1. ABSTRACT
Background: Right ventricular (RV) function is of major importance in many forms of congenital heart disease in adults. The right ventricle is thin walled and has presented problems for both tissue Doppler and speckle tracking methods of determining mechanics. Methods: We studied 6 fresh pig hearts in a model that allowed known volumes to be pumped into the RV and LV simultaneously while RV images were obtained by gated full volume acquisition using a 3.5 MHz transducer on a Toshiba Applio Artida scanner. Calibrated stroke volumes of 20 to 50 cc were delivered. Two triangular arrays of sonomicrometry crystals were placed around the RV free wall 1/3 and 2/3 of the distance from the tricuspid annulus to the RV apex. 4D strain data were computed on the system using 4D wall motion tracking (WMT) to yield the full field of RV and longitudinal and circumferential strains. Results were compared to sonomicrometry in the free wall zones where the crystals were, as analyzed by SonoView.
CONCLUSIONS
The results of this model study were derived from analysis of very high resolution images, which suggested that the new 3D wall motion tracking is an accurate, reproducible and easy to use method for non invasive quantification of RV mechanics.
DISCLOSURE
No relationships to disclose:
Sheetal Krishnakumar Anugraha Rajendran Sarah K. Yang Shahryar Ashraf
Nicole Chang Galyna Kovch
Weihui Shentu, MD Zhiwen Zhou, MD
Muhammad Ashraf, MD
Employed by Toshiba America Medical Systems:
Bill Kenny, RCDS
Berkley Cameron, RCDS
Occasional consultant to TAMS:
David J. Sahn, MD, MACC
Results: In the mid wall zones, both the ultrasound and the sono longitudinal (r = 0.87, p< 0.05) and circumferential strains (r = 0.76, p< 0.05) were highly correlated and interobserver variability for strains was less than 5%. Conclusions: This new 4D WMT method is easy to use and robust. It provides data on RV mechanics accurately and reproducibly.
BACKGROUND
There is much interest in the study of tissue mechanics and volume measurements of the RV chamber to evaluate the heart function. Study of RV mechanics could provide novel insight into dynamic function of the right heart, especially in patients with congenital heart disease and pulmonary hypertension. Recent developments in cardiac imaging have made it possible to compute cardiac mechanics non-invasively.
Angle independent speckle tracking based motion detecting methods have recently attracted the attention of research scientists and cardiologists. These methods use high-resolution echo images for
analysis of cardiac mechanics and have been validated against more invasive sonomicrometry and more expensive MRI. Despite some potential for error due to in-plane decorrelation caused by plane myocardial motion during acquisition, 2D speckle tracking based methods seem to provide reasonable accuracy for LV mechanics.
Symmetrical shape and thick LV walls provide a sufficient number of speckle targets for reproducible tracking. The unique shape and geometry of the RV along with relatively thin walls presents a challenge to conventional 2D based motion-detecting methods. The lack of identifiable anatomical landmarks also presents another difficulty in providing a reproducible selection of 2D imaging planes. We tested the feasibility and accuracy of a new 3D method based on wall motion tracking within a full volume dynamic 3D heart image loop to compute RV mechanics.
METHODS
We studied 6 freshly harvested pig hearts. Both atriums of each heart were excised for easier access to the ventricles. Each heart was then mounted on a rotary actuator of a phantom in a water bath.
Both LV and RV were connected to a separate pulsatile pump through a clear plastic tubing and a latex balloon inserted into each ventricular cavity. Both pumps were capable of delivering a calibrated stroke volume at a controlled rate. Three sonomicrometry crystals were placed around the free wall of the RV, 1/3 and 2/3 of the distance from the tricuspid annulus to the RV apex, in a triangular arrangement.
Both ventricles were simultaneously pumped in synchrony at each stroke volume. We studied five different stroke volumes from 20 to 50cc. ECG gated full volume RV images were obtained using a 3.5 MHz transducer on a Toshiba Applio Artida
Simultaneously Derived Circumferential and Longitudinal Right Ventricular Strains from 4D Ultrasound
Using a New Method for 4D Cardiac Mechanics: Validation by Sonomicrometry
Sheetal Krishnakumar; Anugraha Rajendran; Sarah K. Yang; Shahryar Ashraf; Nicole Chang; Galyna Kovch; Weihui Shentu, MD;
Zhiwen Zhou, MD; Bill Kenny, RCDS; Berkley Cameron, RCDS; Muhammad Ashraf, MD; David J. Sahn, MD, MACC
Oregon Health & Science University, Portland, OR; Toshiba America Medical Systems, Tustin, CA
scanner. After acquiring baseline data at each stroke volume we injected 2-4 ml of glutaraldehyde to a simulate myocardial infarct between sono crystals and the study was repeated.
The image data was processed on system, using 3D wall motion tracking to yield a full view of the RV, longitudinal and circumferential strains. Sonomicrometry data was processed for longitudinal and circumferential strains in Sonosoft. The strain results from the images at each stroke volume were compared to the sonomicrometry derived strain values.
RESULTS
At all stroke volumes 3D Echo derived longitudinal and circumferential RV strain showed a linear correlation with sonomicrometry derived longitudinal strain (r = 0.87, p< 0.05) and circumferential strains (r = 0.76, p< 0.05).
At each stroke volume modeled infarct showed significantly lower strain as compared to normal myocardial tissue.
This 3D Echo based method showed high reproducibility (r=0.96) and inter-observer variability for strain computation was less than 5 percent.
Figure 1. Sonomicrometry crystals anchored to myocardium of the RV and the model setup for this study.