An electrocardiogram (EKG or ECG) is a standard test that provides a snapshot of the heart’s electrical activity. The machine creates a graph of these signals for doctors to analyze. One specific notation that can appear on an EKG report is “low voltage QRS,” which refers to the measured strength, or amplitude, of a part of the heart’s electrical signal. This observation can arise from many circumstances, some related to the heart and others not.
Understanding the EKG Finding
The tracing on an EKG report shows a repeating pattern with each heartbeat, characterized by a series of waves and spikes. The most prominent of these is the QRS complex, which looks like the biggest spike on the graph. This part of the tracing represents the powerful electrical impulse that spreads through the heart’s main pumping chambers, the ventricles, causing them to contract and push blood to the lungs and the rest of the body.
When an EKG report notes “low voltage,” it means the height of this QRS spike is shorter than typically expected. This indicates the electrical signal appears dampened by the time it reaches the recording electrodes on the skin. Clinically, this is defined by a QRS amplitude of less than 5 millimeters in the limb leads (electrodes on the arms and legs) or less than 10 millimeters in the precordial leads (electrodes on the chest).
This finding does not point to a single condition but serves as a flag that requires further context. The reduced amplitude can be caused by factors that interfere with the signal’s transmission or by conditions that affect the heart muscle cells that generate the electricity.
Potential Causes of Low Voltage QRS
A primary group of causes for low voltage QRS involves factors that insulate the heart, muffling its electrical broadcast. Excess fatty tissue in individuals with obesity can act as an insulator, dampening the signal before it reaches the skin. Air trapped in the lungs of a person with emphysema or chronic obstructive pulmonary disease (COPD) can have the same effect. Fluid collecting around the lungs (pleural effusion) can also physically increase the distance between the heart and the EKG electrodes.
Conditions more directly involving the heart are also frequent causes. A notable example is pericardial effusion, the buildup of fluid in the sac surrounding the heart, which can significantly dampen the electrical forces it generates. Certain diseases can infiltrate the heart muscle itself, impairing its ability to produce a strong electrical signal. Conditions like amyloidosis or hemochromatosis can lead to a loss of viable heart muscle and a weaker signal.
Widespread bodily conditions can also result in this EKG finding. Severe hypothyroidism can cause changes throughout the body that may lead to low voltage readings. Generalized swelling (anasarca) can increase the fluid and tissue the electrical signal must pass through. Technical errors, such as incorrect settings on the EKG machine or improper electrode placement, can sometimes be the explanation.
The Diagnostic Process
Observing a low voltage QRS on an EKG is a clue, not a final diagnosis, that prompts a physician to investigate the underlying reason. The first step is a thorough review of the patient’s medical history, current symptoms, and a complete physical examination. This initial context is valuable for narrowing down the potential causes.
To get a direct look at the heart’s structure and function, the most common next step is an echocardiogram. This non-invasive test uses ultrasound waves to create detailed images of the heart. An echocardiogram can show the thickness and pumping action of the heart muscle and is particularly effective at identifying fluid around the heart, as in pericardial effusion. This imaging allows doctors to see if the heart muscle itself is abnormal.
Depending on the clinical picture, other tests may be ordered to complete the evaluation. A chest X-ray can help identify issues like an enlarged heart, excess fluid around the lungs, or signs of lung disease. Blood tests may also be used to check for systemic conditions, such as thyroid hormone levels in suspected hypothyroidism or markers for specific infiltrative diseases.
Implications and Management
The significance of a low voltage QRS finding is entirely dependent on its underlying cause. It is an observation with a wide spectrum of implications, from completely benign to indicative of a serious medical condition. If the low voltage is determined to be a result of a person’s body composition, such as obesity, it may have no direct clinical importance on its own.
When the low voltage QRS points to a specific medical problem, the treatment plan is targeted at that root cause. For instance, if a pericardial effusion is identified as the reason for the dampened signal, medical intervention will focus on draining the excess fluid and treating its cause. If an infiltrative disease like cardiac amyloidosis is diagnosed, the management strategy will revolve around treatments for that specific disease process.
The EKG finding itself is not treated; it serves its purpose by guiding the diagnostic process toward the true issue. Successful management and outcome depend on accurately diagnosing and addressing the specific condition that is causing the electrical signal to appear diminished.