Dear Dr. Amy,
My friend, Sarah, was recently surprised when her older Siamese companion developed sudden blindness. She also has been losing weight and drinking more than usual. Her vet diagnosed her with kidney disease and retinal detachments related to high blood pressure. I didn’t realize pets could have issues with their blood pressure. Can you explain this to me?
Susan in Wesley Chapel
Hypertension (high blood pressure) is a common and silent danger in pets, often underdiagnosed, but can lead to many secondary problems, including accelerated kidney damage, thickening of the left ventricle of the heart (a heart condition called hypertrophic cardiomyopathy), retinal detachments and retinal hemorrhages (leading to sudden blindness), and even blood clots causing strokes and embolisms in the lungs.
The good news is that blood pressure is easy, painless, quick and inexpensive to evaluate by using a small indirect Doppler device with a pediatric sized blood pressure cuff. The most common locations on the body to measure are the front “wrist”, above the rear “ankle” and occasionally under the base of the tail (less accurate but easier in some patients).
Most folks have heard “120 over 80” for humans. The 120 is the systolic number – the highest pressure moment when blood is released from the heart into circulation. The second diastolic number occurs between the pulses. Usually cats range from 90 to 140 mmHg systolic, but nervous felines may be 140 to 170 mmHg. Any finding over 180 mmHg (some are up to 240!) should be treated to avoid blindness, stroke and heart disease. Dogs tend to range between 80 to 120 mmHg; readings over 160 are significant.
High blood pressure in cats is often secondary to hyperthyroidism (an overactive thyroid gland) or kidney disease. Dogs often have kidney disease or Cushing’s disease (hyperadrenocorticism). Recent studies are revealing that 25 percent of diabetic patients have high blood pressure as well. Dogs also can have a true primary hypertension called idiopathic (medical term for “cause unknown”) without an underlying cause.
Cats also can develop secondary heart changes called hypertrophic cardiomyopathy (a thickening of the heart muscle). HCM is the most common form of heart disease in cats, and can be over diagnosed by not identifying high blood pressure as a primary cause. Some HCM cats may be able to stabilize and avoid specific heart medications if blood pressure is medically managed first.
The good news is treatment is elegantly simple. The two most common oral blood pressure drugs in dogs and cats are the calcium channel blockers amlodipine and Ace-inhibitor benazepril.
Norvasc works as a calcium channel blocker by relaxing blood vessels and reducing the intensity of the heart contractions allowing blood to flow more easily. Personally, my clinical goal for cats is a heart rate below 180 blood pressurem (beats per minute) and blood pressure below 160 mmHg. For dogs, a clinical goal of a blood pressure below 140 mmHg is reasonable.
Benazepril is often used in dogs and cats with concurrent kidney or heart disease. In fact, benazepril is benefiting geriatric felines affected by three common diseases that often occur together: kidney disease, HCM, and hypertension. ACE-inhibitors also are a first choice for most canine heart conditions in vet med, as it helps to prevent congestive heart failure, additional heart muscle damage from enzymes (TNF) that accelerated heart disease, and increases survival time.
Most cases of high blood pressure in cats and dogs are related to an underlying primary cause and only with proper management of other conditions can the hypertension be controlled. All patients over the age of 7 in dogs and 10 in cats can benefit from screening twice yearly for blood pressure with regular exams.
If a patient has high blood pressure, owners should avoid meds that raise blood pressure (phenylpropanolamine for urinary incontinence, certain asthma drugs, and steroids). Avoid high salt treats and semi-moist foods that can increase fluid retention and blood pressure rates. This simple and inexpensive screening will create significant benefits for patients who are diagnosed early before more serious damage and problems occur.