EF vs. Strain for Assessing Systolic Function
How do geometric and functional factors affect left ventricular ejection fraction (LVEF)?
The LV was modeled as a thick-walled, truncated ellipsoid; and an analytical mathematical relationship for LVEF was derived using the four parameters of global longitudinal (GLS), circumferential (GCS) strain, wall thickness, and short-axis diameter. The derived equation was validated using retrospective review of echocardiograms from 100 subjects (including patients with coronary artery disease [CAD], patients with angina but without CAD, patients with dilated or hypertrophic cardiomyopathy [HCM], and normal controls) with varying LVEF (ranging from 16% to 72%). The impact of different parameters on LVEF was explored in the model and compared with findings in the patients.
Calculated EF had very good agreement with measured EF (r = 0.95). The mathematical model showed that GCS contributes more than twice as much to EF than GLS. A significant reduction of GLS could be compensated by small increases in GCS or wall thickness, or reduced diameter. The model further demonstrated how EF can be maintained in ventricles with increased wall thickness or reduced diameter despite reductions in both longitudinal and circumferential shortening. This was consistent with similar EF in 20 control subjects and 20 HCM patients who had increased wall thickness and reductions in both circumferential and longitudinal shortening (all p < 0.01).
Reduced deformation despite preserved EF can be explained through geometric factors. Due to geometric confounders, strain better reflects systolic function in patients with preserved EF.
Preserved LVEF can be observed despite reduced myocardial strain (suggestive of LV systolic dysfunction) among patients with ischemic heart disease, diabetes mellitus, hypertrophic cardiomyopathy, and exposure to cardiotoxic chemotherapy agents. This mathematical study, validated using echocardiograms obtained among 100 subjects with varying LVEF, allows discrimination of how various factors affect LVEF; and, importantly, demonstrates how LVEF can remain preserved (with increased LV wall thickness or reduced LV diameter) despite decreased measures of strain. Although LVEF remains of interest in the assessment of LV systolic function, there is good justification for the expanding role of LV strain for the assessment of LV systolic function.
Keywords: Angina Pectoris, Cardiac Imaging Techniques, Cardiomyopathy, Hypertrophic, Cardiotoxicity, Coronary Artery Disease, Echocardiography, Heart Failure, Models, Theoretical, Stroke Volume, Systole
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