1. TWELVE-LEAD INTERPRETATIONBy
Leslie Hernandez, BS, NREMT-P, LP

2. THE HEART One heart Two sides/Two arteries Three layers
Four chambers/valves

3. BLOOD FLOW THROUGH THE HEART
From the Body
Right Atrium
To the Lungs
Right Ventricle
From the Lungs
Left Atrium
To the Body
Left Ventricle

4. THE ELECTRICAL CONDUCTION SYSTEM
SA Node
Intranodal Pathways
AV Junction
AV Fibers
Bundle of His
Septum
Bundle Branches
Purkinje System

5. The Electrical Conduction System

6. THE ECG LEADS ECG Leads Bipolar Leads I, II, and II Unipolar
Leads aVR, aVL, and aVF
Precordial
V1, V2, V3, V4, V5, V6

7. LEAD PLACEMENT

8. THE ELECTROCARDIOGRAM
WAVES, INTERVAL, SEGMENTS AND COMPLEXES

10. INTERVALS AND SEGMENTS
Time Intervals
P–R Interval (PRI) or P–Q Interval (PQI)
120–200 ms
QRS Interval
80–100 ms
S–T Segment
isoelectric
Q–T Interval
360–440 ms

11. P WAVE

12. P-Waves and Atrial Enlargement

13. THE PR INTERVAL ms

14. THE QRS COMPLEX

15. THE T WAVE

16. How to Measure ST-Segment Deviation

17. THE THREE I’S OF THE ACS S–T Segment Changes
Associated with Myocardial Infarctions
Ischemia
Injury
Infarct

18. Two Rules to Follow Changes >1 mm (0.1 mV) are significant If
They occur in two or more contiguous leads

19. Patterns and Localization
Inferior – II, III, and aVF
Septal – V1 and V2
Anterior – V3 and V4
Lateral – I, aVL, V5, and V6

21. 12-Lead ECG Variations in AMI and Angina
Baseline
Ischemia—tall or inverted T wave (infarct), ST segment may be depressed (angina)
Injury—elevated ST segment, T wave may invert
Infarction (Acute)—abnormal Q wave, ST segment may be elevated and T wave may be inverted
Infarction (Age Unknown)—abnormal Q wave, ST segment and T wave returned to normal

22. Conditions that Mimic Injury
Pericarditis
Diffuse or “global” ST-segment changes
Left bundle branch blocks
If possibly new, must treat as MI
Left ventricular hypertrophy
Causes ST-segment elevation
Early repolarization
Ventricular paced rhythms

23. THE NORMAL TWELVE-LEAD

24. ANTERIOR MI

25. ANTEROLATERAL MI

26. Inf. Wall Inj. Or Infarct with RCA
II, III, aVF, and V4R:
Hypotension
Supranodal and AV nodal blocks
Atrial fibrillation / flutter
PAC’s
Significant NTG and MS hemodynamic hypersensitivity

27. INFERIOR MI

28. HEXAXIAL SYSTEM

29. NORMAL AND ABNORMAL AXES
Normal QRS Axis
Normal Left
Axis
(Physiologic)
Abnormal Left
Axis (Pathologic)
Indeterminate
Right Axis

30. Axis Deviation Lead aVF QRS Lead I QRS Left Normal Axis Positive
Negative
Lead aVF QRS
Lead I QRS
Right
EXTREME RIGHT
Left
Normal
Axis

31. AXIS DEVIATION Left Axis Deviation Abnormal finding.
Often associated with hypertension, valvular heart disease, and other disease processes.

32. Left Axis Deviation - Causes
Left ventricular enlargement
Hypertension
Aortic stenosis
Ischemic heart disease
Left bundle branch block and left anterior fascicular block

33. RIGHT AXIS DEVIATION Right Axis Deviation Abnormal finding.
Often associated with COPD and pulmonary hypertension.

34. Right Axis Deviation - Causes
Right ventricular enlargement
COPD
Pulmonary embolism
Congenital heart diseases
Other diseases causing pulmonary hypertension and cor pulmonale
Right bundle branch block and left posterior fascicular block

35. BUNDLE BRANCH BLOCKS Conduction Abnormalities Bundle Branch Blocks
Right Bundle Branch Block

36. BUNDLE BRANCH BLOCKS Conduction Abnormalities The Turn-Signal Rule
QRS > 120 ms throughout the ECG.
Look at the QRS
in V1.
Identify the J point.
Draw a horizontal line.
Triangle pointing up indicates RBBB.
Triangle pointing down indicates LBBB.

37. LEFT BUNDLE BRANCH BLOCK

38. RIGHT BUNDLE BRANCH BLOCK

39. CONDUCTION ABNORMALITIES
Hemiblocks
Left Anterior Hemiblock

40. CONDUCTION ABNORMALITIES
Hemiblocks
Left Posterior Hemiblock

41. CHAMBER ENLARGEMENT Chamber Enlargement Atrial Enlargement
Ventricular Hypertrophy
Causes
Right-sided enlargement and hypertrophy, usually secondary to long-term pulmonary disease.
Left-sided enlargement and hypertrophy, usually secondary to long-term hypertension.

42. RIGHT ATRIAL ENLARGMENT

43. LEFT ATRIAL ENLARGEMENT

44. RIGHT VENTRICULAR ENLARGEMENT

45. LEFT VENTRICULAR ENLARGEMENT

46. Time to Practice