The heart contracts rhythmically due to electrical impulses generated by specialized pacemaker cells. There are two types of cardiac muscle cells: contractile cells that pump blood and pacemaker cells that initiate and conduct electrical impulses. The impulse conducting system consists of the sinoatrial node, atrioventricular node, bundle of His, and Purkinje fibers. An action potential occurs when the membrane potential changes from resting potential (-90 mV) to depolarized (0 mV) and back again due to the movement of ions through membrane channels. Pacemaker cells spontaneously depolarize to initiate each heartbeat.

1. Electrophysiology of
The Heart
dr. Hendyono Lim, SpJP FIHA

2. Impulse-Conducting System
• Contraction of cardiac muscle cells to eject blood is triggered by action
potentials sweeping across the muscle cell membranes
• Heart contracts or beats rhythmically as a result of action potentials
generates by itself, called autorhythmicity, or automaticity.
• There are 2 specialized types of cardiac muscle cells:
– Contractile cells: 99% cardiac muscle cells for mechanical
pumping, do not initiate action potentials
– Autorhytmic cells: do not contract but specialized for
initiating and conductiong the action potentials responsible
for contraction
pacemaker

3. Impulse-Conducting System
• Consist of specialized cells initiate heart-beat and
electrical contractions
– SA node (rate 70 – 80)
– AV Node (rate 40 – 60)
– Right and Left bundle branch (rate 20 – 40)
– Purkinje fibers
pacemaker
20-40 kali
kalo sa node bermasalah akan diambil alih av node (bisa tapi jadi inefisien) -> SSS (six sinus syndrome) -> heart rate turun -
cardiac output ngga cukup - pusing (mau pingsan)
SA node di atrium kanan di epikardial
WPW syndrome -> aksesori pathway

4. Impulse-Conducting System

5. • Rhythmic contraction of the heart relies on electrical impulses along
conduction pathway
– Marker of electrical stimulation  action potential
• 3 types of cardiac cells capable of electrical excitation:
– Pacemaker cells (SA node, AV node)
– Specialized rapidly conducting tissues (e.g. purkinje fibers)
– Ventricular and atrial muscle cells
• Sarcolema each of these cardiac cells is a phospholipid bilayer that is
impermeable ion serve as ion channels, passive cotransporters, and
active transporters.
– Maintain ionic concentration gradients and charge differentials between
inside and outside cardiac cells
Impulse-Conducting System
RBBB, LBBB -> QRS wavenya lebar karena
ngga lewat jalur khusus, cuma dari otot ke
otot

6. • Movement of specific ions across cell
membrane serve as basis of the action
potential
• Passive ion movement depends on:
–Energetic favorability
–Permeability of the membrane for ion
ION MOVEMENT AND CHANNELS
ion dalam otot jantung bekerja keluar masuk otot berdasar permeabilitas / voltage

7. ION MOVEMENT AND CHANNELS
• Energetics
– Direction of passive ion
flux driven by
concentration gradient
and transmembrane
potential (voltage)

8. ION MOVEMENT AND CHANNELS
• Permeability
– Cell membrane at its resting potential is not permeable to
sodium
– Membrane permeability is dependent on the opening of
specific ion channels (e.g. Na+, K+, Ca++)
– Voltage across the membrane determines what fraction of
channels is open
– Gating of channels is voltage sensitive
– Membrane voltages changes during depolarization and
repolarization of the cell, specific channels open and close
membran ada kanal ion khusus

9. ION MOVEMENT AND CHANNELS

10. ION MOVEMENT AND
CHANNELS
• Permeability
– At a voltage of -90 mV (ventricular muscle cell resting
voltage) channels are predominantly closed, Na+ ions cannot
pass through
– Rapid depolarization renders membrane potential less
negative and Na+ ions permeate through the open channels
– Activated channels remain open for only brief time, then
spontaneously close to inactive state
– Inactivated state persists until the membrane voltage
repolarized nearly back to its original resting level

11. RESTING POTENTIAL
• In nonpacemaker cardiac cells at rest, electrical
charge differential between inside and outside
cell corresponds to the resting potential
• Magnitude of resting potential depends on:
– Concentration gradients ions between inside and
outside the cell
– Relative permeabilities of ion channels that are open
at rest

12. RESTING POTENTIAL
• K+ concentration much greater inside cardiac cells
compared with outside
• Protein pump (Na+K+-ATPase) extrudes 3 Na+ ions out
of the cell exchange for the inward of 2 K+ ions
– Maintain intracellular Na+ at low levels and intracellular K+
at high levels
• K+ channels open in resting state when other ionic
channels are closed
– K+ flow outward direction down its concentration gradient

13. RESTING POTENTIAL

14. ACTION POTENTIAL
• Permeability cell
membrane to specific
ions changes because of
voltage-gating
characteristics of the ion
channels
• Each type of channels
has a characteristic
pattern of activation and
inactivation determines
progression of electrical
signal

15. ACTION POTENTIAL
• Cardiac muscle cell
– Resting potential remains stable, at
approximately -90 mV (resting state before
depolarization  phase 4)
– Phase 0
• Na+ channels open, and rapidly enter the cell
• Transmembrane potential progressively less
negative
– Phase 1
• Brief current of repolarization during phase 1
returns membrane potential to approximately 0
mV
• Outward flow of K+ through a type of transiently
activated K+ channel
baru bisa bergerak kalo disenggol sama sel sebelahnya
diluar otot jantung lebih banyak natrium kalsium yang di dalem kalium
begitu pacemaker terdepolarisasi akan menghantarkan ke sel sekelilingnya -> mulai jadi positif sampe titik tertentu ->
pertama terbuka kanal natrium -> natrium masuk -> dalam otot jantung positif sampe ke atas -> kanal tertutup kalium
bekerja -> kalium keluar -> mulai turun
dalam keadaan resting stabil -90 mv

16. ACTION POTENTIAL
• Cardiac muscle cell
– Phase 2
• Long “plateau” phase mediated by the balance of
outward K+ currents, in competition with an inward
Ca++ current through specific L-type calcium channels.
• L-type calcium channels begin open during phase 0,
when membrane voltages reaches approximately -40
mV
• The near equalty current Ca+ inward and K+ outward
resulted membrane voltage does not changes
• As the Ca++ channels gradually inactivate and efflux of
K+ exceed influx of Ca+ then phase 3 begins
kanal dua"nya terbuka -> kalium keluar kanal kalsium terbuka (fase plateau)

17. ACTION POTENTIAL
• Cardiac muscle cell
–Phase 3
•Repolarization returns the
transmembrane voltage back to resting
potential approximately -90 mv.
•Phase 3 completes action potential
cycle, return to phase 4 preparing the
cell for next stimulus for depolarization
kalsium tertutup tersisa kanal kalium

18. ACTION POTENTIAL
• Pacemaker cells
–SA node and AV node
–Self-initiated depolarization in a
rhythmic fashion  automaticity
–Cells undergo spontaneous
depolarization during phase 4, when
threshold voltage is reached, action
potential upstroke is triggered
-60
perlahan dalam keadaan resting potensial aksi -60. ada
sel natriu kalium masuk yang menyebabkan dalam sel
semakin positif. dalam sel pacemaker ada voltage gated.
begitu mencapai -40, kanal kalsium terbuka. terus banjir k-
kalsium masuk ke dalam sel jadi positif. kanal kalium
kebuka keluar kalium jadi negatif lagi pelan".
ada nak atpase, natrium kalsium cotransporter ->
menyeimbangkan

19. ACTION POTENTIAL
• Pacemaker cells
–Maximum negative voltage is
approximately -60 mV, persistently
negative membrane voltage causes
fast sodium channels remain
inactivated
–Phase 4 has an upward slope,
representing spontaneous gradual
depolarization known as pacemaker
current predominantly by Na+ ions.

20. ACTION POTENTIAL
• Pacemaker cells
– Phase 0 upstroke less rapid and reaches
lower amplitude than cardiac muscle
cell. Resulted from fast sodium
channels being inactivated and the
upstroke action potential relying on
Ca++ influx through relatively slow
calcium channels
– Repolarization occurs similar to
ventricular muscle cells, relies on
inactivation of calcium channels and
increased activation of potassium
channels with enhance K+ efflux

21. REFRACTORY PERIODS
• Cardiac potential longer in duration,
supporting prolonged Ca++ entry and
muscle contraction during systole.
• Results in prolonged period of
channel inactivation during muscle is
refractory to restimulation
• This long period allows ventricles
have sufficient time to relax and
refill before next contraction
absolute RP -> walaupun dirangsang dengan voltage
berapapun tidak akan terdepolarisasi
relatif RP -> di fase 3 terutama -> sudah mulai istirahat ->
kalo dirangsang lagi dengan kekuatan lebih tinggi bisa
terdepolarisasi lagi
kanal natrium semua kebuka

22. REFRACTORY PERIODS
• As phase 3 action potential progresses, increasing number
of Na+ channels recover from inactivated to resting states,
then open in response to the next depolarization
• Absolute refractory period refers to period cell completely
unexcitable
• Effective refractory period includes absolute refractory
period include a short interval of phase 3, which
stimulation only produces a localized action potential
• Relative refractory period is the interval during stimulation
triggers an action potential is conducted, but the rise of
action potential is lower because some Na+ channels are
inactivated and some delayed rectifier K+ channels remain
activated, thus inward currect is reduced
• Short “supranormal” period is a less-than-normal stimulus
can trigger an action potential

23. IMPULSE CONDUCTION
• During depolarization, electrical impulse
spreads rapidly along each cardiac cell,
connected through low-resistance gap
junctions
• Speed of tissue depolarization and
conduction velocity depend on inward
current (largely sodium channels)
• Tissues with high concentration of Na+
channels (e.g Purkinje fibers) have a
large and fast inward current  support
rapid conduction
av node pelan biar darah atrium sempet masuk ventrikel sebelum
listrik lanjut his purkinje sebelum ventrikel berkontraksi
atrium fibrilation -> kalo heart rate atrium sangat tinggi (200-300),
nggabisa masuk ke ventrikel karena ada perlambatan di av node
jadi heart rate ngga terlalu tinggi

24. REFERENCES
• Human Physiology: From Cells to Systems, Ninth
Edition. Lauralee Sherwood
• Pathophysiology o heart disease (Lilly);
Pathophysiology o heart disease : a collaborative
project o medical students and aculty / editor,
Leonard S.Lilly. — Sixth edition.