Page 160 - Feline Cardiology

Chapter 11: Hypertrophic Cardiomyopathy 159

dard) therapy of sustained release diltiazem and other Plasma aldosterone concentration was markedly elevated
medications if needed such as diuretics or antiarrhyth- in cats treated with spironolactone (baseline 235 pmol/l;
mics. One group received standard therapy (n = 9) and posttreatment 1000 pmol/l), indicating that aldosterone
the other group received benazepril (n = 19) orally once receptor antagonism was achieved. Approximately one-
a day for a year. Only 7 cats (26%; 4 benazepril, 3 stan- third of cats treated with spironolactone developed
dard therapy) reached the end point evaluation at 1 year, severe ulcerative facial dermatitis, which resolved 4–6
and the remaining either died, developed arterial throm- weeks after discontinuing the medication. The histo-
boembolism, or were lost to follow-up. There was no pathologic diagnosis of necrotizing and ulcerative der-
difference between groups on death or rate of dropout. matitis with superficial to deep eosinophilic and
The authors report a reduction of LV free wall thickness neutrophilic perivascular dermatitis and the resolution
in the benazepril group of 0.1 mm/month, but median of the lesions after discontinuation of the drug are con-
values and standard errors were not published. The sistent with an adverse drug reaction. Therefore, there is
ability to measure actual changes in LV thickness of a lack of evidence of benefit (i.e., no change in echocar- Cardiomyopathies
0.1 mm by echocardiography is doubtful due to the high diographic measurements of left ventricular hypertro-
variability of the method, even though the results were phy, left atrial size, or diastolic function), in asymptomatic
reported to be statistically significant. The second study cats with HCM given spironolactone, yet there is a sig-
was a retrospective, unblinded study evaluating the nificant risk of adverse drug reaction.
effects of enalapril in 19 cats with HCM over 3–6 months Specific antifibrotic drugs are theoretically plausible
of treatment (Rush et al. 1998). Mean interventricular for further investigation in cats with HCM. An unpub-
septal thickness decreased from 7 mm ± 2 mm to 6 mm lished study investigating the effects of pirfenidone, an
± 1 mm, and mean LV free wall thickness decreased from antifibrotic agent used to treat pulmonary fibrosis in
8 mm ± 2 mm to 7 mm ± 2 mm. Mean left atrial diameter humans, was conducted in Maine coon cats with familial
also decreased. Neither study quantified LV mass as an HCM, but the study was discontinued due to the intense
end point, and both relied upon 2-D or M-mode echo- impalatability in cats (K. MacDonald, unpublished
cardiographic measurement of LV free wall and inter- observations). No studies have evaluated the effect of
ventricular septal thickness, which is fraught with colchicine, a microtubule depolymerase with possible
tremendous variability and interday or interobserver antifibrotic, immunomodulator effects, in cats with
error of 18–20% (Chetboul et al. 2004). Since hypertro- HCM.
phy is most often asymmetrical, the LV thickness mea-
surements are extremely site-dependent. In the absence Treatment of Symptomatic Cats with
of convincing evidence to the contrary, it is the authors’ HCM
viewpoint that treatment of asymptomatic cats with
HCM using an ACE inhibitor is unwarranted.
Another pharmacologic target for reduction of myo- Key points
cardial fibrosis and hypertrophy is to block aldosterone
receptors. In a cardiac troponin T transgenic rat model • Furosemide is the most effective and life-saving
of HCM, spironolactone reversed interstitial fibrosis, treatment of cats in congestive heart failure and can be
decreased myocyte disarray by 50%, and improved dia- given at a dose range of 1–4 mg/kg PO q 8–24 hr to for
stolic function assessed by mitral inflow velocity mea- outpatient therapy depending on the severity of heart
failure. The minimal effective dose should be used.
surements (Tsybouleva et al. 2004). The effects of An initial moderate to high dose may be started and
spironolactone in asymptomatic cats with HCM has then rapidly tapered based on respiratory rate, effort,
been studied in a prospective, blinded, placebo con- and evaluation of severity of heart failure by thoracic
trolled study of asymptomatic Maine coon cats with radiographs.
mild to severe familial HCM with diastolic dysfunction • Treatment of acute heart failure includes parenteral
identified on tissue Doppler imaging echocardiography furosemide (2–4 mg/kg q 1–8 hr). The dose and
(MacDonald et al. 2008). The study evaluated the effect frequency should be rapidly tapered once the respiratory
of spironolactone (2 mg/kg PO q 12 h for 4 months) on rate decreases to 50 breaths/minute or less and the
diastolic function assessed by pulsed-wave tissue Doppler effort is decreased. Oxygen therapy with 60–70% FiO 2
imaging, cardiac mass quantified by the truncated ellipse can be provided initially and then decreased to 50% or
formula using echocardiography, left atrial size, and less within 12 hours to avoid barotrauma secondary to
high inspiratory oxygen concentration.
plasma aldosterone concentration. There was no differ- • Transdermal nitroglycerin causes venodilation in
ence in diastolic function or systolic function assessed people, but it has not been evaluated in cats. Its use
by tissue Doppler imaging, LV mass, or left atrial size.