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ECG Analysis Gaby Plimmer Cardiology Nurse practitioner

What is an ECG?. Records electrical activity of the heartGives us information about cardiac rhythm, ischaemia/infarction and some generalised disorders eg electrolyte imbalance4 limb and 6 chest electrodes = 12 lead ECGEach lead gives a different viewpoint of electrical activity in the heart. Anatomy and Physiology.

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ECG Analysis Gaby Plimmer Cardiology Nurse practitioner

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    1. ECG Analysis Gaby Plimmer Cardiology Nurse practitioner

    2. What is an ECG? Records electrical activity of the heart Gives us information about cardiac rhythm, ischaemia/infarction and some generalised disorders eg electrolyte imbalance 4 limb and 6 chest electrodes = 12 lead ECG Each lead gives a different viewpoint of electrical activity in the heart

    3. Anatomy and Physiology

    4. The Normal ECG

    5. 12 lead ECG

    8. Eintoven’s Triangle The direction of the limb leads create a triangle Lead 1: looks from left to right shoulder Lead 2: Looks from left foot to right shoulder Lead 3: Looks from left foot to left shoulder

    9. Augmented Leads AVR looks from right shoulder into the middle AVL looks from left shoulder into the middle AVF looks from the feet to the middle

    11. 12 lead ECG

    12. What do the waves represent? P wave- atrial depolarisation PR interval- start of atrial depolarisation to start of ventricular depolarisation. QRS complex- ventricular depolarisation. ST segment- pause in electrical activity before repolarisation T wave- ventricular repolarisation

    13. The QRS complex Each small square is 0.04 secs (300 large squares in a minute) PR interval - 0.12 - 0.2 secs (3-5 small squares) QRS complex- < 0.12 secs (< 3 small squares) ST segment = isoelectric T wave = usually positive, except AVR (possibly V1)

    14. How to interpret a rhythm Is there any electrical activity? Is the QRS rhythm regular or irregular? What is the ventricular (QRS) rate? Is the QRS complex width normal or prolonged? Is atrial activity present? How is atrial activity related to ventricular activity?

    15. Is the QRS rhythm regular or irregular? Unclear at rapid heart rates Compare R-R intervals

    16. What is the ventricular rate? Regular rhythm Count the number of large squares between two consecutive QRS complexes and divide this into 300 eg if 4 large squares between two QRS complexes the rate is 300/4 = 75bpm Irregular rhythm Count the number of QRS complexes in 30 large squares (6 secs), then multiply by 10 eg if 12 QRS complexes occur in 30 large squares the rate is 12x10=120bpm

    17. Is the QRS width normal or prolonged? Normal (narrow) QRS: < 0.12 s (< 3 small squares) originates from above the venticles

    18. Is the QRS width normal or prolonged? Prolonged QRS (> 0.12 s) arises from: ventricular myocardium Left or right bundle branch block paced rhythm If rhythm is fast, presume it is ventricular until proven otherwise as this is the most dangerous

    19. Is atrial activity present? Can be difficult to establish Lead II and V1 offer best views of atrial activity Always look at rhythm strip Some tachycardias may require transient slowing to reveal atrial activity eg vagal manoeuvres

    20. How is atrial activity related to ventricular activity? Is there one P wave to every QRS? Is the PR interval constant? If there is sometimes more than one P wave to one QRS this is likely to be a heart block and specialist review is required

    21. Atrial Fibrillation

    22. Atrial Fibrillation Rate – usually fast Irregular QRS width – normal P wave – not present – ‘wandering’ baseline

    23. Atrial Fibrillation The commonest arrhythmia, accounting for 10-15 % of the elderly population Loss of atrial systole reduces vent filling, reducing blood pressure Risk of emboli therefore warfarin should be considered in the elderly

    24. Causes of Atrial Fibrillation Thyrotoxicosis Hypertension Heart failure Valve disease IHD Infections Excessive alcohol

    25. Atrial Fibrillation

    26. Atrial Flutter

    27. Atrial Flutter Rate – usually fast (atrial rate usually 300bpm. Ventricular rate depends on conduction through AV node ) Usually regular QRS width – normal P wave – no classic P waves. ‘saw’ tooth pattern usually present

    28. Atrial Flutter

    29. Ventricular Ectopics

    30. Heart Blocks

    31. Heart Block: First Degree

    32. Second Degree Heart Block Type 1

    33. 2nd Degree Heart Block Type 2 Mobitz type 2 AV block

    34. 2:1 AV Block Rate – variable P wave – normal morphology QRS – normal Conduction – alternate P waves not followed by QRS complexes Rhythm - regular

    35. Heart Block: Third Degree Site of pacemaker: AV node (narrow QRS) 40 – 50bpm Ventricular myocardium (wide QRS) 30 - 40 bpm

    36. Heart block summary… First degree heart block Prolonged PR interval but constant 2nd degree heart block Mobitz type I AV block (Wenckebach): Gradual lengthening of the PR interval with each beat, until one P wave fails to produce a QRS complex

    37. Heart block summary… Mobitz type II AV block: The PR interval is fixed and normal, but occasionally a P wave fails to produce a QRS complex Third degree AV block (complete heart block) There is no relationship between P waves and QRS complexes

    38. Myocardial Infarction & Ischaemia

    39. Pathological Q waves Q wave is at least 1small square wide (0.04 secs) Q wave is greater than 25% in depth compared to the height of the R wave in the same complex As a Q wave forms the height of the R wave diminishes Pathological Q waves are usually present in leads that are orientated in a similar direction, eg II, III,AVF.

    40. Pathological Q waves

    41. Myocardial Infarction/Ischaemia Look for abnormalities in ST segment and T wave ST segment should normally be iso-electric If the ST segment is below the baseline this suggests ischaemia If the ST segment is above the baseline this suggests myocardial infarction

    42. Myocardial infarction ST segment elevation represents myocardial tissue injury and occurs in the leads overlying the area of infarction Accompanied by reciprocal ST depression Chest pain and new left bundle branch block = acute MI

    43. ECG criteria for acute MI

    44. Evolution of an acute MI

    45. Territories of the ECG V1-V4 – Anterior I, AVL, V5-V6 – Lateral V1-V3 – Antero-septal II, III, AVF – Inferior Reciprocal changes V1-V3 with positive R wave in V1-V2 – Posterior

    46. Antero-lateral myocardial infarction

    47. Inferior MI

    48. Infero-Posterior MI

    49. NSTEMI Non ST Elevation Myocardial Infarction Symptoms suggesting MI Possible ECG abnormalities- ST segment depression or T wave inversion Usually does not develop Q waves (but may do) Elevated cardiac enzymes (Troponin) High risk of total coronary occlusion

    50. Non ST elevation MI

    51. Myocardial Ischaemia If the ST segment is below the baseline this suggests ischaemia ST depression often returns to the baseline when pain resolves T wave inversion can be a sign of ischaemia but is less specific

    52. ST Depression

    53. T Wave Inversion

    54. How right bundle branch block occurs. The initial impulse activates the intra-ventricular septum from left to right Next the left bundle branch activates the left ventricle The impulse then crosses the intra-ventricular septum to activate the right ventricle

    55. Right bundle branch block

    56. Left bundle branch block The impulse activates the intra-ventricular septum from right to left. The impulse then travels down the right bundle branch Finally the impulse activates the left ventricle via the right side

    57. Left bundle branch block The impulse activates the intra-ventricular septum from right to left. The impulse then travels down the right bundle branch Finally the impulse activates the left ventricle via the right side

    58. Left ventricular hypertrophy

    59. Left ventricular hypertrophy by voltage criteria The R wave in V5 or V6 exceeds 25mm The S wave in V1 or V2 exceeds 25mm The total of the R wave in V5 or V6 plus the S wave in V1 or V2 exceeds 35mm NB – not for young, thin individuals A diagnosis of LVH can only be confirmed by Echocardiography

    60. Any Questions?

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