1. ECG Practice Exam Answers (some at least)
Scott Ewing, D.O.
November 3, 2005

3. Normal ECG

4. Normal Intervals

5. Left Bundle Branch Block

6. Right Bundle Branch Block

7. QT Interval Heart rate dependent QTc  0.44-0.46 sec
QTc = QT /  RR in seconds
Causes long QTc
Hereditary
Drugs (many antiarrhythmics, tricyclics, phenothiazines, and others)
Electrolyte abnormalities ( K+, Ca++, Mg++)
CNS disease (especially subarrachnoid hemorrhage, stroke, trauma)
Hereditary LQTS (e.g., Romano-Ward Syndrome)
Coronary Heart Disease (some post-MI patients)

8. QT interval duration is greater than 50% of the RR interval, a good indication that it is prolonged
Increased risk for malignant ventricular arrhythmias, syncope, and sudden death

9. Normal frontal plane axis
-30º - 100º

10. Axis #1
No isoelectric lead in this ECG, the two closest leads are I and aVL
If I isoelectric, the axis would be +90º
If aVL isoelectric, the axis would be +60º
Compromise is +75º (The two closest leads are always 30 degrees apart)

11. Axis #2 Lead I is isoelectric
Perpendiculars to lead I are +90 and -90º
Leads II, III, aVF are positive
Therefore, the axis must be +90º

12. Axis #3
No isoelectric lead in this ECG, the two closest leads are II and aVF
If aVF isoelectric, the axis would be 0º
If II isoelectric, the axis would be -30º
Compromise is -15º (The two closest leads are always 30 degrees apart)

13. Axis #4 Lead aVF is isoelectric
Perpendiculars to lead aVF are 0 and +180º
Leads I, II, aVL are positive
Therefore, the axis must be 0º

14. Axis #5 (Bonus)

15. Axis #5 (Bonus) Lead I is negative, which usually means RAD
Lead II is the isoelectric lead, which almost always means -30 degrees
But in this example the axis is 180 degrees away from –30 (look at I, III and aVL)
Unusual right axis deviation +150º

16. Northwest axis (no man's land)
emphysema
hyperkalaemia
lead transposition
artificial cardiac pacing
ventricular tachycardia

17. Right Axis Deviation 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

18. Left Axis Deviation 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
injection of contrast into left coronary artery