Establishing 24-hour Holter reference intervals for clinically healthy puppies.

Normal Holter reference intervals have not been established for dogs <1 year of age. This lack of Holter reference intervals inhibits the ability to screen puppies for early indicators of heart disease, especially in breeds that have inherited cardiac arrhythmias (e.g. German Shepherd Dogs) or a high incidence of arrhythmic heart disease (e.g. Boxer dogs). The objective of this project was to establish Holter minimum, average, and maximum heart rates and incidence of arrhythmias in clinically healthy dogs <1 year of age and to compare these results to previously reported Holter data for their adult counterparts. Forty-four client-owned clinically healthy puppies between 12 and 51 weeks of age were prospectively studied. Age was determined by date of birth and corroborated by dental examination. Puppies were deemed healthy based on history and physical examination. Puppies with heart murmurs underwent echocardiographic examination. Dogs with physiologic heart murmurs were included. Twenty-four hour ECG recordings were obtained using a digital Holter system. The median (interquartile range) Holter minimum, average, and maximum heart rates were 51 bpm (43-60 bpm), 99 bpm (85-113 bpm), and 274 bpm (257-291 bpm), respectively. The median for ventricular and supraventricular arrhythmias was 0. Ventricular and supraventricular premature complexes were identified in 4/44 (9%) and 6/44 (13%) puppies, respectively. Second degree atrioventricular block was identified in 2/44 puppies (5%). Overall, minimum, average, and maximum Holter heart rates of puppies are higher than adult dogs. The incidence of ventricular and supraventricular premature complexes in puppies is similar to adult dogs.