High resolution speckle tracking dobutamine stress echocardiography reveals heterogeneous responses in different myocardial layers: implication for viability assessments.

BACKGROUND: Speckle-tracking echocardiography (STE) can be used to quantify wall strain in 3 dimensions and thus has the potential to improve the identification of hypokinetic but viable myocardium on dobutamine stress echocardiography (DSE). However, if different myocardial layers respond heterogeneously, STE-DSE will have to be standardized according to strain dimension and the positioning of the region of interest. Therefore, the aim of this study was to create a high-resolution model for ejection time (ET) strain and tissue flow in 4 myocardial layers at rest, during hypoperfusion, and during dobutamine challenge to assess the ability of STE-DSE to detect deformation and functional improvement in various layers of the myocardium.
METHODS: In 10 open chest pigs, the left anterior descending coronary artery was constricted to a constant stenosis, resulting in 35% initial flow reduction. Fluorescent microspheres were used to measure tissue flow. High-resolution echocardiography was performed epicardially to calculate ET strain in 4 myocardial layers in the radial, longitudinal, and circumferential directions using speckle-tracking software. Images were obtained at rest, during left anterior descending coronary artery constriction (hypoperfusion), and during a subsequent dobutamine stress period.
RESULTS: Dobutamine stress at constant coronary stenosis increased flow in all layers. ET strain increased predominantly in the midmyocardial layers in the longitudinal and circumferential directions, whereas subendocardial strain did not improve in either direction.
CONCLUSION: Dobutamine stress influences ET strain differently in the various axes and layers of the myocardium and only partially in correspondence to tissue flow. Longitudinal and circumferential functional reserve opens the potential for the specific detection of midsubendocardial viable tissue by high-resolution STE. Copyright 2010 American Society of Echocardiography. Published by Mosby, Inc. All rights reserved.