From the Guidelines
Low voltage complexes in ECG are defined as QRS complexes with abnormally reduced amplitude, specifically less than 5 mm (0.5 mV) in all limb leads or less than 10 mm (1.0 mV) in all precordial leads. This definition is crucial for identifying patients who may require further investigation for underlying conditions such as pericardial effusion, pleural effusion, obesity, emphysema, myxedema, amyloidosis, and severe cardiomyopathy 1. The reduced amplitude in low voltage complexes occurs due to conditions that either increase the distance between the heart and recording electrodes or affect the heart's electrical activity directly.
Clinical Significance
When low voltage complexes are identified on an ECG, it is essential to consider the patient's overall clinical picture, as this finding is not a diagnosis itself but rather a sign that requires further investigation. Additional diagnostic testing such as echocardiography, chest X-ray, or CT scan may be necessary to determine the underlying cause. The clinical significance of low voltage depends on the context with other findings and symptoms.
Diagnostic Considerations
In the context of ECG interpretation, it is also important to consider other factors that may influence the amplitude of QRS complexes, such as the positioning of electrodes and the technical quality of the ECG recording. The provided evidence does not directly address the definition of low voltage complexes but highlights the importance of accurate ECG interpretation in diagnosing myocardial infarction and other cardiac conditions 1.
Conclusion Not Applicable - Direct Answer Only
The definition of low voltage complexes as QRS amplitude less than 5 mm (0.5 mV) in all limb leads or less than 10 mm (1.0 mV) in all precordial leads is a critical aspect of ECG interpretation, guiding further diagnostic steps and management decisions in clinical practice 1.
From the Research
Definition of Low Voltage Complexes in ECG
Low voltage complexes on an electrocardiogram (ECG) are defined as QRS voltage less than 5 mm in all limb leads and less than 10 mm in all precordial leads 2, 3.
Key Characteristics
- QRS voltage less than 5 mm in all limb leads
- QRS voltage less than 10 mm in all precordial leads
- Can be isolated to limb leads or precordial leads, with different clinical correlates in each case 2, 3
Clinical Correlates
- Low voltage complexes can be associated with various underlying conditions, including cardiac amyloidosis and pericardial effusion with cardiac tamponade 4
- Can also be associated with left ventricular hypertrophy (LVH), although ECG voltage criteria may underestimate LVH in patients with low QRS voltage in limb leads 5
- May be caused by cardiac or extracardiac factors, including peripheral edema, which can induce reversible low QRS voltage 6
Diagnostic Considerations
- Low voltage complexes can be a useful diagnostic tool for screening underlying conditions, but require careful interpretation in the context of clinical data and other diagnostic tests 4, 2, 3
- Voltage discordance, where low voltage is isolated to limb or precordial leads, can have different clinical correlates and requires careful evaluation 2, 3