Page 184 - Clinical Small Animal Internal Medicine

152 Section 3 Cardiovascular Disease

VetBooks.ir Box 16.2 Advanced ultrasound techniques speckle patterns created within the myocardium on
Tissue Doppler imaging
Tissue Doppler imaging (TDI) is a relatively recently routine 2D gray‐scale echocardiographic images and sub-
sequent assessment of myocardial motion (myocardial
developed ultrasound technique which allows the quan- tissue velocity, strain and strain rate, and also LV rotation).
tification of regional myocardial function from measure- One of its major advantages, compared to Doppler‐based
ments of myocardial velocities in real time (Figure 16.32). techniques (TDI or TDI‐derived techniques), is its inde-
The 2D color TDI has been shown to be repeatable and pendence of both cardiac translation and the insonation
reproducible in the awake cat and dog, and is more sen- angle.
sitive than 2D and M‐mode echocardiography in detect-
ing myocardial dysfunction of different etiologies in
these species, even when overt myocardial changes are Other ultrasound techniques
absent. This technique may therefore be used for the Three‐dimensional (3D) echocardiography allows 3D visu-
early detection of systolic and diastolic myocardial alter- alization of the heart. Good‐quality real‐time or live 3D
ations associated with dilated or hypertrophic cardiomy- imaging of the beating heart can now be obtained thanks
opathies, and may be particularly useful in the case of to advancements in computer technology and the devel-
equivocal 2D and M‐mode results. opment of fully sampled matrix‐array transducers. One of
the major advantages of 3D echocardiography over 2D
Strain and strain rate imaging imaging is its greater accuracy for the evaluation of car-
diac chamber volumes (thus avoiding conventional echo-
Strain and strain rate imaging are two quantitative TDI‐ cardiographic geometric modeling). Another application
derived imaging techniques, allowing measurement of of 3D imaging is to acquire realistic views of cardiac valves
myocardial segmental deformation (contraction or and assess complex or equivocal congenital abnormalities
stretching) and rate of deformation, respectively (see (e.g., shunts), which can be particularly useful when plan-
Figure 16.32). Myocardial strain represents the deforma- ning a surgical correction.
tion of a myocardial segment over time, and is expressed Transesophageal echocardiography uses a transducer
as the % change from its original dimension. Myocardial mounted at the tip of a flexible endoscope and allows
−1
strain rate (expressed in s ) is the temporal derivative of imaging of the heart from the esophagus (instead of
strain, and therefore describes the rate of myocardial through the chest wall, as for transthoracic echocardi-
deformation. Strain and strain rate imaging therefore offer ography). The advantage of transesophageal echocar-
a direct evaluation of regional intrinsic active myocardial diography is the acquisition of high‐quality images, as it
function.
avoids the anatomic structures (skin, subcutaneous tissue,
ribs, lungs), which may affect the quality of conventional
Speckle tracking echocardiography transthoracic echocardiography. Potential indications
for transesophageal echocardiography in veterinary
Two‐dimensional speckle tracking echocardiography is medicine include analysis of specific cardiovascular
the most recently developed ultrasound technique abnormalities (thrombosis, aneurysm, cardiac tumors),
allowing quantitative assessment of regional myocardial cardiac monitoring during anesthesia or catheterization,
function (Figure 16.33). This non‐Doppler technique is and evaluation of surgical procedures such as ductus
based on identification and frame‐by‐frame tracking of arteriosus closure.