What is an ECG?

1. What is an ECG? A graphical representation of the electrical events taking place in the heart during each beat.

2. The human body is a very good volume conductor and if electrodes are placed on body surface they will pick up the action potential current and when they are connected to galvanometer with the help on a conducting wire then these currents are recoded on a moving paper as the pen needle of galvanometer deflects or moves.if the wave of depolarization in the heart moves towards the positive electrode an upward deflection occurs but if wave of depolarization moves away towards negative electrode then a downward deflection is produced.the needle stays at neutral point and paper displays an isoelectric line when the myocardium is polarized (resting), completely depolarized or completely hyperpolarized.Durin these three conditions there is no movements of electrical charges and therefore no movement of needle.

3. Electrocardiogram ECG (EKG) • Surface electrodes record electrical activity deep within body - How possible? • Reflects electrical activity of whole heart not of single cell! • EC fluid = “salt solution” (NaCl)  good conductor of electricity to skin surface • EKG tracing =  of all electrical potentials generated by all cells of heart at any given moment

4. Recording of ECG In order to record a standardized ECG ,there are internationally accepted conventions to record accurate and standard ECG • For each 1mv input , there must be 1 cm deflection of pen or stylus • Speed of paper ( 25mm/sec) • Placement of electrodes

5. The two electrodes connected to a conducting wire constitute a “ LEAD” A lead is said to be bipolar if both electrodes are active and their potential difference will determine the voltage of that particular lead. Alead is known as unipolar if all the current is recorded by one active electrode and the second is kept at zero.This is augmentation so all unipolar limb leads are known as augmented unipolar limb leads and written as aVR,aVL,aVF. “a” stands for augmented.

6. LEADS • Bipolar leads , both electrodes are active V1 – V6 • Unipolar leads , one is active and other is inactive ,aVR ,aVL, aVF.

8. + I – LA RA – – II III + + LL Einthoven’s Triangle and the 3 Limb Leads: Fig 14-19

9. The sum of voltages at the corners of an equilateral triangle with the source of current (heart) in the center is zero.so if we know the volatge of two bipolar limb leads the electric potential of the third lead can be calculated by the formula:I+III=II this is einthoven’s law.read it from the chapter 11 of guyton with the given example.RA is -0.2mv, LA is+0.3mv and LF is +1.0mv calculate the voltages of lead I,II and III.

13. Mean QRS vector of ventricular depolarization determines the mean electrical axis of the heart which is +59 degrees directed to the cardiac apex.the normal range of cardiac axis is from -30 degree to +110 degree.

14. Placement of unipolar precordial chest leads on precordium

15. V1 is in right fourth intercostal space along sternal border • V2 is in left 4th intercostal space along sternal border • V3 is between V2 and V4 • V4 is at the apex • V5 is in left 5th intercostal space along anterior axillary line • V6 is in left 5th intercostal space along mid axillary line

16. V1 and V2 represent right ventricular activity • V3 and V4 represent activity of ventricular septum • V4 and V5 represent left ventricular activity

18. ECG PAPER • Along horizontal axis , time or duration is represented in seconds • Along vertical axis amplitude is represented in mv • Side of one small square vertically is equal to 0.1 mv • Side of one small square horizontally is 0.04 seconds • in one second there will be 25 small square

19. ECG PAPER • P WAVE • QRS WAVE • T WAVE

20. P WAVE • +VE wave due to atrial depolarization ,which occur just before atrial systole • 0.1-0.2 mv ( 1-2 small square) • Duration is 0.1 sec( 2.5 square) • Top coincide with time when cardiac impulse reaches AV node

22. QRS COMPLEX • Q wave is -ve • R wave is +ve • S wave is -ve • It is due to ventricular depolarization just before ventricular systole or contraction • Q wave is due to depolarization of upper part of ventricular septum • R wave is due to depolarization of lower part of septum and apex of heart

23. QRS COMPLEX • S wave is due to depolarization of wall and base of ventricle • Voltage of QRS from peak of R to bottom of S is about 1 mv or more than 1 mv • Duration is 0.08—0.1 sec • peak of R wave coincide with onset of ventricular systole

24. T wave is +ve wave due to ventricular repolarization • Voltage is 0.2-0.3 mv • Duration is o.25-0.27 sec

25. Standardized EKG’s • Time and voltage calibrations are standardized as shown on figure 11-1. Figure 11-1; Guyton & Hall

26. Cardiac Cycle- the timing of mechanical waves with ECG

27. EKG Concepts • The P wave immediately precedes atrial contraction. • The QRS complex immediately precedes ventricular contraction. • The ventricles remain contracted until a few milliseconds after the end of the T repolarization wave. • The atria remain contracted until the atria are repolarized, but an atrial repolarization wave cannot be seen on the electrocardiogram because it is obscured by the QRS wave.

28. An Electrocardiogram

29. ECG SEGMENTS • Segments are isoelectric • PQ / PR SEGMENT , from end of P wave to beginning of QRS complex • ST SEGMENT , from end of S wave to the beginning of T wave

30. ECG INTERVALS • PR/ PQ INTERVAL From beginning of P WAVE to the beginning of QRS complex • Represent atrial depolarization and conduction through AV node • 0.16 sec average ( 0.12-0.2 ) • QRS INTERVAL , It is duration of QRS complex • Duration is 0.08-0.1 sec • VAT,( ventricular activation time ) , From beginning of Q WAVE to the peak of R wave

31. ECG INTERVALS • QT INTERVAL , From the beginning of Q wave to the end of T wave . • it represents ventricular depolarization and ventricular repolarization • Duration is 0.36-0.4 sec • RR INTERVAL it is the interval between two successive R WAVES , • IT is equal to duration of one cardiac cycle . (0.8 sec)

32. It is used to find out heart rate • Heart rate = 60/RR • 60/0.8= 75 /MIN • HR= no of small sq in 60 sec/ no of small sq bt two successive R wave • HR =no of cardiac cycle x 10

36. Correlation of plasma K+ level and the ECG, assuming that the plasma Ca2+ level is normal.

37. INTRODUCTION TO HEART BLOCKS • OCCUR WHEN THERE IS A PARTIAL OR COMPLETE INTERRUPTION IN THE CARDIAC ELECTRICAL CONDUCTION SYSTEM. • CAN OCCUR ANYWHERE IN THE ATRIA BETWEEN THE SA NODE AND THE AV JUNCTION. • IN THE VENTRICLES BETWEEN THE AV JUNCTION AND PURKINJE FIBERS. For more medical presentations - www.pmcosa.com

38. Normal heart rates in children. • Newborn: 110 – 150 bpm • 2 years: 85 – 125 bpm • 4 years: 75 – 115 bpm • 6 years+: 60 – 100 bpm

39. Arrhythmias resulting from block of heart signals within the intracardiac conduction pathways. Sino-atrial block Incomplete atrioventricular block. Complete atrioventricular block Bundle branch blocks Hemiblocks

41. Anatomical Basis • The SA node consists of two main groups of cells: • A central core of pacemaking cells (“P cells”) that produce the sinus impulses. • An outer layer of transitional cells (“T cells”) that transmit the sinus impulses out into the right atrium. • Sinus node dysfunction can result from either: • Failure of the P cells to produce an impulse. This leads to sinus pauses and sinus arrest. • Failure of the T cells to transmit the impulse. This leads to sino-atrial exit block.

42. Intrinsic causes of sick sinus syndrome. • Idiopathic Degenerative Fibrosis (commonest). • Ischaemia. • Cardiomyopathies. • Infiltrative Diseases e.g. sarcoidosis, haemochromatosis. • Congenital abnormalities.

43. Sick sinus syndrome.extrinsic causes. • Drugs e.g. digoxin, beta-blockers, calcium channel blockers. • Autonomic dysfunction. • Hypothyroidism. • Electrolyte abnormalitites — e.g. hyperkalaemia.

44. ECG abnormalities seen in sick sinus syndrome. • Sinus Bradycardia. • Sinus Arrhythmia – associated with sinus node dysfunction in the elderly in the absence of respiratory pattern association. • Sinoatrial Exit Block. • Sinus Arrest — pause > 3 seconds. • Atrial fibrillation with slow ventricular response. • Tachy-brady syndrome.

45. Sino-atrial exit block. • Sino-atrial exit block is due to failed propagation of pacemaker impulses beyond the SA node. • The sino-atrial node continues to depolarise normally. • However, some of the sinus impulses are “blocked” before they can leave the SA node, leading to intermittent failure of atrial depolarisation (dropped P waves).

46. Causes • Sick sinus syndrome • Increased vagal tone (athletes) • Vagal stimulation (surgery, pain) • Inferior myocardial infarction • Myocarditis • Drugs: digoxin, beta-blockers, calcium channel blockers, amiodarone.

47. SA Exit Block. • There is shortening of PR interval progressively and suddenly no P wave.

48. SA EXIT BLOCK. • Another type of SA block black arrow indicates dropped P wave as a result the 4th QRS is a junctional escape beat fllowed by a non conducted P wave.

49. Sinoatrial exit block.

50. First Degree Heart BlockDefinition • PR interval > 0.2 sec(five small squares) • ‘Marked’ first degree block if PR interval > 0.3sec • Examples