Page 167 - Feline Cardiology

166 Section D: Cardiomyopathies

The most common devastating sequelae to severe HCM channel blocker is to be avoided since it may cause severe
are congestive heart failure, arterial thromboembolism, negative inotropic and chronotropic effects and hypo-
or sudden cardiac death due to a severe arrhythmia or tension. Ventricular arrhythmias that require treatment
large intracardiac thrombus. Complications may also include ventricular tachycardia, frequent ventricular
arise secondary to medical treatment of heart failure. couplets and triplets, or frequent multiform ventricular
Progressive prerenal azotemia, dehydration, and hypo- premature complexes with R on T phenomenon.
kalemia are the most common complications of heart Atenolol is the first choice ventricular antiarrhythmic,
failure therapy. Cats with underlying renal insufficiency followed by sotalol or mexiletine. A combination of a
may be precarious heart failure patients, and may beta blocker and mexiletine may be necessary. Omega 3
develop significant exacerbation of azotemia and dehy- fatty acids may provide adjunctive treatment for ven-
Cardiomyopathies insufficiency that are diagnosed with heart failure are cardiac cachexia by reducing endogenous levels of tumor
tricular arrhythmias, and may also aid in treatment of
dration on heart failure therapy. Cats with known renal
necrosis factor.
cautiously treated with lower doses of furosemide, and
renal values are more frequently monitored—initially in
Monitoring the Asymptomatic Cat
5–7 days after starting medications, then a 2–4 weeks
later and then potentially every 3 months. Once the
gression of ventricular hypertrophy and diastolic dys-
heart failure is stabilized, low-dose ACE inhibitor therapy Echocardiography is the main tool for monitoring pro-
may be started (consider benazepril or ramipril since function in asymptomatic cats with HCM. Progressive
their blood levels are not increased by presence of renal concentric hypertrophy (moderate to severe) and wors-
insufficiency), and a renal panel checked before and after ened SAM (moderate to severe) may indicate the need
up-titration. ACE inhibitor induced functional azotemia to start a beta blocker or calcium channel blocker.
may occur in some cats and is identified as moderate to Progressive left atrial dilation occurs when there are
severe azotemia that develops after starting an ACE increased diastolic filling pressures with progressive
inhibitor. Cats with moderate or severe azotemia are heart disease, and heart failure or arterial thromboem-
often anorexic, which worsens dehydration and perpet- bolism may be sequelae. Radiographs may be taken in
uates the vicious circle of azotemia. These patients often cats with echocardiographic evidence of severe left
require temporarily stopping the furosemide, perma- atrial dilation to assess for presence of congestive heart
nently discontinuing the ACE inhibitor, and judicious failure. Repeat echocardiograms can be done every 4–12
use of fluids. Daily subcutaneous fluids can be adminis- months, depending on the disease severity, whether
tered for several days (50–75 ml SC) and then stopped, there is static or progressive cardiac disease, and finan-
and then the furosemide restarted and slowly up-titrated. cial considerations. Often young purebred cats require
Potassium gluconate or spironolactone can be given to more frequent follow-up (every 3–6 months) since they
cats with significant hypokalemia secondary to diuretic tend to have more severe and rapidly progressive heart
therapy. disease. Progressive left atrial dilation is an ominous
Chronic weight loss is another complication of heart sign of progressive diastolic dysfunction and elevated
failure, and is likely due to poor nutritional intake and left atrial pressure, with high risk of heart failure or
catabolic influences of inflammatory cytokines such as arterial thromboembolism. Cats with significant left
tumor necrosis factor. Renal prescription diets that are atrial dilation should have repeat thoracic radiographs
moderately sodium restricted are sometimes given to cats every 3–5 months to identify early heart failure, so
with heart failure, and may be appropriate provided they heart failure medications can be started prior to devel-
contain sufficient protein and energy. See Chapter 24. opment of significant dyspnea. Perceptive and engaged
Cats with HCM may develop significant tachyar- owners can be trained to monitor resting respiratory
rhythmias as the heart disease progresses. These cats rate and respiratory effort, and may alert the doctor if
may have episodes of weakness, syncope, or marked there is a persistently elevated respiratory rate (≥40
lethargy. Atrial fibrillation or supraventricular tachycar- breaths/min) on multiple consecutive measurements
dia may develop secondary to severe left atrial dilation several hours apart. Owners can be counseled that a
and pathologic remodeling. Antiarrhythmic therapy is mildly increased resting respiratory rate and effort may
indicated for treatment of rapid and/or symptomatic not necessarily represent a cardiac emergency, but it
supraventricular tachyarrhythmias and ventricular may necessitate reevaluation to assess for development
tachycardia (see Chapter 18). Supraventricular arrhyth- of heart failure.
mias (atrial fibrillation and supraventricular tachycar- Echocardiographic assessment of spontaneous con-
dia) can be treated with atenolol, diltiazem, or sotalol. trast should also be done periodically in cats with HCM
Concurrent use of both a beta blocker and calcium and left atrial dilation and if present, this finding would