Cardiology Week 3 Summary

Question 11

What are the criteria and causes for low voltage on a 12-lead ECG?

Total QRS height in precordial leads <10 mm and limb leads <5 mm


  1. Myocardial disease
    • ischemia
    • infiltrative (e.g. amyloidosis)
    • dilated cardiomyopathy
    • myocarditis
  2. Pericardial effusion
  3. Thick chest wall / barrel chest: COPD, obesity
  4. Generalized edema
  5. Hypothyroidism/myxedema
  6. Inappropriate voltage standardization

Question 12

What are the causes of left axis deviation (LAD) on ECG?

  1. Left anterior hemiblock
  2. Inferior myocardial infarction
  3. RV apical pacing & middle cardiac vein pacing
  4. WPW / pre-excitation / bypass tract
  5. Pulmonary Emphysema
  6. Hyperkalemia
  7. Ventricular ectopic rhythms
  8. Mechanical shifts: Expiration, high diaphragm from pregnancy, ascites, abdominal tumors, etc.
  9. Endocardial cushion defects, some other acyanotic and cyanotic congenital lesions
  10. Normal variation

Note 1: LVH is not a cause. Left axis deviation is associated with LBBB but LBBB is not a cause of LAD.

Note 2: LAD is does not invariably accompany LVH. Significant LAD suggest presence of myocardial disease in the LV apart from pure hypertrophy.

Marriott 8th ed. 1987 p. 50-55

Question 13

What are the causes of right axis deviation (RAD) on ECG?

  1. Right ventricular hypertrophy
  2. Right bundle branch block
  3. Left posterior hemiblock
  4. Lateral infarction
  5. Dextrocardia
  6. Ventricular ectopic rhythms
  7. WPW/ Preexcitation / Bypass tract
  8. Mechanical shifts – inspiration, emphysema
  9. Normal variation

Note 1: Left posterior hemiblock is a diagnosis of exclusion of RAD when all the other causes are excluded.

Question 14

What is the CHADS2 score for assessing the risk for stroke among patients with atrial fibrillation?

CHADS2 Score:

Risk factor Points
Congestive Heart Failure 1
Hypertension 1
Age>75 1
Diabetes 1
Stroke/TIA (prior) 2
CHADS2 Score Stroke Risk (%/Yr) Anticoagulation Recommendation
0-1 1.9-2.8 (low) Aspirin 81-325mg
2-3 4.0-5.9 (mod) Coumadin (INR 2-3)
4-6 8.5-18.2 (high) Coumadin (INR 2-3)

CHADS2 risk prediction for non-valvular A-Fib

Question 15

Among patients with wide-complex tachycardia, what are the clues to help distinguish between ventricular tachycardia (VT) versus supraventricular tachycardia (SVT) with aberrancy?

Clinical clues:

Presenting symptoms Not Helpful
History of CAD and previous MI VT
Physical Exam:

  • Cannon “a” waves
  • Variable S1

  • VT
  • VT
Carotid sinus massage/adenosine terminate arrhythmia SVT*
AV dissociation VT
Capture or fusion VT
QRS width>140 msec VT
Extreme axis deviation
(left or right superior axis)
Positive QRS concordance
(R wave across chest leads)
Negative QRS concordance
(S wave across chest leads)
may suggest VT
Axis shift during arrhythmia VT (polymorphic)

*if patient >65 and previous MI or structural heart disease, then chance of VT is >95%.

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