The use of strain, strain rate, and displacement by 2D speckle tracking for assessment of systolic left ventricular function in goats: applicability and influence of general anesthesia

Abstract

Background: Assessment of left ventricular (LV) systolic function can be achieved by conventional echocardiographic methods, but quantification of contractility, regional myocardial function, and ventricular synchrony is challenging. The goal of this study was to investigate the applicability of two-dimensional speckle tracking (2DST) to characterize segmental and global wall motion for assessment of LV function and LV synchrony in healthy goats. We aimed to describe the techniques, report normal values of a variety of 2DST indices, and determine the influence of general anesthesia.

Methods: Prospective study on 22 healthy female Saanen goats (3.7 ± 1.1 y, 60.2 ± 10.5 kg [mean ± SD]). All goats underwent two transthoracic echocardiographic examinations, the first standing and unsedated and the second 7.4 ± 3.5 days later during isoflurane anesthesia and positioned in sternal recumbency. Data analyses were performed offline, blinded, and in random order. Left ventricular longitudinal, radial and circumferential strain and strain rate as well as longitudinal and radial displacement were measured using 2DST methods. Summary statistics were generated and differences of 2DST variables between myocardial segments and treatments (i.e., awake vs. anesthetized) were assessed statistically (alpha level=0.05).

Results: Echocardiographic analyses by 2DST were feasible in all goats and at both time points. Longitudinal systolic strain, strain rate and displacement followed a gradient from apex to base. Absolute systolic strain was generally lower and strain rate was higher in awake goats compared to anesthetized goats. Circumferential and radial indices did not consistently follow a segmental pattern. Generally, peak strain occurred later in anesthetized goats compared to awake goats. General anesthesia did not significantly influence LV synchrony.

Conclusions: 2SDT is a valid method for non-invasive characterization of LV wall motion in awake and anesthetized goats. The results of this study add to the understanding of LV mechanical function, aid in the diagnosis of global and segmental LV systolic dysfunction, and will be useful for future cardiovascular studies in this species. However, effects of anesthesia and species-specific characteristics should be considered when goats are used as animal models for human disease.

Figure 1

Post-systolic motion in left ventricular long-axis and short-axis recordings. Prevalence of post-systolic motion (PSM) in awake and anesthetized goats. Post-systolic motion was diagnosed where peak strain occurred after aortic valve closure. A: PSM based on timing of longitudinal peak strain (tε_L), B: PSM based on timing of circumferential peak strain (t_εC) at the apical short-axis level (SAX-AP), C: PSM based on timing of radial peak strain (t_εR) at the apical short-axis level (SAX-AP), D: PSM based on t_εC at the papillary muscle short-axis level (SAX-PM), E: PSM based on _tεR at the papillary muscle short-axis level (SAX-PM), F: PSM based on t_εC at the chordal short-axis level (SAX-CH), G: PSM based on t_εR at the chordal short-axis level (SAX-CH).

Figure 2

Segmental 2DST analyses of left ventricular long-axis recordings. A: ε_L, longitudinal peak strain. B: SR_L-sys, longitudinal peak systolic strain rate. C: SR_L-E, longitudinal peak early-diastolic strain rate. D: SR_L-A, longitudinal peak late-diastolic strain rate. E: D_L, longitudinal peak displacement. F: D_T, transverse peak displacement. Box-and-whisker diagrams, with the line near the middle of the box indicating the median, the top and the bottom of the box indicating the upper and lower quartile, and the whiskers indicating the 5^th and 95^th percentile observations, respectively. P values of the F test are listed next to each graph; factors for which multiple comparison post hoc testing was performed are displayed in italics. Segments and treatments marked with the same letter were not significantly different from each other when undergoing post hoc testing for multiple comparisons.

Figure 3

A-C. Segmental 2DST analyses of left ventricular short-axis recordings at the apical level (A), at the papillary muscle level (B) and at the chordal level (C). A: ε_C, circumferential peak strain. B: ε_R, radial peak strain. C: DR, radial peak displacement. D: SR_C-sys, circumferential peak systolic strain rate. E: SR_C-E, circumferential peak early-diastolic strain rate. F: SR_C-A, circumferential peak late-diastolic strain rate. G: SR_R-sys, radial peak systolic strain rate. H: SR_R-E, radial peak early-diastolic strain rate. I: SR_R-A, radial peak late-diastolic strain rate. Box-and-whisker diagrams, with the line near the middle of the box indicating the median, the top and the bottom of the box indicating the upper and lower quartile, and the whiskers indicating the 5^th and 95^th percentile observations, respectively. P values of the F test are listed next to each graph; factors for which multiple comparison post hoc testing was performed are displayed in italics. Segments and treatments marked with the same letter were not significantly different from each other when undergoing post hoc testing for multiple comparisons.

Figure 4

Segmental timing of peak strain in left ventricular long-axis and short-axis recordings. Segmental timing of peak strain, expressed as the time interval from the electrocardiographic R wave to longitudinal, circumferential, and radial peak strain of each segment. A: Time to longitudinal peak strain (t_εL) in left ventricular long-axis recordings. B: Time to circumferential peak strain (t_εC) in left ventricular short-axis recordings at the apical level. C: Time to radial peak strain (t_εR) in left ventricular short-axis recordings at the apical level. D: Time to circumferential peak strain (t_εC) in left ventricular short-axis recordings at the papillary muscle level. E: Time to radial peak strain (t_εR) in left ventricular short-axis recordings at the papillary muscle level. F: Time to circumferential peak strain (t_εC) in left ventricular short-axis recordings at the chordal level. G: Time to radial peak strain (t_εR) in left ventricular short-axis recordings at the chordal level. Box-and-whisker diagrams, with the line near the middle of the box indicating the median, the top and the bottom of the box indicating the upper and lower quartile, and the whiskers indicating the 5^th and 95^th percentile observations, respectively. P values of the F test are listed next to each graph; factors for which multiple comparison post hoc testing was performed are displayed in italics. Segments and treatments marked with the same letter were not significantly different from each other when undergoing post hoc testing for multiple comparisons.