Systemic hypertension (SH) – a persistent increase in the systemic blood pressure – is now commonly recognised in clinics. Older cats are at an increased risk of developing SH (Bijsmans et al., 2015) and a recent study found the estimated incidence risk of hypertension for cats aged nine and above to be 23.7 percent (Conroy et al., 2018).
Types of hypertension
Secondary SH is most commonly diagnosed in cats with underlying medical conditions – in particular, CKD and hyperthyroidism – while idiopathic (primary) SH accounts for less than 20 percent of cases. Situational (white coat) hypertension is when “false positive” high blood pressure readings occur due to stress. On average, the “white coat” effect increases systolic blood pressure (SBP) by 15 to 20mmHg, but one study showed this effect is highly variable, with SBP decreasing in some cats and increasing as much as 75mmHg in others (Belew et al., 1999).
Given the potentially life-threatening consequences of genuine hypertension, attention should be given to looking for target organ damage (TOD) alongside high readings to confirm genuine hypertension and for high readings not to be assumed to be due to situational hypertension. The target organs most vulnerable to hypertensive damage are the eyes, brain, kidneys and heart.
Recently, the American College of Veterinary Internal Medicine published a classification system based on blood pressure and the associated risk of TOD (Table 1).
The author follows icatcare’s guidelines for preventative healthcare, which recommend 6- to 12-monthly SBP assessment in healthy cats from the age of seven years (catcare4life.org). Blood pressure should also be assessed in cats that present with:
- Ocular disease (blindness, hyphaema, retinal detachment/oedema)
- Associated diseases – particularly CKD and hyperthyroidism; unexplained proteinuria
- Cardiac abnormalities (murmur, gallop, left ventricular hypertrophy)
- Behavioural or neurological signs – especially in older cats
The author recommends Doppler measurement of blood pressure where possible, in conscious cats. Oscillometric machines tend to overestimate low blood pressure and underestimate high blood pressure in cats. If choosing an oscillometric machine, an HDO (high definition oscillometry) machine is recommended. A full ocular examination is essential to look for evidence of TOD (Figures 1 and 2).
Using a Doppler machine in conscious cats
Sites to measure SBP include the common digital artery (forelimb) and coccygeal artery (tail). An inflatable cuff (30 to 40 percent of the limb/tail circumference) is placed. Clipping is not required.
Prepare the area by wiping with surgical alcohol and then apply a liberal quantity of ultrasound coupling gel to the area and to the Doppler probe. Place the probe over the prepared area, turn the machine on and gently move the probe over the skin until a signal is detected. Do not apply excessive pressure as this could impede blood flow. Once regular pulsatile blood flow is heard, inflate the cuff to 20 to 30mmHg above the point where the sound of blood flow is obliterated. Deflate the cuff slowly. The point at which blood flow can first be detected clearly and consistently again is the SBP. Deflate the cuff completely and repeat five times over two to three minutes; calculate the average SBP.
Management of hypertensive cats
A high SBP (greater than 160mmHg) in addition to evidence of TOD is diagnostic for SH; treatment should commence immediately. Persistently high SBP (greater than 160mmHg on three occasions over a two-to four-week period) is also consistent with a diagnosis of SH and treatment is justified, especially if the cat is known to have underlying diseases which increase the risk of SH. SBP readings above 180mmHg are especially worrying with respect to risk of future TOD. Anti-hypertensive agents used include:
Calcium channel blocker
- Amlodipine 0.625 to 1.25mg/cat q24h
- Typically reduces SBP by 30 to 70mmHg (Taylor et al., 2017)
- Considered first choice treatment (Acierno et al., 2018)
Angiotension receptor blocker
- Telmisartan 2 to 3mg/kg q24h as sole therapy
- Typically reduces SBP by 20mmHg (Glaus et al., 2018)
- Can be used in combination with amlodipine (1mg/kg/day telmisartan plus standard dose of amlodipine
The aim of management is to reduce SBP readings to an “ideal” reference range (120 to 140mmHg) and to identify and treat potential underlying/associated conditions (such as CKD). Earlier diagnosis helps to reduce the incidence of life-limiting and life-threatening TOD. Amlodipine is the current treatment of choice for severe hypertension and many cats can be successfully managed on a once-a-day dose of this medication.
A recently published retrospective study found 57.6 percent of cats blind at presentation regained some vision following treatment (Young et al., 2018) and even in those cats with blindness and other significant hypertensive TOD, clinical improvement is often reported as an improved quality of life.