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Practical Electrocardiography Introduction

Practical Electrocardiography Introduction. Scott Ewing, D.O. Cardiology Fellow August 2, 2006. Syllabus. Introduction Axis Determination Atrial Arrhythmias, Bradycardias, and AV Conduction Block Junctional and Broad Complex Tachycardias

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Practical Electrocardiography Introduction

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  1. Practical Electrocardiography Introduction Scott Ewing, D.O. Cardiology Fellow August 2, 2006

  2. Syllabus • Introduction • Axis Determination • Atrial Arrhythmias, Bradycardias, and AV Conduction Block • Junctional and Broad Complex Tachycardias • Myocardial Ischemia and Acute Myocardial Infarction • Conditions Affecting the Left Side of the Heart • Conditions Affecting the Right Side of the Heart • Conditions Not Primarily Affecting the Heart • Exercise Tolerance Testing

  3. Introduction • Anatomy • EKG Paper • Lead Placement • Normal EKG • Axis Determination

  4. His-Purkinje Conduction System

  5. The EKG Paper • Time intervals indicated for the thick and thin vertical grid lines on the EKG paper are appropriate for the standard paper speed of 25 mm/sec • Amplitudes indicated for the thick and thin horizontal grid lines are appropriate for the standard gain of 10 mm/mV • Each small square is therefore 0.04 s × 0.1 mV, and each large square is 0.20 s × 0.5 mV

  6. Depolarization

  7. Normal EKG

  8. EKG Limb Leads

  9. EKG Limb Leads

  10. Willem Einthoven (1860 – 1927) • Dutch doctor and physiologist • Invented the first practical electrocardiogram in 1903 • Nobel Prize Medicine in 1924 • Died in Leiden in the Netherlands and is buried in the graveyard of the Reformed Church at 6 Haarlemmerstraatweg in Oegstgeest

  11. EKG Augmented Limb Leads

  12. EKG Frontal Plane

  13. EKG Frontal Plane

  14. EKG Precordial Leads

  15. Normal Findings • Tall R waves • Prominent U waves • ST segment elevation (high­take off, benign early repolarization) • Exaggerated sinus arrhythmia • Sinus bradycardia • Wandering atrial pacemaker • Wenckebach phenomenon • Junctional rhythm • 1st degree heart block

  16. Waveform Review

  17. P Wave

  18. P Wave

  19. P Wave • Atrial activation begins in the SA node • Spreads in radial fashion to depolarize the right atrium, interatrial septum, then the left atrium • Last area of the left atrium to be activated is the tip of the left atrial appendage • Normal amplitude • Seldom exceeds 0.25 mV normally in limb leads • In precordial leads, positive component is normally less than 0.15 mV

  20. P Wave Characteristics • Positive in leads I and II • Best seen in leads II and V1 • Commonly biphasic in lead V1 • < 3 small squares in duration • < 2.5 small squares in amplitude

  21. P Wave – Lead II

  22. P Wave – Lead V1

  23. PR Interval / Segment

  24. P Wave

  25. PR Interval • Beginning of P wave to beginning of QRS complex • Interval between the onset of atrial depolarization and onset of ventricular depolarization • Time required for the activation impulse to advance from atria through the AV node, bundle of His, bundle branches, and the Purkinje fibers until ventricular myocardium begins to depolarize • Does not include duration of conduction from SA node proper to the right atrium

  26. PR Interval / Segment

  27. PR Interval • Normal PR Interval • 0.12-0.20 seconds (adults) • Shorter in children, longer in older persons • May become shorter as sinus rate increases • Should be taken from lead with the largest and widest P wave and longest QRS duration • Such selection avoids inaccuracies incurred by using leads in which the early part of the P wave or QRS complex is isoelectric

  28. PR Interval • Most of the AV conduction time is consumed by impulse conduction proximal to the His bundle • Normal AH interval= 50-130 ms • Normal HV interval= 35-55 ms • Longer AH interval is result of slower conduction through AV node

  29. PR Segment • Horizontal line between the end of the P wave and the beginning of the QRS complex • Duration depends on the duration of the P wave as well as the impulse conduction through the AV junction • Usually isoelectric, however it is often displaced in a direction opposite to the polarity of the P wave • Depressed in most of the conventional leads except aVR • Displacement is mainly due to atrial repolarization

  30. PR Interval – Lead II

  31. QRS Complex

  32. QRS Complex

  33. QRS Complex • Q wave – Any initial negative deflection • R wave – Any positive deflection • S wave – Any negative deflection after an R wave

  34. QRS Complex

  35. QRS Complex • Resultant electrical forces generated from ventricular depolarization • Begins at the middle third of the left interventricular septal surface • Spreads in a rightward direction • Right ventricle begins to depolarize shortly after the initiation of left ventricular activation

  36. Ventricular Depolarization

  37. QRS Complex • Soon after septal activation, the impulse arrives at most of the subendocardial layer of the myocardium of the apical and free wall of both ventricles through the Perkinje network and spreads in all directions • Impulse spreads in endocardial to epicardial direction

  38. QRS Complex • Basal portion of septum and the posterobasal portion of the free wall of the LV are last areas of depolarization • LV contributes most of the QRS forces due to larger muscle mass • Polarity and amplitude of the QRS complex in the various leads are determined by the relation between these vectors and the lead axes

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