What is the significance of global longitudinal strain?

Significance of Global Longitudinal Strain (GLS)

Global longitudinal strain (GLS) is a superior and more sensitive marker for detecting subclinical myocardial dysfunction than ejection fraction, allowing early identification of cardiac abnormalities before symptoms or ejection fraction decline occur.

Definition and Measurement

• GLS measures the longitudinal contraction of the myocardium using speckle-tracking echocardiography (STE)
• It reflects primarily subendocardial layer function, which is the first to be affected in most cardiac pathologies
• Normal GLS values range from -18% to -22% (more negative values indicate better function)
• Values are reported as percentages, with the following interpretations:
  • Normal: > -18% (more negative)
  • Borderline: -16% to -18%
  • Abnormal: ≤ -16% (less negative) 1

Clinical Importance and Advantages

Early Detection of Dysfunction

• GLS detects subclinical myocardial damage before ejection fraction decline 2
• Longitudinal function impairment precedes circumferential strain alterations and LVEF reduction 2
• A 10-15% early reduction in GLS during therapy is the most useful parameter for predicting cardiotoxicity 2

Superior Sensitivity

• GLS is more sensitive than ejection fraction in detecting:
  • Chemotherapy-induced cardiotoxicity 2
  • Hypertensive heart disease 2
  • Valvular heart disease progression
  • Cardiomyopathies 3

Prognostic Value

• GLS provides incremental predictive value in patients undergoing echocardiography 2
• A GLS value ≤ -10% is associated with higher risk of worsening heart failure and mortality in HFrEF patients 4
• GLS is the most powerful predictor of cardiac events in patients with depressed LV function (cutoff value of -7%) 5

Clinical Applications

Cardio-Oncology

• GLS can detect early signs of cardiotoxicity during cancer treatment:
  • A ≥11% relative reduction in GLS predicts subsequent cardiotoxicity 2
  • GLS abnormalities can be detected within 3 months of starting cardiotoxic therapies, before LVEF changes 2
  • Allows for earlier intervention to prevent irreversible cardiac damage

Heart Failure Assessment

• Valuable in both HFrEF and HFpEF:
  • In HFpEF, GLS is frequently abnormal despite preserved EF 2
  • In HFrEF, GLS provides independent prognostic information beyond LVEF 4
  • Helps predict 30-day readmission risk in HFpEF patients 2

Valvular Heart Disease

• GLS deterioration often precedes symptoms or LVEF decline in patients with valvular disease
• Helps determine optimal timing for intervention in asymptomatic patients with severe valvular disease
• Provides prognostic information in patients with mitral and aortic valve diseases 6

Cardiomyopathies

• Useful in monitoring disease progression in various cardiomyopathies
• In Becker muscular dystrophy, GLS detected LV dysfunction in 77.5% of patients while LVEF was reduced in only 60% 3
• GLS showed significant deterioration over time while LVEF remained stable in these patients 3

Technical Considerations and Limitations

• Vendor variability: Measurements should be performed using the same vendor's equipment for serial assessments 1
• Image quality significantly affects accuracy of measurements
• Loading conditions and heart rate can influence GLS values
• A GLS reduction <8% from baseline is not considered clinically meaningful, while >15% reduction is very likely abnormal 2

Conclusion

GLS represents a significant advancement in cardiac imaging that allows for earlier detection of myocardial dysfunction, better risk stratification, and more precise monitoring of disease progression and treatment response compared to conventional echocardiographic parameters like LVEF. Its ability to detect subclinical cardiac dysfunction makes it an invaluable tool in modern cardiovascular assessment.