Systemic Hypertension

Introduction

Hypertension is defined as the pathological elevation of arterial blood pressure. There are two main types of hypertension, systemic hypertension (affects the systemic circulation) and pulmonary hypertension (affects the pulmonary circulation). This article will cover systemic hypertension. Blood pressure in veterinary patients is not measured routinely; therefore hypertension is usually only diagnosed after clinical signs become apparent.

Primary systemic hypertension is an idiopathic increase in arterial blood pressure. Secondary systemic hypertension is an increase in arterial blood pressure secondary to a pathological process.

The ocular system, cardiovascular system, and nervous system are the most vulnerable to elevated arterial blood pressures. However, some endocrine disturbances have also been found to predispose animals to hypertension.

Signalment

Dogs: male > female; obese animals; middle to old age

Cats: middle to old age.

Clinical Signs

Signs are the result of ischemia, oedema, and/or haemorrhage of the affected areas, so are specific to the affected area.

Neurological signs include depression, seizures, syncope, paresis, vestibular signs and ataxia. Cardiac signs include left ventricular hypertrophy, heart failure, systolic murmur and gallop rhythms. Ocular signs are common especially in cats, where this is often the first noted clinical sign. Retinal detachment, degeneration or haemorrhage as well as blindness are features of the disease here. Renal signs include proteinuria. Kidney disease can be caused by hypertension, but can also be the cause of hypertension. Chronic renal failure is the most common cause of hypertension showing clinical signs in dogs and cats. Endocrine signs include hyperthyroidism (cats) and hyperadrenocortiscm and diabetes mellitus is dogs.

Diagnosis

History and clinical signs may be suggestive of the disease, so upon physical examination a blood pressure measurement should be taken. Systolic pressure > 175mmHg indicates hypertension in a relaxed dog or cat and diastolic pressure > 100mmHg indicates hypertension in a relaxed dog or cat. However, most cats and many dogs are not relaxed when in the veterinary clinic environment so accurate readings can be difficult.

Methods of measuring blood pressure are the direct method, which is invasive. This uses an indwelling catheter to measure systolic, diastolic, and mean arterial pressures. This is usually saved for very ill patients or those undergoing anaesthesia. The indirect and non-invasive methods are Doppler Flow Technique which is good for large dogs, but very inaccurate for cats. Also the Oscillometric Technique which is best for small dogs and is good for cats too.

Treatment and Control

Cats:

Treat the underlying problems first. Pharmacological treatment can be by calcium channel blockers (e.g. amlodipine). Blood pressure should be monitored regularly.

Dogs:

Again, treat the underlying cause and monitor blood pressure. Dogs with renal disease have a range of pharmacological options that can be used in controlling the disease. These include ACE-inhibitor e.g. enalopril, given alone or in combination with some of the other treatments listed next. Calcium channel blocker e.g. amlodipine, sodium restricted diet, beta blockers (e.g. atenolol), diuretics e.g. furosemide and vasodilators e.g. enalopril.

Prognosis

Cats with hypertension are more successfully treated than dogs.

References

Ettinger, S.J. and Feldman, E. C. (2000) Textbook of Veterinary Internal Medicine Diseases of the Dog and Cat Volume 2 (Fifth Edition) W.B. Saunders Company

Ettinger, S.J, Feldman, E.C. (2005) Textbook of Veterinary Internal Medicine (6th edition, volume 2) W.B. Saunders Company

Merck & Co (2008) The Merck Veterinary Manual (Eighth Edition) Merial

Nelson, R.W. and Couto, C.G. (2009) Small Animal Internal Medicine (Fourth Edition) Mosby Elsevier