Diagnostic criteria

  The amplitude of QRS complexes in limb leads are < 5mm (0.5mV).

  The amplitude of QRS complexes in precordial leads are
< 10mm (1 mV).



Low voltage is seen in patients with

  Pericardial effusion

  Constrictive pericarditis

  Hypothyroidism

  Amyloidosis

  Morbid obesity

  Pneumothorax

  Pleural effusion

  Emphysema

  Scleroderma

  Acute pulmonary embolism

  Anasarca



Low voltage only in limb leads

  Although not specific, this has been reported to be more frequent in patients with dilated cardiomyopathy.




In some patients with congestive heart failure, the
preexisting low voltage may disappear after vigorous
diuretic therapy
.



Observation of the following triad suggests the need for exclusion of pneumothorax

  Isolated low voltage in lead I

  Poor R wave progression in chest leads

  Lead aVF
/Lead I QRS amplitude ratio is > 2



References

  Journal of Electrocardiology 2008;41:281-286.

  Am J Emerg Med 2008;26:959-962.






ECG 1. Low voltage in a patient with long-standing emphysema.

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ECG 2. If a patient with preexisting low voltage has acute myocardial infarction, it may be difficult to recognize the
ST segment
elevation
at a first glance.

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ECG 3. The above ECG is from a morbid obese woman a body mass index of 49.
Low voltage is seen in the limb leads.
This patient has long-standing hypertension and is taking 4 antihypertensive drugs daily.

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ECG 4. The above ECG is from a 58 years-old man with pericardial effusion and shows low voltage.

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ECG 5a. The above ECG is from a 63 years-old hypertensive diabetic woman. There is low voltage in limb leads.
Also the
PR interval is prolonged : first degree atrioventricular (av) block.
The low voltage makes it difficult to recognize the prolonged PR in interval in limb leads at first glance.

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ECG 5b. Then the ECG was recalibrated at
20 mm/mV .
Now
P waves and the prolonged PR interval are easily discernible in limb leads.

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ECG 6a. The ECG above is from an 82 years-old woman with orthopnea.
Echocardiography showed mild mitral stenosis and right heart failure, but no pericardial effusion.
She has atrial fibrillation with a high ventricular response.
Diuretic and digoxin therapy were initiated.
Calibration of the ECG is 10 mm/mV but still low voltage is seen in limb leads.

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ECG 6b. After losing 7 kgs of body weight with vigorous diuresis in several days, her complaint of orthopnea disappeared.
The rhythm is still atrial fibrillation but amplitude of the QRS complexes are increased now.
Calibraiton of the ECG is still 10 mm/mV.
Digoxin effect is also seen in the above ECG (sagging-type ST segment depression in precordial leads, I, II and aVF).

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ECG 7. The ECG above is from a 73 years-old man with dilated cardiomyopathy.
Low QRS voltage is seen only in limb leads.
Although not specific, the low voltage confined to limb leads is seen more frequently
in patients with dilated cardiomyopathy.

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ECG 8. The ECG above is from a 68 years-old diabetic woman with coronary artery disease.
Because of the low QRS voltage,
P waves are difficult to see at first glance.

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ECG 9a. The ECG above is from a 55 years-old man with coronary artery disease.
Both limb leads and precordial leads show low voltage.
The patient had experienced acute inferoposterior myocardial infarction in the past.
Now, he has left ventricular systolic dysfunction with an Ejection Fraction of 35%.
Inferior leads show negative T waves. Lead II shows q wave while leads III and aVF show subtle initial r waves.
In this patient, the only ECG abnormality to suggest posterior wall involvement is the presence of
(relatively) tall R wave and T wave in lead V2.
There is also left axis deviation.

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ECG 9b. The compact ECG above is derived from ECG 9a.