in diameter, and ___-___um of _______ _______ fibers), 2) histologically, it has minimal _______ _________, 3) it has ____ _______ that directly connect it to _______ muscle fibers, 4) it is located _________ in the _________ RA wall, immediately __________ and just _______ to the ____ opening in the _______ ________, 5) it has the property of ___________/_____-________

flattened, ellipsoid; 3; 15; 1; 3-5; 10-15; atrial contractile; contractile filaments; gap junctions; atrial; subepicardially; posterolateral; inferior; lateral; SCV; sulcus terminalis; automaticity/self-excitation

internodal pathways have been _________ in the past; they are the ________ anatomical conduction pathways

controversial; perferential

internodal pathways: 1) they are __________ identifiable, 2) they are not _________ from other _________, meaning the ____ can spread directly to the other __________, 3) “________ __________” of the cardiomyocytes with a higher characteristic of _________ permits the recognition of “_____” or “_____”, 4) it is the ________ electrical route, 5) it allows _____ to ______ conduction

microscopically; insulated; cardiomyocytes; AP; cardiomyocytes; preferential alignment; transmission; bands or bundles; shortest; node to node

the middle tract is also called the _________ pathway; it connects the SA node to the ____ _______; it runs _________ to the ____ then descends within the _______ ______ (likely joining the _________ bundle) as it enters the ____ _______

Wenkebach; AV node; posteriorly; SVC; atrial septum; anterior; AV node

the posterior tract is also called _________ pathway; it leaves the ____ ________ through the _________ _________ going towards the _________ valve past the ____ to enter the _________ portion of the ____ _________

Thorel’s; SA node; crista terminalis; eustachian; CS; posterior; AV node

the anterior tract _________ into ___ pathways (the _______ tract and _______ _______)

bifurcates; 2; anterior; Bachmann’s Bundle

the anterior tract _______ along the ______ _______ to connect with the ________ part of the AV node; Bachmann’s bundle is AKA _______ ______/______ that electrically connects the ____ and ____

descends; interatrial septum; anterior; interatrial band/bridge; RA and LA

Bachmann’s bundle is in the most _______ of the myocardial layers (____________) and has nearly _________ alignment of ________ _______/______; as it crosses at _______ of ________, the change in _______ _______ may be a substrate for ____

superficial; subepicardial; parallel; myocardial strands/cells; boundary of bundle; fiber orientation; Afib

the AV node part of the _____ _________; AV node is AKA ________ node

Koch Triangle; Tawara’s

the Koch triangle:

1. posterior boarder: the _______ _____ of the fused _________ and ________ valves = the ________ of _______

2. anterior boarder: the ________/_________ of the _______ ______ of the _________ ________

3. inferior boarder: the ________ _________ _________

fibrous extension; eustachian and thebesian; tendon of Todaro; annulus/hinge; septal leaflet; tricuspid valve; coronary sinus orifice

at the _____ of the Koch triangle is the AV node and is the ________ ________ _________ of the septum where the _______ of ____ penetrates inferiorly

apex; central fibrous body; Bundle of His

notice that the ________ extensions of the AV node are thought to account for the slow pathways of nodal reentry pathways

inferior

AV node has ____ ______ with electrical _________ __________ called ________; we think the AV delay is because of the ______ and _____ pathways (which are often ______)

gap junctions; communication proteins; connexin; fast and slow; ablated

slow pathway has a ________ conduction time and ________ refractory period, but the fast pathway has a ________ conduction time and ________ refractory period; this is prime substrate for ________ _______ (_____)

longer; shorter; faster; longer; reentry tachys (AVNRT)

bundle of his penetrates the _________ ________; it is the most ________ part of the his-purkinje system; the fibers are insulated by a _______ ________; it receives input from the ____ ________ and sometimes _________ _______; unlike the AV node, it is NOT __________ _______ and has minimal ______ _________; it ______ once leaving the central fibrous body; it is a potential landmark used in ___ ______ _________

cardiac skeleton; proximal; fibrous sheath; AV node; transitional fibers; heavily innervated; blood supply; bifurcates; AV node ablations

pacing at the bundle of His allows for a more ______ and ______ activation of the ventricles

rapid and normal

the AP normally travels from the ___ ______ to the _________, but sometimes if there are ________ _________, then the AP uses ________ _________

AV node; ventricles; muscle bridges; accessory pathways

4 types of accessory pathways

1. atrio-ventricular

2. atrio-fasicular

3. atrio-nodal

4. fasciculo-ventricular

the most common accessory pathway is the _______ of _______; it is an ______-_______ bypass that connects the _____ ________ to the _______ ________; on ECG it shows a ______ ______ because of ventricular ________; it can lead to _____ that is commonly ablated

Bundle of Kent; atrio-ventricular; atrial myocardium; ventricular myocardium; delta wave; preexcitation; WPW

another common pathway is the _______ pathway that is an ______-________ bypass that _________ _________ connections between the ______ _____ (____ _____) and the ______

Mahaim; atrio-fascicular; decrementally conducts; distal RA (AV node); RBB

the ______ pathway is an ______-______ bypass that originates in the ____ ______ and terminates in the ____ _____ ______ (______ of ____)

James; atrio-nodal; low atrium; low AV node (bundle of His)

the last type of accessory pathway is a ________-_________ bypass that connects the ________ ________ __________ to ________ _________

fasciculo-ventricular; distal conduction system to ventricular myocardium

orthodromic AVRT: AP travels _________ through AV node and ________ through accessory pathway resulting in a ________ QRS

antegrade; retrograde; normal

antidromic AVRT: AP travels _________ through AV node and _________ through accessory pathway resulting in a ________ QRS and a ______ ______

retrograde; antegrade; wide; delta wave

LBB splits into _________, the ________/_________ branch (________) and _________/__________ branch (________)

fascicles; anterior/superior; fascicle; posterior/inferior; fascicle

the RBB continues _________ from the bundle of his along the _____ side of the ________ _________ and through the _________ ________

inferiorly; right; interventricular septum; moderator band

Purkinje fibers travel _______ the _________ of the RV and LV and within the __________

within the trabeculations; myocardium

the histological differences in the rapid conduction of these fibers: 1) _____ _________, 2) _____ _______-gated ____ _________

gap junctions; fast voltage-gated Na+ channels

cells are more _______ at rest because of an unequal distribution of ______ ______ _______

negative; electrically charged ions

there is more K+ on the __________ of the cell

there is more Na+ on the _________ of the cell

there is more Ca++ on the ________ of the cell

inside; outside; outside

K+ wants to go ____ the cell

Na+ wants to go ____ the cell

Ca++ wants to go ____ the cell (a HUGE __________ _________ with more Ca++ _______ of the cell)

out; into; into; concentration gradient; outside

the RMP is maintained by the _________ _________ pulling K+ out of the cell (the cell membrane is _________ ________ to K+) and the ________ _________ pulling K+ into the cell

concentration gradient; selectively permeable; electrical gradient

only the ____ channels are open at rest (the cell membrane is ________ ________ to this ion)

K+; selectively permeable

once depolarization occurs, we need to get the cell back to the _____; there are _______ methods of returning it, mostly, we need to get rid of ___ in order for the heart to relax

RMP; multiple; Ca++

more Ca++ uptake/removal efficiency leads to a better __________ effect (the effect of _________ ________); this means the heart is able to _____ better and ______ _______ better

lusitropic; myocardial relaxation; fill; pump blood

4 ways to return the cell to RMP

1. SERCA pumps

2. NCX pumps

3. Na+ ATPase pump (AKA Na+/K+ pump)

4. Ca++ ATPase pump

SERCA pumps account for ___-___% of Ca++ removal; this pump is located on the ________ ________ (___); the heart cannot ________ (______) until the Ca++ has been taken up; Ca++ gets taken up into the ___ by the SERCA pumps with the use of ___ (in the name of the pump is the ______ that drives the breakdown of ____ into ____);

70-75%; sarcoplasmic reticulum (SR); relax (diastole); SR; ATP; enzyme; ATP into energy

____________ is a protein molecule that inhibits SERCA when it is _______________; during exercise, the __________ nervous system stimulates the ______________ of it which ________ its ability to inhibit SERCA (this means Ca++ is taken up _____ and the heart can ______ better)

phospholamban; unphosphorylated; sympathetic; phosphorylation; removes; more; relax

NCX pumps account for ___-___% of Ca++ removal; it trades ___ Na+ for ___ Ca++; Na+ goes ____ the cell and Ca++ goes ____ the cell; there is ____ energy used because it is driven by the __________ __________

20-25%; 3; 1; in; out; no; concentration gradient

__________ __________ inhibit the NCX, leaving behind ____ Ca++, leading to a longer _________ phase for improved ___________ __________

positive inotropes; more; contraction; ventricular emptying

Na+ ATPase pumps are also called ____/____ pumps; they exchange ___ K+ for ___ Na+; K+ goes ____ the cell and Na+ goes ____ the cell; this is important for reestablishing the ____ because the ____ pumps messed with the Na+ concentrations; this pump requires _______ in the form of ____

Na+/K+; 2; 3; in; out; RMP; NCX; energy; ATP

Ca++ ATPase pumps account for about ___% of Ca++ removal; they use ____ to remove Ca++ ___ of the cell, reestablishing the _____

1; ATP; out; RMP

how many phases in a Ca++ dependent cell/nodal cell AP?

3

the 3 phases of Ca++ dependent/nodal cell APs are

0, 3, and 4

phase 4 is the ________ ________ phase; it is due to the “________” channels (channels that allow ____ to _____ _____ into the cell; they do allow in a tiny bit of ___ too, but mainly it is ____)

unstable resting; funny; Na+ to slowly leak; Ca++; Na+

what’s “funny” about these channels? well, most Na+ channels are _______ and cannot _______ at -60/-50/-40 mV, but these are unique in that they are a little bit _____ at these levels of mVs, allowing ____ and a little bit of ____ to _____ _____ the cell

inactive; function; open; Na+; Ca++ to leak into

unstable RMP in the nodal cells is due to these _____ ______ and ____ slowly leaking in; eventually when enough ____ leaks in, the cell reaches _________ _________, opening the ____ channels (leads to phase ___)

funny channels; Na+; Na+; threshold potential; Ca++; 0

phase 0 is the _________ phase; it is when ____ channels allow it ___ the cell, causing the nodal ________ ________ (or _________); during this phase, there is no ______ _____ movement

depolarization; Ca++; into; action potential; depolarization; fast Na+

why is Ca++ coming into the cell? because of the __________ _________ (______ Ca++ ions inside) and the _________ _________ (the inside of the cell is more _______)

concentration gradient; less; electrical gradient; negative

the “action” portion of the action potential is the movement of ___ ____ the cell

Ca++ into

Ca++ channels are open for a ____ _____ before closing; then the ____ channels open (which leads to phase ___)

little bit; K+; 3

phase 3 is the _________ phase; it is when the ____ channels open, allowing it ____ of the cell

repolarization; K+; out

what do the K+ channels do? the depolarization just let in a lot of ________ ions, so when Ca++ channels close, and no more Ca++ comes in, the ________ _______ K+ channels open up to move K+ _____ of the cell; this allows the cell to become more _______ until it gets back to its _____; then the K+ channels _____ and start the cycle over again with the leaking ____in phase ___

positive; delayed rectifier; out; negative; RMP; close; Na+; 4

during phase 3, the Na+ channels are still ________ (except the ______ channels)

inactive; funny

nodal cells have a _______ refractory period, so they repolarize _________ than myocardial cells; this means the nodal cells ________ and _______ the lower level pacemakers with a ________ refractory period (this characteristic of nodal cells is referred to as ________ __________)

shorter; quicker; override and suppress; longer; override suppression

non-pacemaker cell action potentials have ___ phases

5

the 5 phases of the non-pacemaker cell APs are

0, 1, 2, 3, and 4

phase 0 is driven all by ______ ____ channels; when threshold potential is met, ____ channels open and ___ flows in; ___ ______ decreases/stops when the ___ channels open

fast Na+; Na+; Na+; K+ outflow; Na+

why does Na+ come in so fast? 1) the _______ ______ and 2) the ________ ______; (there is more Na+ ______ the cell to begin and the ________ of the cell is more negative to begin; this leads to Na+ having a large potential driving it _____ the cell)

concentration gradient; electrical gradient; outside; interior; into

phase 1 is the _________ of Na+ channels and the opening of the _______ ____ channels leading to a slow ______ of ___; this phase is the ________ and slight ________ on the AP graph

inactivation; gated K+; outflow of K+; overshoot; repolarization

the Na+ channels are open for a _____ ____ before closing _______; as the Na+ channels inactivate, ____ ions ______ leave the cell, resulting in a small _________

little bit; rapidly; K+; slowly; repolarization

phase 2 is the “_______” phase; it is when the ___ channels open and the influx of ____ equals the amount of ____ going out

plateau; Ca++; Ca++; K+

delayed rectifier ___ channels open up, moving equal amounts of K+ _____ the cell as Ca++ is moving ____ the cell; this results in a ________ on the AP graph

K+; out; in; plateau

the plateau phase enhances ________ _______ (which in turn enhances _______ ______ (which is the amount of blood leaving the ________ with each beat)); a longer plateau means a longer _________, squeezing out more _______ ______

ventricular emptying; stroke volume; ventricles; contraction; stroke volume

phase 3 is the inactivation of ___ channels and the activation of ________ ________ ____ channels; the ____ channels close and don’t allow any more ______ ____ ions to enter the cell; the ___ channels open and move ___ ions ____ of the cell, working the cell back towards __________ (the ____)

Ca++; delayed rectifier K+; Ca++; positive Ca++; K+; K+; out; repolarization; RMP

phase 4 is getting rid of ___ to completely ________ the cell to its _____

Ca++; repolarize; RMP

mechanisms during phase 4 include 1) _____ pumps that remove a _________ of the Ca++, 2) ____ pumps also remove Ca++, but now the ___ is back in the cell, 3) so the ___/___ pumps have to restore the correct values, 4) ___ ______ pumps also remove Ca++ with the use of ______ via ___

SERCA; majority; NCX; Na+; Na+/K+; Ca++ ATPase; energy via ATP

the methods of removing Ca++ brings the membrane potential back to the resting value of ____mV, that is… until the ___ ______ delivers Na+ that brings it back up to the ________ _______, starting the cycle over again (phase ___)

-90; AV node; threshold potential; 0

the nodal characteristic of _________/________ ________ is due to the ___ _______ _________ during phase ___

automaticity/spontaneous rhythmicity; Na+ funny channels; 4

why is electrophysiology clinically important? _____ affect the ______ _________ _________

drugs; cardiac action potential

3 drug type examples and what they do:

1. Ca++ blockers lower force of contraction

2. Na+ blockers slow HR

3. K+ blockers prolong refractory

class 1 drugs impact phase ___ and are a ___ channel blocker

class 2 drugs impact phase ___ and are a ____ blocker

class 3 drugs impact phase ___ and are a ____ channel blocker

class 4 drugs impact phase ___ and are a ____ channel blocker

0; Na+; 4; beta; 3; K+; 2; Ca++

the shape of APs can reflect the _________ ________, __________ ________, and _________

conduction velocity, refractory period, and automaticity

the shape of APs can affected by _________ stimuli, _________ stimuli (like ____-______ stimuli), and ______

internal; external; neuro-hormonal; meds

BPM of:

1. SA node

2. atria

3. AV node

4. BoH

5. BBs

6. Purkinje system

7. ventricles

60-100; none; 40-60; 25-40; 25-40; 25-40; none

m/s conduction velocity of:

1. SA node

2. atria

3. AV node

4. BoH

5. BBs

6. Purkinje

7. ventricles

under 0.1; 1-1.2; 0.02-0.05; 1.2-2; 2-4; 2-4; 0.3-1

basically showing the AV node is ________, the BBs are ________, the purkinje network is ________, and the ventricular myocardium is _________

slow; fast; fast; slow

RMP of:

1. SA node

2. atria

3. AV node

4. his bundle

5. ventricles

50-60; 80-90; 60-70; 90-95; 80-90

basically showing the SA and AV nodes have a _____ negative RMP, so they are more ___________

less; excitable

ms AP duration of:

1. SA node

2. atria

3. AV node

4. his bundle

5. ventricles

100-300; 100-300; 100-300; 300-500; 100-200

refractoriness in skeletal muscle only has _________ ________ periods due to their ___ channels

absolute refractory; Na+

but cardiac muscle has ________ _________ and ___________ _________ periods

effective refractory and relative refractory

refractoriness depends on the percentage of ______ ____ channels that have ________ from their _______ state and are therefore capable of _______ again (this is phase ___); (these channels must fully _______ before they can _______, but they cannot ______ when they are in the ________ state)

fast Na+; recovered; inactive; reopening; 0; close; reopen; close; inactive

4 levels of refractoriness:

1. absolute refractory period

2. effective refractory period

3. relative refractory period

4. supranormal period

absolute RP is when cells are _________ to a new stimulus (aka phase ___); cardiac contractility modulation by impulse dynamics uses this concept to help heart failure patients: they _______ the heart during this period to increase ____ during ______ to increase the heart’s __________

unexcitable; 2; stimulate; Ca++; systole; contractility

effective RP is when stimuli can produce a _________ AP, but it is not ______ enough to actually _________

localized; strong; propogate

relative RP is when stimuli can trigger a _________ AP, but the ______ of _____ is less than the normal AP

conducted; rate of rise

supranormal period is when an AP is triggered by a _______ than normal ________

less; stimulus