A Visual Guide to ECG Interpretation
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Chapter 9 • Voltage Abnormalities
The Low-Voltage ECG
Criteria Voltage is considered low in the limb leads when the average QRS amplitude is less than 5 mm and low in the precordial leads when the average QRS amplitude is less than 10 mm.
Low voltage can result from cardiac causes in which the myocardium fails to generate significant voltage. Low voltage can also result when sufficient voltage signal is attenuated by extracardiac factors. Some of these decrease the signal by increasing the distance from the heart to the chest wall.
The Differential Diagnosis
Cardiac Causes
Extracardiac Causes
Ischemic Myocardium
Air
Fluid
Adipose
Other
Severe cardiomyopathy
Hypothyroidism
Pneumothorax
Pericardial Effusion Large Pleural Effusion
Morbid Obesity
Possibly from a combination of pericardial effusion and low thyroid hormone.
Especially left-sided pneumothorax
Cardiac amyloidosis Infiltrated Myocardium
Hypothermia
Especially left-sided pleural effusion
COPD
Subcutaneous emphysema
Anasarca
Constrictive pericarditis
Electrical Alternans
QRS Wave Alternans
Pericardial Effusion
Alternating voltage of the QRS complex results from the pendular motion of the heart within a fluid-filled pericardial space.
Supraventricular Tachycardias
Alternans can also occur at very high heart rates seen in reentrant supraventricular tachycardias. Copyright © 2021 Wolters Kluwer, Inc. Unauthorized reproduction of the content is prohibited.
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