Ecg ppp.pptx 2

A Basic approach to interpretation of the 12 lead ECG

1. ECG Clinical Skills School of undergraduate medical education UKZN March 2012 Dr RM Abraham

2. PRACTICAL APPROACH TO A 12 LEAD ECG OBJECTIVES INTRODUCTION USES ELECTRICAL CONDUCTION SYSTEM OF THE HEART RECORDING AN ECG THE NORMAL ECG AND INTERPRETATION REPORTING AN ECG

3. ECG Stands for Electrocardiogram or Electrocardiograph. Diagnostic tool that measures and records the electrical activity of the heart during the cardiac cycle. Term ECG introduced by Willem Einthoven in 1893.In 1924 Einthoven received the Nobel prize for his life's work in developing the ECG.

4. USES Extremely useful, easy, non- invasive, and relatively cheap to carry out. ECG used as an adjunct to Hx and clinical examination. In the hands of an experienced practitioner, can be used to detect a wide range of cardiac pathologies.

5. USES Essential for Dx and Mx of abnormal cardiac rhythms. Assist in the Dx of chest pain. Assist in the Mx of Myocardial infarction. Assist in the Dx of the cause of breathlessness. Pre-operatively-surgery done under GA, done to detect unsuspected cardiac pathologies that might worsen with the stress of surgery and anesthesia. Routinely done to people in occupations that- 1) stress the heart e.g. professional athletes or firefighters. 2) involve public safety e.g. commercial airplane pilots, train drivers and bus drivers.

6. ELECTRICAL CONDUCTION SYSTEM OF THE HEART To fully understand how an ECG reveals useful information, a basic understanding of the anatomy and physiology of the heart is essential. The heart has its own electrical system to keep it running independently of the rest of the body's nervous system. All 4 chambers have an extensive network of nerves, electrical impulses travelling through them trigger the chambers to contract with perfectly synchronized timing. Revise: Electrical discharge initiated in SA node  Atrium AV node Bundle of His right and left bundle branches Purkinje fibres within the Ventricles

7. Electrical conduction system

8. RECORDING AN ECG As the heart undergoes depolarization(contraction) and repolarization(relaxation),electrical currents are generated and spread not only within the heart but throughout the body, because the body acts as a volume conductor. This electrical currents/activity generated by the heart can be measured by an array of "electrodes" placed on the body surface. The electrodes are connected by wires to an ECG recorder that measures potential differences btw selected electrodes and the electrical picture obtained is called a "Lead". The recorded tracings is called an electrocardiogram(ECG).

9. RECORDING AN ECG ELECTRODES : Detect the electrical signals of the heart from the surface of the body. 4 Limb electrodes- placed on each arm and leg. 6 Chest electrodes- placed at defined locations on the chest. V1 right 4 th ICS parasternally. V2left 4 th ICS parasternally. V3midway btw V2 and V4 V4left 5 th ICS mid- clavicular line (the imaginary line that extends down from the midpoint of the clavicle). V5 left 5 th ICS ant- axillary line (the imaginary line that runs down from the point midway between the middle of the clavicle and the lateral end of the clavicle) V6left 5 th ICS mid- axillary line (the imaginary line that extends down from the middle of the patient's armpit.)

10. RECORDING AN ECG Limb and chest electrodes

11. RECORDING AN ECG LEADS : The views or the electrical picture of the heart. There are 12 view points of the heart: 6 Standard Leads(I,II,III,AVR,AVL, AVF) 6 chest Leads(V1-V6)

12. RECORDING AN ECG Standard leads: recorded from the electrodes attached to the limbs, look at the heart in a vertical plane(i.e from the sides or the feet): Leads I,II and AVL looks at the lat.surface of the heart. Leads III and AVFLooks at the inferior surface of the heart. Leads AVRlooks at the right atrium.

13. RECORDING AN ECG Chest leads looks at the heart in a horizontal plane (i.e from the front and the left side) Lead V1&V2 look at the R. ventricle. Lead V3&V4look at the interventricular septum. Lead V5&V6look at the ant.&lat.walls of the L. ventricle.

14. RECORDING AN ECG Steps when recording an ECG: 1)The pt. must be supine and relaxed(to prevent muscle tremor, as contraction of skeletal muscles will be detected by the electrode). 2)Connect the limb and chest electrodes correctly. Good electrical contact btw the electrodes and skin is essential. May be necessary to shave the chest in a male pt. 3)The ECG machine/recorder must be calibrated to a std signal of 1 millivolt, this should move the stylus vertically 1cm or 2 large squares. 4)Record the 6 standard leads- 3 or 4 complexes are sufficient for each lead. 5)Record the 6 chest(V) leads. ECG machines records changes in electrical activity by drawing a trace on a moving paper strip. All ECG machines run at a standard rate (25mm/sec) and use paper with standard-sized squares. Each small square represents 0.04secs,each large square(5mm) represents 0.2secs,so there are 5 large squares per second and therefore 300 large squares per minute.

15. THE NORMAL ECG (Basic shape of the normal ECG) The letters P,Q,R,S,T were chosen arbitrarily in the early days. The P,Q,R,S and T deflections are all called waves. The Q,R and S waves together make up a complex. Interval btw the beginning of P wave and beginning of QRS complex is called the PR interval. Interval btw end of the S wave and beginning of the T wave is called the ST 'segment'.

16. COMPONENTS OF THE ECG COMPLEX P Wave first upward deflection represents atrial depolarization usually 0.10 seconds or less ( less that 3 small squares) usually followed by QRS complex

17. COMPONENTS OF THE ECG COMPLEX QRS Complex Composition of 3 Waves Q, R & S represents ventricular depolarization usually < 0.12 sec(less than 3 small squares)

18. COMPONENTS OF THE ECG COMPLEX Q Wave first negative deflection after P wave depolarization of interventricular septum from left to right not always seen

19. COMPONENTS OF THE ECG COMPLEX R Wave first positive deflection following P or Q waves Depolarisation of the main mass of the ventricles

20. COMPONENTS OF THE ECG COMPLEX S Wave Negative deflection following R wave Depolarisation of the area of the heart near the base

21. COMPONENTS OF THE ECG COMPLEX PR Interval time impulse takes to spread from the SA node through the atrial muscle and AV node, down the Bundle of His and into the ventricular muscle The PR interval is therefore a good estimate of AV node function from beginning of P wave to beginning of QRS complex normally 0.12 - 0.2 sec(less than 1 large square) may be shorter with faster rates

22. COMPONENTS OF THE ECG COMPLEX QRS Interval time impulse takes to depolarize ventricles (shows how long excitation takes to spread through the ventricles) Atrial repolarisation hidden by ventricular depolarisation Represents normal conduction through AV node and bundle of His from beginning of Q wave to beginning of ST segment usually < 0.12 sec(less than 3 small squares)

23. COMPONENTS OF THE ECG COMPLEX ST Segment early repolarization of ventricles measured from end of QRS complex to the onset of T wave Usually <0.32sec(less than 8 small squares) Is an isoelectric line elevation or depression may indicate abnormality

24. COMPONENTS OF THE ECG COMPLEX QT interval - ventricular depolarisation and ventricular repolarisation Measured from the onset of the QRS complex to the end of the T wave

25. COMPONENTS OF THE ECG COMPLEX T Wave repolarization of ventricles concurrent with end of ventricular systole

26. COMPONENTS OF THE ECG COMPLEX U wave - Inconstant finding due to slow repolarization of the Purkinje fibres and papillary muscles

27. HOW TO REPORT/ANALYSE AN ECG This takes the form of a description followed by an interpretation of an ECG. Description should always be given in the same sequence. Patient and ECG details(Name, date, time) Rhythm Rate Conduction intervals Cardiac axis Description of QRS complex Description of ST segments and T waves

28. RHYTHM RHYTHM Measure R-R intervals across strip Should find regular distance between R waves Classification Regular Irregular Regularly irregular Irregularly irregular Regular rhythm-A P wave should precede every QRS complex with consistent PR-interval Sinus rhythm Irregular rhythm-No P wave preceding each QRS complex with an irregular rateAtrial fibrillation

29. RATE RATE- Regular rhythm R-R method divide 300 by # of large squares between consecutive R waves E.g. 3 large squares btw consecutive R waves Hrt rate=300/3 =100beats/min Hrt rate>100bpm (Sinus tachycardia) Hrt rate<60bpm (Sinus bradycardia) RATE- Irregular rhythm Count RR or PP intervals over a six-second period (i.e. 30 x 5mm blocks) and multiply this figure by 10. E.g 30 large squares contain 10 QRS complexes (30 large squares correspond to 6 secs) Rate = 10 x 10 = 100 beats/min

30. CONDUCTION INTERVAL Conduction interval PR Interval Constant? Less than 0.20 seconds (1 large box) Short PR interval Rapid conduction through AV node Long PR interval1 st degree AV block

31. CARDIAC AXIS Cardiac axis Normal Cardiac axis (-30 and +90 degrees) The direction of the axis can be derived most easily from the QRS complex in leads I,II,and III With a normal cardiac axis, the wave of depolarization is spreading towards leads I,II,and III  predominantly upward deflection in all these leads RVH(Right ventricular hypertrophy)Axis swings towards the right (btw +90 and -150 degrees) deflection in lead I is downwards Right axis deviation RVH secondary to COPD (Pulm. condition putting a strain on the right side of the heart) LVH(Left ventricular hypertrophy)Axis swings to the left (btw -30 and -150 degrees) deflection in lead III is predominantly downwardsLeft axis deviation LVH secondary to systemic hypertension

32. DESCRIPTION OF QRS COMPLEX AND ST SEGMENT QRS complex Duration of QRS complex <0.12sec(less than 3 small squares) Broad/wide QRS complexbundle branch block ST segment and T wave Depressed ST segment  Ischaemic heart disease Elevated ST segment and T wave inversion Acute Myocardial infarction

33. ECG TRACINGS Normal sinus rhythm Rate- 60-100bpm Rhythm-regular P waves-normal PR interval-0.12-0.20sec QRS duration-0.04-0.12sec Any deviation from above is sinus tachycardia, sinus bradycardia or arrhythmias 1 st Degree AVB Prolonged PR interval(>0.20sec)

34. ECG TRACINGS Atrial tachycardia Rate->150-250bpm Rhythm-regular P wave-upright/normal PR interval-0.12-0.20sec QRS complex-0.04-0.12sec Atrial flutter Rate-250-300bpm Rhythm-Atrial: regular; Vent: varies P waves- Big F waves-Saw tooth pattern PR interval-normally constant, may vary QRS complex-0.04-0.12sec Atrial Fibrillation Rate-Atrial:350-750bpm,Vent:varies Rhythm-irregularly irregular ventricular P waves-little F waves, no pattern PR interval-no discernable P wave QRS complex-0.04-0.12sec

35. ECG TRACINGS Ventricular tachycardia Rate-100-250bpm Rhythm-usually regular P waves-If present, not associated PR interval-none QRS complex- >0.12sec Ventricular fibrillation Rate-none Rhythm- Chaotic, no set rhythm P waves-absent PR interval-absent QRS complex-not discernable

36. ECG TRACINGS Depressed ST segment Myocardial ischaemia Elevated ST segment Myocardial infarction Asystole Rate-no electrical activity Rhythm-no electrical rhythm P waves- absent PR interval- absent QRS complex- absent

37. ECG Analysis A monitoring lead can tell you: How often the myocardium is depolarizing How regular the depolarization is How long conduction takes in various areas of the heart The origin of the impulses that are depolarizing the myocardium A monitoring lead can not tell you: Presence or absence of a myocardial infarction Axis deviation Chamber enlargement Right vs. Left bundle branch blocks Quality of pumping action Whether the heart is beating!!!  It is possible to be in cardiac arrest with a normal ECG signal (a condition known as pulseless electrical activity also known by the older term Electromechanical Dissociation ).

38. ECG Analysis An ECG is a diagnostic tool, NOT a treatment! No one was ever cured by an ECG!! Treat the patient not the monitor!!!

39. REFERENCES The ECG Made Easy by John R.Hampton Medical Science Naish, Revest, Syndercombe Court (2009) Elsevier ECG protocol Review of Medical Physiology by William F. Ganong Dr Matthews for all protocols and copy of Naish chapter on ECG To the whole team (Drs Gan, Ntando,& Motala) at clinical skills unit, ukzn for input and advice