Collapse, syncope, and exercise intolerance occur intermittently and are typically described by the owner rather than the clinician; therefore, identification of a cause can be difficult. As a result, only 40% to 50% of such dogs are assigned a final diagnosis. This study assessed the long-term outcome for dogs that presented with collapse, syncope, or exercise intolerance. Clinical records of dogs evaluated for syncope or collapse or those that underwent electrocardiogram screens were examined from 2 veterinary practices. Owner telephone interviews were used for follow-up. Dogs were classified into 4 groups based on clinical history: collapse, syncope, exercise intolerance, and dogs that did not fit the previous categories. A total of 177 cases with collapse (n = 59), syncope (n = 59), exercise intolerance (n = 38), and other episodes (n = 21) were included in the study; etiology was unknown. Follow-up was available for 153 of the cases. Collapse was most commonly seen in Labrador retrievers and border collies, syncope in boxers, and exercise intolerance in Labrador retrievers. Resolution of clinical signs occurred in 64 cases, continued clinical signs were noted in 35 cases, a diagnosis was made or treatment was initiated in 17 cases, and 37 dogs died (18 deaths likely associated with the original presentation). Death and clinical deterioration related to collapse problems were associated with 16.2% of cases. Death was significantly more common in boxers (36%) compared with other breeds; death and clinical deterioration without a definitive diagnosis were not frequently seen in dogs other than boxers.

Commentary: Results from this study can definitely assist in the prediction of clinical outcomes in canine patients that present with collapse without a definitive diagnosis. This is valuable predictive information for the veterinarian presented with a collapsing dog and no diagnosis, but should not substitute for an adequate clinical workup in collapse patients. It also behooves the clinician to exercise a more aggressive diagnostic and therapeutic course for boxers with collapse, syncope, and exercise intolerance.—Indu Mani, DVM, DSc

A retrospective study of 153 cases of undiagnosed collapse, syncope, or exercise intolerance: The outcomes. Barnett L, Martin MWS, Todd J, et al. J SMALL ANIM PRACT 52:26-31, 2011.