Page 139 - Feline Cardiology

138 Section D: Cardiomyopathies

(Bright et al. 1999; Schober et al. 2003). A normal dia-
stolic filling pattern consists of a relatively short isovolu-
mic relaxation time (IVRT), a predominant early filling
wave (E), and an early to late (A) diastolic filling wave,
creating a ratio (E : A) >1 (Zile and Brutsaert 2002). In
normal anesthetized cats, echocardiographically mea-
sured IVRT was found to be highly correlated with inva-
sive measurements of isovolumic relaxation (tau,
r = 0.78), with a mean IVRT of 71 ± 17 ms (Schober et A
al. 2003). Delayed relaxation causes prolongation of E
Cardiomyopathies eration time, and decreased E:A ratio (<1). Cats with
IVRT, reduced E wave velocity, prolonged E wave decel-

HCM commonly have evidence of delayed relaxation by
PW Doppler (Figure 11.20). In cats with HCM, IVRT is
prolonged to 76 ± 3.1 ms versus 46 ± 3.3 ms in normal
anesthetized cats (Bright et al. 1999). Early mitral inflow
is also reduced (0.54 ± 0.04 m/s versus 0.7 ± 0.04 m/s), A
deceleration rate is slower, and atrial systolic flow veloci-
ties are increased (0.48 m/s versus 0.29 ± 0.04 m/s) in
cats with HCM compared to normal cats (Bright et al.
1999). These abnormalities are consistent with the
pattern of delayed relaxation. As diastolic dysfunction
worsens, the LA pressure rises and results in an increased S
E wave amplitude and E : A >1 similar to the normal
mitral inflow waveforms. This is termed the “pseudo-
normal” phase, and causes ambiguity in diagnosis of
diastolic dysfunction using PW Doppler of the mitral Em
inflow. Measurement of pulmonary venous flow by PW Am
Doppler is useful to identify an increased retrograde
pulmonary venous flow during atrial systole (termed B
either pulmonary vein in atrial systole [PVa] or atrial Figure 11.20. Diagnosis of diastolic dysfunction using pulsed-
reversal [Ar] wave) in the pseudonormal phase (see wave Doppler and tissue Doppler imaging echocardiography in
Figure 11.19). In the most extreme form of diastolic a cat with severe hypertrophic cardiomyopathy. (A) Pulsed-wave
dysfunction, the left atrial pressure and LV stiffness are Doppler echocardiography of the mitral inflow showing delayed
greatly increased, resulting in rapid early diastolic ven- relaxation pattern indicative of early diastolic dysfunction. (B)
tricular filling with an abrupt decrease in filling due to Pulsed-wave tissue Doppler imaging echocardiography of the lat-
the stiff ventricle and a restrictive filling pattern. This eral mitral annulus showing diastolic dysfunction.
pattern is summarized as reduced IVRT, decreased A delayed relaxation pattern is commonly seen in cats with HCM,
deceleration time, E : A ratio >2, and possibly a decreased and is identified by pulsed-wave Doppler interrogation of the
A wave duration compared to the pulmonary venous mitral inflow (see Figure 11.19), which shows reduced E wave
velocity, reduced E:A ratio (<1), and prolonged deceleration time.
PVa (Ar) wave. Pulsed-wave tissue Doppler imaging can be done at the mitral
Although widely used as a simple, noninvasive method annulus using the left apical 4-chamber view (B), with the gate
to assess diastolic function, PW Doppler mitral inflow placed in alignment with the myocardial motion. The velocity of
characteristics are greatly impacted by filling pressures the longitudinal myocardial fibers is measured in this way. This
and the LA : LV pressure gradient. For example, peak pulsed-wave TDI tracing of the same cat in (A) shows severely
early mitral inflow velocity was found to be moderately impaired diastolic function with a markedly reduced early mitral
correlated with LV filling pressure in normal anesthe- annular diastolic velocity (Em or E’), and Em:Am velocity. E = early
tized cats (r = 0.48) (Peterson et al. 1993). Increased left mitral inflow; A = mitral inflow during atrial systole; Em = early
atrial pressure may mask a delayed relaxation pattern. diastolic mitral annular velocity; Am = late diastolic mitral annu-
Oppositely, increased heart rate, decreased preload, and lar velocity during atrial systole; S = mitral annular velocity during
increased afterload accentuate a delayed relaxation systole.
pattern (Movsowitz et al. 1993). Consequently, there has
been a search for noninvasive methods to assess diastolic