TDIderived twist data were calculated as follows: - PowerPoint PPT Presentation

Title: TDIderived twist data were calculated as follows:


1
Cardiac Twist Quantification in a Novel in Vitro
Porcine Left Ventricular Model by Tissue
Doppler and 2D Speckle Tracking A Comparison in
Accuracy and Precision Xiao-Yue Han, Tara Gu,
Galym Imanbayev, Tommy Tee, Nick Farris, Hai-Yue
Han, Clifton D Fuller, Ling Hui, Muhammad Ashraf,
David J Sahn Oregon Health Science University,
Portland, OR

• TDI-derived twist data were calculated as
  follows
• Sample regions were defined on the 2D
  echocardiographic images using EchoPAC. Average
  distance between sample regions and the
  rotational center was noted.

Conclusions ST is superior to TDI with respect
to the quantification of cardiac twist in both
accuracy and precision. Quantified cardiac twist
offers a new parameter to assess heart form and
function. BACKGROUND Left ventricular (LV)
torsion (or twist) results from the shortening of
oblique LV fibers and is defined as the
counterclockwise rotation of the ventricular apex
with respect to the base. LV twist plays an
integral role in systole and diastole and serves
to be a clinically sensitive index of cardiac
function. Although the LV twisting paradigm has
been likened to wringing of a towel in much of
the literature explaining that LV twisting
squeezes the LV cavity and thus augments
systole this analogy fails to adequately
clarify the role of LV twist in diastolic
function. The untwisting of the LV cavity has
been suggested to effect a negative pressure
gradient in the left ventricle, producing a
suction force that actively contributes to
diastolic filling. Next-generation cardiac
ultrasound systems and image analyses software
offer practitioners novel methods of
quantitatively evaluating heart function. Two of
these methods tissue Doppler imaging (TDI) and
2D echocardiographic speckle tracking (ST) are
discussed here in the context of evaluating their
ability to accurately and precisely report
cardiac twist in a novel porcine LV model.
ABSTRACT Background Advancements in cardiac
ultrasound have enabled practitioners to look at
heart anatomy and physiology more completely and
with greater authority. New parameters for
assessing heart function have emerged through the
development and application of tissue Doppler
(TDI) and 2D echocardiographic speckle tracking
(ST). Our study focused on the quantification of
twist in the left ventricle (LV). Methods We
isolated the LV from five freshly harvested pig
hearts and inserted a 9 balloon the balloon was
connected to a pulsatile pump which facilitated
physiologic systole and diastole. The apex and
mitral ring were attached to separate ends of a
rotational actuator, producing cardiac torsion in
synchrony with pumping. Three stroke volumes and
three degrees of twist were applied in pairs (SV,
degrees of twist 20cc, 15 40cc, 30 60cc,
45). 2D short axis echocardiographic images were
obtained using a 7 MHz probe GE Vivid 7 Dimension
ultrasound system. Data were exported to EchoPac
PC for offline analysis. EchoPac quantified twist
using the ST method easily. Relating integrated
myocardial velocity vectors to myocardial
circumference yielded twist data derived from
TDI. Results For 15, 30, and 45 degrees of
twist, TDI reported 16.4 1.6, 32.7 1.7, and
59.2 2.4 respectively ST reported 14.6
0.6, 31.8 1.4, and 52.3 1.3. There is a
strong correlation between ST derived values and
known values (r2 0.99) similarly, TDI also
revealed a strong correlation with known values
(r2 0.97). However, there was a statistically
significant difference between TDI and ST
reported values (p lt .0005). Moreover, twist
quantified by TDI showed a significantly higher
variance than the respective ST values (p lt
.0005).
METHODS We designed and built a highly accurate
and precise in vitro porcine LV model that
produced physiologic LV twist and longitudinal
compaction in synchrony with a LV filling and
emptying. Using our model,
three different stroke volumes and twist were
applied in pairs SV, degrees of twist 20cc,
15 40cc, 30 60cc, 45. 2D short axis
echocardiographic images were obtained using a 7
MHz probe GE Vivid 7 Dimension ultrasound system.
Data were exported to EchoPAC PC for offline
analysis. IMAGE ANALYSES EchoPAC PC quantified
twist data from the 2D echocardiographic images
using embedded ST software. Relating integrated
myocardial velocity vectors to myocardial
circumference yielded twist data derived from TDI.

• where v(t) is the average absolute velocity of
  sample regions and ds is the average distance
  between the same region and the rotational
  center.
• RESULTS
• There is a strong association between ST derived
  twist data and known values (r2 0.99, LSRL)
  similarly, TDI also reveals a strong relationship
  with actual twist values (r2 0.97, LSRL).

Observing the above grave and table,
there exists a proportional bias As the degrees
of actual twist increases, the accuracy and
precision of both methods decrease (TDI to a
greater extent). However, at physiologically
relevant degrees of twist, precision and accuracy
are maximized. CONCLUSION ST is the superior
method of quantifying cardiac twist and does not
exhibit angle dependencies. DISCLOSURE No
relationships to disclose Xiao-Yue Han Tara
Gu Galym Imanbayev Tommy Tee Nick
Farris Hai-Yue Han Clifton D Fuller Ling
Hui Muhammad Ashraf David J Sahn
Mean Standard Deviation