The use of low sodium diets associated with drugs such as diuretics and ACE inhibitors is common practice in dogs with heart failure. Since no studies have ever been conducted to examine the benefits or problems associated with this approach, veterinarians have based themselves on extrapolated data from the human since the 1960s in applying the restriction, and have begun to perform several studies in healthy dogs.
From these studies it was clear that the response to the administration of a low-sodium food could be very different in dogs with CHF, therefore, some authors recommended the administration of a low sodium diet at the first sign of heart disease.
The aim of this study was to determine the clinical, echocardiographic and neurohormonal effects of a low sodium diet compared to a moderate sodium diet in dogs undergoing medical therapy for heart failure.
Materials and methods
SUBJECTS
Dogs with stable CHF were studied without further pathologies, divided into 6 classes: (functional class II – IV modified by the New York Heart Association).
- class I dogs without any limitation, physical activity does not cause symptoms;
- class II slight limitation of physical activity, ordinary physical activity causes symptoms;
- class III marked limitation of physical activity, less effort than ordinary activity leads to symptoms;
- class IV inability to perform any activity without symptoms, symptoms present at rest;
Heart failure was secondary to dilated cardiomyopathy (DCM) or chronic valve disease (CVD).
The dogs were treated in a standardized way, as follows: category I (ACE inhibitor only at 0.5 mg / kg every 24 hours), category II (ACE inhibitor plus furosemide), category III (ACE inhibitor, furosemide and digoxin), category IV (furosemide, digoxin and ACE inhibitor at high doses [0.5 mg / kg every 12 hours]), category V (category 4 plus the addition of spironolactone) and category VI (category 5 plus the maximum dosage of furosemide). Within each category, furosemide was administered at the lowest possible dose to check for clinical signs. The owners agreed to feed their dogs exclusively with the studio’s diets without any other dog food or table food. After a complete physical examination, standard 2-D and M-mode echocardiograms were performed and the systolic volume index (ESVI) and diastolic volume index (EDVI) were calculated Lateral and dorsoventral thoracic radiographs were performed and vertebral cardiac scores were calculated. Venous samples were taken and urine samples obtained. After the analyzes, the dogs underwent the low sodium (LS) diet or the moderate sodium (SM) diet for 4 weeks each according to a randomized, double-blind, cross-over scheme. On days 0, 28 and 56, echocardiography and chest radiography were performed and blood was analyzed for electrolytes and neurormones.
RESULTS
Fourteen dogs completed the study (9 with CVD and 5 with DCM). Electrolyte abnormalities were a common finding during the study and serum sodium and chloride concentrations decreased significantly with the LS diet. Neurormones did not change significantly between diet groups.
Dogs with CVD responded differently to diet and other treatments than dogs with DCM. As a result, dogs with CVD were analyzed separately and serum sodium and chloride concentrations were found to decrease even more in the LS diet than in the MS diet.
The electrocardiographic and radiographic parameters did not show significant variations, while the echocardiographic parameters varied significantly.
DISCUSSION
Clinically, few changes have been observed between dogs who eat LS and MS diets. Both diets were found to be extremely palatable.
The LS and MS diets used in the present study appeared to be too low in magnesium to maintain normal serum concentrations of magnesium in 50% of dogs. In contrast, many commercial diets designed for dogs with heart failure (including those used here) contain high concentrations of potassium to compensate for the potential urinary loss of potassium due to the use of furosemide. The current widespread use of ACE inhibitors, which promote potassium retention, may require a re-evaluation of the optimal dietary content of potassium because both the present study and previous studies have identified hyperkalaemia as a frequent event with the use of ACE-inhibitors.
Echocardiographic changes supported a beneficial effect of the LS diet, but without data on mortality it is not possible to determine the long-term benefit of these results.
The reduction in heart size observed with the LS diet was most pronounced in dogs with CVD. However, these cardiac changes were not reflected in changes in neurohormone concentrations.
Although the drugs may have influenced neurohormonal concentrations, the study was designed to determine the effects of diet, rather than drugs, on measuring outcomes.
Recent data do not specify quantities in particular and rather focus on the percentage of sodium in the diet (i.e. moderately limited or severely limited). A similar method was used to select the sodium content of the 2 diets used in the present study.
A problem not addressed in this study is the role of chloride, which can also be important in clinical and neurohumoral responses in heart failure.
In the present study, the beneficial effects of the LS diet on cardiac size were much more pronounced in dogs with CVD than in dogs with DCM. Although some clinicians treat all dogs with CHF equally, the fundamental differences in these 2 diseases may require differentiated and tailored medical and nutritional therapy.
These divergences may be due to the fact that dogs with DCM took a much smaller difference in sodium during LS and MS diets than dogs with CVD, due to differences in calorie intake on a kcal / kg basis.
Numerous limitations may have influenced the current study. One factor is the small number of subjects due to the early termination of the study.
Another limitation is the fact that the sodium dosages provided by the LS and MS diets were not so markedly different.
Another limitation of this study was the use of clinical patients. Patients received a variety of drugs at different dosages and had different home environments, which, given the small sample size, may have introduced significant variability. Future studies should ideally use a larger sample size with a single cause of CHF to minimize variability. Finally, the results of this study may not be applicable to the general population of dogs with CHF. The dogs enrolled in this study were a selected population due to the need for exclusive feeding of the study’s diets for 8 weeks.
Even if future studies confirm the benefits of a low sodium diet in dogs with CHF, a more realistic approach may be needed to recommend a commercial dog food that also respects the owner’s animal management habits.