The traditional measure of Left Ventricular Ejection Fraction (EF) quantifies the volume of blood pumped out of the heart with each beat. While widely used, EF is a relatively late indicator of heart muscle damage, as it measures overall volume change and can remain normal even when the heart muscle is beginning to struggle. A more sensitive measurement has emerged in cardiology to detect subtle changes in heart function much earlier: Global Longitudinal Strain (GLS). This measure offers a quantitative assessment of the heart muscle’s intrinsic ability to deform, providing a detailed picture of its health. GLS has become an important tool for the early detection and management of various cardiac conditions, often identifying dysfunction before it is visible through traditional methods.
Defining Global Longitudinal Strain
Global Longitudinal Strain is a measure of the percentage change in the length of the heart muscle, or myocardium, during the cardiac cycle. The term “strain” refers to the deformation of a material relative to its original length, representing the muscle’s ability to shorten and return to its resting state. The heart muscle contracts in three directions—longitudinal (from base to apex), circumferential (around the short axis), and radial (thickening of the wall)—but the longitudinal component is the most clinically relevant for assessing overall left ventricular function.
The heart’s architecture features muscle fibers predominantly oriented longitudinally in the subendocardial layer, the most vulnerable area to injury. Because of this arrangement, longitudinal shortening, measured as GLS, is a highly sensitive index of overall muscle health. Unlike Ejection Fraction, which is a volume-based measurement influenced by the shape and size of the ventricle, GLS directly reflects the contractility of the muscle fibers themselves, making it superior for identifying subclinical heart dysfunction.
The Technology Behind Measurement
Measuring Global Longitudinal Strain requires advanced cardiac ultrasound, a procedure known as echocardiography. The specific technique used to calculate GLS is called Speckle Tracking Echocardiography (STE). This technology analyzes the movement of tiny, naturally occurring acoustic markers, or “speckles,” within the gray-scale ultrasound image of the myocardium.
The STE software identifies these unique speckle patterns and tracks their movement frame-by-frame throughout the heart’s contraction and relaxation phases. By observing how far these speckles move toward each other, the system calculates the degree of muscle deformation and the velocity of that deformation. GLS is derived by averaging the longitudinal strain values from multiple segments of the left ventricle, typically across the three apical imaging planes. This sophisticated tracking process allows for an objective, quantitative measurement of muscle function.
Understanding the GLS Score
The numerical output of a GLS measurement is always expressed as a negative percentage, such as -18% or -20%. This negative sign is a convention in physics and cardiology, indicating the heart muscle is shortening during contraction. A more negative percentage represents greater shortening and healthier function, as a value of -20% means the muscle fibers contracted by 20% of their original length.
For a healthy adult heart, the Global Longitudinal Strain score typically falls in a range more negative than -18%, with values between -18% and -22% considered normal. A score that is less negative, such as -16% or closer to zero, signifies reduced muscle deformation and is an early indicator of impaired function. This impairment often suggests a reduction in the intrinsic contractility of the muscle fibers, even if the Ejection Fraction is still within normal limits.
A change in the GLS score over time is often more significant than the single absolute value itself. In clinical practice, a relative reduction of 10% to 15% from a patient’s baseline GLS measurement is considered a significant change, signaling a meaningful decline in heart health. For instance, a patient whose GLS drops from a baseline of -20% to -17% has experienced a 15% relative reduction, which would be a cause for concern and may prompt an adjustment in treatment.
Clinical Applications in Heart Health
Global Longitudinal Strain is a powerful tool in several areas of heart health due to its ability to detect subclinical dysfunction. One primary application is in cardio-oncology, the field focused on the heart health of cancer patients. Many chemotherapy agents, particularly anthracyclines, can be toxic to the heart muscle, potentially leading to heart failure.
GLS is used to monitor these patients, as it can detect cardiotoxicity weeks or months before a measurable drop in Ejection Fraction occurs. If a patient’s GLS score shows a significant relative decrease during chemotherapy, clinicians can intervene early with cardioprotective medications to prevent further damage without interrupting the life-saving cancer treatment. This early warning capability is also valuable in identifying subclinical dysfunction in individuals with underlying cardiovascular risk factors like diabetes or high blood pressure.
Furthermore, GLS has shown considerable value in predicting future adverse cardiac events. Studies have demonstrated that an impaired GLS score can predict a worse prognosis, including a higher risk of heart failure hospitalization or death, even in patients who appear clinically stable. This predictive strength is often greater than that of Ejection Fraction, allowing doctors to better stratify a patient’s risk and guide treatment decisions. GLS integration into standard cardiac assessment provides an objective and reproducible measure.