Facts Hypertension (HTN), also called high blood pressure or arterial hypertension, is a medical condition that describes elevated blood pressure in a dog’s arteries. When a dog has high blood pressure, its heart has to work harder than normal to circulate blood through its body. The condition may be either primary or secondary HTN: primary hypertension is diagnosed when there is no underlying cause; and secondary hypertension is diagnosed when another disease or illness causes the high blood pressure. HTN can refer to elevated systolic blood pressure, diastolic blood pressure, or both. Systolic is the pressure in the blood vessels when the heart muscle is contracting and diastolic is the pressure in the blood vessels when the heart is relaxed between contractions. It is impossible to accurately measure diastolic pressure in dogs without inserting a catheter into one of its arteries, so only systolic is measured. In domestic dogs, the systolic measurement should not be above 160. High blood pressure is a worry because of the potential damage to the blood vessels, potential ruptures and bleeding, and embolism. A dog’s eyes and kidneys are particularly vulnerable if it has HTN, because of the tiny blood vessels that supply these organs.
Causes Vets don’t know what causes primary hypertension. There may be genetic factors. Primary hypertension is very rare. Secondary hypertension is, by definition, high blood pressure caused by or resulting from another disorder or medical condition. Most cases of hypertension in dogs are of this type. Some possible causes include hyperthyroidism, Diabetes mellitus, Cushing’s Disease, acromegaly, polycythemia, glomerular disease, advanced renal disease, and diseases that involve the renal glands. Systems that can also be affected by high blood pressure are the eyes, renal glands, liver, and lungs. Some medications may also cause secondary HTN. Other potential causes include anxiety or stress, severe pain, or a high-salt diet.
Prevention There is no way to effectively prevent primary high blood pressure in dogs. Secondary HTN can be prevented if the underlying cause is prevented. At the very least, this form may be treated, managed, or cured when the originating cause is treated.
Symptoms Dogs with hypertension will often not show any symptoms. Dogs who have long-term HTN may develop one or more signs of the condition, including blood in the urine, dilated pupils, ocular hemorrhage, retinal detachment, nose bleeds, circling, enlarged kidneys, abnormally small kidneys, seizures, acute onset of blindness, partial paralysis, ataxia, protein in the urine, disorientation, heart murmurs, and enlarged thyroid gland. If you think your dog’s vision has changed, or notice a change in the appearance of your dog’s eyes, get it to a vet immediately.
Dogs at Risk Older dogs are more at risk than younger dogs when it comes to developing high blood pressure. The most common causes of secondary hypertension are kidney, thyroid, liver, or endocrine disease, and the dogs that develop these medical conditions are at higher risk. Both males and females can develop HTN. Greyhounds tend to have a higher-than-normal blood pressure compared to other breeds; the cause for this is unknown.
Testing and Diagnosis There are two ways to diagnose high blood pressure in dogs: direct and indirect. Direct measurement is highly invasive, since it requires placing a catheter into one of the dog’s arteries and measure the pressure of the blood flowing through the artery. This can be uncomfortable for the dog, but it is the most accurate way to measure the blood pressure. With indirect measurement, an inflatable cuff is placed around the base of the tail or a lower limb of the dog. The tail or limb is held still near heart level of the dog by a technician while the vet measures the pressure using a mechanical or digital blood pressure monitoring device. Alternatively, blood pressure may be measured using an ultrasound Doppler flow pressure monitor. It should be noted that dogs, just like humans, can suffer from “white coat syndrome,” a case where a dog’s blood pressure rises due to the trip to the vet clinic. Blood pressure should be taken at the end of a visit rather than at the beginning, to allow the dog to become accustomed to its environment and the vet. Additionally, a series of tests – usually five – are compared to determine a diagnosis of high blood pressure, in case one or more of the results are artificially high due to stress.
Treatment and Prognosis Treatment for high blood pressure usually involves a two-prong approach: first, the underlying cause should be controlled or cured, if possible. That will often cause the blood pressure to return to normal. Secondly, the high blood pressure itself should be treated. In animals with extremely high blood pressure, or in animals where the underlying cause is not treatable, the hypertension must be treated immediately to reduce the risk to the organs. Some possible treatment protocols for high blood pressure may include dietary modification, exercise restriction, surgery, or blood pressure-lowering medications. Prognosis for dogs with high blood pressure depends upon the initial cause for the condition, the amount of time the dog suffers from HTN before it is diagnosed and treated, and the success of the treatment itself.