1. Clinical SkillsSchool of undergraduate medical education UKZNMarch 2012 Dr RM Abraham

2. PRACTICAL APPROACH TO A 12LEAD ECGOBJECTIVES INTRODUCTION USES ELECTRICAL CONDUCTION SYSTEM OF THEHEART 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 lifes work in developing the ECG. 4. USESExtremely useful, easy, non- invasive, and relativelycheap to carry out.ECG used as an adjunct to Hx and clinical examination.In the hands of an experienced practitioner, can be usedto 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 detectunsuspected cardiac pathologies that might worsen withthe 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 SYSTEMOF THE HEARTTo fully understand how an ECG reveals useful information, a basicunderstanding of the anatomy and physiology of the heart is essential.The heart has its own electrical system to keep it running independently ofthe rest of the bodys 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) andrepolarization(relaxation),electrical currents are generated andspread 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 bemeasured by an array of "electrodes" placed on the body surface. The electrodes are connected by wires to an ECG recorder thatmeasures potential differences btw selected electrodes and theelectrical 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 thesurface of the body. 4 Limb electrodes- placed on each arm and leg. 6 Chest electrodes- placed at defined locations on the chest. V1right 4th ICS parasternally. V2left 4th ICS parasternally. V3midway btw V2 and V4 V4left 5th ICS mid- clavicular line(the imaginary line that extendsdown from the midpoint of the clavicle). V5left 5th ICS ant- axillary line (the imaginary line that runs downfrom the point midway between the middle of the clavicle and thelateral end of the clavicle) V6left 5th ICS mid- axillary line (the imaginary line that extendsdown from the middle of the patients armpit.) 10. RECORDING AN ECGLimb and chest electrodes 11. RECORDING AN ECG LEADS: The views or theelectrical picture of theheart. There are 12 view points ofthe heart: 6 StandardLeads(I,II,III,AVR,AVL, AVF) 6 chest Leads(V1-V6) 12. RECORDING AN ECG Standard leads: recorded fromthe electrodes attached to thelimbs, look at the heart in avertical plane(i.e from the sidesor the feet): Leads I,II and AVLlooks at thelat.surface of the heart. Leads III and AVFLooks at theinferior surface of the heart. Leads AVRlooks at the rightatrium. 13. RECORDING AN ECG Chest leads looks at theheart in a horizontal plane(i.e from the front and theleft side) Lead V1&V2look at theR. ventricle. Lead V3&V4look at theinterventricular septum. Lead V5&V6look at theant.&lat.walls of the L.ventricle. 14. RECORDING AN ECG Steps when recording an ECG: ECG machines records changes in1)The pt. must be supine and relaxed(to electrical activity by drawing a trace prevent muscle tremor, as contraction of on a moving paper strip. skeletal muscles will be detected by the electrode).2)Connect the limb and chest electrodes All ECG machines run at a standard correctly. Good electrical contact btw the rate (25mm/sec) and use paper with electrodes and skin is essential. May be standard-sized squares. necessary to shave the chest in a male pt.3)The ECG machine/recorder must be Each small square represents calibrated to a std signal of 1 millivolt,0.04secs,each large square(5mm) this should move the stylus vertically 1cm or 2 large squares.represents 0.2secs,so there are 54)Record the 6 standard leads- 3 or 4large squares per second and complexes are sufficient for each lead.therefore 300 large squares per5)Record the 6 chest(V) leads.minute. 15. THE NORMAL ECG(Basic shape of the normal ECG) The letters P,Q,R,S,T were chosenarbitrarily in the early days. The P,Q,R,S and T deflections are allcalled waves. The Q,R and S waves together makeup a complex. Interval btw the beginning of Pwave and beginning of QRScomplex is called the PR interval. Interval btw end of the S wave andbeginning of the T wave is called theST segment. 16. COMPONENTS OF THE ECGCOMPLEX 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 ECGCOMPLEX QRS Complex Composition of 3 Waves Q, R & S represents ventriculardepolarization usually < 0.12 sec(less than3 small squares) 18. COMPONENTS OF THE ECGCOMPLEX Q Wave first negative deflectionafter P wave depolarization ofinterventricular septumfrom left to right not always seen 19. COMPONENTS OF THE ECGCOMPLEX R Wave first positive deflection following P or Q waves Depolarisation of the main mass of the ventricles 20. COMPONENTS OF THE ECGCOMPLEX S Wave Negative deflection following R wave Depolarisation of the area of the heart near the base 21. COMPONENTS OF THE ECGCOMPLEX 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 ECGCOMPLEX 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 ECGCOMPLEX ST Segment early repolarization of ventricles measured from end of QRS complex to the onset of T wave Usually 100bpm (Sinus6 secs)tachycardia) Rate = 10 x 10 = 100 beats/minHrt rate150-250bpm 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: A monitoring lead can not tell you: How often the myocardium is Presence or absence of a depolarizing myocardial infarction How regular the Axis deviation depolarization is Chamber enlargement How long conduction takes in Right vs. Left bundle branch various areas of the heart blocks The origin of the impulses that Quality of pumping action are depolarizing the Whether the heart is myocardium beating!!! It is possible to bein cardiac arrest with a normalECG signal (a condition knownas pulseless electrical activityalso known by the older termElectromechanicalDissociation ). 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 Naishchapter on ECGTo the whole team (Drs Gan, Ntando,& Motala) atclinical skills unit, ukzn for input and advice