Page 285 - Feline Cardiology

292 Section G: Congestive Heart Failure

medicine, and is unlikely to cause harm. Gloves must be manner in healthy anesthetized cats (Pascoe et al. 2006).
worn by the administrator of the ointment to avoid Dobutamine can be used in cats with hypotension and
absorption. Transdermal nitroglycerin (1/8–1/4 inch low output heart failure, significant hypoperfusion evi-
[2-5 mm] q 6 hr), applied to hairless region on the inside denced by marked elevation in lactate and decreased
of the pinna, alternating ears for each treatment; alterna- venous oxygen partial pressure (PvO 2 ), or in cats that are
tive technique is application and then removal 12 hours not responding adequately to aggressive diuretic therapy
later, to be repeated with 12 hours on and 12 hours off with end-stage diseases causing myocardial failure or
cycles for 3 days may be administered for 1 to 2 days ventricular volume overload (i.e., ventricular septal
during hospitalization of acute heart failure. Long-term defect, mitral regurgitation). In human cardiology,
daily use at home is not recommended due to the toler- dobutamine is used routinely as a bridge to final resolu-
ance and loss of effect that develops after 18 to 24 hours tion of the heart problem (e.g., heart transplantation).
of treatment, as well as risk of owner absorption of the Since short-term cures are uncommon in feline cardiol-
transdermal medication at home. Sodium nitroprusside ogy, the use of dobutamine should consider the patient’s
can be used in cats with acute severe systemic hyperten- context. For example, in one cat with end-stage DCM,
sion or in cats with refractory severe heart failure that dobutamine may be appropriate to provide the owner
are not responding to aggressive diuretic therapy. with an assurance that every option was used (and indeed
the cat may respond and have an acceptable quality of
Nitroprusside is a balanced arterial and venous vasodila-
Congestive Heart Failure Nitroprusside is sensitive to light, heat, and moisture, and the same application of dobutamine may be perceived as
life for some time thereafter), but in another similar cat
tor with a very short half-life, facilitating rapid titration.
delaying an inevitable death. It is clearly indicated for
deterioration is evidenced by a color change to brown or
initial stabilization of cats with a reversible form of heart
blue. It should be protected from light by wrapping the
container and IV line with aluminum foil and can be
disease, such as taurine deficiency induced myocardial
used for up to 24 hours. Careful blood pressure monitor-
common than myocardial failure in cats, low output
ing is necessary to avoid significant hypotension.
Hypotension can be quickly reversed by discontinuing failure or tachycardiomyopathy. Because HCM is more
heart disease may be first addressed in these patients by
the drug, and blood pressure usually recovers within restoring intravascular blood volume with fluid resusci-
several minutes. Nitroprusside can cause cyanide toxicity tation if the cat is hypovolemic, and if there is a lack of
in people and likely in animals. In a study of pediatric improvement in hypotension, vasopressors such as
cardiac patients, elevated cyanide levels were indepen- dopamine may be started rather than dobutamine.
dently predicted by mean dose, cumulative dose, and Pimobendan is a potent positive inotrope with addi-
acid-base excess values (Moffett and Price 2008). Doses tional moderate balanced vasodilating properties. It is
of ≥1.8 mcg/kg/min predicted an elevated cyanide con- used (off-label) in cats with congestive heart failure and
centration with 89% sensitivity and 88% specificity myocardial failure (i.e., DCM, end-stage ventricular
(Moffett and Price 2008). There are no pharmacologic volume overload caused by a ventricular septal defect or
studies evaluating nitroprusside in cats, and doses mitral regurgitation), but its use in cats with heart failure
reported are anecdotal (0.5–10 mcg/kg/min) and extrap- from other cardiac diseases is controversial. No feline
olated. Given the potential of cyanide toxicity, the recom- pharmacokinetic studies have been done, but a dose of
mended dose is <2 mcg/kg/min for less than 24 hours for 0.1–0.25 mg/kg PO q 12 hr has been reported anecdot-
acute, short-term treatment of fulminant heart failure. ally in cats with heart failure (MacGregor et al. 2010;
Dobutamine is a potent beta-adrenergic agent that Sturgess and Ferasin 2007). Adverse side effects appear
stimulates the beta-1 adrenergic receptors and increases to be uncommon (5/161 cats, 3%) and may include
myocardial contractility. It may be used in animals with vocalization, agitation, anorexia, vomiting, and consti-
acute heart failure secondary to systolic dysfunction pation, and may not require discontinuation of the drug
(e.g., DCM, end-stage ventricular volume overload from (MacGregor et al. 2010); however, retrospective studies
mitral regurgitation or ventricular septal defect) and is such as these cannot document the absence of adverse
often combined with the balanced vasodilator nitroprus- effects with certainty. One cat with congestive heart
side for synergistic effects of increased cardiac output, failure due to mitral valve dysplasia and systolic anterior
decreased afterload, and decreased diastolic ventricular motion of the mitral valve developed severe hypotension
filling pressures. Doses of 5–15 mcg/kg/min increase (systolic blood pressure decreased from 97 mm Hg to
cardiac index in healthy, anesthetized cats by 2 to 2.5 60 mm Hg) several hours after administration of pimo-
times baseline and increase contractility greater than bendan, necessitating discontinuation of the drug
dopamine or epinephrine (Pascoe et al. 2006). Mild sinus (Gordon 2010). Pimobendan is a phosphodiesterase III
tachycardia may occur at subinotropic doses of 2.5 mcg/ inhibitor and a calcium sensitizing agent, which increases
kg/min, and heart rate increases in a dose-dependent contractility by increasing the binding of calcium to