Clinical presentation, management and survival in dogs with persistent atrial standstill in the United Kingdom.

Objectives: To investigate the clinical and echocardiographic presentation of dogs with persistent atrial standstill (PAS), identify variables measured at first presentation that could predict their survival and document the progression of the disease after pacing.
Materials and Methods: Retrospective study of medical records of dogs diagnosed with PAS at three referral hospitals of the United Kingdom over seven years.
Results: Twenty-six dogs were diagnosed with PAS during the study period. Median age of the population was three years (range: 7 months-12.5 years). The most common clinical sign was syncope (14/26). Twenty-four dogs received artificial pacemakers (PM). Major complications after PM implantation were observed in four dogs (4/24). Serial echocardiographic examinations showed that cardiac dimensions of PAS dogs with left atrial or left ventricular dilation at first presentation did not return to reference range after pacing. Further dilation of the cardiac chambers, recurrence of congestive heart failure (CHF) or development of new episodes of CHF were documented in 7, 4 and 10 PAS dogs despite pacing respectively. Median survival time for cardiac-related deaths after PM implantation was 1512 days (18-3207). Neither CHF nor echocardiographic variables at presentation predicted survival after PM implantation in PAS dogs.
Conclusions: PAS is an uncommon bradyarrhythmia, occurring in young adult dogs. Affected dogs were often presented with syncope. Whilst syncope resolved, cardiac remodelling persisted after PM implantation. Long-term survival was favourable after PM implantation and was not predicted by congestive status or cardiac chamber size at first presentation.