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Generation and reading of the 12 lead ECG

Generation and reading of the 12 lead ECG. AWC Chow. The 12 lead ECG. Advantages Common clinical tool Independent marker of cardiac disease Non-invasive Rapid information acquisition Cheap Gold standard for arrhythmia management. The 12 lead ECG. Disadvantages Average of potentials

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Generation and reading of the 12 lead ECG

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  1. Generation and reading of the 12 lead ECG AWC Chow

  2. The 12 lead ECG Advantages • Common clinical tool • Independent marker of cardiac disease • Non-invasive • Rapid information acquisition • Cheap • Gold standard for arrhythmia management

  3. The 12 lead ECG Disadvantages • Average of potentials • Limited resolution • Snapshot of activity • Electrical and not haemodynamic data

  4. Non-specialised atrial tissue Left bundle Anterior superior fascicle Right bundle Posterior inferior fascicle

  5. - +/- +

  6. History of the ECG • 1842 -Carlo Matteucci shows that an electric current accompanies each heart beat. • 1874 - Sanderson and Page record the heart's electrical current with a capillary electrometer • 1887 - British physiologist Augustus D. Waller publishes the first human electrocardiogram. • 1901 - Einthoven develops the string galvometer • 1910 – Eithoven’s triangle

  7. Theoretical consideration • Myocytes have a resting potential • Transmembrane flux create voltage difference - activation • Cellular coupling cause rapid deploarisation • Ionic flux seen ECG deflections

  8. Theoretical considerations • Resting state - no potential/field change • Depolarisation - boundary potential change • Represented as a dipole/vector • Restitution of polarity: repolarisation

  9. Theoretical considerations • Greater muscle mass • Larger potential change • Larger voltage changes of ECG • Direction of activation dependent on • Site of initiation • Specialised conduction system distribution • Anatomical considerations • Barriers (scar, valves) • Muscle mass

  10. RA LA I II III RL LL

  11. aVR +210 aVL -30 I 0 II +60 III +120 aVF +90

  12. PR T P QT QRS

  13. Diagnostic criteria for LVH There are many different criteria for LVH. • Sokolow + Lyon (Am Heart J, 1949;37:161) S V1+ R V5 or V6 > 35 mm • Cornell criteria (Circulation, 1987;3: 565-72) SV3 + R avl > 28 mm in men SV3 + R avl > 20 mm in women • Framingham criteria (Circulation,1990; 81:815-820) R avl > 11mm, R V4-6 > 25mm S V1-3 > 25 mm, S V1 or V2 + R V5 or V6 > 35 mm, R I + S III > 25 mm • Romhilt + Estes (Am Heart J, 1986:75:752-58) Point score system

  14. Causes of RBBB • normal finding in children and tall thin adults • right ventricular hypertrophy • chronic lung disease even without pulmonary hypertension • anterolateral myocardial infarction • left posterior hemiblock • pulmonary embolus • Wolff-Parkinson-White syndrome - left sided accessory pathway • atrial septal defect • ventricular septal defect

  15. Causes of LBBB • left anterior hemiblock • Q waves of inferior myocardial infarction • artificial cardiac pacing • emphysema • hyperkalaemia • Wolff-Parkinson-White syndrome - right sided accessory pathway • tricuspid atresia • ostium primum ASD

  16. ECG Analysis • Rate 60-100b/min • Rhythm SR • PR <200ms • QRS <120ms • Axis -30 to +120 • QT interval <500ms • ST segment

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