1. What are the most commonly used criteria to diagnose left ventricular hypertrophy (LVH)?
■ R wave in V5-V6 + S wave in V1-V2 > 35 mm
■ R wave in lead I + S wave in lead III > 25 mm
2. What are the most commonly used criteria to diagnose right ventricular hypertrophy (RVH)?
■ R wave in V1 > 7 mm
■ R/S wave ratio in V1 > 1
3. What criteria are used to diagnose left atrial enlargement (LAE)?
■ P wave total width of > 0.12 sec (3 small boxes) in the inferior leads, usually with a double-peaked P wave
■ Terminal portion of the P wave in lead V1 > 0.04 sec (1 small box) wide and > 1 mm (1 small box) deep
4. What electrocardiogram (ECG) finding suggests right atrial enlargement?
■ P-wave height in the inferior leads (II, III, and aVF) > 2.5 to 3 mm (2.5-3 small boxes)
5. What is the normal rate of a junctional rhythm?
The normal rate is 40 to 60 beats/min. Rates of 61 to 99 beats/min are referred to
as accelerated junctional rhythm, and rates of 100 beats/min or higher are referred to as
junctional tachycardia.
6. How can one distinguish a junctional escape rhythm from a ventricular escape rhythm in a patient with complete heart block?
Junctional escape rhythms usually occur at a rate of 40 to 60 beats/min and will usually be narrow complex (unless the patient has a baseline bundle branch block), whereas ventricular escape rhythms will usually occur at a rate of 30 to 40 beats/min and will be wide complex.
7. Describe the three types of heart block.
First-degree heart block: The PR interval is a fixed duration of more than 0.20 seconds.
Second-degree heart block: In Mobitz type I (Wenkebach), the PR interval increases until a P wave is nonconducted. The cycle then resets and starts again. Mobitz type I second-degree heart block is sometimes due to increased vagal tone and is usually a relatively benign finding. In Mobitz type II, the PR interval is fixed and occasional P waves are nonconducted. Mobitz type II second-degree heart block usually indicates structural disease in the atrioventricular (AV) node or His-Purkinje system and is an indication for pacemaker implantation.
Third-degree heart block: All P waves are nonconducted, and there is either a junctional or ventricular escape rhythm. To call a rhythm third-degree or complete heart block, the atrial rate (as evidenced by the P waves) should be faster than the ventricular escape rate (the QRS complexes). Third-degree heart block is almost always an indication for a permanent pacemaker.
8. What are the causes of ST segment elevation?
Acute myocardial infarction (MI) due to thrombotic occlusion of a coronary artery
Prinzmetal’s angina (variant angina), in which there is vasospasm of a coronary artery
Cocaine-induced MI, in which there is vasospasm of a coronary artery, with or without additional thrombotic occlusion
Pericarditis, in which there is usually diffuse ST segment elevation
Left ventricular aneurysm Left bundle branch block (LBBB)
Left ventricular hypertrophy with repolarization abnormalities
J point elevation, a condition classically seen in young African-American patients but that can be seen in any patient, which is felt due to ‘‘early repolarization’’
Severe hyperkalemia
9. What are the electrocardiographic findings of hyperkalemia?
Initially, a ‘‘peaking’’ of the T waves is seen. As the hyperkalemia becomes more profound, ‘‘loss’’ of the P waves, QRS widening, and ST segment elevation may occur. The preterminal finding is a sinusoidal pattern on the ECG.
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10. What are the ECG findings in pericarditis?
The first findings are believed by some to be PR segment depression caused by repolarization abnormalities of the atria. This may be fairly transient and is often not present by the time the patient is seen for evaluation. Either concurrent with PR segment depression or shortly following PR segment depression, diffuse ST segment elevation occurs (see ECG example in Chapter 53 on Pericarditis). At a later time, diffuse T-wave inversions may develop.
11. What is electrical alternans?
In the presence of large pericardial effusions, the heart may ‘‘swing’’ within the large pericardial effusion, resulting in an alteration of the amplitude of the QRS complex.
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12. What is the main ECG finding in hypercalcemia and hypocalcemia?
With hypercalcemia the QT interval shortens. With hypocalcemia, prolongation of the QT interval occurs as a result of delayed repolarization.
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13. What ECG findings may be present in pulmonary embolus?
Sinus tachycardia (the most common ECG finding)
Right atrial enlargement (P pulmonale)—tall P waves in the inferior leads
Right axis deviation & T wave inversions in leads V1-V2
Incomplete right bundle branch block (IRBBB)
S1Q3T3 pattern—an S wave in lead I, a Q wave in lead III, and an inverted T wave in lead III. Although this is only occasionally seen with pulmonary embolus, it is said to be quite suggestive that a pulmonary embolus has occurred.
14. What is torsades de pointes?
Torsades de pointes is a ventricular arrhythmia that occurs in the setting of QT prolongation, usually when drugs that prolong the QT interval have been administered. It may also occur in the setting of prolonged QT syndrome and other conditions. The term was reported coined by Dessertenne to describe the arrhythmia, in which the QRS axis appears to twist around the isoelectric line. It is usually a hemodynamically unstable rhythm that can further degenerate and lead to hemodynamic collapse.
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15. What are cerebral T waves?
Cerebral T waves are strikingly deep and inverted T waves, most prominently seen in the precordial leads, that occur with central nervous system diseases, most notably subarachnoid and intracerebral hemorrhages. They are believed to be due to prolonged and abnormal repolarization of the left ventricle, presumably as a result of autonomic imbalance. They should not be mistaken for evidence of active cardiac ischemia.
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