Global Longitudinal Strain (GLS) is a modern, sensitive, and non-invasive measurement of heart function. It offers detailed insights into how well the heart muscle is working, going beyond traditional assessments.
What is Global Longitudinal Strain?
Global Longitudinal Strain (GLS) is a sophisticated measure of how the heart muscle deforms, focusing on the lengthening and shortening of the left ventricle, the heart’s main pumping chamber. This deformation is expressed as a percentage, indicating the change in length relative to the original length of the muscle. GLS quantifies the shortening of muscle fibers in the longitudinal direction during contraction.
GLS is typically measured using an echocardiogram, an ultrasound of the heart. During this imaging procedure, specialized software tracks tiny speckles within the heart muscle to calculate its movement and deformation. This provides a comprehensive assessment of the left ventricle’s ability to contract and relax efficiently.
Typical Values for Global Longitudinal Strain
GLS values are typically expressed as negative percentages, representing the shortening of the heart muscle during contraction. A more negative number indicates better heart muscle function. For healthy adults, commonly accepted normal GLS values generally range from approximately -18% to -22% or even more negative.
A GLS value greater than -18% (e.g., -17% or -16%) can be considered borderline. A value less negative than -16% (e.g., -15% or -14%) is generally regarded as abnormal.
Why Global Longitudinal Strain Matters
Global Longitudinal Strain is gaining recognition as a more sensitive indicator of early heart dysfunction compared to traditional measures like ejection fraction (EF). EF, which estimates the percentage of blood pumped out of the ventricle, can remain normal even when subtle damage to the heart muscle has occurred. This is because GLS specifically assesses the longitudinal fibers, which are often the first to be affected in many heart conditions. The heart can sometimes compensate for longitudinal dysfunction by increasing its circumferential (around the heart) and radial (thickening) movements, thereby maintaining a normal EF despite underlying issues.
Abnormal GLS values can signal a decline in heart function even before symptoms appear or before EF changes are noticeable. For instance, a reduction in GLS can be an early warning sign of heart failure, even in patients with preserved ejection fraction. GLS is also particularly valuable in monitoring patients undergoing chemotherapy, as it can detect cardiotoxicity (heart damage) induced by certain cancer treatments sooner than EF. A reduction of more than 15% in GLS from baseline in these patients can indicate cardiotoxicity, prompting adjustments to treatment or the initiation of cardioprotective medications.
Moreover, GLS has shown prognostic value, helping predict future cardiac events and mortality. In patients with chronic heart failure, GLS has been linked to the severity of the condition and is associated with increased risks of cardiac and all-cause mortality, independent of other clinical factors. It also aids in differentiating causes of left ventricular hypertrophy and can be associated with the rapid onset of symptoms and a worse prognosis in severe aortic stenosis.
Factors Affecting Global Longitudinal Strain Values
Several factors can influence Global Longitudinal Strain values, making it important for doctors to consider a patient’s overall health and individual characteristics when interpreting results. Age is a factor; GLS values may slightly decrease with advancing age. Minor differences in GLS have also been observed between sexes.
Various medical conditions can impact GLS, even in the absence of overt heart disease. For example, conditions like high blood pressure, diabetes, and obesity have been shown to pathologically reduce GLS, often due to changes in the heart muscle structure, such as left ventricular hypertrophy. Coronary artery disease and certain valvular heart diseases can also affect GLS. A reduced GLS has been associated with long-standing, uncontrolled high blood pressure, overweight status, and related metabolic changes.
Furthermore, technical aspects of the echocardiogram can introduce variability. Different ultrasound equipment manufacturers use varying software for GLS calculations, which can lead to slight differences in reported values. Image quality during the echocardiogram procedure also plays a role, as clear images are needed for accurate speckle tracking. These factors underscore why a comprehensive clinical assessment, rather than just a single GLS number, is always necessary for accurate diagnosis and management.