Origin and Conduction of the Signal to Contract

Origin and Conduction of the Signal to Contract

Origin and Conduction of the Signal to Contract

Origin and Conduction of the Signal to Contract

TimingTiming• adequate rateadequate rate• time to filltime to fill• adjustableadjustable

TimingTiming• adequate rateadequate rate• time to filltime to fill• adjustableadjustable

CoordinationCoordination• atrial syncytiumatrial syncytium• pausepause• ventricular ventricular

syncytiumsyncytium

CoordinationCoordination• atrial syncytiumatrial syncytium• pausepause• ventricular ventricular

syncytiumsyncytium

P

The PacemakerThe Pacemaker

AV

Sinoatrial NodeSinoatrial Node

Sep

tum

RA LA

Fibrous skeleton

Right Ventricle Left

Ventricle

His Bundle

SA

Atrioventricular Node

Maximum Diastolic Potential

Time (ms)

-100

+20

-60

-20

200 6000 400

Membrane Potential(mV)

Spontaneous Depolarization

Ca++Ca++

Refractory

Period

gCa

Ca++

K+

gK

(K open)

K+

gK

(K open)↑

gCa, T?↑

gNa in if,

K+

K close ↑K+

gK

K close↓

gNa in if, hyperpolarization-activated current↑

Threshold for Ca,L

Ca++

gCa, L↑

Origin and Conduction of the Signal to Contract

Origin and Conduction of the Signal to Contract

TimingTiming• adequate rateadequate rate• time to filltime to fill• adjustableadjustable

TimingTiming• adequate rateadequate rate• time to filltime to fill• adjustableadjustable

CoordinationCoordination• atrial syncytiumatrial syncytium• pausepause• ventricular ventricular

syncytiumsyncytium

CoordinationCoordination• atrial syncytiumatrial syncytium• pausepause• ventricular ventricular

syncytiumsyncytium

Sep

tum

RALA

Fibrous skeleton

Right Ventricle

Left Ventricle

AV

Atrial DepolarizationAtrial Depolarization

His Bundle

SA

RALA

RV LV

Sep

tum

SA

AV

Left bundle branch of Purkinje

network

Right bundle branch of Purkinje network

His Bundle

AV

Connective Tissue Right Atrium

Right Ventricle

Slow Slow conductionconduction

small cellssmall cellsslow slow

depolarizationdepolarizationfew gap few gap

junctionsjunctionsLow pass Low pass filterfilter

Reserve Reserve PacemakerPacemaker

Slow Slow conductionconduction

small cellssmall cellsslow slow

depolarizationdepolarizationfew gap few gap

junctionsjunctionsLow pass Low pass filterfilter

Reserve Reserve PacemakerPacemaker

Atrioventricular NodeAtrioventricular Node

Nodal fibers

Bundle of His fibers

Nodal fibers

Fibrous skeleton of the HeartFibrous skeleton of the Heart

Connective Tissue InsulationConnective Tissue Insulation

Atrium

Ventricle

Ventricular Septum

His BundleHis Bundle

Bundle of His

RALA

RV LV

Sep

tum

SA

AV

Left bundle branch of

Purkinje network

Right bundle branch of Purkinje network

Right bundle branch of Purkinje network

Left bundle branch of Purkinje network

AV

Connective Tissue Right Atrium

Right Ventricle

His Bundle

Bundle of His

RALA

Fibrous skeleton

Right Ventricle

Left Ventricle

SA

AV His Bundle

Sep

tum

Purkinje NetworkPurkinje Network

Left bundle branch of Purkinje network

Right bundle branch of Purkinje network

Purkinje FibersPurkinje Fibers

Normal Myocardium

Nerves

Purkinje FibersPurkinje Fibers

Large fiber diameterLarge fiber diameter Rapid depolarizationRapid depolarization Many gap junctionsMany gap junctions

High speed conduction of the signal to contractHigh speed conduction of the signal to contract

Large fiber diameterLarge fiber diameter Rapid depolarizationRapid depolarization Many gap junctionsMany gap junctions

High speed conduction of the signal to contractHigh speed conduction of the signal to contract

Ventricular DepolarizationVentricular Depolarization

RALA

Fibrous skeleton

Right Ventricle

Left Ventricle

SA

AV His Bundle

Sep

tum

Left bundle branch of Purkinje network

Right bundle branch of Purkinje network

Impulse Conduction TimeImpulse Conduction Time

Costanzo Fig 4-13

TerminologyTerminologyEpicardium and Endocardium are connective tissue & endothelium or mesothelium.

Only the myocardium contains cardiac muscle.

Ventricular Action Potential DurationVentricular Action Potential Duration

Epicardium

Endocardium

Ventricular RepolarizationVentricular RepolarizationEpicardium

Endocardium

Subepicardial Myocardium

Subendocardial Myocardium

depolarization

Predominant path of repolarization

AV

Autonomic Influence on PacemakerAutonomic Influence on Pacemaker

Sep

tum

RA LA

Fibrous skeleton

Right Ventricle Left

Ventricle

His Bundle

SA

Parasympathetic Effect on Pacemaker CellsParasympathetic Effect on Pacemaker CellsMembrane Potential (mV)

-100

+20

-60

-20

200 8006000 400Time (ms)

1000

No autonomic influenceHeart period = 600 ms

Parasympathetic influenceHeart period = 1000 ms

Slower rise to peak

More negative maximum diastolic potential

Slower spontaneous depolarization

⇒↓ i f

open KAch ⇒ ↑ PK++K+

Ach

ATP

c-AMP-opening of Ca++ channelsc-AMP

out in

Gi

Gi

AC

M2

Vagal Influence at RestVagal Influence at Rest

Heart Rate(beats/min)

120

110

100

60

90

70

80

50

40

Dose of Atropine(Acetylcholine receptor antagonist)

Sympathetic Effect on Pacemaker CellsSympathetic Effect on Pacemaker CellsMembrane Potential (mV)

-100

+20

-60

-20

200 8006000 400Time (ms)

1000

No autonomic influenceHeart period = 600 ms

Sympathetic influence

Heart period = 400 ms

Faster spontaneous depolarization

dV/dt during depolarization

Faster repolarization

NE

C-AMP

ATPAC

GS

ß1

out in

Na+ If opens at less negative

membrane potential

+

Ca++PO4

PKAactive PKAinactive

Ks (more rapid repolarization)

dV/dt during depolarization

120

110

100

60

90

70

80

50

40

Heart Rate(beats/min)

Atropine

Atropine (Achreceptor antagonist)

Propranolol (ß-receptor antagonist)

Propranolol

Autonomic Innervationof the AV nodeAutonomic Innervationof the AV node

Parasympathetic Ganglion Cells

ParasympatheticParasympathetic slower conductionslower conduction more filteringmore filtering slower pacemakerslower pacemaker

SympatheticSympathetic faster conductionfaster conduction less filteringless filtering faster pacemakerfaster pacemaker

ParasympatheticParasympathetic slower conductionslower conduction more filteringmore filtering slower pacemakerslower pacemaker

SympatheticSympathetic faster conductionfaster conduction less filteringless filtering faster pacemakerfaster pacemaker

The Electrocardiogram(ECG)

The Electrocardiogram(ECG)

or is it EKG?or is it EKG?or is it EKG?or is it EKG?

Completely PolarizedCompletely Polarized

0+

-

+-

Ref Exp

+ + + + ++ + + + +- - - - - - - ---

0

muscle

Potential Difference(voltage)

Time

Potential Difference(voltage)

Reference Electrode

Exploring Electrode

voltmeter

DepolarizingDepolarizing

0+

-

+- 0

Ref Exp

+ + + + +- - - - -+ + + + +

- - - - -

depolarization

DepolarizedDepolarized+- 0

Ref Exp

+ + + + ++ + + + +- - - - - - - ---

0+

-

RepolarizingRepolarizing+- 0

Ref Exp

repolarized

0+

-

- - - - -+ + + + +

+ + + + +- - - - -

RepolarizedRepolarized+- 0

Ref Exp

0+

-

+ + + + ++ + + + +

- - - - - - - ---

repolarized

- - - - -+ + + + ++ + + + +- - - - -

Wave of depolarization

+ + + + +- - - - -- - - - -+ + + + +

+-

Septum

LV LV free wall

RV

LA

Lead I

Generation of Lead I ECGGeneration of Lead I ECG

ReferenceElectrode

Right Arm

ExploringElectrode

Left Arm

depolarized

normally polarized

dipole vector