by Dr. Jeremy Orr, DVM, DVSc, Diplomate ACVIM, Cardiology
One of the most common questions veterinary cardiologists receive from both their clients and referring veterinarians are the options for medical therapy for those patients with asymptomatic heart disease. At the present time, we estimate that as much as 10% of the canine population is affected by heart disease. Many of us are comfortable with therapy once clinical signs develop (congestive heart failure) but admittedly there are many differing opinions on how to manage those patients in their occult phase of their disease. Unfortunately, evidence based medicine for therapeutic options for asymptomatic patients is largely lacking. However, there have been some recent exciting new options for Dobermans with occult dilated cardiomyopathy (DCM) and I wanted to take the opportunity to not only present this information, but summarize what we know about therapies for other forms of heart disease in our canine patients.
Dilated Cardiomyopathy (DCM)
DCM is a devastating myocardial disease which most commonly afflicts larger breed dogs, with the Doberman Pinscher being over-represented. In the Doberman, we know the disease is characterized by a prolonged occult phase (2-3 years) before overt clinical signs of heart failure (dyspnea, exercise intolerance, syncope) develop. Once heart failure develops, the prognosis is grave with average survival times reported at 2-4 months, with a 90% fatality rate by 1 year post diagnosis. Given the prevalence of DCM in the Doberman breed (estimated at 25-50% of adult dogs affected), the current recommendation is to screen Dobermans (especially those with familial history of disease, or those with recently acquired murmurs or arrhythmias) with echocardiography annually after the age of 5 years. New advances in echocardiography such as Tissue Doppler imaging (which assesses the speed of wall motion) have allowed earlier detection of dogs with occult disease. The utility of this screening is that we may identify those patients with early evidence of disease in an effort to delay their progression, especially given the grave prognosis even with supportive therapy once symptoms develop. A retrospective study in 2009 demonstrated that therapy with benazepril (0.5 mg/kg dose once daily) in the occult phase of disease significantly delayed the onset to overt disease compared to those dogs who did not receive benazepril (454 versus 356 days)1. These results are similar to the human literature where ACE inhibitors are an important therapeutic option for those patients with asymptomatic ventricular dysfunction. Recently, the multi-center prospective, placebo controlled and blinded study PROTECT revealed a significant delay to heart failure or sudden death (718 days versus 441 days) for Dobermans receiving pimobendan at standard dosages (0.25 mg/kg dose twice daily) versus those receiving placebo2. Furthermore, the study also showed that the median survival time was significantly longer in the pimobendan versus the placebo group (623 versus 466 days). These two studies demonstrate the importance of early detection of occult disease as it provides an opportunity to prolong the lives of affected Dobermans. This extra time is significant, especially given the poor prognosis once symptoms develop.
These results may apply to Dobermans only and future studies evaluating these claims in non-Doberman breeds will likely be lacking. Presently there is a study evaluating pimobendan in Irish Wolfhounds with occult DCM and results thus far have been encouraging with a survival benefit for dogs receiving pimobendan. For this reason, I still consider these therapeutic options in non-Doberman breeds with occult DCM.
1. O’Grady MR, O’Sullivan ML, Minor SL, Horne R. Efficacy of benazepril hydrochloride to delay the progression of occult dilated cardiomyopathy in Doberman Pinchers. J Vet Intern Med 2009; 23: 977-983.
2. Summerfield NJ, Boswood A, O’Grady MR, et al. Efficacy of Pimobendan in the prevention of congestive heart failure or sudden death in Doberman Pinschers with preclinical dilated cardiomyopathy (the PROTECT study). J Vet Intern Med 2012; 26:1337-1349.