1. of Segmental Dysfunction in Myocardial Ischemia
ABSTRACT
Background: Two-dimensional (2D) echo provides only subjective information on segmental dysfunction due to limited scanning windows and is error prone due to out-of-plane myocardial motion. We tested a new three-dimensional (3D) based strain analysis method. Methods: We studied 5 adult pigs that underwent midline sternotomy to expose the heart for high resolution ultrasound scanning directly from the surface of the heart. The left anterior descending coronary artery (LAD) was isolated from the vein and arbitrarily divided into three equal zones from the left ventricular (LV) apex distally to the origin of the first diagonal branch proximally. Baseline full volume 3D image loops were acquired from the apex with a Toshiba Applio Artida ultrasound system. The LAD was then ligated in the distal-most zones first and the visibly ischemic area, as shown by changes in color, was measured on the epicardium and full volume 3D images were acquired. Studies were repeated with ligation of the LAD in proximal zones. Images were analyzed offline with wall motion tracking (WMT) software to obtain segmental 3D strain curves from apex to base in 3D image loops. Results: Extending the level of LAD ligation proximally increased the size of the ischemic zone as measured by color changes on the ischemic area of the cardiac surface that correlated with a consistent alteration of the apex-to-base gradient of peak 3D segmental strain. Conclusions: WMT could provide an objective evaluation of myocardial dysfunction in coronary ischemia.
CONCLUSIONS
Quantitative 3D strain maps and the apex to base strain gradient as computed from high frame rate full volume 3D image loops by WMT program, could provide an objective evaluation of myocardial dysfunction in coronary ischemia.
DISCLOSURE
No relationships to disclose:
Muhammad Ashraf
Zhiwen Zhou
Jill Panosian
Cole Streiff
Uyen Truong
Employed by TAMS:
Berkley Cameron
Occasional consultant to TAMS:
David J. Sahn
BACKGROUND
Echocardiography derived strain and strain rate have emerged as a robust quantitative technique to evaluate dynamic heart function, and has attracted the attention of clinicians and imaging scientists.
Data regarding accuracy, feasibility and applications of this relatively new imaging modality is rapidly accumulating. Strain imaging is being tested extensively in a variety of clinical settings, including the evaluation of mechanical dysfunction in ischemic heart disease and cardiac resynchronization therapy.
Although strain imaging provides an objective assessment of mechanical dysfunction in ischemic heart disease, this information is limited to myocardial tissue within the scanning window in 2D echocardiography. Since the dynamic heart function is a continuous interaction of linear and twisting motion in all three dimensions. Acquisition of 2D images with static scanner can move myocardial tissue out of scanning window, and result in erroneous strain computation due to in-plane decorrelation. Therefore 2D echo based strain provides only subjective assessment about the extent of myocardial dysfunction and is subject to errors as well due to through plane myocardial motion.
More recently 3D echocardiography has allowed dynamic imaging of whole beating heart with resolution high enough to track speckles and the compute strain in full volume image loop. Ability to track myocardial motion in 3D has allowed simultaneous assessment of radial, circumferential and longitudinal strain. The quantitative estimation of regional dysfunction along with delineation of the extent of mechanical dysfunction from full volume3D image sequences would have important clinical implications.
In this study we sought to evaluate the feasibility of 3D echo based strain to delineate the extent of ischemic myocardial dysfunction.
METHODS
We studied 5 adult pigs that underwent midline sternotomy under inhalation anesthesia to expose the heart for high resolution ultrasound scanning directly from the surface of the heart. Vital signs, body temperature and oxygen saturation was continually monitored.
The left anterior descending coronary artery (LAD) was isolated from the vein and arbitrarily divided into three equal zones from the left ventricular (LV) apex distally to the origin of the first diagonal branch proximally.
Baseline full volume 3D image loops were acquired from the apex with a Toshiba Applio Artida ultrasound system. Frame rate was maximized at high density scanning including LV walls in the pyramidal volume.
The LAD was then occluded in the distal-most zones first and the visibly ischemic area, as shown by changes in color, was measured on the epicardium. The full volume 3D images were acquired from apical window similar to baseline images.
Studies were repeated by occluding LAD in middle and then proximal zones. Images were analyzed offline with wall motion tracking (WMT) software to obtain segmental 3D strain curves from apex to base in 3D image loops.
Apex to Base Strain Gradient, as Computed From a New 3D Echo Based Strain Method, Provides Quantitative Assessment
of Segmental Dysfunction in Myocardial Ischemia
Muhammad Ashraf, MD; Zhiwen Zhou, MD; Jill Panosian, BS; Berkley Cameron, RCDS; Cole Streiff, BA;
Uyen Truong, MD; David J. Sahn, MD, MACC
Oregon Health & Science University, Portland, OR, USA; Toshiba America Medical Systems, Tustin, CA, USA
RESULTS
Strain results from all LV segments were projected as color coded maps in a quantitative parametric display and time to peak curves.
Visibly ischemic area was measured from the color change on epicardium, and the dysfunctional myocardial area was measured from the parametric display in end-systolic frames, at each level of LAD occlusion.
Extending the level of LAD occlusion proximally increased the size of ischemic zone as measured from color change on the surface of heart, which correlated with the size of dysfunctional myocardium as quantified from parametric strain maps.
An apex to base gradient was detected between peak strain values in apical and basal LV segments, which showed a corresponding increase with the size of visibly ischemic and dysfunctional myocardial area.
Points of LAD occlusion
WMT program process full volume 3D image loop for speckle tracking to compute strain in all 16 LV segments simultaneously and display as color coded parametric strain maps and curves