Global Longitudinal Strain (GLS) is an advanced measure of the heart’s mechanical function, providing a precise assessment of the subtle movements of the heart muscle, or myocardium. This measurement is derived from an echocardiogram, a specialized ultrasound of the heart. GLS quantifies the percentage change in muscle fibers as the heart contracts. Understanding this measurement helps clinicians detect very early signs of change in heart health, often before a person feels any symptoms. This article clarifies what GLS is and outlines the values considered typical for a healthy heart.
Defining Global Longitudinal Strain
Global Longitudinal Strain (GLS) measures the deformation of the heart muscle along its long axis, running from the base to the apex, or tip. This percentage change in length during the heart’s contraction phase, known as systole, reflects the efficiency of the muscle fibers. GLS utilizes a sophisticated imaging technique called speckle tracking echocardiography (STE), which tracks thousands of natural acoustical markers, or “speckles,” within the myocardium.
The measurement of GLS is expressed as a negative percentage because healthy heart muscle fibers shorten during contraction. For instance, a value of -20% means the muscle has shortened by 20% from its resting length. A more negative number indicates better function, as it signifies a stronger contraction. This process provides a quantitative, objective measure of myocardial contractility that is highly reproducible.
The longitudinal fibers run from the base to the apex and are primarily located in the subendocardial layer, the innermost region of the heart wall. This layer is particularly vulnerable to injury from conditions like reduced blood flow or high blood pressure. By measuring GLS, clinicians gain a window into the health of this delicate layer. The resulting numerical value represents the average contraction efficiency across all segments of the left ventricle.
Clinical Significance and Application
The primary value of Global Longitudinal Strain lies in its ability to detect subclinical myocardial dysfunction, which is damage or impairment that occurs before the heart’s function is noticeably reduced by conventional metrics. This early detection capability allows for interventions to be initiated much sooner, potentially preventing the progression to serious conditions like heart failure. GLS acts as a sensitive warning signal that the heart muscle is under stress, even when the overall pumping function appears normal.
One significant application is monitoring patients receiving chemotherapy, particularly cardiotoxic agents that can damage the heart muscle. A decrease in GLS can signal the onset of cardiotoxicity before the patient develops symptoms, allowing oncologists to adjust treatment plans to protect the heart. GLS is also widely used in managing patients with chronic conditions like hypertension and diabetes, which place a constant load on the heart. In these cases, a deteriorating GLS value indicates an increased risk of future heart failure or cardiovascular events.
GLS provides important prognostic information across a wide range of cardiac diseases, including valvular heart disease and different forms of cardiomyopathy. The measurement offers incremental predictive value regarding a patient’s long-term outcome and risk of adverse events. A less negative GLS measurement is consistently associated with a higher risk of hospitalization or mortality, making it a powerful tool for risk stratification.
Establishing Normal and Reference Ranges
The generally accepted range for a healthy Global Longitudinal Strain in adults is typically a value better than -18% to -20%. A more negative number, such as -22%, represents a stronger, more efficient contraction and is considered more favorable. Values between approximately -16% and -18% are often classified as borderline, suggesting a need for careful monitoring. A result less negative than -16%, such as -15% or -14%, usually indicates some degree of abnormal myocardial function requiring further investigation.
Interpreting the precise numerical value requires consideration of several factors, as there is no single, absolute cut-off number. One major source of variability is vendor dependency, meaning the reference ranges can differ slightly depending on the ultrasound machine manufacturer and the specific software used to calculate the strain. For serial monitoring of a patient over time, it is highly recommended to use the same equipment and software platform to ensure consistency in the measurements.
Patient-specific characteristics also influence what is considered a typical GLS value. Research indicates that GLS values tend to become less negative with increasing age, reflecting a natural, gradual decline in heart muscle performance over a lifetime. Additionally, women often exhibit slightly more negative GLS values than men. Factors such as a patient’s blood pressure and body surface area can also affect the final reading.
Due to this variability, many clinical laboratories establish their own specific reference range based on their patient population and the particular ultrasound equipment they use. Clinicians typically use the specific lower limit of normal (LLN) for their laboratory to define an abnormal result. Therefore, a result should always be interpreted in the full context of the patient’s individual characteristics and the laboratory’s established normal range.
GLS Compared to Ejection Fraction
Global Longitudinal Strain offers a distinct advantage over the standard measure of heart function, the Left Ventricular Ejection Fraction (EF). Ejection Fraction quantifies the volume of blood pumped out of the left ventricle with each beat, essentially measuring the difference between the volume of blood in the chamber before and after contraction. In contrast, GLS is a measure of tissue mechanics, quantifying the actual deformation, or percentage shortening, of the heart muscle fibers themselves.
This difference explains why GLS is considered a far more sensitive indicator of early heart muscle damage. GLS can often detect subtle impairment in the muscle fibers while the overall pumping volume, as measured by EF, remains within the normal range. The heart can initially compensate for minor damage to the longitudinal fibers, keeping the EF stable, but GLS reveals the underlying loss of muscle shortening.
In clinical practice, GLS and EF are regarded as complementary measures that provide a more complete picture of cardiac health. EF remains the established metric for diagnosing advanced heart failure, but GLS provides the predictive power for identifying patients at risk before their EF declines. GLS is also a more reproducible measurement than EF, meaning it is less prone to variation between different operators or analysts, which enhances its reliability for tracking changes over time.