Two dimensional analysis of left ventricular myocardial regional and global contractility using speckle tracking post aortic valve replacement for aortic stenosis

Introduction: Abnormalities in regional left ventricular (LV) function in severe aortic stenosis (AS) have yet to be appropriately characterized. Often patients with severe aortic stenosis have subclinical left ventricular systolic dysfunction despite having preserved ejection fraction and fractional shortening on conventional echocardiography. In these patients, the occult, systolic abnormalities are underestimated and have been shown to contribute to symptoms, morbidity and mortality. Two-dimensional strain ( ) and strain rate imaging (SRI), are new ultrasound (US) indices for quantifying regional wall deformation. Mitral annular velocities derived from tissue Doppler imaging (TDI) have already been shown to complement established parameters in evaluating early systolic and diastolic performance post aortic valve replacement. However, the widespread use of this methodology remains limited. This finding can likely be attributed to the fact that Doppler-derived velocity and deformation data are one-dimensional, that is, only the velocity and deformation component along an image line can be assessed, resulting in an angle –dependency of the measurements. Tissue velocity 2D strain and strain rate imaging with speckle tracking is a novel method of assessing regional as well as global "contractility". This method overcomes many limitations inherent in assessing myocardial functioning with current methodology, mainly it is reproducible, objective, and is independent of myocardial translation, tethering and furthermore as speckle tracking is derived from B mode images is independent of Doppler angle. The applicability of this technology to patients with aortic valve stenosis and subclinical systolic dysfunction and its clinical significance has not been evaluated.
Objectives: The general aims of this study were to compare regional displacement, tissue velocity, strain ( ) and strain rate (SR) in severe AS pre and post operatively. Specifically, we sought, to investigate whether Speckle derived tissue velocity and SR could be useful to detect subtle left ventricular (LV) dysfunction in patients with severe aortic stenosis but preserved ejection fraction, and if they can reliably detect improvements in regional myocardial function after aortic valve replacement (AVR). We hypothesize that those patients with severe AS will have significantly reduced peak systolic and peak early diastolic displacement, strain and strain rates at baseline compared with normal controls, despite having normal ejection fraction and fractional shortening as assessed by conventional echocardiography. In addition, we hypothesise that post AVR; deformation patterns will show an early (4-16 weeks) improvement in the myocardial strain and strain rate preceding any changes in LV systolic and diastolic dysfunction assessed by conventional echocardiography.
Methodology: Our study prospectively analyzed 24 consecutive patients in total. Ten control subjects (5 women, 5 men, and mean age 29.6 ± 5.7.3 years) provided normal values of tissue displacement, velocity strain and strain rate. We then, prospectively analyzed 10 patients with severe aortic stenosis and preserved EF and FS, with speckle imaging derived tissue displacement, velocity, strain and strain rate imaging pre –operatively (mean age 71.14± 16.15) and four of these patient post operatively (mean age 79.25 ± 1.7) for aortic valve replacement. This was done as part of routine pre-operative and post-operative transthoracic echocardiography using standard views, with the exception that all studies would need to be done on the GE Vivid 7 digital ultrasound system. Speckle derived imaging data is derived from standard B mode (Grey scale images), with a frame rate of between 40- 90 frames/s. Post-operative TTE’s were performed at 4-20 weeks after discharge. Baseline characteristics were taken from the standard pre-operative baseline study including basic 2 D valve area, EF, wall thickness and geometry, and Doppler flow data. Exclusion criteria: Patients with prior cardiac surgery including CABG or other valve replacement, more than moderate mitral valve or aortic regurgitation and chronic kidney disease (Cr >180), emergent aortic valve replacement, or endocarditis. Informed consent was obtained on all patients, and they were only included if they consent. No surgery was delayed for purpose of the study if the proper hardware/GE VIVID system was not available.
Conclusion: Our results indicate that a reduction of displacement, tissue velocity, strain, and strain rate may be a sensitive marker of subtle, subclinical, subendocardial myocardial dysfunction. More over, these parameters seemed to be superior to conventional echocardiography in detecting subtle improvements in myocardial function after AVR before LV dimensions and LV function showed improvement.