ECG Review: PED 596

1. ECG Review: PED 596

2. Electrophysiology Review

3. Myocardial Action Potential 2 +40 1 AP 0 3 0 mV 4 4 -100 ECG

4. Measured in the Cardiac Cell Resting Potential = -90mV Depolarization = Phase 0 Repolarization = Phase 3 Measured at the Skin Surface Resting Potential = Isoelectric Line Depolarization = +/- deflection Repolarization = “T-Wave” AP ECG

5. Myocardial Action Potential 2 +40 1 AP 0 3 0 mV 4 4 -100 ECG

6. ECG Basics • ECG graphs: • 1 mm squares • 5 mm squares • Paper Speed: • 25 mm/sec standard • Voltage Calibration: • 10 mm/mV standard

7. ECG Paper: Dimensions 5 mm 1 mm Voltage ~Mass 0.1 mV 0.04 sec 0.2 sec Speed = rate

8. Cardiac Cycle: ECG WAVES • Normal ECG formation / conduction: • P Wave: Atrial depolarization/contraction • QRS Waves: Ventricular depolarization/contraction • T Wave: Ventricular Repolarization • PR and QT Intervals…conduction problems

9. ECG: Cardiac Cycle

11. Cardiac Cycle Basics: • Begins with SA Node depolarization • P – P = 1 Cycle • Heart rate (pulse) is determined by ventricle depolarization/contraction • R – R = 1 heart beat

12. Calculating Heart Rates from ECG’s: Step One • Sinus Rhythm: Each QRS complex is preceded by P wave • NSR: Within the intrinsic rate of the SA Node: 60-100 bpm • Tachycardia: >100 bpm • Bradycardia: < 60 bpm

13. Step Two: • Count the number of small squares between R – R waves (X): • Divide 1500 by X: • Rate = 1500 / X Example: X = 20 1500 / 20 =75 Rate = 75 bpm

14. Why “1500 / X”? • Paper Speed: 25 mm/ sec • 60 seconds / minute • 60 X 25 = 1500 mm / minute • Take 6 sec strip (30 large boxes) • Count the P/R waves X 10 OR

15. Rhythm ID: Algorithm • P-Wave: What is the atrial rhythm? < 0.12 sec (3 mm) • QRS: What is the ventricular rhythm? <0.10 sec (<3 mm) • P-R Interval: Is AV conduction normal? 0.12-0.20 sec (3-5 mm) • Any unusual complexes? • IS IT DANGEROUS?

16. Rhythms Involving Errors in Formation: P and QRS • Normal and Ectopic Rhythms • Sinus: “Normal” • Atrial: “Ectopic” • Junctional Rhythms: “Escape” • Retrograde Atrial Depolarization • Ventricular Rhythms:

17. P-Wave: • 1.SA Node “fires” • 2. Right and Left Atria Depolarize • 3. AV Node “fires” • Questions: • P waves present? • Regular rhythm? • 1/QRS? AV Node SA Node LA/RA Depol

18. Atrial Fibrillation:

19. Atrial Flutter: 2:1 Ventricular “capture” Ventricles only respond to every other Atrial conduction

20. Multi-focal origins -chaotic Rate: >400 bpm IRREGULAR-R Cardiac Output is Negligible: One focus - organized Rate: 200-400 bpm REGULAR - R Cardiac Output is compromised Fibrillation vs. Flutter? Atria contribute ~20% of the total Cardiac output: A-Fib is non-lethal

21. P-Interpretation: Irregular • Premature Beats: Narrow P waves: PAC’s • Atrial Flutter: >1P/QRS, classic “saw tooth” morphology

22. Summarize: Atrial Rhythms / Supraventricular Rhythms • Sinus: Normal, Tachy, Brady • Absent P: V-tach, A-fib, Junctional Rhythm • Irregular P: A-Flut, PAC

23. Ventricles: QRS Rhythms • Regular rhythms? • R-R intervals equivalent • Regular “irregular” rhythms? • R-R intervals equivalent with occasional irregularities • Irregular rhythms? • R-R intervals irregular

24. Regular “Irregular” • Premature Beats: PVC • Widened QRS, not associated with preceding P wave • Usually does not disrupt P-wave regularity • T wave is “inverted” after PVC • Followed by compensatory ventricular pause

25. Notice a Pattern in the PVC’s?

26. PVC Patterns: • PVC: 1 Isolated beat • Couplet: 2 consecutive PVC’s • Bigeminy: PVC every other beat • Non-Sustained VT: >3 beats for less than 1 minute • Sustained VT: > 1 minute of ventricular tachycardia

27. CONDUCTION ARRHYTHMIAS AV-Blocks

28. Ectopic Focus or Conduction Disturbance? • Ectopic Beats: • Premature and/or wide QRS complexes • Absent and / or abnormal P waves • AV Blocks: • Prolonged P-R intervals • Irregular P:R ratios • Ventricular: Bundle Branch Blocks • Wide QRS / Normal P-R

29. Bottom Line: • The Speed of conduction in the Atria and ventricles is similar (Very Fast) • The AV Node Necessarily slows down conduction to allow time for the ventricles to fill before contraction • About 50% of the cardiac cycle is “held up” at the AV-Node

30. BLOCKS: • Conduction is slowed or interrupted • A-V Blocks occur in the conduction between the atria and ventricles • Ventricular Blocks: Occur in the Bundle Branches

31. Atrio-Ventricular Blocks: • SA Node fires, but conduction is impaired: Normal P-RI = 0.14-0.22 seconds (3-5 mm) • Degrees of Block: • 1°: Conduction delayed, but QRS captured • 2°: Partial Block: Occasional ventricular “capture” • 3°: Complete: Atria and ventricles completely dissociated

32. First Degree Block: • Prolonged P- R interval • In otherwise healthy middle-aged men, not related to CAD • Regular P – P and R – R rhythms • When T – P interval is very short, coronary artery filling is compromised

33. 1° AV Block: PRI > 0.20

34. Second Degree Block: • Type I: Wenckebach • P-R Interval gets progressively longer until the AV conduction is completely blocked: • When AV conduction blocked, there is not QRS complex • QRS is normal

35. p p P Wenckebach: 2° AV Block P>R, progressive PR- interval

36. Second Degree Block: • Type II: • Regular ventricular rate – slow • 2:1, 3:1 or 4:1 P:R waves • Only occassional but regular ventricular capture • QRS is normal

37. 2° AV Block: Note 2:1 P:R following Arrow.

38. Third Degree (Complete) AV Block • AV conduction is completely dissociated • Ventricles contract at intrinsic rate (30-40 bpm) • Normal P waves, but more than QRS waves • QRS complexes may be normal or widened

39. 3° AV Block: P and R dissociation

40. Identifying AV Blocks: Name Conduction PR-Int R-R Rhythm

41. Most Important Questions of Arrhythmias • What is the mechanism? • Problems in impulse formation? (automaticity or ectopic foci) • Problems in impulse conductivity? (block or re-entry) • Where is the origin? • Atria, Junction, Ventricles?

42. Rhythm Documentation: • Rate and Regularity • Identification of Rhythm • A-V association but ectopic focus in either atria or ventricle • A – V are independent: conduction block (rates may be similar or not)

43. 12-Lead ECG Interpretations

44. Terminology: • Lead: Recording of wave of depolarization between negative and positive electrodes • Einthoven Triangle: An equilateral triangle depicting the leads of the frontal plane (I-III and aVR – aVL) • Frontal Plane: Vertical plane of the body, separating the front from back • Transverse Plane: Horizontal plane separating the top from the bottom

45. Frontal Plane Leads: • Standard (bipolar) Leads: • I: RA- to LA+ • II: RA- to LL+ • III: LA- to LL+ • Augmented Vector (Unipolar) Leads • aVR: to RA+ • aVL: to LA+ • aVF: to LL+

46. Blue Segment: -30° to +90° Is normal “QRS axis”

47. QRS Axis? • Used to determine right or left heart hypertrophy or other anatomical anomalies • But How do we Determine Axis?

48. The heart is situated in the chest at an angle from right arm to left hip: Waves of Depolarization Travel from the Right shoulder To the left hip.

49. The ECG deflection (-/+) is determined by the direction of the depolarization wave relative to the “reading” or POSITIVE electrode

50. Like So: ECG: Depolarization wave - + Lead I - + + -