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Survival Study After Diagnosis of Feline Hypertension

October 23, 2018

Conroy M, Chang Yu-Mei, Brodbelt D, Elliott J. Survival after diagnosis of hypertension in cats attending primary care practice in the United Kingdom. J Vet Intern Med. 2018 Oct 13. doi: 10.1111/jvim.15307.

As part of Winn’s campaign focus on feline kidney disease, this retrospective study looks at hypertension as a common disease in older cats, with up to 13% of healthy cats ≥ 9 years of age being diagnosed with the condition. In other studies, the frequency increases to 87% when cats have concurrent disease.

Guidelines have attempted to standardize the hypertension definition based on estimated risk of target organ damage (TOD). The following lists the risk levels based on systolic blood pressure (SBP):

SBP  < 150 mm Hg = normotensive (minimal risk)
SBP  150-159 mm Hg = borderline hypertensive (low risk)
SBP  160-179 mm Hg = hypertensive (moderate risk)
SBP  ≥ 180 mm HG = severely hypertensive (severe risk)

The main underlying diseases associated with hypertension are chronic kidney disease (CKD) and hyperthyroidism. Idiopathic hypertension (no underlying concurrent disease present) is estimated to occur in up to 20% of cases. Managing and diagnosing hypertension early has a goal of decreasing the risk of TOD – which can occur in the brain, eyes, heart or kidneys. Ocular TOD is the most easily recognized condition associated with hypertension in clinical practice. Target organ damage can result in significant morbidity which includes blindness, ventricular hypertrophy, proteinuria, and hypertensive encephalopathy. Currently, amlodipine, a calcium channel blocker, is the most commonly administered medication recommended and used for treatment of hypertension due to its effectiveness at decreasing blood pressure in hypertensive cats.

As part of establishing these guidelines, the International Renal Interest Society (IRIS) staging for hypertension looks at survival time. Estimates for median survival time has previously been reported as being up to 490 days in cats that were not proteinuric at diagnosis compared to median survival time estimated to be 162 days in cats that were proteinuric at diagnosis. Urine protein: creatinine ratio has been found to be correlated with decreased survival when adjusted for IRIS stage at the time of diagnosis.

In light of the importance of blood pressure and a deficiency of information on hypertension in cats, the aims of this study were to estimate the proportion of cats in the UK receiving blood pressure assessment (BPA), describe cats diagnosed with hypertension, and investigate survival after diagnosis of hypertension in cats presented to primary care practices (PCPs) in the UK.

The authors found of the 347,889 cats presented to 244 PCPs for a two-year period from January 1, 2012 to December 31, 2013 that 8001 cats were identified as potentially having had their blood pressure assessed and 2442 (30.5%) of these cases were reviewed in detail. A blood pressure assessment was completed during the study period in 1445 (59.2%) of cats. This resulted in an estimated 1.34% of cats received BPA during this time period. In cats ≥ 9 years the percentage increased to 4.4%.  Over 90% of the cats were assessed using blood pressure measurements. The remainder was predicted to be normotensive or hypertensive by ocular examination or clinical signs alone.

Of the 1445 cats that had BPAs, 282 cats were diagnosed as hypertensive, resulting in an estimated incidence risk of 19.5%. Incidence increased with age and was higher in crossbred cats than in purebred cats. Most cats were found to be in the severe risk category (92.2%; 260) at diagnosis, 6.1%  (14) were in the moderate risk category and 0.9% (2) in the low risk category at the time of diagnosis.

Amlodipine was the most common treatment prescribed with the most common initial dose of 0.625 mg daily. A total of 43 (22.3%) of cats receiving amlodipine had a dose increase during follow up with the median time to dose change of 38 days. Other treatments used for blood pressure control were benazepril, or a combination of amlodipine and benazepril followed by propranolol, atenolol and enalapril, or no treatment at all.

The authors comment that the study shows 1 in 75 cats had BP assessed during the study period, increasing to just under 1 in 23 of cats ≥ 9 years. They suggest these findings indicated blood pressure measurement is not commonly used to screen cats known to be at risk of developing hypertension (eg, the aged cat, cats with CKD and those with hyperthyroidism). Recommendations were that cats with a diagnosis of CKD or hyperthyroidism or healthy cats ≥ 9 years to have regular blood pressure measurements because of increased risk of hypertension. An earlier diagnosis of hypertension may decrease the number of cats presenting with evidence of TOD, as noted in another study. A decreasing quality of life (QOL) can be the result of the harm hypertension creates with target organ damage. In this study, QOL was the most reported reason for euthanasia in many of the most severely affected cats. Early diagnosis of hypertension before associated clinical signs occur was found to have improved survival for cats. Regular blood pressure monitoring after diagnosis and institution of treatment was also recommended. (VT)

See also:
Bijsmans EJ, Doig M, Jepson RE, et al. Factors influencing the relationship between the dose of amlodipine required for blood pressure control and change in blood pressure in hypertensive cats. J Vet Intern Med. 2016 Sep;30(5):1630-163