ELEKTROFISIOLOGI JANTUNG

DENNY AGUSTININGSIH

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Two Types of Cardiac Muscle Cells

Ordinary: Make up 95%- 99% of all heart muscle cells.

Also called worker cells or contractile cellsBiochemically similar to red skeletal muscleSlow to fatigue

Specialized: make up remaining 1%-5%Also called autorythmic or automatic cells Responsible for initiation and/or transportation of electrical impulses through the heart pacemaker potential

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The Pacemaker Cells

MEKANISME DEPOLARISASI DAN REPOLASASI

---------------------

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

++++++++++++++

+++++++++++++

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

-----------------------

Awal depolarisasi Awal repolarisasi

Depolarisasi sempurna

stimulasi Resting state

+/--/+

- Depolar karena masuknya ion Ca, Na - Repolarisasi karena keluarnya ion Kalium dimudahkan oleh parasimpatis

Mem

bra

ne

Pot

enti

al (

mV

) 0

-40

-60

Time (msec)DepolarizationSpontaneous

ThresholdPotential

Ca

++ in

K+ out

Ca (T-type)

Na

K

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Sinoatrial Node

Atrioventricular Node

CONDUCTING SYSTEM

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Extrinsic Influences

Autonomic nervous system: utk menyelaraskan denyut cor

Hormonal influences: tiroid meningkatkan denyut cor

Ionic influencesTemperature influences: tubuh demam

denyut cor meningkat mrangsang hipotalamus agar kerja cor cepat shg membuang panas

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Cardiac Arrhythmias

Tachycardia: Heart rate in excess of 100bpm

Bradycardia: Heart rate less than 60 bpm

Sinus arrhythmia: Heart rate varies 5% during respiratory cycle and up to 30% during deep respiration

Premature atrial contractions: Occasional shortened intervals between one contraction and succeeding, frequently occurs in healthy people

MYOGENIC CONDUCTION

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Cardiac myocyte action potential:

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AP-contraction relationship:

AP in skeletal muscle is very short-lived AP is basically over before

an increase in muscle tension can be measured.

AP in cardiac muscle is very long-lived AP has an extra component,

which extends the duration. The contraction is almost

over before the action potential has finished.

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Mechanism of Cardiac Muscle Excitation, Contraction & Relaxation

Figure 14-11: Excitation-contraction coupling and relaxation in cardiac muscle

OCT 2008 DENNY AGUSTININGSIH 15

mV

+20

-90

0

4

0

12

3

AbsoluteRefractoryperiod

0 400200100 300

RelativeRefractoryperiod

Period ofSupranormalexcitability

Masa refraktor absolute: saat ion Ca masuk otot, cor g bisa dirangsan tujuannya agar cor tidak ada fase tetani/ kejang

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Electrocardiogram (ECG)Composite of all action potentials of

nodal and myocardial cells detected, amplified and recorded by electrodes on arms, legs and chest

OCT 2008 DENNY AGUSTININGSIH 17

EKG:

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P

Q

R

S

T

OCT 2008 DENNY AGUSTININGSIH 19

P

Q

R

S

T

OCT 2008 DENNY AGUSTININGSIH 20

P

Q

R

S

T

0.5 Sec

1 sec