ELEKTROFISIOLOGI JANTUNGIrawan Yusuf

Tujuan Pokok BahasanDiscuss the ionic basis of the resting potential in atrial and ventricular cells. Discuss the ionic basis of each of the four phases of the action potential in "working" myocardial (atrial and ventricular) cells and Purkinje cells, and of the two phases of the action potential in (S-A and A-V) nodal cells. Discuss the ionic basis of diastolic depolarization (phase 4); explain why these mechanisms differ between nodal and Purkinje cells; list the pacemakers of the heart and their approximate firing rates in order of fastest to slowest. Discuss the ionic basis of the absolute and relative refractory periods, and how faster heart rates shorten these periods. Discuss the ionic basis of propagation of action potentials throughout the heart; list the factors that affect conduction velocity; list approximate conduction velocities, in the different regions of the heart, from slowest to fastest; explain why such velocities are fast or slow. Describe the mechanisms that underlie the positive and negative chronotropic and dromotropic effects of sympathetic and parasympathetic neurotransmitters. Given clinically relevant situations of electrophysiological disturbances.

PendahuluanMengawali aktifitas mekanik jantungPotensial aksi yang lebih lama dibandingkan sel saraf dan otot rangkaSetiap bagian jantung mempunyai karakteristik potensial aksi yang khasMenjadi dasar untuk memahami kelainan irama jantung

Semilunar valves(aortic & pulmonary)Tricuspid (AV) ValveBicuspid (AV; mitral) ValveLALVRVRAHeart Valves and Major Blood VesselsAorta (to the systemiccirculation)SuperiorVena cavaPulmonary Arteries(to lungs)Pulmonary Veins(from lungs)InferiorVena cavaRA: right atriaLA: left atriaRV: right ventricleLV: left ventricle interatrial septum interventricular septumapex ventricular muscle

Dasar Ionik Aktifitas Listrik JantungDisebabkan oleh pergerakan arus ion dari luar sel kedalam sel atau sebaliknya melalui saluran ion (ion channel)Pergerakan ion terjadi akibat perbedaan konsentrasi ion di dalam dan di luar sel

Konsentrasi ion di dalam dan diluar selIonEkstrasel (mM)Intrasel (mM)

Na+145 12

K+ 4135

Ca2+ 210-4

Cl-150 5

Struktur dan Fungsi Saluran IonMerupakan protein integral pada membran sel otot jantung dan pacemaker cellsBersifat selektif terhadap ion tertentuArah pergerakan ion ditentukan oleh perbedaan konsentrasi ion di luar dan di dalam selProses gating diatur oleh rangsangan listrik, kimia dan mekanik

Potensial Aksi Pada Otot JantungMempunyai lima fase, masing-masing:Fase 0 (upstroke, fast depolarization)Fase 1 (early repolarization)Fase 2 (plateau)Fase 3 (fast repolarization)Fase 4 (resting membrane potential)Terdapat dua jenis potensial aksi:Potensial aksi cepat (fast responses)Potensial aksi lambat (slow responses)

Cardiac Action Potential(differ from cell to cell: sizeand channel numbers)LengthPlateauCa++ (Em and contraction)K+ channel closureTime (msec)

Cardiac versus Skeletal Muscle AP

Gap JunctionPlasma membraneCardiac Muscle Cells are Electrically Connected via Gap JunctionsCardiac Muscle Cellsdesmosome(protein fibres)desmosome resist stretching important as it occurs every time the heart fills (cardiac cycle)

gap junction passage of currentsteps in conduction intercalated disksarcomershypertrophy: reduced contraction

Dasar Ionik Potensial Membran IstirahatPotensial membran istirahat berkisar antara -80 mV sampai -90 mV pada otot ventrikel, lebih positif pada otot atrium, nodus AV dan nodus SADitentukan oleh pergerakan ion K+ keluar sel, dan aktifitas pompa Na+-K+ (Na+-K+ pump)

Dasar Ionik Potensial AksiFase 0 (depolarisasi cepat)

Disebabkan oleh arus ion Na+ kedalam sel (INa) melalui activation gate (m gate)Pada saat potensial membran (Vm) mencapai 30 mV-40 mV terjadi proses inaktifasi saluran Na+, inactivation gate (h gate) mulai tertutupProses inaktifasi saluran Na+ mendasari masa refrakter

Dasar Ionik Potensial AksiFase 1 (repolarisasi awal)

Merupakan repolarisasi awal yang berlangsung singkatTerjadi akibat inaktifasi saluran Na+ dan aktifasi saluran K+Terjadi pergerakan K+ keluar sel yang berlangsung singkat (Ito, transient outward current) Fase ini sangat menonjol pada potensial aksi di serabut Purkinje

Dasar Ionik Potensial AksiFase 2 (plateau)

Merupakan fase yang paling panjangTerjadi akibat INa, ICa dan IK, IK1 dan ItoICa masuk melalui saluran Ca2+ tipe L dan TICa berperan dalam proses kontraksi jantung dengan memicu pelepasan Ca2+ intrasel di retikulum sarkoplasma (Ca2+-induced Ca2+ release)Modifikasi ICa melalui saluran Ca2+ dengan obat-obatan dapat mengurangi atau meningkatkan kontraksi jantung

Dasar Ionik Potensial AksiFase 3 (repolarisasi cepat)

Fase ini terjadi bila arus K+ keluar sel melebihi masuknya arus Ca2+ (ICa)Ito menentukan lamanya fase 2 atau awal fase 3, terutama pada atriaIK1 (inwardly rectified), memegang peranan paling penting pada proses repolarisasi

SISTIM KONDUKSI JANTUNG

Sistem konduksi jantung berfungsi untuk menyebarkan aktifitas listrik ke seluruh otot jantungSistim konduksi jantung terdiri dari:nodus SA (pacemaker utama jantung)traktus internodalnodus AVberkas Hisserabut Purkinje

1. Sinoatrial (SA) node3. Atrioventricular (AV) node4. AV bundle(Bundle of His)LVRV5. Right and left bundle branches6. Purkinje fibres2. Internodal pathwayscoordinated contractiongap junctions conduction fibres: larger diameter atria ventricles: separated by fibrous bundlesThe Conduction System of the Heart(pacemaker conduction fibres contractile fibres )

a. AP is initiated in the SA noded. AP travel rapidlythrough the branchbundlesf. restb. AP are conductedthroughoutthe atria very rapid large cellsc. Conduction slows at the AV node small cellse. AP spreadthroughtheventricles(bottom to top)

SISTIM KONDUKSI JANTUNGPenyebaran Potensial aksi

Kecepatan penghantaran potensial aksi tergantung dari struktur dan sifat sel masing-masing sistem konduksiTerjadi perlambatan penyebaran potensial aksi dari atria ke ventrikel karena:memungkinkan pengisian ventrikel yang optimaloptimasi kontraksi ventrikelmemaksimalkan proses ejeksi ventrikelDepolarisasi berakhir pada bagian posterobasal ventrikel kiri, konus pulmonal dan bagian atas septum

Kecepatan konduksi pada jaringan sel otot jantungJaringanKecepatanLamaFrekwensikonduksi (m/det)konduksi (det)kali/menit)

Nodus SA 0.05 0.15 60-100Otot atrial 1.0-1.2 0.15Nodus AV 0.02-0.05 0.08 40-45Berkas His 1.2-2.0 0.08 25-40Purkinje 2.0-4.0 0.08 25-40Otot Ventrikel 0.3-1.0 0.08

Gangguan Irama JantungGangguan pembentukan impulsGangguan penghantaran impulsGangguan pembentukan dan penghantaran impuls

Dasar-dasar ionik aritmiaPerubahan pada potensial membran istirahatMenurunnya potensial membran istirahatPerubahan kecepatan fase 0Menurunnya membran potensial istirahatBerubahnya aktifitas saluran Na+ dan Ca2+Perubahan pada fase 1 sampai 3Lamanya fase 2Lamanya proses repolarisasi (fase3)

Gangguan Pembentukan ImpulsOtomatisitas normalKecepatan abnormal: Takikardi dan BradikardiIrama abnormal: Impuls prematureOtomatisitas abnormalTrigger activityEarly after depolarization (EAD)Delayed after depolarization (DAD)

Gangguan Konduksi ImpulsPerlambatan dan hambatan konduksiBlok SABlok AVBlok percabangan berkas HisMekanisme reentry

ELECTROCARDIOGRAMAs the heart undergoes depolarization and repolarization, the electrical currents that are generated spread not only within the heart, but also throughout the body. This electrical activity generated by the heart is generally measured by an array of electrodes placed on the body surface and the resulting tracing is called an electrocardiogram (ECG, or EKG).The different waves that comprise the ECG represent the sequence of depolarization and repolarization of the atria and ventricles.

ELECTROCARDIOGRAMUses of the EKGHeart Rate Conduction in the heart Arrythmias Direction of the cardiac vector Damage to the heart muscle Provides NO information about pumping or mechanical events in the heart

Normal ECG

ELECTROCARDIOGRAMThe P-wave represents the wave of depolarization that spreads from the SA node throughout the atria and is usually 0.08 to 0.1 seconds (80-100 ms) in duration. The period of time from the onset of the P-wave to the beginning of the QRS is termed the PR interval and normally ranges from 0.12 to 0.20 seconds. This interval represents the time between the onset of atrial depolarization and the onset of ventricular depolarization.The QRS complex represents ventricular depolarization. The duration of the QRS complex is normally 0.06 to 0.1 seconds indicating that ventricular depolarization normally occurs very rapidly.

ELECTROCARDIOGRAMThe isoelectric period (ST segment) following the QRS is the time at which the entire ventricle is depolarized and roughly corresponds to the plateau phase of the ventricular action potential. The T-wave represents ventricular repolarization and is longer in duration than depolarization (i.e., conduction of the repolarization wave is slower than the wave of depolarization). The QT interval represents the time for both ventricular depolarization and repolarization to occur, and therefore roughly estimates the duration of an average ventricular action potential. This interval can range from 0.2 to 0.4 seconds depending upon heart rate.

The Normal EKG recorded on the Bipolar Limb Leads