IVRT Increases With

↓ LA pressure ↑ AO pressure

Delayed relaxation

Left Auricle Flow

The left auricle fills during ventricular systole and empties during atrial contraction late in diastole (Figure 3.64). There are other flows recorded at the pulsed-wave Doppler site at the junction of the left auricle and atrium, but they are inconsistently recorded. Feline auricular emptying velocity ranges from .19–1.0 m/sec, and filling velocity ranges from .24 to .93 m/sec (124).

There is a very weak correlation between left auricular flow and left atrial area or diameter in cats. Age, heart rate, weight, sex, and blood pressure have no effect on left auricular flow. Stasis of blood flow is associated with lower than normal auricular flow and predisposition toward thrombus formation (124,125).

Measurement and Assessment of Tissue Doppler Imaging

Measurement

Tissue Doppler imaging (TDI) provides information regarding myocardial velocity in selected areas of the myocardium. A pulsed-wave gate placed over the myocardium shows both systolic and diastolic myocardial motion, which is used to evaluate diastolic and systolic function (Figure 3.67) (126). Using either color-tissue Doppler or pulsed-wave tissue Doppler yields the same myocardial motions, a positive systolic motion (Sm or S′), an early diastolic motion (Em or E′), a late diastolic motion (Am or A′). They also provide measurements of isovolumic relaxation time (IVRT) and isovolumic contraction time (IVCT).

Color TDI must be analyzed off line. One or more pulsed-wave gates may be placed anywhere over the color sector on the stored TDI video loop and wall motion is displayed. Pulsed-wave TDI is instantaneously generated during the exam by placing the PW gates over the color TDI sector. Peak Sm, Em, and Am velocity are measured (Figure 4.48). Color TDI also allows multiple pulsed-wave gates to be placed over the color TDI sector during off line analysis. Gradients of color TDI Sm, Em, and Am can be obtained between basal and apical sections of myocardium on apical views or between epicardial and endocardial locations on transverse and parasternal long-axis views (Figure 4.49). Isovolumic relaxation time is measured from the end of Sm to the beginning of Em. Isovolumic contraction time is measured from the end of Am to the beginning of Sm (Figure 4.50) (127–136).

Figure 4.48 Color-tissue Doppler images show the following myocardial motions: a positive systolic motion (Sm or S′),an early diastolic negative motion (Em or E′), a late diastolic negative motion (Am or A′). The colored lines correspond to the color gates placed over the TDI color sector on the twodimensional image to the left. RV = right ventricle, RA = right atrium, LV = left ventricle, LA = left atrium.

Figure 4.49 Gradients of color TDI Sm, Em, and Am can be obtained between basal and apical sections of myocardium on apical views (Figure 4.48) or between epicardial and endocardial locations on (A) transverse and (B) parasternal long-axis views. Each colored line corresponds to a gate location on the two-dimensional image. LV = left ventricle.

Figure 4.50 Isovolumic relaxation time (IRT) is measured from the end of S′ to the beginning of E′. Isovolumic contraction time (ICT) is measured from the end of A′ to the beginning of S′. (A) pulsedwave TDI, (B) color TDI.

Assessment

Color TDI and PW TDI measurements are not interchangeable, and each modality has its own set of reference values. Color TDI evaluates mean myocardial velocity while PW TDI measures peak myocardial velocity in a segment of myocardium. Color TDI is also recorded at lower fame rates than PW TDI (130). These factors cause color TDI values to be lower than PW TDI values (137).

Tissue Doppler Imaging

Color TDI—mean myocardial velocity

PW TDI—peak myocardial velocity

Color TDI velocities are lower than PW TDI velocities.

Reference values are not interchangeable.

There is a gradient from high to low tissue velocity from the base of the heart to the apex on apical four-chamber views in all walls (Figure 4.48). Endocardial color tissue velocity is higher than epicardial velocity obtained on radial fibers on both longand short-axis right parasternal-imaging planes (Figure 4.49). These gradients exist throughout the cardiac cycle in cats and dogs for systolic

and diastolic waves. The motion is synchronous in that all points along the long or short axis of the heart exhibit coordinated motion with no lag in time (Figure 4.49) (127,128,135,138). There is a breed effect on several TDI variables in both cats and dogs; breeds with specific ranges are listed in the appendices (127,128,139).

There is less variability between observers and daily examinations when TDI is applied to longitudinal fibers on apical images versus radial fibers on transverse images in man. This may be because of less translational and rotational motion on apical views. In dogs, day-to-day variability of longitudinal E′ is less than 3.5 and 5.6% in basal segments of both the right and left ventricular lateral walls, respectively. Other TDI values in dogs obtained at the base of the right and left ventricular walls on apical views have intra day and inter day variability of less than 15% (133).

Color TDI

Gradient from high to low

Base to apex on all longitudinal walls

Endocardium to epicardium on radial fibers

RV velocity greater than LV longitudinal velocity

One study in cats found repeatability of radial TDI, values for the left ventricular wall had an unacceptable degree of variability at >20% when obtained from right parasternal transverse and longaxis planes. This study also showed longitudinal velocity measured by TDI on left apical fourchamber imaging planes were much more repeatable with variation of approximately 20% with the exception of TDI measurements at the lateral tricuspid annulus (130). Chetboul and others however found good repeatability and acceptable variations of less than 20% in all TDI parameters from both right parasternal radial analysis of wall motion and from left apical assessment of longitudinal fibers with the exception of velocity recorded at the apex of the heart (138). This is a technique that requires practice to build technical proficiency, and greater variability is seen between observers than with one observer in almost all studies.

Color TDI in the horse has poorer repeatability while PW TDI had variations of less than 15% in most areas of the transverse left and right ventricular chambers with the exception of the caudal left ventricular wall (131,132). Epicardial to endocardial gradients have high coefficients of variability and are not considered to be very reliable in the standardbred and thoroughbred horse (131).

Parameters that reflect diastolic function include peak early diastolic motion (Em), peak late diastolic annular motion (A′), isovolumic relaxation time (IVRT), deceleration rate of the early diastolic motion (Em dec rate), and the Em:Am ratio (Figure 4.50). There is a weak but significant inverse relationship between peak early diastolic velocity Em and age in both cats and dogs. This is thought to be related to an age-related increase in cardiac mass, wall thickness, and intracellular matrix in man and is potentially also the case in animals. Late RV diastolic velocity, Am, and the ratio of Em:Am, IVRT, are minimally affected by age in cats or dogs but is affected by weight in dogs (119). These parameters are also unaffected by heart rate (119). Early diastolic deceleration rate, Em dec rate, in the cat is very weakly correlated to heart rate but is not affected by age (134). Increased IVRT is a sensitive indicator of diastolic myocardial failure (impaired relaxation) in man, and since it is not affected by age or heart rate, it has the potential to do so in the cat as well.

Tissue Doppler evaluation of mitral annular motion on the lateral left ventricular wall is less load dependent than PW Doppler of transmitral flow. The ratio of E:Em correlates with left atrial pressure.

Preload affects pulsed-wave tissue Doppler variables in clinically healthy dogs. Increased right