A novel feature-tracking echocardiographic method for the quantitation of regional myocardial function: validation in an animal model of ischemia-reperfusion

Abstract

Objectives: The aim of this study was to validate a novel, angle-independent, feature-tracking method for the echocardiographic quantitation of regional function.

Background: A new echocardiographic method, Velocity Vector Imaging (VVI) (syngo Velocity Vector Imaging technology, Siemens Medical Solutions, Ultrasound Division, Mountain View, California), has been introduced, based on feature tracking-incorporating speckle and endocardial border tracking, that allows the quantitation of endocardial strain, strain rate (SR), and velocity.

Methods: Seven dogs were studied during baseline, and various interventions causing alterations in regional function: dobutamine, 5-min coronary occlusion with reperfusion up to 1 h, followed by dobutamine and esmolol infusions. Echocardiographic images were acquired from short- and long-axis views of the left ventricle. Segment-length sonomicrometry crystals were used as the reference method.

Results: Changes in systolic strain in ischemic segments were tracked well with VVI during the different states of regional function. There was a good correlation between circumferential and longitudinal systolic strain by VVI and sonomicrometry (r = 0.88 and r = 0.83, respectively, p < 0.001). Strain measurements in the nonischemic basal segments also demonstrated a significant correlation between the 2 methods (r = 0.65, p < 0.001). Similarly, a significant relation was observed for circumferential and longitudinal SR between the 2 methods (r = 0.94, p < 0.001 and r = 0.90, p < 0.001, respectively). The endocardial velocity relation to changes in strain by sonomicrometry was weaker owing to significant cardiac translation.

Conclusions: Velocity Vector Imaging, a new feature-tracking method, can accurately assess regional myocardial function at the endocardial level and is a promising clinical tool for the simultaneous quantification of regional and global myocardial function.

Figure 1. Short-Axis Views During Baseline, Dobutamine Infusion, and LAD Occlusion, and the Corresponding Velocity, Strain, and SR Curves Obtained by VVI

Note the increased amplitude of the velocity vectors and velocity, strain, and strain rate (SR) values during dobutamine infusion and the dyskinetic motion, positive strain, and SR pattern during left anterior descending coronary artery (LAD) occlusion. End-diastole and end-systole (time of peak –dP/dt) are shown in blue lines. Values of the regional function parameters are shown. VVI = Velocity Vector Imaging.

Figure 2. Changes in Strain During Occlusion-Reperfusion and Pharmacologic Manipulation

Circumferential strain measured by Velocity Vector Imaging (VVI) and sonomicrometry in the ischemic zone during various hemodynamic states. Dob. = dobutamine; Occl = occlusion.

Figure 3. Example of Changes in Hemodymanic and Regional Function During the Protocol

Recordings of strain (top), left ventricular pressure (LVP) (middle), and electrocardiogram (ECG) (bottom) from a single experiment during baseline, dobutamine infusion, and left anterior descending coronary artery (LAD) occlusion. Blue line = sonomicrometry; red line = Velocity Vector Imaging.

Figure 4. Relation of Strain by VVI to SM in the Ischemic Zone

Plots showing the relation between circumferential and longitudinal strain values by Velocity Vector Imaging (VVI) and sonomicrometry (SM) in the ischemic zone and corresponding Bland-Altman plots.

Figure 5. Relation of SR by VVI to SM in the Ischemic Zone

Plots showing the relation between circumferential and longitudinal strain rate (SR) by Velocity Vector Imaging (VVI) and sonomicrometry (SM) in the ischemic segments and corresponding Bland-Altman plots.

Figure 6. Changes in Strain During Occlusion-Reperfusion and Pharmacologic Manipulation in the Nonischemic Zone

Circumferential strain measured by VVI and sonomicrometry in the nonischemic zone during various hemodynamic states. Abbreviations as in Figure 2.

Figure 7. Circumferential and Longitudinal Strain by VVI at the Exact Intramyocardial Level of the Ultrasound Crystals

Relation of strain by Velocity Vector Imaging (VVI) to strain by sonomicrometry in ischemic segments at the level of intramyocardial crystals.

Figure 8. Endocardial Velocity Versus Strain Measurements

Relation of circumferential endocardial velocity by Velocity Vector Imaging to strain measurement by sonomicrometry in the ischemic and nonischemic zones.