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
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