بسم الله الرحمن الرحيم

1. بسم الله الرحمن الرحيم ﴿و ما أوتيتم من العلم إلا قليلا﴾ صدق الله العظيم الاسراء اية 58

2. Cardiac Action Potential and Basis of ECG By Dr. Abdel Aziz M. Hussein Assist Prof. Medical Physiology

3. Cardiovascular System Pulmonary circuits Heart is the pump Systemic circuits

4. Heart • The heart is a hollow muscular organ Site: • Left side of the thoracic cavity partly behind the sternum. Size and weight: • It is in the size of a man's fist • It weighs about 320 gm in males. • In female it weighs about 250gm. Chambers: • 4 chambers = 2 atria + 2 ventricles Atria Ventricles

6. Wall of Heart • Its wall consists of 3 layers; Epicardium Endocardium Myocardium

7. Myocardial Muscle fibers 1. Nodal fibers 3. Contractile fibers Atria 2. Conducting fibers Ventricle

9. Myocardial Muscles Myocardium is composed of 3 types of ms fibers; a) Nodal ms fibers e.g. Sinoatrial (SA) node and Atrioventricular node. • SAN is the normal pacemaker of heart from which the cardiac impulse initiated. b) Conducting ms fibers include AV bundle, bundle branches and Purkinje fibers. • These fibers conduct the cardiac impulse from atria to ventricles.

11. Myocardial Muscles c) Contractile ms fibers • They consist of atria and ventricles. • The primary function of cardiac muscle cell is to contract to pump blood into arteries • Electrical changes within the cardiac muscle cell initiate this contraction.

12. Pumping Action of Heart

13. Pumping Action of Heart

14. Membrane Potentials of Cardiac Ms • There are 2 types of membrane potentials on the cardiac muscle cell • One during rest called resting membrane potential (RMP) • And the second during action called action potential or cardiac impulses

15. Resting Membrane Potential • RMP is the potential difference across cell membrane during rest i.e. inside the membrane is negative and outside is positive • Its value differs according to type of muscle fiber e.g. in SAN it is -65 mv, and in ventricle ms is -90 mv • It is measured by galvanometer with 2 microelectrodes one is inserted inside the cell and the other is placed outside the muscle cell

16. Resting Membrane Potential

18. Resting Membrane Potential • Ionic basis of RMP • K+ diffusion to outside (main cause) • Na+ diffusion to inside (little effect) • Electrogenic Na+-K+ pump

20. Cardiac Action Potentials • Action potentials occur when the membrane potential suddenly depolarizes and then repolarizes back to its resting state. • So cardiac potential consists of 2 phases; • Depolarization phase(inside cell become +ve and outside become –ve) mainly due to Na and Ca influx (inflow inside cell) • Repolarization phase (inside cell become -ve and outside become +ve) mainly due to K efflux (outflow outside the cell)

21. RMP Depolarization Repolarization

22. Ionic basis of Cardiac Action Potentials Repolarization phase Depolarization phase

23. Cardiac Action Potentials

24. Spread of Cardiac Action Potentials in heart • The excitation wave (depolarization followed by repolarization) is initiated by the pace maker of the heart (SAN). • Then it spreads through the atrial fibers in a rapid rate (1m/sec) to converge on the AVN. • The conduction in the AVN is very slow (0.05 m/sec). • The depolarization wave then travels rapidly down the AV bundle, bundle branches (1m/sec) and the purkinje fibers (4m/sec) to all parts of the ventricles.

28. Recording of electrical activities of heart • The body is a good conductor of electricity because tissue fluids have a high concentration of ions that move (creating a current) in response to potential differences. • The potential difference of about 120 mV between a depolarized and a resting area of heart muscle generates in the area of the heart an electric field that projects and conducted to the body surface.

30. Recording of electrical activities of heart • These potential differences can be detected by electrodes put on the skin surface and amplified and recorded as a tracing on paper or on a monitor

31. Electrocardiogram (ECG)

32. Electrocardiogram (ECG) Def. ECG is a record of the electrical activities of the cardiac muscle

33. Electrocardiograph (ECG) Apparatus: The apparatus used for recording the electrical activities of the heart is called electrocardiograph or ECG ECG apparatus consists of; Recording galvanometer Electrodes

34. Electrodes Galvanometer

35. Leads ◊ Def., It is the particular arrangement of 2 electrodes of the ECG galvanometer.

36. Leads Bipolar Limb leads Unipolar leads ◊ Types :

37. Bipolar Limb Leads They measure the potential difference between 2 limbs at different levels of potential. Lead I (RA (-) and LA (+)) Lead II (RA (-) and LF (+)) Lead III (LA (-) and LF (+))

38. Bipolar Limb Leads Lead I Lead III Lead II

39. Einthoven`s Triangle and Law Einthoven`s triangle is an equilateral triangle, the sides of which represent the 3 bipolar leads & the heart lies in its centre. Einthoven`s law the sum of voltage in lead I and Lead III = voltage in lead II

41. Lead I Lead II Lead III

42. Unipolar Leads V leads + VR VL + + ECG Central t. -

43. Unipolar Leads They measure the potential at one point. The potential at one pole (-ve) of ECG is made zero by connecting it to central terminal that receives electordes from (RA, LA, and LF) Positive pole (exploring electrode may be placed at; Limbs → unipolar limb (VR, VL and VF) Chest → unipolar chest (V1- V6)

45. Unipolar Limb Leads They measure the potential at limbs (RA, LA and LF) The voltage of potentials recorded by these leads is weak, so it must be augmented to form aVR, aVL, and aVL This done by disconnection of electrode connected to central terminal to limb to be augmented

46. Augmented Unipolar Limb Leads VR aVR + ECG Central term. -

47. Unipolar chest Leads MAL MCL AAL V1 V2 V3 V6 V5 V4

48. Unipolar chest Leads 6 unipolar chest leads from V1 to V6. V1 (Rt 4thintercostal space) V2 (Lt 4thintercostal space) V3 (midway between V2 and V4) V4 (Lt 5thintercostal space midclavicular line V5 (Lt 5thintercostal space anterior axillary line ) V6 (Lt 5thintercostal space midaxillary line )

49. 12 Leads

50. 12 Leads