Global Longitudinal Strain (GLS) is an advanced measurement of heart function that provides a non-invasive way to assess the left ventricle, the heart’s primary pumping chamber. This technique offers a detailed evaluation of the health of the heart muscle itself.
Measuring Heart Muscle Function
Global Longitudinal Strain is measured during a procedure called an echocardiogram, which uses ultrasound waves to create images of the heart. The “strain” in GLS refers to the degree of deformation or change in shape of an object. In this context, it quantifies the percentage of shortening that occurs in the heart muscle fibers as the left ventricle contracts to pump blood. This provides a direct assessment of the muscle’s contractile capability.
The technology enabling this measurement is known as speckle-tracking echocardiography. During an echocardiogram, the ultrasound system captures natural acoustic patterns, or “speckles,” within the heart muscle tissue. Advanced software then tracks the movement of these speckles from one frame to the next throughout the cardiac cycle. This tracking allows for a precise calculation of the extent to which the muscle fibers are shortening.
To visualize how speckle-tracking works, one might imagine drawing a series of dots along the length of a rubber band. As the rubber band is stretched and then released, one could track the movement of these dots relative to each other to measure how much the band’s length changes. Speckle-tracking technology applies a similar principle to the heart muscle, providing a detailed, quantifiable measure of its function as it beats.
Understanding GLS Values
The results of a Global Longitudinal Strain test are expressed as a negative percentage, such as -20%. Understanding this value can be counterintuitive, as a more negative number signifies a healthier and stronger heart muscle function. For instance, a GLS value of -21% indicates better contractility than a value of -16%.
While specific ranges can vary slightly depending on the laboratory and the ultrasound equipment manufacturer, general guidelines are used for interpretation. A normal GLS value is typically considered to be -18% or more negative (e.g., -20%, -22%). Values in the range of -16% to -18% are often classified as borderline or indicating mildly reduced function. A GLS value that is less negative than -16% is generally interpreted as moderately to severely reduced.
These numerical values provide a quantitative assessment of the heart muscle’s intrinsic health. Factors such as age and sex can influence what is considered a normal GLS value for an individual.
Clinical Applications of GLS
The clinical use of GLS is centered on its ability to detect early signs of heart muscle dysfunction, often before changes are apparent with other tests. For example, in cardio-oncology, GLS is used to monitor patients undergoing chemotherapy. Certain cancer treatments can be cardiotoxic, and serial GLS measurements can detect small changes in heart function early, which allows for adjustments to the treatment regimen to mitigate heart damage.
GLS is also important in the management of heart failure, particularly for patients who have heart failure with a preserved ejection fraction (HFpEF). In these individuals, the heart’s main pumping measurement appears normal, yet they experience symptoms of heart failure. GLS can unmask the underlying muscle dysfunction that contributes to the condition, helping to assess prognosis and guide therapeutic strategies.
For individuals with valvular heart disease, such as aortic stenosis where the aortic valve narrows, GLS helps evaluate the strain on the heart muscle. It can quantify the impact of the diseased valve on ventricular function, even when other metrics seem stable. This information can assist in determining the optimal timing for valve replacement surgery. Additionally, GLS aids in differentiating between various types of cardiomyopathies, or diseases of the heart muscle, by revealing distinct patterns of strain.
GLS Compared to Ejection Fraction
Global Longitudinal Strain is often compared to a more traditional measure of heart function, the Left Ventricular Ejection Fraction (LVEF). LVEF measures the percentage of blood that is pumped out of the left ventricle with each heartbeat. For decades, LVEF has been a primary method for assessing how well the heart is pumping.
The main advantage of GLS over LVEF lies in its heightened sensitivity. GLS provides a direct measurement of the health and contractility of the myocardial fibers themselves. In contrast, LVEF is a more global measure of overall pumping capacity. This means that LVEF can remain in the normal range even when the underlying heart muscle has already begun to weaken.
This distinction is important in the early detection of cardiac dysfunction. Conditions such as long-standing hypertension, diabetes, or early-stage cardiotoxicity from medication can cause subtle damage to the heart muscle that GLS can detect. LVEF may only show a decline after significant damage has already occurred. For this reason, GLS is considered a more direct and earlier indicator of changes in myocardial health, while LVEF reflects a pumping function that may falter later in the disease process.