Validation of heart rate spot-check protocol to measure circadian variation and heart rate in healthy dogs and dogs with atrial fibrillation.

INTRODUCTION: Alternatives for out-of-clinic heart rate (HR) measurement are required to optimise the management of atrial fibrillation (AF) in dogs. Additionally, the presence of circadian variation (CV) in HR in pet dogs remains unknown. We aimed to identify the number and duration of spot-checks required for an accurate estimation of 24-hour HR in canine AF. Circadian variation in HR was examined in healthy dogs and dogs with AF, and spot-check-derived HR was compared with a CV-derived gold standard. MATERIALS AND METHODS: Ambulatory electrocardiogram data from healthy dogs and dogs with AF were retrospectively analysed. Heart rate was calculated from the entire recording and pre-defined periods (spot-checks) of one hour to 30 and 60 s in duration. Circadian variation in HR was determined by cosinor analysis. Bias and limits of agreement of means and median HR with mesor HR were determined by correlation and Bland-Altman analysis. RESULTS: Circadian variation in HR was identified not only in 18/22 healthy dogs and 14/21 AF dogs but only on ambulatory electrocardiogram recordings. Four-hourly spot-checks provided the most accurate estimate of mesor HR in healthy dogs (bias of the median over 30 s 7.70, limits of agreement 7.48), whereas, in dogs with AF, four, six and eight-hourly spot-checks provided reliable estimates of mesor HR (bias within -1.29 and -29.5). CONCLUSIONS: Four, six and eight-hourly HR spot-checks can estimate 24-hourly HR in dogs with AF. There was CV in HR in most healthy pet dogs and dogs with AF. Spot-check protocols cannot identify CV in HR.

Coronary arteriovenous malformation in a dog with a complex arrhythmia and hypothyroidism.

A four-year-old Japanese Akita was referred for investigation of lethargy, exercise intolerance, and an irregular heart rhythm. He was diagnosed with atrial fibrillation, a complex ventricular arrhythmia, and hypothyroidism. Echocardiography identified a nest of anomalous vessels surrounding the heart and shunting into the pulmonary artery. Computed tomography confirmed a coronary arteriovenous malformation consisting of a coronary-to-pulmonary arterial communication and an associated complex nest of tortuous vessels, which was thought to be an incidental finding. Clinical signs improved with levothyroxine and antiarrhythmic treatment. Describing an unusual coronary artery anomaly as well, this case serves as a reminder to critically evaluate the hemodynamic significance of structural cardiac disease and to screen for systemic disease in patients with arrhythmias.

Poincaré plots as a measure of heart rate variability in healthy dogs.

INTRODUCTION: Poincaré plots remain largely unused for heart rate variability (HRV) analysis in dogs. The aims of this study were to describe, qualitatively and quantitatively, Poincaré plots in healthy dogs, to compare them with other methods of HRV analysis, to assess their day-to-day variability and to investigate the effect of activity on the plots. ANIMALS: Twenty-five healthy dogs. METHODS: Poincaré plots, their standard descriptors, and other measures of HRV were generated from 24-hour ambulatory electrocardiographic recordings and 6 hours of rest and activity. RESULTS: The 24-hour Poincaré plot demonstrated a 'Y' pattern. The arms of the 'Y' were derived mostly from periods of rest and activity populated the stalk. The quantitative descriptors of the plot had strong correlations in the time-domain, with weaker correlations in the frequency-domain. Individuals showed low day-to-day variability of the plot pattern and of the standard deviation of points along the major axis of the plot (SD2), which measures overall HRV. Day-to-day variability was higher for the standard deviation of points perpendicular to the major axis of the plot (SD1), which is a measure of short-term HRV, and for the SD1/SD2 ratio. CONCLUSIONS: Twenty-four-hour Poincaré plots in healthy dogs show a 'Y' pattern with subtle variations unique to the individual. The amount of activity and rest within the recording has a significant effect on the plot. Quantitative analysis of the plot can be used as a surrogate for time-domain analysis of HRV but visual analysis of the pattern provides additional information.

How contrast affects stereoacuity.

Stereoacuity and its dependence on contrast were measured at four spatial frequencies separated by 1 octave steps. Using a method of adjustment, observers adjusted the retinal disparity of an aperiodic narrow-band stimulus until it appeared in the depth plane defined by two flanking reference lines. Variations in contrast affected stereoacuity (the standard deviation of ten depth settings), with better performance observed at higher contrasts. Data were fit with straight lines (on a log-log plot), indicating a power-law dependence on contrast; the slope was steeper at lower spatial frequencies. These findings are consistent with the idea that disparity is computed from the responses of size-tuned mechanisms characterized by nonlinear contrast transfer functions. In a second experiment, the effects of interocular differences in contrast on stereoacuity were studied for two conditions. In the first condition, one eye always viewed a high-contrast target while the other eye viewed targets of successively lower contrast; in the second condition, one eye always saw a target of near-threshold contrast while the other eye saw targets of successively higher contrast. When the fixed contrast was high, stereoacuity deteriorated steadily as the interocular difference in contrast increased; the loss of stereoacuity was greatest at the lowest spatial frequency. When the fixed contrast was low, however, small increases in the contrast to one eye had no deleterious effect on stereoacuity. Once interocular contrast settings exceeded a certain difference, stereoscopic acuity began to deteriorate at lower spatial frequencies. These results address the issue of the stage of visual processing at which contrast exerts its influence on stereopsis.

How to achieve integration on the human side of the merger.

Blake and Mouton use an actual case of a successful merger to show how their Interface Conflict-Solving Model, based on behavioral science principles, can be used to achieve integration. The authors outline the history of the two organizations, give illustrations of the kinds of changes that were necessary to more from the actual state of affairs within each organization to the conditions needed for synergy, and explain how the merging organizations collaborated to develop a model for the interface. The merger is evaluated from the perspective of what happened during the two years following the merger. Blake and Mouton also elaborate on the dynamics of group behavior that they took into consideration in designing the Interface Conflict-Solving Model: the effects of group members' shared history; the natural tensions that typically exist between groups that have a functional relationship and misperceptions and distortions that arise as a result of these tensions; and win-lose competitiveness instead of a win-win mentality as a shared expectation. Finally, the authors show how shared participation can overcome inappropriate and debilitating competition.