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Gary D. Norsworthy, DVMDiplomate, ABVP (Feline)

Larry P. Tilley, DVMDiplomate, ACVIM

Jorgensen Laboratories, Inc.1450 N. Van Buren Avenue

Loveland, CO 80538800-525-5614

Definition

Hypertension, commonly called high bloodpressure, is a sustained elevation in eithersystolic or diastolic arterial blood pressureabove normal range. Several values are foundin the current veterinary literature for whatconstitutes hypertension in cats. Someauthors feel that systolic values above 160mmHg are abnormal. Other authors definehypertension as systolic values above 200mmHg. It has been shown that stress andenvironmental factors can influence bloodpressure readings; therefore, some of the variation in these values is likely due to theconditions under which the readings weremade. However, there appears to be universalagreement that systolic readings above 200mmHg are abnormal.

Causes

Primary or essential hypertension is a common disease in humans. However, it isapparently a rare disease in the cat, if itoccurs at all. Most cases of feline hyperten-sion have been closely related to two diseasemechanisms: 1) Diseases that increaseperipheral resistance (chronic renal failure),and 2) Diseases that increase cardiac output(hyperthyroidism).

Chronic renal disease is the most commondisease that increases peripheral resistance. A very simplified explanation states that aged,shrunken kidneys, that normally receive 20%of the cardiac output, are unable to accommodate that amount of blood.Therefore, blood is regurgitated into the aorta.However, many cats that are hypertensiveonly have a slight degree of azotemia andmay have kidneys of relatively normal size.

Hypertension in Feline Patients

Gary D. Norsworthy, DVM, DABVPLarry P. Tilley, DVM, DACVIM

This observation has caused us to seek otherexplanations. Several rationales have beengiven for how hypertension is related to renalfailure in human patients. These include fail-ure to excrete a normal quantity of salt or fluid,stiffening of the venous capacitance system,alterations in adrenergic activity, activation ofthe renin-angiotensin-aldosterone axis withincreased peripheral resistance and salt retention, stimulation of renopressor systems,and suppression of renodepressors orprostaglandins. However, none of these hasbeen proved. One study (JAAHA 11/94) foundthat 65% of cats with chronic renal diseasewere hypertensive.

Hyperthyroidism is the most common diseasethat causes increased cardiac output.Thyrotoxic cardiomyopathy is a common find-ing in hypertensive cats. It has several effectson the feline heart, the sum of which result intachycardia, left ventricular hypertrophy, andincreased contractility. The heart is hyperkinet-ic, resulting in increased cardiac output. Onestudy found that 23% of hyperthyroid catswere hypertensive.

It is important to understand these mecha-nisms and their likely causes. The clinicalimpact is that documented hypertensive catsshould have a diagnostic workup that includesrenal and thyroid tests.

Clinical Signs

The typical clinical presentation for hyperten-sive cats is sudden onset retinal blindness.Owners report that their cats have suddenlystarted walking into walls and furniture. Sincethis presentation is so dramatic, we are likelyto see these cats only a few hours after theonset of blindness, a fortunate occurrencetherapeutically.

Retinal blindness associated with hyperten-sion is usually due to retinal detachment. Thedetached and folded retina can be seen with adirect or indirect ophthalmoscope. However, inmany cats, the changes are so dramatic thatthey may be seen without special equipment.(Figures 1a, b)

Another clinical sign is retinal hemorrhage,which usually precedes retinal detachment.Most cats with retinal hemorrhage, but withoutdetachment, are not blind. However, thesecats may exhibit reduced pupillary light reflexor, if unilateral, anisocoria. (Figure 2)Hypertension may cause arterial bleeding inother organs, including the brain, which mayresult in stroke-like signs of seizures, incoordi-nation, circling, or excessive vocalization.(Figure 3)

Figure 1a: Fixed and dilated pupils are characteristic ofcats that are blind due to hypertension.

Figure 1b: Retinal detachment can be seen from the11:00 to 5:00 position even without an opthalmoscope.

Figure 2: The left pupil is larger than the right due togreater retinal hemorrhage. The cat’s systolic bloodpressure was 230 mmHg, and it was hyperthyroid. Thepupils equalized two months following thyroidectomy.

Figure 3: This cat was presented for circling which wasdue to a stroke. Its systolic blood pressure was 290mmHg.

Diagnosis

When retinal blindness occurs in a geriatriccat, it is important to consider hypertension asthe first differential. Rapid commencement oftherapy is extremely important in restoringvision, so blood pressure readings should beperformed first. Blood pressure can be meas-ured directly with intraarterial catheterizationand by using several indirect methods.However, Doppler technology is the one thatis non-invasive, non-stressful, and reliable incats. The technique is described below.

Other signs of hypertension may be detected.Palpation or auscultation of the heart usuallyreveals a pounding beat. Filling of a syringeduring blood collection from a peripheral vein,such as the cephalic, is much faster. Both ofthese should heighten one’s index of suspi-cion for hypertension. Clinical findings thatmay signal one of the causes of hypertensionare decreased renal size, as determined bypalpation, radiography, or ultrasound, and apalpable thyroid lobe.

Appropriate diagnostic tests include a CBC,chemistry profile,T4, urinalysis, and abdominaland cardiac imaging (radiographs or ultra-sound). (Figure 4) These tests usually revealthe presence of renal disease, thyroid diseaseor both.

If your geriatric patient with retinal blindness isnot hypertensive, other causes of retinal blind-ness should be considered. Tests for felineinfectious peritonitis, FeLV antigen, toxoplas-mosis, and fungal diseases are appropriate.

******Using the Doppler Blood Pressure Monitor

The doppler blood pressure monitor detectsthe flow of blood in arteries. The radial, cranialtibial, and median coccygeal arteries are themost practical to monitor. Our preference isthe cranial tibial artery because the hair

clipping that is required is least noticeable.However, the other two arteries are accept-able and preferred by some. When the mediantibial artery is used, a 2-4 cm cuff is placedabove the hock. The width of the cuff is criticalwhen using oscillometric technology, but it isnot as critical with Doppler technology.

Stress is a significant factor that must be mini-mized to get meaningful blood pressure read-ings. Following an automobile ride to yourhospital, allow your patient a few minutes torest in a quiet place. Be sure your patient isnot exposed to dogs and other cats. If possi-ble, place your client and patient in a quietexamination room and have the owner holdand reassure it for a few minutes. The pres-ence of the owner is very helpful in relievingyour patient’s stress. Take advantage of this, ifpossible.

Simple Steps for Success

1) Assemble the Doppler unit before address-ing the cat. Plug in the headphones and placethe ear pieces over your ears.

2) Have the owner hold the cat on your exami-nation table. Placing a towel or blanket underthe cat can help make it more comfortable andmore relaxed.

3) Clip a 1 x 2 cm patch of hair immediatelyproximal to the tarsal pad or carpal pad or onthe ventral surface of the tail about 4-5 cmfrom the body, depending upon which artery isto be used. (Figure 5)

4) Position the cuff proximal to the hock, proxi-mal to the elbow, or at the base of the tail,depending upon which artery is to be used.

5) Turn on the unit and set the volume in thehigh range. If the volume is too low, arterialsound may not be detected.

6) Apply a thin coat of coupling gel to the skin.

7) Apply coupling gel to the ventral surface ofthe transducer.

8) Position the transducer over the artery. Themedian tibial artery is usually slightly medial tomidline. It will be necessary to move the trans-ducer until the swishing of the blood is heardin the artery. Hold it in place with your thumb.(Figure 6) It may be necessary to apply firmpressure to assure proper contact betweenthe transducer and the skin.

9) Squeeze the bulb on the manometer untilthe pressure in the cuff exceeds that of the

Figure 4:The small left kidney is typical of chronic renal disease in old cats.

Figure 6: The transducer is held in place with the thumb.Firm pressure is required; however, too much pressurecan close the artery.

Figure 5: Hair is shaved over the cranial tibial artery sothe transducer can make good contact with the skin.

Figure 7: The position of the needle on the manometer isnoted when the arterial swish returns.

artery. At that point the swishing of blood inthe artery will no longer be heard. (Figure 7)Note that filling the cuff too rapidly may frighten your patient.

10) Slowly bleed off the pressure in the cuff bysqueezing the manometer’s trigger. When thepressure in the cuff falls below the arterialpressure, the arterial swishing sound can beheard again. This should be noted and record-ed as the systolic pressure.

11) The conventional approach is for sevenmeasurements to be taken. Discard the high

and low readings and average the remainingfive. This is considered the systolic bloodpressure and is measured in mmHg.However, some stressed cats may relax dur-ing the course of the examination. These catswill have several readings at a higher level fol-lowed by several at a lower level. The formershould be ignored, and the latter consideredas the accurate ones.

The diastolic pressure can be detected insome cats by closely watching the dial of themanometer. It oscillates at the diastolic pres-sure level. However, a reproducible reading isnot always possible, especially in cats that arestressed due to catecholamine influence (thatmakes the vessels more stiff than normal),cats that are cold, and very small patients.However, the important measurement is sys-tolic blood pressure in the cat.

Technique Tips

Do not tape the transducer in place, as is rec-ommended by some. The slightest movementof the cat’s foot or leg will often move thetransducer enough that the arterial sounds arelost. Instead, hold the transducer in place withyour thumb. If the artery is lost, slight move-ment of your thumb can relocate it. This ismuch faster than having to untape and retape.

Firm pressure is required to make adequatecontact between the transducer and the skin.However, do not place too much pressure onthe transducer with your thumb or you willmechanically shut off the artery with the trans-ducer.

Use the maximal volume that is comfortable toyour ears. Too little volume may cause you tomiss the sounds.

Use the headphones. Although they aresomewhat cumbersome, they minimize thestress of the procedure. The sounds of theexternal speaker frightens many cats, elevat-ing

their blood pressure. The headphones bypassthe external speaker so the cat no longerhears the harsh sounds. (Figure 8)

Comfortably extend the cat's leg. If it is flexed,the blood flow through the artery may beabnormally restricted giving no readings orfalsely low readings. (Figures 9a, b)

You may notice that the blood pressure read-ings decline as you are making the sevenmeasurements. This means that the cat ismore comfortable and less stressed. Theseare actually more accurate readings, so dis-card the ones that were initially made.

The transducer is fragile (and expensive toreplace). It may be damaged by dropping it orby striking it against something solid. Treat itwith utmost care.

The use of ultrasound gel is essential for mak-ing good contact between the transducer andthe skin. However, do not use ECG paste orbaby oil. These products may cause deteriora-tion of the resin surface of the transducer.

Ultrasound gel is water soluble. Remove itfrom the transducer after each use.

Figure 8: Headphones are used to bypass the externalspeaker to prevent frightening the cat.

Treat the Underlying Disease

Cats with hyperthyroidism should be startedon methimazole (Tapazole). The average ini-tial dose is 5 mg q12h PO. Definitive treat-ment options for this disease are long-termmethimazole, thyroidectomy, and radioactiveiodine therapy. Most cats that are treated suc-cessfully for hyperthyroidism maintain a nor-motensive state without further specific bloodpressure therapy.

Cats with renal failure should be consideredfor further diagnostics, including an ultrasoundexamination, renal biopsy, and excretory uro-gram, to further delineate the etiology of therenal disease. However, geriatric cats withvery small kidneys are typically diagnosedwith end-stage renal disease or idiopathictubulointerstitial nephritis. Aggressive treat-ment for renal failure should commence. Asthe BUN and creatinine improve, blood pres-sure should be monitored. A few cats becomenormotensive and no longer need therapy forhypertension on a long-term basis.

Summary

Hypertension is a serious threat to geriatriccats because it is associated with two com-mon diseases of elderly cats; hypertensionand chronic renal failure. Blood pressuredeterminations should be performed on allaged cats for the purpose of early detection ofhypertension and on all cats with retinal dis-ease. Hypertension causes retinal blindnessand can easily complicate the signs of cardiacdisease and systemic metabolic disorders.

Other Uses for Blood Pressure Monitoring

A Doppler blood pressure monitor can also beused in the following situations:

1. As a surgical monitor: The transducer canbe taped in place during surgery so the pulsecan be audibly monitored in a hands-free fash-ion.

2. For suspected thromboembolic disease:Thromboembolic disease most often occurssecondary to hypertrophic cardiomyopathy. Ifblood flow impairment is suspected to anylimb, the Doppler can be used to determinethe blood flow in the distal artery of the limb. Ifa thrombus is present, the blood pressure willbe very low or zero.

3. For suspected vascular compromise to atraumatized limb or tail: The Doppler can beused in a similar manner as above when vas-cular impairment is suspected due to trauma.

4. For monitoring renal failure patients:Hypertension may be an ongoing disease incats that are undergoing treatment for chronicrenal disease. The only way to know ifhypotensive therapy is indicated and to prop-erly adjust the dose is to perform serial bloodpressure determinations.

Suggested Readings

Goodwin JK. Systemic Hypertension. In:Norsworthy GD, ed. The Feline Patient:Essentials of Diagnosis and Treatment.Philadelphia: Williams and Wilkins, 1998.

Thornhill JA. Hypertension, Systemic. In: TilleyLP, Smith FWK, eds. The Five Minute ClinicalConsult. Philadelphia: Williams and Wilkins,1997:706-707.

Jorgensen Laboratories, Inc.Loveland, Colorado