Case 16 — Text
Text from “Small Animal Cardiovascular Medicine”
Systemic Hypertension
Etiology
By far the most common cause of systemic hypertension in dogs is renal disease. Renal disease and hyperthyroidism are the two most common causes of systemic hypertension in cats. The incidence of systemic hypertension in cats with renal failure ranges from 61% to 73%. Systemic hypertension ranges from mild to severe with most cats in the mild to moderate range (systolic 151–180 mmHg; diastolic 101–120 mmHg). Of 39 cats with hyperthyroidism from one study, 87% had systemic hypertension. In a study of dogs with renal disease, 61% had systemic hypertension. Of those with glomerular disease, 80% had systemic hypertension. In the same study, 59% of dogs with hyperadrenocorticism had systemic hypertension. Recent findings suggest that about 70% of dogs with diabetes mellitus have elevated systemic pressures. Pheochromocytoma is a rare cause of systemic hypertension in dogs.
Renal Failure
The mechanisms by which renal failure causes systemic hypertension in dogs and cats have not been adequately studied. In humans, an inability to excrete appropriate amounts of sodium and water with resultant hypervolemia appears to be the primary mechanism early in the course of renal disease although increased systemic vascular resistance may predominate in chronic renal failure. Reduced renal blood flow or localized renal ischemia leading to increased renin secretion also probably plays a role. However, dogs and cats with renal failure rarely have a clinically significant response to diuretic administration and administration of an ACE inhibitor often produces no or only a very mild response. Dogs and cats with systemic hypertension secondary to renal failure are more responsive to and often require agents that dilate systemic arterioles. Amlodipine is currently the favorite drug for treating cats with systemic hypertension due to renal failure. Prazosin, hydralazine, and possibly amlodipine are the most effective agents in dogs.
Table 26-2: Drugs Used to Treat Systemic Hypertension
| Drug | Line | % Success (estimate) | Expected Decline |
|---|---|---|---|
| ACE inhibitor | 1st | 50% | <10 mmHg |
| Diltiazem | 1st | 50% | <10 mmHg |
| Prazosin | 1st | 50% | 10–20 mmHg |
| Beta Blocker | 2nd? | ? | ? |
| Furosemide | 2nd? | ? | ? |
| Hydralazine | 3rd? | >90% | 10–50 mmHg |
| Amlodipine | 1st (Cats); 3rd? (Dogs) | >90% (Cats) | 40 mmHg (avg decrease in SBP) |
SBP = systolic blood pressure