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Approach to Hypertension

By Erika de Papp, DVM, DACVIM
internalmedicine@angell.org
angell.org/internalmedicine
617-541-5186

 

One of the biggest challenges facing veterinary practitioners attempting to manage hypertension in dogs and cats is accuracy of the measurement. Unless addressing a crisis in which target organ damage is believed to have been caused by hypertension, it is often best to take repeated blood pressure measurements over time, prior to instituting therapy. Currently, there is no device for indirect blood pressure measurement that has been validated for use in conscious dogs and cats. Additionally, given the known presence of “white coat” hypertension in many of our patients, this adds to the challenge of an accurate diagnosis.

Developing a standard approach to recording the blood pressure is important, keeping a few key concepts in mind. If at all possible, the patient should be in a quiet, calm environment. In an ideal situation, the patient either has the blood pressure obtained after being in a quiet room for five to 10 minutes prior to an exam or has a visit dedicated solely to checking the blood pressure. In most cases, it is best if the client is present to help keep the patient relaxed. The cuff should be as close to the heart base as possible with respect to vertical distance, so the patient is often best kept in sternal or lateral recumbency. The tail can be a useful appendage since it is close to the heart base and many patients are resistant to manipulation of their feet and forelegs. In our hospital, we find the Doppler technique to be most reliable, and less affected by mild motion than the oscillometric methods such as the Petmap. However, it is important that the person operating the machine is comfortable with whatever technology they choose. When choosing a cuff size, the width should be 30-40% of the circumference of the site being used. We attempt to get at least three reliable readings during a single session, and average these to determine the value that is recorded in the record. The ACVIM consensus statement from 2018 recommends five to seven readings, throwing out the first reading of the session. The average of the readings or all readings is recorded, as well as the machine used, the site of the measurement, and the cuff size. This is crucial so that subsequent measurements are consistent. If the animal is particularly agitated, this is also recorded in the patient record. For patients in which anxiety precludes getting an accurate reading but for whom we have significant concerns, we will often recommend trying to have a house-call vet come to the client’s home to see if a more meaningful result can be obtained.

Hypertension is defined as a sustained increase in systolic blood pressure. Once it has been established that a patient is hypertensive, the type of hypertension must then be determined:

  1. Situational, or “white coat,” hypertension
  2. Secondary; associated with a disease, drug side effect, or toxin exposure
  3. Idiopathic, or essential, hypertension

The diseases most commonly associated with hypertension in dogs include chronic kidney disease, protein-losing nephropathy, hyperadrenocorticism (naturally occurring and iatrogenic), obesity, and pheochromocytoma. Less commonly, we see primary hyperaldosteronism, diabetes mellitus, and hypothyroidism as causes.

In cats, the common causes of hypertension are chronic kidney disease, hyperthyroidism, hyperaldosteronism, obesity, and diabetes mellitus.

Drugs that are commonly associated with secondary hypertension include glucocorticoids, erythropoietic agents, phenylpropanolamine, and phenylephrine.

Hypertension can result in damage to organs, referred to as target organ damage (TOD). The specific tissues most at risk include the kidneys, brain, heart and vasculature, and eyes. Unfortunately, many of our patients don’t present for treatment until they have already sustained target organ damage. Patients that present with signs of target organ damage and patients that have diseases associated with secondary hypertension or are on medications associated with hypertension all fall into the population of patients in which blood pressure should be monitored.

Because of the difficulty in obtaining accurate measurements and the low known incidence of hypertension in young, healthy animals, the ACVIM consensus statement does not recommend routine monitoring of blood pressure in healthy young patients. However, due to the possibility of occult diseases in the geriatric population, it is reasonable to institute routine screening in dogs and cats at age nine and above. At this time, in our hospital, we routinely measure blood pressure in hospitalized patients, but most of the outpatients only routinely have blood pressure monitored if there is underlying disease or suspected TOD.

The following algorithm has been set forth by the ACVIM for monitoring at-risk patients.

Treament

Once hypertension has been identified and the decision has been made to move forward with treatment, there are a number of drug classes that can be used. Renin-angiotensin-aldosterone system (RAAS) inhibitors are often the first-choice antihypertensive agents in dogs. Within this category, the ACE inhibitors have been used most frequently (see chart for dosing). An alternative choice would be an angiotensin receptor blocker (ARB) such as telmisartan, and we sometimes use these drugs concurrently, particularly in dogs with significant proteinuria that is not responsive to single-agent therapy.

Calcium channel blockers (amlodipine) are also effective antihypertensive agents, but their use as sole agents in dogs is not recommended due to the fact that they cause preferential dilation of the afferent arterioles in the kidney, which may result in increased glomerular capillary pressure and subsequent glomerular damage. The initial use of amlodipine in conjunction with an ACE inhibitor or ARB is often instituted if hypertension is severe (SBP > 200 mmHg).

Due to dilation of the efferent arterioles caused by the RAAS inhibitors, we recommend checking a renal panel one week after instituting therapy or after a dose increase, due to the possibility of reduced GFR and progressive azotemia, especially since many of these patients have renal disease.

For dogs (and cats) in which pheochromocytoma is the known or suspected cause of hypertension, an alpha blockade with phenoxybenzamine is the treatment of choice.

The use of amlodipine in cats as a first-line antihypertensive agent is recommended based on known efficacy. The ACVIM recommends a starting daily dose of 0.625mg for cats with systolic blood pressure < 200 mmHg, and 1.25mg for cats with BP > 200 mmHG, irrespective of size.

Recently, the FDA approved telmisartan, marketed as Semintra, for treating hypertension in cats. A double-blinded placebo controlled trial in Europe showed a statistically significant reduction in blood pressure in the telmisartan treated group compared to placebo in cats with naturally occurring hypertension. Telmisartan has not been used enough clinically in the U.S. yet to know if it will become the favored antihypertensive agent for cats.

Diuretics are often used for treatment of hypertension in human medicine, but are not recommended as first-line drugs for cats and dogs, especially since many of our patients have renal disease and are often already dehydrated.

In cats with known or suspected hyperaldosteronism, treatment with an aldosterone antagonist such as spironolactone is recommended. However, amlodipine is often started initially or concurrently for adequate blood pressure control.

Beta blockers are often used in hyperthyroid cats, especially in the face of severe tachycardia and cardiac dysfunction with hypertrophic cardiomyopathy.

Emergency management is needed in patients that present with acute and sometimes life-threatening signs of TOD, such as seizures, collapse, acute blindness, severe arrhythmias, etc. These cases should be referred to a 24-hour emergency facility for parenteral therapy and careful monitoring, to achieve a sustained but controlled reduction in blood pressure.

The chart following is adapted from the ACVIM consensus statement as an easy reference guide for commonly used oral antihypertensive agents for both dogs and cats.

Class Drug Usual oral dosage
Angiotensin converting enzyme inhibitor Benazepril D: 0.5 mg/kg q12‐24h
C: 0.5 mg/kg q12h
Enalapril D: 0.5 mg/kg q12‐24h
C: 0.5 mg/kg q24h
Angiotensin receptor blocker Telmisartan C: 1 mg/kg q24h
D: 1 mg/kg q24h
Calcium channel blocker Amlodipine D/C: 0.1‐0.25 mg/kg q24h
(up to 0.5 mg/kg in cats and dogs)
C: 0.625‐1.25 mg per cat q24h
α1 blocker Phenoxybenzamine D: 0.25 mg/kg q8‐12h or 0.5 mg/kg q24h
C: 2.5 mg per cat q8‐12h or 0.5 mg/cat q24h
Aldosterone antagonist Spironolactone D/C: 1.0‐2.0 mg/kg q12h
β blocker Propranolol D: 0.2‐1.0 mg/kg q8h
(titrate to effect)
C: 2.5‐5 mg/cat q8h
Atenolol D: 0.25‐1.0 mg/kg q12h
C: 6.25‐12.5 mg/cat q12h

Once therapy has been instituted, it is recommended to recheck the blood pressure again for clinically stable patients in approximately one week and adjust dosing as needed. If at all possible, it is useful to have the same doctor or technician perform the repeat measurement for consistency.

Blood pressure measurement remains a challenging task in veterinary medicine, especially in light of situational hypertension. However, when combining the results of repeated measurements with the clinical picture, we stand to gain valuable information for our patients and have a greater chance of meaningful therapeutic intervention prior to development of significant TOD. As more widespread use of newer therapeutics comes into play, additional recommendations are sure to be forthcoming.

 

References

  1. J Vet Intern Med 2018; Aug 29; 1-20. ACVIM Consensus statement: Guidelines for the identification, evaluation, and management of systemic hypertension in dogs and cats. Acierno MJ, Brown S, Coleman AE, et al.
  2. J Vet Intern Med 2018; Dec 18. Efficacy of long-term oral telmisartan in cats with hypertension: Results of a prospective European clinical trial. Glaus TM, Elliott J, Herberich E, et al. 307.
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