ECG Differential Diagnoses: Instant Reviews

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Chapter 24 ECG Differential Diagnoses Instant Reviews

This chapter presents a series of boxes that summarize selected aspects of ECG differential diagnosis for easy reference. For the most part the boxes recap topics covered in this book. However, some advanced topics are briefly mentioned, with additional discussion available in references cited in the Bibliography.

Low-Voltage QRS Complexes

1. Artifactual or spurious, e.g., unrecognized standardization of the ECG at half the usual gain (i.e., 5 mm/mV). Always check this first!

2. Adrenal insufficiency (Addison’s disease)

3. Anasarca (generalized edema)

4. Cardiac infiltration or replacement (e.g., amyloid, tumor)

5. Cardiac transplantation, especially with acute or chronic rejection

6. Cardiomyopathies: dilated, hypertrophic, or restrictive types

7. Chronic obstructive pulmonary disease

8. Constrictive pericarditis

9. Hypothyroidism/myxedema (usually with sinus bradycardia)

10. Left pneumothorax (mid-left chest leads)

11. Myocardial infarction, usually extensive

12. Myocarditis, acute or chronic

13. Normal variant

14. Obesity

15. Pericardial effusion/tamponade (latter usually with sinus tachycardia)

16. Pleural effusions

∗Dilated cardiomyopathies may be associated with a paradoxical combination of relatively low limb lead voltage and prominent precordial voltage.

Wide QRS Complex (Normal Rate)

I. Intrinsic intraventricular conduction delay (IVCD)∗

A. Left bundle branch block and variants
B. Right bundle branch block and variants
C. Other (nonspecific) patterns of IVCD

II. Extrinsic (“toxic”) intraventricular conduction delay

A. Hyperkalemia
B. Drugs: class I antiarrhythmic drugs and other sodium channel blocking agents (e.g., tricyclic antidepressants and phenothiazines)

III. Ventricular beats: premature, escape, or paced

IV. Ventricular preexcitation: Wolff-Parkinson-White pattern and variants

∗ Bundle branch block patterns may occur transiently. Note also that a spuriously wide QRS complex occurs if the ECG is unintentionally recorded at fast paper speeds (50 or 100 mm/sec).

Left Axis Deviation (QRS Axis of −30° or More Negative)

I. Left ventricular hypertrophy

II. Left anterior (hemiblock) fascicular block (strictly, −45° or more negative)

III. Inferior wall myocardial infarction (typically with QS waves in leads II, III, and aVF)

IV. Endocardial cushion defects (congenital), especially ostium primum atrial septal defects

Right Axis Deviation (QRS Axis of +90° or More Positive)

I. Artifact: left-right arm electrode reversal (look for negative P wave and negative QRS complex in lead I)

II. Normal variant, especially in children and young adults

III. Dextrocardia

IV. Right ventricular overload

A. Acute (e.g., pulmonary embolus or severe asthmatic attack)
B. Chronic
1. Chronic obstructive pulmonary disease
2. Any cause of right ventricular hypertrophy (e.g., pulmonary stenosis, secundum atrial septal defects, or primary pulmonary hypertension)

V. Lateral wall myocardial infarction

VI. Left posterior (hemiblock) fascicular block; note: need to exclude all other causes of right axis deviation and rigorously requires marked rightward axis (+110–120° or more)

QT(U) Prolongation (Long QT Syndromes)

I. Acquired long QT syndrome

A. Electrolyte abnormalities
1. Hypocalcemia
2. Hypokalemia
3. Hypomagnesemia
B. Drugs∗
1. Class IA or III antiarrhythmic agents (e.g., quinidine, procainamide, disopyramide, dofetilide, ibutilide, sotalol, dronedarone, and amiodarone)
2. Psychotropic agents (e.g., phenothiazines, tricyclic antidepressants, tetracyclic agents, atypical antipsychotic agents, haloperidol)
3. Many others: arsenic trioxide, chloroquine, methadone, certain antibiotics (e.g., erythromycin, levofloxacin, and pentamidine), etc.
C. Myocardial ischemia or infarction (especially, with deep T wave inversions)
D. Cerebrovascular injury (e.g., intracranial bleeds)
E. Bradyarrhythmias (especially high-grade atrioventricular heart block)
F. Systemic hypothermia
G. Miscellaneous conditions
1. Liquid protein diets
2. Starvation
3. Arsenic poisoning

II. Congenital (hereditary) long QT syndromes (LQTS)

A. Romano-Ward syndrome∗∗ (autosomal dominant disorders)
B. Jervell and Lange-Nielsen syndrome (autosomal recessive disorder associated with congenital deafness)

∗ For an excellent, updated review of drugs associated with the acquired long QT syndrome and torsades de pointes risk, see the Arizona Cert website: http://www.azcert.org/medical-pros/drug-lists/browse-drug-list.cfm.

∗∗ The Romano-Ward syndrome is the classic, general term used to designate a number of specific, inherited abnormalities in ion channel function (“channelopathies”) that are associated with prolongation of ventricular repolarization (long QT-U) and increased risk of torsades de pointes (see Chapter 16). These hereditary ion channel (potassium, sodium, or calcium) disorders can prolong and increase heterogeneity of ventricular repolarization.

Q Waves

I. Physiologic or positional factors

A. Normal variant septal Q waves
B. Normal variant Q waves in leads V1, V2, aVL, III, and aVF
C. Left pneumothorax or dextrocardia (loss of lateral R wave progression)

II. Myocardial injury or infiltration

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