Lecture 02 - Basics of Cardiac Electrophysiology.pptx

Automaticity - the property of cardiac cells to generate spontaneous depolarize and trigger
action potentials.
Excitability - the ability to respond to certain stimuli by producing action potentials or impulses of electrical signal.
Conductivity - each muscle cell can pass electrical impulses from cell to cell
Refractory Period - after an action potential initiates, the cardiac cell is unable to initiate another action potential for some duration of time
Contractility - the action of muscle fibers to shorten in length (contraction)

1. B a s i c s f C a r d i a c E l e c t r o ph y s i o l o g y Dr:SANAIHSAN

2. H u m a n H e a r t Hollow, muscular, pumping organ. Located in middle mediastinum. Covered by Pericardium. Four chambers Rt. And Lt. Atria Rt. And Lt. Ventricles Valves; AV valves – Tricuspid and Mitral valve Pulmonary and Aortic valves

3. Great Vessels SVC, IVC Pulmonary Trunk (RPA,LPA) Pulmonary Veins Aorta Two pumps; Right heart – pulmonary circulation Left heart – systemic circulation

4. Pulmonary C i r c u l a t i o n V s . S y s t e m i c C i r c u l a t i o n

5. Cardiac Muscle Cells 2 main types of cardiac myocytes Conducting Cells (Pacemaker Cells, Nodal Cells) Contractile Cells (Non- Pacemaker Cells) Conducting cells Specialized cells - ability to spontaneously depolarize. Comprises electrical system of the heart. Contractile cells Provides contraction of the heart chambers. Consists of contractile proteins (actin, myosin). Forms bulk of the myocardium.

6. P r o p e r t i e s o f C a r d i a c M y o c y t e s Automaticity - the property of cardiac cells to generate spontaneous depolarize and trigger action potentials . Excitability - the ability to respond to certain stimuli by producing action potentials or impulses of electrical signal . Conductivity - each muscle cell can pass electrical impulses from cell to cell Refractory Period - after an action potential initiates, the cardiac cell is unable to initiate another action potential for some duration of time Contractility - the action of muscle fibers to shorten in length (contraction)

7. A c t i o n P o t e n t i a l in C o nd u c t i n g C e ll s Occurs in SA node, Av node cells. The key features of these action potentials are the property of automaticity, as well as the fact that the depolarization phase is slower, and with a shorter APD than “fast- channel” action potentials. Phases : Phase 4 Phase Phase 3

8. N o d a l cell No stable RMP : - 60 mv Funny Sodium channels (leaky) Slow channels – Na+ into the cell T- type Ca++ channels (opens at - 55mv) – Ca++ gets inside the cell Na+ channels + Ca++ channels opening together reach threshold potential: - 40 mv At threshold potential, L- type Ca++ channels (voltage- sensitive) open : Ca++ gets into the cell and reaches approx. +40mv = Depolarization At +40mv L- type Ca++ channels close, and voltage gated K+ channels open : K+ (efflux) = Repolarization Voltage reaches - 60 mv (repolarization), K+ channels close, funny Na+ channels open (Na+ influx)

9. Gap Junctions (connexion proteins) Structural proteins (Desmosomes = Cadherin + desmoplakin + keratin) keeps the cells intact during diastole Gap Junction + Desmosomes = Intercalated discs  +ive charge ions moves from one cell to other through gap junctions.

10. A c t i o n P o t e n t i a l in C o n t r a c t i l e C e ll s Occurs in atrial, ventricular myocardium, His- Purkinji system. These action potentials have a true resting potential, a rapid depolarization phase, and a prolonged plateau phase. Phases : Phase Phase 1 Phase 2 Phase 3 Phase 4

11. C o n t r a c t i l e cell RMP: - 85 mv to - 90mv  +ive ions moved into the cell causes threshold potential: - 70mv Voltage gated Na+ channels open at - 70mv: Na+ flows inside the cell (depolarization- Phase 0) Na+ inflow causes depolarization, and causes opening of Ca++ channels and reaches +10mv At 10mv Na+ channels close, at same time K+ channels open causes: K+ efflux (Phase1) The voltage drops to 0mv, at 0mv voltage gated L- type Ca++ channels: Ca++ influx K+ efflux, Ca++ influx = No change in membrane potential (plateau – Phase2 about 250ms) L- type Ca++ channels closes, K+ channels open: K+ (efflux) repolarization (Phase 4). Reaches RMP, and rest for a brief period of time until +ive charges gets inside from the nodal cells and reaches threshold potential.

12. Sarcoplasmic reticulum – Ca++ sensitive channels Ca++ can bind to RYR- 2, or it can binds to a protein (Calmodulin) and binds to Ryanodine receptor type - 2 (RYR- 2) on SR, and open ion channels – Ca++ starts flowing out of SR into sarcoplasm. Ca++ binds to troponin C, and causes muscle contraction. Ca++ uptake by ER, and to the ECF. The same pumps are located on Sarcolemma and ER. Ca++ - H+ ATPase Na+ - Ca++ exchanger

13. E l e c t r i c a l S y s t e m o f the H e a r t Special system ; Generate rhythmical impulses – causes rhythmical contraction of cardiac myocytes Propagate these impulses rapidly throughout the heart The parts of the heart conduction system can be divided into; Nodal tissue - those that generate action potentials Conducting fibers - those that conduct them This system allows atria to contract about 1/6 th of a second before ventricle- this allows the blood to fill the ventricles before they contract.

14. C o m p o n e n t s o f H e a r t ’ s E l e c t r i c a l S y s t e m SA Node Internodal Fibers AV node Bundle of His (Atrioventricular Bundle) Bundle branches Right Bundle Branch Left Bundle Branch Left Anterior Fascicle Left Posterior Fascicle 6) Purkinji fibers

15. S i n o atrial ( S i n u s ) N o d e Structure: Small, flattened, ellipsoid 3mm wide, 15mm long, 1mm thick Location: Superior- posterolateral wall of RA Below and slightly lateral to SVC opening Blood Supply: RCA – 55% LCx – 45% Rate of impulse generation: 70-80bpm

16. I n t e r n o d a l F i b e r s Location: Special conducting pathways in atrial wall Function: To transmit impulses from SA node to AV node & LA Types: Three fibers Anterior: Bachman Middle: Wenckebach Posterior: Thorel

17. A t r i o ventricular ( A V ) N o d e Location: Subendocardially in medial wall of RA 1cm above CS ostium Basal attachment of septal leaflet of Tricuspid valve Blood supply: RCA: 90% LCx: 10% Normal conduction delay: About 0.12 second Low number of gap junctions Smaller diameter of AV nodal cells

18. B u nd l e o f H i s ( A t r i o v e n t r i c u l a r B u nd l e ) The bundle of His is a group of fibers that carry electrical impulses through the center of the heart. Bundle of His divides into; Right Bundle Branch – Right Ventricle Left Bundle Branch – Left Ventricle Function: It transmits the electrical impulses from the atrioventricular node to the point of the apex of the fascicular branches via the bundle branches. The fascicular branches then lead to the Purkinji fibers, which provide electrical conduction to the ventricles, causing the cardiac muscle of the ventricles to contract at a paced interval. Swiss Cardiologist - Wilhelm His Jr. (1893)

19. B u nd l e B r a n c h e s Two branches of the bundle of His Left Bundle Branch Right Bundle Branch Location both bundle branches are located along the interventricular septum The left bundle branch further divides into the left anterior fascicle and the left posterior fascicle. Function: These structures lead to a network of thin filaments known as Purkinje fibers. They play an integral role in the electrical conduction system of the heart by transmitting cardiac action potentials to the Purkinje fibers.

20. P u r k i n j i F i b e r s Location: Purkinje fibers are located in the inner ventricular walls - beneath the endocardium, subendocardium. Function: Purkinje fibers allow the heart's conduction system to create synchronized contractions of its ventricles. Essential for maintaining a consistent heart rhythm.

21. T H A N K Y O U