• Open Access

Effect of Pimobendan or Benazepril Hydrochloride on Survival Times in Dogs with Congestive Heart Failure Caused by Naturally Occurring Myxomatous Mitral Valve Disease: The QUEST Study


  • The planning of the QUEST trial was started in 2002. The trial protocol was finalized at an investigator meeting in September 2003. There was a follow-up meeting in September 2005, and the submitted manuscript was finalized and approved by the investigators at a meeting in December 2007. The QUEST trial publication committee consisted of Jens Häggström, Adrian Boswood, Michael O'Grady, and Olaf Jöns. The study was funded by Boehringer Ingelheim Animal Health GmbH.

Corresponding author: J. Häggström, DVM, PhD, Faculty of Veterinary Medicine and Animal Science, Swedish University of Agricultural Sciences, Uppsala, Sweden; e-mail: jens.haggstrom@kv.slu.se.


Background: Myxomatous mitral valve disease (MMVD) continues to be an important cause of morbidity and mortality in geriatric dogs despite conventional therapy.

Hypothesis: Pimobendan in addition to conventional therapy will extend time to sudden cardiac death, euthanasia for cardiac reasons, or treatment failure when compared with conventional therapy plus benazepril in dogs with congestive heart failure (CHF) attributable to MMVD.

Animals: Two hundred and sixty client-owned dogs in CHF caused by MMVD were recruited from 28 centers in Europe, Canada, and Australia.

Methods: A prospective single-blinded study with dogs randomized to PO receive pimobendan (0.4–0.6 mg/kg/d) or benazepril hydrochloride (0.25–1.0 mg/kg/d). The primary endpoint was a composite of cardiac death, euthanized for heart failure, or treatment failure.

Results: Eight dogs were excluded from analysis. One hundred and twenty-four dogs were randomized to pimobendan and 128 to benazepril. One hundred and ninety dogs reached the primary endpoint; the median time was 188 days (267 days for pimobendan, 140 days for benazepril hazard ratio = 0.688, 95% confidence limits [CL] = 0.516–0.916, P= .0099). The benefit of pimobendan persisted after adjusting for all baseline variables. A longer time to reach the endpoint was also associated with being a Cavalier King Charles Spaniel, requiring a lower furosemide dose, and having a higher creatinine concentration. Increases in several indicators of cardiac enlargement (left atrial to aortic root ratio, vertebral heart scale, and percentage increase in left ventricular internal diameter in systole) were associated with a shorter time to endpoint, as was a worse tolerance for exercise.

Conclusions and Clinical Importance: Pimobendan plus conventional therapy prolongs time to sudden death, euthanasia for cardiac reasons, or treatment failure in dogs with CHF caused by MMVD compared with benazepril plus conventional therapy.