Dogs with mitral valve disease
Cardiac disease in many dogs remains asymptomatic for long periods, often years. This is especially true in dogs with mitral
valve endocardiosis. Previously, little benefit has been shown in starting treatment in these dogs before CHF onset. If it
were possible to predict that CHF would occur in the near future, owners could be more vigilant for the typical signs, and
treatment would be started. A multicenter study presented at the ACVIM Forum looked at the ability of NT-proBNP to predict
the onset of CHF.3
Sixty-six dogs that had mitral valve endocardiosis and an enlarged left atrium were included in the study. The dogs underwent
a complete cardiac workup every two to nine months. The dogs were followed, on average, for 276 days, with some being monitored
for more than four years.
During the study period, almost half the dogs developed overt CHF with radiographic evidence of pulmonary edema. The researchers
looked at the data from the visit immediately before CHF developed to see what parameters would be predictive of impending
CHF in comparison with those visits in which CHF did not develop. NT-proBNP concentrations were significantly different, with
a median concentration of 3,001 pmol/L and an interquartile range (IQR; middle 50 percent of results) of 2,255 to 3,001 prior
to CHF, and a median of 1,600 IQR of 984 to 2,863.
Not surprisingly, it also was discovered that heart size was predictive of CHF development. Dogs that developed CHF had, on
average, a bigger left atrium, higher vertebral heart score and higher ratio of left ventricular internal diameter in diastole
to aortic diameter. Using a cutoff of > 2,150 pmol/L for NT-proBNP, sensitivity for detecting impending CHF was 77.4 percent
and specificity was 68.6 percent. Within six months, 36 percent of dogs that had a concentration greater than 3,000 pmol/L
went on to develop CHF.
The results of this study are, in a way, not surprising. With mitral valve endocardiosis, there's a progressive increase in
heart size until failure occurs, often after many years. As the heart enlarges, stretch occurs, which results in increased
release of NT-proBNP by the myocytes. The more the heart is stretched, the higher the BNP and, of course, the bigger the heart
on imaging studies. The ability to measure some of the parameters is dependent on a high-quality and reproducible echocardiogram.
Vertebral heart score is a relatively crude method to assess the heart and, as such, would be difficult to use as a predictive
test in individual patients.
This study suggests that NT-proBNP can be useful in practice to assess the likelihood that CHF will develop in the near future.
In dogs with very high concentrations or a steep increase in NT-proBNP concentrations between visits, CHF is much more likely
to develop in the near future. This means owners need to be reminded to monitor closely for signs of CHF, such as weakness,
exercise intolerance and especially cough. If these signs develop, it's vital the owner present the pet to a veterinarian
as soon as possible for evaluation, since it's likely these signs are indicators that the heart is beginning to fail and treatment
should be instituted. However, given that even with the highest concentrations, only one-third of the dogs went on to develop
CHF within six months, high NT-proBNP concentrations are not sufficient reason alone to start treating mitral valve endocardiosis.