Geometric Factors Assist Assessment of Ventricular Systolic Function
Strain better reflects systolic function in patients with preserved ejection fraction (EF) when geometry is considered a confounder. According to a combined mathematical and echocardiographic study published August 14 in the Journal of the American College of Cardiology, the use of geometric factors explains the paradox of reduced myocardial shortening in the presence of preserved EF.
Thomas M. Stokke, MD, et al., analyzed an mathematical equation showing the relationship between EF and four parameters (left ventricular ejection fraction [LVEF], global longitudinal strain [GLS], global circumferential strain [GCS] and LV wall thickness and LV short-axis diameter) by applying it to 100 subjects with EF ranging from 16 percent to 72 percent. The researchers split the study population evenly: 20 patients had coronary artery disease, 20 had dilated cardiomyopathy, 20 had hypertrophic cardiomyopathy and 20 were normal control patients. All underwent a two-dimensional grayscale echocardiography examination, performed with either Vivid 7 or E9 scanners.
Results showed that GCS contributes twice as much to EF compared with GLS. For example, when GLS changed from 0 percent to –20 percent, EF increased by 16 percentage points; however, when GCS changed from 0 percent to –20%, EF increased by a total of 36 percentage points.
"Wall thickness substantially influenced EF: a 1 cm increase in thickness increased EF by approximately 13 percentage points," write the study authors. They note that a small increase of GCS, wall thickness or reduced diameter could compensate for a significant reduction of GLS.
Results also demonstrated that increased wall thickness or smaller LV diameter could result in a more maintained EF, despite reductions in longitudinal and circumferential shortening. This finding was consistent with EF results in the 20 control and 20 hypertrophic cardiomyopathy patients. "Effectively, this means that myocardial function can vary greatly without changing EF," add the authors.
"The mathematical expression we present is advantageous over computational simulation methods, as it provides a direct equation that investigators can easily implement and allows for direct validation." They conclude, "EF is not a good measure of systolic function in many patient groups, and assessment of strain seems to be a better quantification of systolic function."
In a related editorial comment, James L. Januzzi Jr., MD, FACC, and Y. Chandrashekhar, MD, FACC, agree with the study authors' "illustrative" findings and suggestions to "index LVEF with these important geometric parameters to give the most balanced assessment of ventricular performance possible."
They also highlight how "strain imaging may help to untangle the conundrum that is [heart failure with preserved EF] HFpEF: given the repeated futility in therapeutic trials for HFpEF predicated on the use of LVEF […] it begs the question whether an LVEF standard could be abandoned for such patients."
They conclude, "Only with a better understanding of this newer means of LV functional assessment can we know for sure whether it will move the needle forward for better recognition and treatment of our patients with heart muscle disease."
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