به نام یکتای جهان آفرین

1. به نام یکتای جهان آفرین

2. ECG H.R Tohidypour

3. Cardiac Physiology Electrocardiography OVERVIEW

4. VEINS ARTERIES brings blood back to heart distributes blood from heart Diagnosis Cardiac Physiology Electrocardiography

5. Diagnosis Cardiac Physiology Electrocardiography Atria Ventricles

6. Diagnosis Cardiac Physiology Electrocardiography Sinoatrial Node Atrioventricular Node

7. Conduction System of the Heart: A Conceptual Model for Illustration Inter-nodal Tract Left Bundle Branch AV Node Septal Depolarization Fibers Bundle of HIS SA Node James Fibers Anterior Superior Fascicle Posterior Inferior Fascicle Right Bundle Branch Bundle of Kent

8. Basic conduction mechanisms • Sinoatrial node (SA node)- primary pacemaker of the heart • Atrioventricular node (AV node) • His Bundle • Bundle branches • Purkinje fibers

9. Extrinsic Innervation of the Heart • Heart is stimulated by the sympathetic cardioacceleratory center • Heart is inhibited by the parasympathetic cardioinhibitory center

10. Cardiac Cycle • Cardiac cycle refers to all events associated with blood flow through the heart • Systole – contraction of heart muscle • Diastole – relaxation of heart muscle

12. Diagnosis Cardiac Physiology Electrocardiography

13. Introduction to Electrocardiography (ECG, EKG) • Electrocardiography - graphic recording of the electrical activity • (potentials) produced by the conduction system and the myocardium • of the heart during its depolarization / re-polarization cycle. • During the late 1800's and early 1900's, Dutch physiologist Willem • Einthoven developed the early electrocardiogram. He won the Nobel • prize for its invention in 1924. • Hubert Mann first uses the electrocardiogram to describe • electrocardiographic changes associated with a heart attack in 1920. • The science of electrocardiography is not exact. The sensitivity and • specificity of the tool in relation to various diagnoses are relatively low • Electrocardiograms must be viewed in the context of demographics, • health histories, and other clinical test correlates. They are especially • useful when compared across time to see how the electrical activity of • the heart has changed (perhaps as the result of some pathology).

15. Design considerations: differential recordings • ECG recording is differential = recorded as potential difference between two leads. • This is due to presence of significant electric noise. Typically 60 Hz noise is present and equally distributed over the entire body patients body. Noise amplitude ~100mV, ECG signal amplitude ~1-5 mV <<100mV!!! Subtractions of two signals, recorded from two • different locations will eliminate noise.

16. Differential recording of ECG

17. Accessories used

19. R T P Q S Diagnosis Cardiac Physiology Electrocardiography

20. Diagnosis Cardiac Physiology Electrocardiography R T P Q S

21. 1 1 SA node AV node 2 1 THE CONDUCTING SYSTEM OF THE HEART SA node depolarizes. 2 Electrical activity goes rapidly to AV node via internodal pathways. SA node 3 Internodal pathways Depolarization spreads more slowly across atria. Conduction slows through AV node. 3 AV node 4 Depolarization moves rapidly through ventricular conducting system to the apex of the heart. A-V bundle 4 Bundle branches Purkinje fibers Depolarization wave spreads upward from the apex. 5 5 Purple shading in steps 2–5 represents depolarization. Electrical Conduction in Heart

22. Electrical Activity P wave: atrial depolarization START P The end R PQ or PR segment: conduction through AV node and A-V bundle T P P QS Atria contract. T wave: ventricular Repolarization ELECTRICAL EVENTS OF THE CARDIAC CYCLE Repolarization R T P QS Q wave P Q ST segment R R wave P R Q S P R Ventricles contract. Q P S wave QS

25. R 1 sec T P Q S 0.5 Sec Diagnosis Cardiac Physiology Electrocardiography

26. The normal electrocardiogram is composed of a P wave, a QRS complex, and a T wave. • The QRS complex is often, but not always, three separate waves: the Q wave, the R wave, and the S wave. • The P wave is caused by electrical potentials generated when the atria depolarize before atrial contraction begins. • The QRS complex is caused by potentials generated when the ventricles depolarize before contraction, that is, as the depolarization wave spreads through the ventricles.Therefore, both the P wave and the components of the QRS complex are depolarization waves.

28. Normal Voltages in the Electrocardiogram. • The recorded voltages of the waves in the normal electrocardiogram depend on the manner in which the electrodes are applied to the surface of the body and how close the electrodes are to the heart. • When one electrode is placed directly over the ventricles and a second electrode is placed elsewhere on the body remote from the heart, the voltage of the QRS complex may be as great as 3 to 4 millivolts.

29. When electrocardiograms are recorded from electrodes on the two arms or on one arm and one leg, the voltage of the QRS complex usually is 1.0 to 1.5 millivolt from the top of the R wave to the bottom of the S wave; the voltage of the P wave is between 0.1 and 0.3 millivolt; and that of the T wave is between 0.2 and 0.3 millivolt.

30. Comparison of an ECG and a myocardial action potential

31. P-Q or P-R Interval. The time between the beginning of the P wave and the beginning of the QRS complex is the interval between the beginning of electrical excitation of the atria and the beginning of excitation of the ventricles. This period is called the P-Q interval. The normal P-Q interval is about 0.16 second. (Often this interval is called the P-R interval because the Q wave is likely to be absent.)

32. Q-T Interval. Contraction of the ventricle lasts almost from the beginning of the Q wave (or R wave, if the Q wave is absent) to the end of the T wave. This interval is called the Q-T interval and ordinarily is about 0.35 second.

33. Rate of Heartbeat as Determined from the Electrocardiogram • The rate of heartbeat can be determined easily from an electrocardiogram because the heart rate is the reciprocal of the time interval between two successive heartbeats. If the interval between two beats as determined from the time calibration lines is 1 second, the heart rate is 60 beats per minute. The normal interval between two successive QRS complexes in the adult person is about 0.83 second. This is a heart rate of 60/0.83 times per minute, or 72 beats per minute.

38. Limb Leads • Standard ECG Leads (The Einthoven limb leads) are defined as follows According to the Einthoven triangle and Kirchhoff’s voltage law, the standard lead voltages have the following relationship: Hence only two of these three leads are independent.

41. Wilson Central Terminal • Unipolar potential definition by Frank Norman Wilson (1890-1952): unipolar potentials should be measured with respect to the central terminal (CT). • To satisfy the conservation law of current, the total current into the CT from the limb leads must add to zero. Thus, we have:

43. Goldberger Augmented Lead • Three additional limb leads, VR, VL, and VF are obtained by measuring the voltage between each limb electrode and the Wilson CT. For instance, the left leg lead is given by: E. Goldberger observed in 1942 that these signals can be augmented by omitting that resistance from the Wilson CT, which is connected to the measurement electrode. In this way, the aforementioned three limb leads, VR, VL, and VF may be replaced with a new set of leads that are called augmented leads. The equation for augmented left leg lead is:

44. Three additional leads can be obtained by comparing each limb lead potential with the central terminal voltage. For example, from (*) we have, for the right arm, If, in creating the CT voltage, the connection to RA is dropped, then in place of (VR) we have:

45. A comparison of Eq. VR with Eq. aVR shows the augmented signal to be 50% larger than the signal with the Wilson CT chosen as reference.

46. Electrocardiographic Leads • Three Bipolar Limb Leads • Chest Leads (Precordial Leads) • Augmented Unipolar Limb Leads

47. Three Bipolar Limb Leads • Lead I. In recording limb lead I, the negative terminal of the electrocardiograph is connected to theright armand the positive terminal to the left arm. • Lead II. To record limb lead II, the negative terminalof the electrocardiograph is connected tothe right armand the positive terminal to the left leg. • Lead III. To record limb lead III, the negative terminal of the electrocardiograph is connected to theleft armand the positive terminal to the left leg.

49. Chest Leads (Precordial Leads) • Often electrocardiograms are recorded with one electrode placed on the anterior surface of the chest directly over the heart at one of the points.This electrode is connected to the positive terminal of the electrocardiograph, and the negative electrode, called the indifferent electrode, is connected through equal electrical resistances to the right arm, left arm, and left leg all at the same time, as also shown in the figure. Usually six standard chest leads are recorded, one at a time, from the anterior chest wall, the chest electrode being placed sequentially at the six points shown in the diagram. The different recordings are known as leads V1, V2, V3, V4, V5, and V6.