1. ECG Review: PED 596

2. Electrophysiology Review

3. Myocardial Action Potential2
+40 1 AP 3 mV 4 4
-100
ECG

4. AP ECG 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”

5. Myocardial Action Potential2
+40 1 AP 3 mV 4 4
-100
ECG

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

7. ECG Paper: Dimensions Voltage ~Mass Speed = rate 5 mm 1 mm 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: 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? 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/QRS? 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. Fibrillation vs. Flutter?
One focus - organized
Rate: bpm
REGULAR - R
Cardiac Output is compromised
Multi-focal origins -chaotic
Rate: >400 bpm
IRREGULAR-R
Cardiac Output is Negligible:
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 = 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>R, progressive PR- interval
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
1°:
P = R
> .20
Regular
2°:Mobitz I
P > R
Progressive
Irregular II
Constant
3°:
Grossly
(20-40 bpm)

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 - + + -

51. Normal QRS Deflections (ve = + / -) Check Leads: I and aVF
Positive: Leads I-III, aVL, aVF, V4-V6
Negative: avR, V1-V2
Both Negative and Positive: V3

52. The Following Quadrant System Quickly Identifies QRS Axis Deviation

53. Interpreting Axis Deviation:
Normal Electrical Axis:
(Lead I + / aVF +)
Left Axis Deviation:
Lead I + / aVF –
Pregnancy, LV hypertrophy etc
Right Axis Deviation:
Lead I - / aVF +
Emphysema, RV hypertrophy etc.

54. NW Axis (No Man’s Land) Both I and aVF are –
Check to see if leads are transposed (- vs +)
Indicates:
Emphysema
Hyperkalemia
VTach

55. “Seeing” the heart in the Transverse plane: The Chest Leads+ V5 + V4 V1 V3 + - + V2 -

56. ST Segment Analysis: Ischemia Diagnosis
Key Reference Points:
Isoelectric line: Use the PR segment as reference
J-Point: Point at which QRS complex ends and ST segment begins
Most Common Measurement:
sec (>1-2 mm) past J-Point
ST Slope: Downsloping > Horizontal > Upsloping (questionable/angina)

57. ST-Depression >1.0 mm depression: >2.0 mm depression
Downsloping: Very predictive
Horizontal: Very predictive
Upsloping: Predictive if angina present
>2.0 mm depression
Usually indicative of ischemia

58. Positive Co-Conditions – Signals More Severe CAD:
Exertional Hypotension
Angina that limits exercise
Exercise capacity < 6 METs
ST changes at RPP < 15,000
ST changes persist into recovery

59. Determining Regions of CAD: ST-changes in leads…
RCA: Inferior myocardium
II, III, aVF
LCA: Lateral myocardium
I, aVL, V5, V6
LAD: Anterior/Septal myocardium
V1-V4

60. Regions of the Myocardium:
Lateral
I, AVL,
V5-V6
Anterior /
Septal
V1-V4
Inferior
II, III, aVF