Page 324 - Feline Cardiology

Chapter 21: Systemic Hypertension 333

coma. Old retinal hemorrhages or scars may be seen as and troubleshooting to abolish these errors is essential
retinal hyperreflectivity (see Figure 21.6). for optimal patient care.
In hypertensive cats, palpation of the heartbeat can
reveal an abnormally strong apex beat if there is consid­ White Coat Effect
erable ventricular hypertrophy. Cardiac auscultation In an experiment, healthy cats with radiotelemetric
may reveal a heart murmur, gallop sound, or both. Heart implants measuring direct arterial pressure continu­
murmurs in otherwise normal­appearing cats are a ously were allowed to acclimate for at least 2 weeks to
common reason for referral of feline patients for BP their housing. One at a time, each of 6 such cats then
measurement and complete cardiovascular examina­ underwent simulated veterinary visits consisting of a
tion. This may explain the high prevalence of heart short drive in a car to the veterinary hospital, transpor­
murmurs in both hypertensive cats (36/58, 62%) and tation to a noisy waiting room for a 10­minute wait, a
normotensive controls (81/113, 72%). A gallop sound, complete physical examination, and a standard blood
however, is significantly more likely to be associated with pressure measurement using the Doppler technique.
systemic hypertension (9/58 cats, 16%) than normoten­ The radiotelemetry equipment identified that during
sion (0/113, 0%). The presence of the gallop sound is these mock visits, the systolic BP of cats varied from −29
independent of the degree of hypertension: 9/58 hyper­ (decrease of 29 mm Hg compared to resting) to +75
tensive cats with a gallop sound had a mean systolic BP (increase of 75 mm Hg) compared to radiotelemetry­
of 245 mm Hg, whereas 49/58 hypertensive cats without recorded 24­hour baseline (Belew et al. 1999), with a
a gallop sound had a mean systolic BP of 244 mm Hg. mean of +18 mm Hg. There was variation between the
Palpation of the neck of cats with systemic hyperten­ cats, but also within each cat during repeated visits, and
sion may reveal thyroid gland enlargement or a thyroid the artificial increase in BP tended to decrease with sub­
nodule. The presence of such changes does not equate sequent visits. This experiment clarifies the white coat
to hyperthyroidism, since the thyroid lesion may not be effect in cats, and it reinforces the importance of careful
functional, and serologic assessment of thyroid levels is selection of the proper environment for measuring
warranted (Feldman and Nelson 2004). Similarly, the blood pressure (Belew et al. 1999). Because of this sub­
absence of a palpable thyroid is not a basis for ruling out stantial confounding effect, some veterinarians, techni­ Systemic Hypertension
hyperthyroidism if other elements of the history and cians, and other cat owners with access to Doppler
physical exam are suggestive, and here again thyroid equipment measure cats’ BP at home. The same param­
serology is appropriate if other clinical findings support eters for determining normotension versus hyperten­
hyperthyroidism because an adenomatous thyroid gland sion apply; home measurement merely reduces the
may simply have descended through the thoracic inlet travel and veterinary facility components of the white
or originated from ectopic thyroid tissue in the thorax, coat effect. Therefore, and as for in­clinic measurements,
where it is not palpable (Feldman and Nelson 2004). serial home measurements may provide important,
Abdominal palpation may reveal diffusely small kidneys additional information beyond 1 or 2 one­time BP
in the cat with typical chronic renal disease or enlarged determinations.
(typically bilaterally) kidneys in chronic renal disease
caused by polycystic kidney disease or renal lymphoma. Wrong Cuff Size
An extremely unusual finding would be the palpation of A falsely high BP may be recorded if an excessively large
an adrenal mass, consistent with two very rare causes of sphygmomanometer cuff is used (see below for discus­
systemic hypertension in the cat: hyperaldosteronism sion of cuff size).
and pheochromocytoma.

Wrong Cuff Location—Too Proximal
DIFFERENTIAL DIAGNOSIS A falsely high BP may be recorded if the cuff is placed

In many instances, determining the presence or absence proximal to the tarsus or elbow, as was originally
of a truly and clinically significantly elevated blood suggested when the Doppler technique was introduced
pressure is the most difficult question concerning in cats.
systemic hypertension. Is a given feline patient hyper­
tensive or not? Sphygmomanometer Calibration
Figure 21.1 presents the consensus recommendation The clinical standard in feline medicine is a spring­
issued by the American College of Veterinary Internal operated sphygmomanometer and cuff apparatus.
Medicine for answering this question. Some common However, these instruments are not routinely calibrated
errors lead to misdiagnosis of systemic hypertension, against direct arterial measurements, but such calibration