Question 11
What are the criteria and causes for low voltage on a 12-lead ECG?
Definition:
Total QRS height in precordial leads <10 mm and limb leads <5 mm
Etiology:
- Myocardial disease
- ischemia
- infiltrative (e.g. amyloidosis)
- dilated cardiomyopathy
- myocarditis
- Pericardial effusion
- Thick chest wall / barrel chest: COPD, obesity
- Generalized edema
- Hypothyroidism/myxedema
- Inappropriate voltage standardization
Question 12
What are the causes of left axis deviation (LAD) on ECG?
- Left anterior hemiblock
- Inferior myocardial infarction
- RV apical pacing & middle cardiac vein pacing
- WPW / pre-excitation / bypass tract
- Pulmonary Emphysema
- Hyperkalemia
- Ventricular ectopic rhythms
- Mechanical shifts: Expiration, high diaphragm from pregnancy, ascites, abdominal tumors, etc.
- Endocardial cushion defects, some other acyanotic and cyanotic congenital lesions
- 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?
- Right ventricular hypertrophy
- Right bundle branch block
- Left posterior hemiblock
- Lateral infarction
- Dextrocardia
- Ventricular ectopic rhythms
- WPW/ Preexcitation / Bypass tract
- Mechanical shifts – inspiration, emphysema
- 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:
|
|
| 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) |
VT |
| Positive QRS concordance (R wave across chest leads) |
VT |
| 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%.
