Page 67 - Feline Cardiology

62 Section B: Diagnostic Testing

Diagnostic Testing RV LV

RA LA

Figure 7.8. A 4-chamber view obtained from the
left apical view. Transmitral and transtricuspid flow
(ventricular filling) are parallel with the ultrasound
beam in this alignment, which optimizes Doppler
studies. RA = right atrium, LA = left atrium; LV = left
ventricle; RV = right ventricle.

P wave. However, if the heart rate is reasonably slow instantaneous pressure gradient across the mitral valve.
(<180 bpm), two separate phases of diastolic flow are In the normal animal, the peak E wave velocity exceeds
generally recorded. The E wave corresponds to early, the peak A wave velocity (E/A >1). With advancing left
passive filling, and the A wave corresponds to late, active ventricular myocardial disease, the filling pattern pro-
filling (atrial contraction) and follows the P wave on the gressively changes. In cats with reduced left ventricular
ECG. Normal values in the cat are listed in Table 7.3. A compliance, the early diastolic flow (E wave) is smaller,
similar flow pattern is present when evaluating tricuspid the rate of deceleration is reduced, and the peak velocity
inflow. If mitral or tricuspid regurgitation is noted, or of the A wave increases in absolute and relative terms.
any turbulent flow pattern is recognized with color or Unfortunately, interpretation of transmitral flows can be
pulsed-wave Doppler, velocity of the flow should be difficult because of “pseudonormalization” where the
measured with continuous-wave Doppler. The pressure E/A ratio returns to normal, although the cat has diastolic
gradient (PG) across the valve can be estimated by using dysfunction. With pseudonormalization, increased left
the modified Bernoulli equation [PG (in mm atrial pressure causes early opening of the mitral valve
2
Hg) = 4 × V , where V = velocity in m/s]. Normally, the and augmented passive filling of the left ventricle (because
gradient (pressure difference) between atrium and ven- the LA to LV gradient is increased). Also, ventricular
tricle or between ventricle and great vessel should be pressure rises more rapidly than normal causing the late
close to zero when the valve separating the two struc- diastolic LA to LV gradient to be lower than normal, with
tures is open; elevations suggest obstruction (stenosis) a resultant reduction in the transmitral A wave. In
between the two structures. humans, this stage is considered “transitional” and occurs
when the increased LV stiffness has lead to elevated left
atrial (LA) pressure. However, as LV stiffness and LA
ECHOCARDIOGRAPHIC ASSESSMENT pressure continue to increase, further changes in the
OF DIASTOLIC FUNCTION
transmitral flow pattern occur, resulting in a “restrictive”
Diastolic function is difficult to assess echocardiographi- transmitral filling pattern. The restrictive pattern is char-
cally; however, an overview can be ascertained using acterized by tall and narrow E waves, small A waves, and
several Doppler measurements. In the cat, where the shortened isovolumetric relaxation and deceleration
most common heart diseases cause diastolic dysfunction, times (Bright et al. 1999) (Figures 7.9, 7.10).
these measurements are critical to obtaining a complete In addition to the phenomenon of pseudonormaliza-
study. Transmitral flow, discussed above, reflects the tion, the transmitral flow pattern can also be adversely