Twenty-four hour ambulatory electrocardiography in healthy dogs: reference intervals and measurement variability.

Objectives: Published normative data acquired by ambulatory electrocardiographic monitoring of healthy dogs of diverse lineage are sparse. Reference intervals and indices of measurement variability have not been published.

Materials and methods: Forty-nine healthy dogs were subject to ambulatory electrocardiography. After exclusions, the reference sample consisted of 44 dogs. Eight of these dogs were randomly selected and subject to a second ambulatory electrocardiographic recording no more than 10 days after the first. Reference intervals for minimum, maximum and mean heart rates and for PR intervals were determined. The repeatability coefficient was used to define measurement variability.

Results: When recordings that included greater than 100 ventricular ectopic complexes - presumed to reflect subclinical disease - were excluded, ventricular ectopic complexes were rare; the median (range) number of complexes was 0 (0 to 17). Second-degree atrioventricular block was recorded in 25% of subjects. Reference intervals for minimum, maximum and mean heart rates, respectively, were 15 to 42, 194 to 294 and 50 to 93 bpm. PR intervals were positively correlated with body weight. Based on calculated repeatability coefficients, differences in minimum, maximum and mean heart rates from serially obtained recordings, respectively, of 12, 44 and 11 bpm are within the expected ranges of measurement variability.

Clinical significance: Reference intervals for heart rates and PR intervals obtained from ambulatory electrocardiographic are proposed. Repeatability coefficients, which provide an estimate of what might represent a clinically relevant change when serially acquired ambulatory electrocardiographic recordings are compared, are reported. PR intervals were positively correlated with body size. These data might be of use when reviewing ambulatory electrocardiographic recordings.