Page 140 - Problem-Based Feline Medicine

132 PART 3 CAT WITH SIGNS OF HEART DISEASE

Typically there is progressive weight loss with a good Electrocardiographic findings
appetite. Sinus tachycardia (Heart rate > 220 bpm) is common.
Increased R wave amplitude (>0.9 mV), supraventricu-
A heart murmur is heard in some cases, and a gallop
lar premature beats and ventricular arrhythmias are
rhythm may be noticed.
commonly found.
Tachycardia is persistent even at rest. Many cats
have heart rates above 240 bpm. Echocardiographic findings
Heart chambers may be of normal size but in many
Arrhythmias are present in more advanced cases.
cases, some degree of ventricular concentric hyper-
A hyperkinetic peripheral pulse, usually the femoral trophy is present. Interventricular septum and LV free
pulse, is very easy to palpate. wall measurements in diastole are greater than 6 mm.
Loud heart sounds and a strong precordial impulse are The “typical” hyperthyroid heart shows mild to moder-
typically present, which is the result of increased ate increase in wall thickness (see above), upper range
sympathetic tone and decreased fat deposits over of normal ventricular chamber size (LV diastolic
the chest. dimension 16–17 mm) and increased contractility
(fractional shortening higher than 55%) reflecting
Increased respiratory rate or panting is particularly
hyperdynamic cardiac function.
seen in cats in a crisis (thyroid storm). This may be
mistaken for respiratory distress when it is only hyper- Variable degrees of left atrial dilation are present.
ventilation.
In some cases (usually advanced cases), a dilated
Respiratory distress may occur secondary to heart form of cardiomyopathy may be seen. It is difficult
failure when pulmonary edema and/or pleural effusion to differentiate from restrictive or dilated cardiomy-
are present. opathy.
Cats are often difficult to handle and owners report a
change in behavior (irritability and restlessness). Systemic blood pressure
Polyuria, polydipsia and vomiting are seen in approxi-
Hypertension is commonly found. Systolic arterial
mately 50% of the cases.
blood pressure, measured by Doppler technique, con-
Palpable thyroid nodules are common. sistently above 180 mmHg is diagnostic.

Diagnosis Treatment

An increased serum total thyroxine (T ) is usually Antithyroid drugs (Methimazole, Carbimazole),
4
diagnostic. The upper range of normal is 51 nmol/L radioactive iodine and thyroidectomy are treatment
(4.0 μg/dl). choices for hyperthyroidism (for further details refer to
page 305).
A single random serum T level is usually diagnostic.
4
Tachycardia and hypertension should be treated with
If a random serum T level does not confirm the disease
4 beta-blocking drugs. This class of drugs controls the
in a highly suspected case, repeat serum T or free T in
4 4 cardiovascular effects of hyperthyroidism and improves
1–2 weeks or perform a T suppression test.
3 clinical signs.
Beta-blockers do not decrease serum thyroid hor-
Radiographic findings
mones. Beta-blockade therapy is discontinued upon
Heart size varies from normal to severe dilation of all
normalization of serum thyroid hormones and resolu-
chambers.
tion of cardiovascular signs.
Pleural effusion and/or pulmonary edema may be pres- ● Propranolol 0.5–1.0 mg/kg PO q 8 h OR
ent in severe cases. ● Atenolol 12.5 mg/cat PO q 12 h.