Page 121 - Feline Cardiology

120 Section D: Cardiomyopathies

sympathetic tone and is significantly higher (median HR thyroid gland therefore suggests a <10% likelihood of
150 bpm ± 23 bpm, non-restrained in the veterinary hyperthyroidism. However, the presence of an enlarged
hospital) compared to at home (132 bpm ± 19 bpm, thyroid gland does not automatically equate to hyper-
measured by telemetry) in normal cats (Abbott 2005). thyroidism, because many cats have thyroid gland
Furthermore, tachycardia is not useful to distinguish enlargement and normal serum thyroid hormone levels
asymptomatic cats with HCM from cats with CHF or (and no clinical hyperthyroidism). Clinical complaints
arterial thromboembolism (Atkins et al. 1992). such as polyuria, polydyspia, polyphagia in the face of
Premature beats are occasionally ausculted in cats with weight loss, and behavioral changes such as hyperactiv-
HCM, and premature ventricular complexes are more ity or lethargy, should spark the suspicion of hyperthy-
commonly associated with heart disease in cats than in roidism and prompt measurement of serum thyroxine
Cardiomyopathies ties may include an irregularly irregular rhythm if there such as retinal detachment or hyphema raises suspicion
concentration. Identification of ocular abnormalities
dogs (Côté and Jaeger 2008). Other rhythm abnormali-
for presence of systemic hypertension, and mandates
is atrial fibrillation or runs of tachycardia if there is
measurement of systolic blood pressure. Physical signs
supraventricular tachycardia or ventricular tachycardia.
suggestive of acromegaly, such as a broad forehead and
Therefore, cats with irregularly irregular rhythms,
bursts/runs of tachycardia, or unusually low heart rates
with intractable diabetes mellitus, may suggest an excess
(e.g., <150 beats/minute in the exam room) may reason- prognathism particularly in an adult cat >10 years old
ably be suspected of having heart disease, and both elec- of circulating growth hormone (i.e., acromegaly) as a
trocardiography and echocardiography are justified in secondary cause of left ventricular hypertrophy and
these patients. As discussed above, many cats (up to prompts a more specific workup for acromegaly.
69%) with HCM have no clinical abnormalities or
abnormal history (Paige et al. 2009). DIFFERENTIAL DIAGNOSIS
Femoral pulses are usually unremarkable unless there
is a marked tachyarrhythmia or low output heart failure.
Palpation of femoral pulses in cats may be difficult and Key Points
pulses may feel attenuated or reduced in some normal
cats due to certain factors such as obesity or examiner • Systemic hypertension, hyperthyroidism, and
variability. Therefore, assessment of pulse quality should acromegaly are secondary causes of concentric
be combined with palpation of the warmth of the extrem- ventricular hypertrophy, which reverses several months
after effective treatment of the disease.
ities, evaluation of the color of the nail beds, and other • SAM of the mitral valve is a hallmark pathologic feature
assessments of peripheral circulation to assess perfusion. of HCM, and occasionally it can occur in cardiac diseases
Cats with congestive heart failure may have tachy- causing secondary ventricular hypertrophy or in normal
pnea, dyspnea, orthopnea, and increased adventitious cats that are catecholamine-driven (anxiety, stress, fear).
lung sounds. Dyspnea was present on physical examina- Mitral valve dysplasia is the most common differential
tion in 36% of cats diagnosed with HCM in a study of diagnosis for SAM of the mitral valve.
61 cats with HCM, yet only 8% had abnormal respira- • Rare causes of infiltrative myocardial diseases include
tory sounds on auscultation (Ferasin et al. 2003). cardiac neoplasia such as rhabdomyosarcoma or
Therefore, absence of abnormal respiratory lung sounds lymphoma.
does not rule out heart failure. Cats with pleural effusion
may have, depending on the volume of the effusion,
muffled lung sounds ventrally, tachypnea, and some- On physical exam, the differential diagnoses for heart
times increased abdominal effort or orthopnea. murmurs, dyspnea, arterial thromboembolism, and
Careful evaluation for other physical abnormalities syncope are discussed in Chapters 1, 4, 20, and 2,
associated with systemic diseases (i.e., hyperthyroidism, respectively.
systemic hypertension, acromegaly) that cause “second- Secondary causes of left ventricular concentric hyper-
ary” and compensatory left ventricular hypertrophy is trophy (increased end-diastolic ventricular wall or septal
essential in cats suspected of having cardiac disease. The thickness measured by echocardiography) are the main
thyroid gland should be palpated and may be enlarged differential diagnoses for HCM. Systemic hypertension
in cats with hyperthyroidism with or without HCM. A and hyperthyroidism are the most common causes of
palpable thyroid gland is present in 91% of hyperthyroid secondary concentric hypertrophy. Systemic hyperten-
cats, and this finding warrants measurement of serum sion increases left ventricular afterload and systolic wall
thyroxine levels (see Chapter 1) (Feldman and Nelson stress, which trigger the cardiomyocytes to replicate side
2004). Careful palpation that fails to identify an enlarged by side to cause increased wall thickness (i.e., concentric