Page 142 - Feline Cardiology

Chapter 11: Hypertrophic Cardiomyopathy 141

in genotypically affected Maine coon cats compared to E/Vp by TDI was moderately correlated in LV end-
normal domestic shorthaired cats, and is further diastolic pressure in anesthetized normal cats (R = 0.64)
decreased in genotypically affected Maine coon cats (Schober et al. 2003). No studies have evaluated the
that have the abnormal phenotype of concentric left ability of E/E’ to predict PCWP pressure in cats with
ventricular hypertrophy (MacDonald et al. 2007). HCM.
Therefore, it appears that diastolic dysfunction is an Although diastolic dysfunction is the main patho-
early pathophysiologic abnormality in Maine coon physiologic abnormality in HCM, there is evidence of
cats with familial HCM, and is independent of left reduced longitudinal systolic function on TDI in
ventricular concentric hypertrophy. Similarly, TDI was humans, transgenic rabbits, and cats with HCM
able to detect diastolic dysfunction in all carrier cats (Nagueh et al. 2001; Meurs et al. 2000; Koffas et al. 2006;
and affected cats prior to development of concentric Vinereanu et al. 2001; Tabata et al. 2000; Yip et al. 2002).
hypertrophy in a family of cats affected by dystrophin- Decreased systolic function in HCM is counterintuitive,
deficient hypertrophic muscular dystrophy (Chetboul since the ventricular wall motion often appears hyper- Cardiomyopathies
et al. 2006). Thus, evidence exists to support TDI as a dynamic. However, if the systolic myocardial function is
diagnostic modality that detects HCM earliest, even more carefully assessed using TDI echocardiography,
before measurable ventricular hypertrophy in some regional or global systolic dysfunction may be identified
cats. in patients with HCM, even prior to an end-stage
Future applications of TDI may include improvement remodeling with overt systolic failure. This is likely due
in accuracy of prognosis for patients with heart disease. to the pathophysiology of HCM, where sarcomeric sys-
For example, peak early diastolic mitral annular velocity tolic and diastolic dysfunction is the earliest myocardial
(E’) is a powerful predictor of outcome in a variety of defect. S’ (but not fractional shortening), is lower in
cardiovascular conditions including HCM (Wang et al. cats with HCM without left ventricular outflow tract
2003; Sanderson et al. 2004; McMahon et al. 2004). E’ obstructions compared to normal cats (Koffas et al.
was the strongest predictor of cardiac mortality of all the 2006). Cats with reduced S’ velocity in this study had
TDI variables in people with various cardiac diseases in normal fractional shortening, which illustrates that
one study: E’ <3 cm/s was associated with over a fivefold fractional shortening is an insensitive test for systolic
increased risk of cardiac death (Wang et al. 2003). In myocardial function and may be confounded by many
another study, unlike traditional mitral inflow Doppler other factors such as preload. Systolic dysfunction
indices, E’ also correlated with severity of heart failure appears to be more common in cats with severe HCM
(New York Heart Association functional class) and exer- and heart failure than asymptomatic cats because all
cise capacity in adults with HCM (Matsumura et al. cats with heart failure secondary to HCM had decreased
2002). In children with HCM, transmitral E/septal E’ S’ velocities in one study (Koffas et al. 2006). Similar
predicted risk of death, cardiac arrest, ventricular tachy- findings of systolic impairment detected by TDI have
cardia, and significant cardiac symptoms (McMahon been described in human medicine and in genetic
et al. 2004). The index of transmitral E/E’ is a useful, models of HCM. S’ velocities were reduced by 12–31%,
noninvasive method to estimate LV filling pressure in and time to peak systolic velocity was increased
normal people (r = 0.87) and people with HCM (r = 0.8) in people with HCM (Vinereanu et al. 2001; Tabata
(Nagueh et al. 1997, 1999). Changes in pulmonary capil- et al. 2000). S’ velocities are even reduced in humans
lary wedge pressure (PCWP) in patients with HCM are or rabbits with β-MHC mutations prior to develop-
also tracked by changes in E/E’ (Nagueh et al. 1999). E/E’ ment of LV hypertrophy (Nagueh et al. 2000, 2001).
≥10 predicts LV filling pressure (just before atrial systole) In normal humans, the radial systolic velocity is
of >15 mm Hg, and yields the best sensitivity (92%) and lower than the longitudinal velocity at the mitral
specificity (85%). In dogs with acute experimentally annulus, but this relationship is reversed in people
induced mitral regurgitation, E/E’ is highly correlated with HCM, indicating that longitudinal fibers may
(r = 0.83) with mean left atrial pressure (Oyama et al. be more affected than circumferential fibers (Tabata
2004). An LA pressure >20 mm Hg is highly probable et al. 2000). S’ velocities are reduced in hypertrophied
when mean E/E’ is >9.1 (Oyama et al. 2004). Color as well as nonhypertrophied regions (Tabata et al.
M-mode measurement of the early diastolic mitral 2000). There is no difference in systolic and diastolic
inflow of blood can be used to calculate the velocity of TDI velocities in obstructive versus nonobstructive
flow propagation (Vp). The slope of the first aliasing HCM. Postsystolic thickening is another indication of
inflow velocity is the velocity of propogation (Vp) along systolic impairment, which occurs when part of the left
the left ventricle during early diastole. Vp progressively ventricular wall contracts after the end of the T wave
decreases as the diastolic function worsens. Mitral inflow while other parts of the ventricle undergo isovolumic