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The objective of this study was to compare the cardiopulmonary effects of a xylazine or romifidine loading-dose, followed by a constant rate infusion (CRI) of the sameα2-agonist. Nine research horses were treated in a randomized, blinded, crossover design with xylazine or romifidine. After instrumentation, a loading dose of intravenous xylazine (1 mg/kg) or romifidine (80 µg/kg) was administered, immediately followed by a CRI of xylazine (0.69 mg/kg/h) or romifidine (30 µg/kg/h) for a duration of 2 h. Cardiopulmonary variables were recorded before bolus administration, during CRI, and for 1 h after discontinuing drug administration. A significant decrease in haemoglobin concentration (tHb), arterial oxygen content (CaO2), oxygen delivery (ḊO2), mixed venous partial pressure of oxygen, heart rate, and cardiac output (Q̇t) followed the loading dose with both treatments. Carotid arterial blood pressure (ABP), systemic vascular resistance, and right atrial pressure (RAP) increased significantly. The increased ABP was followed by a significant decrease compared to baseline. Mean pulmonary arterial pressure increased significantly with romifidine only. No significant changes in stroke volume, arterial partial pressure of oxygen, and oxygen consumption were observed. Changes in Q̇t and RAP were more pronounced with romifidine. During CRI, tHb, and CaO2 were significantly higher with romifidine, whereas ḊO2 did not differ between treatments. Overall, cardiopulmonary effects were more pronounced and lasted longer with romifidine compared to xylazine. However, during CRI, there was no difference in ḊO2 between drugs. With both α2-agonists, cardiovascular effects were most pronounced after loading dose administration and tended to stabilize during CRI. [ABSTRACT FROM AUTHOR]

• Heart rate variability (HRV) analysis is used to diagnose atrial fibrillation (AF). • HRV is used by 'smart' wearable human medical devices. • In horses, HRV analysis is used to identify arrhythmias at rest and during exercise. • Standardised, good quality recordings are important for accurate HRV analysis. Heart rate variability (HRV) analysis has been performed on ECG-derived data sets for more than 170 years but is currently undergoing a rapid evolution, thanks to the expansion of the human and veterinary medical technology sector. Traditional HRV analysis was initially performed to identify changes in vago-sympathetic balance, while the most recent focus has expanded to include the use of complex computer algorithms, neural networks and machine learning technology to identify cardiac arrhythmias, particularly atrial fibrillation (AF). Some of these techniques have recently been translated for use in the field of equine cardiology, with particular focus on improving the diagnosis of arrhythmias both at rest and during exercise. This review focuses on understanding the basic HRV variables and important factors to consider when collecting data for use in HRV analysis. In addition, the use of HRV analysis for the diagnosis of arrhythmias is discussed from human, small animal and equine perspectives. Finally, the future of HRV analysis is briefly introduced, including an overview of future developments in this rapidly expanding and exciting field. [ABSTRACT FROM AUTHOR]

Objective To evaluate the non-calibrated, minimally invasive cardiac output ( CO) monitor FloTrac/Vigileo (FloTrac) against thermodilution ( TD) CO in standing horses. Study design Prospective, experimental trial. Animals Nine adult horses weighing a median (range) of 535 (470-602) kg. Methods Catheters were placed in the right atrium, pulmonary artery and carotid artery under local anaesthesia. CO was measured 147 times by TD and FloTrac and indexed to body weight. Changes in CO were achieved with romifidine or xylazine and dobutamine constant rate infusions. Bland-Altman analysis, concordance and polar plot analysis were used to assess agreement and ability to track changes in CO. Results Mean ± standard deviation COTD of 48 ± 16 mL kg−1 minute−1 (range: 19-93 mLkg−1 minute−1) and mean COFloTrac of 9 ± 3 mLkg−1 minute−1 (range: 5-21 mL kg−1 minute−1) were measured. Low agreement with a large mean bias of 39 mL kg−1 minute−1 and wide limits of agreement of 8-70 mL kg−1 minute−1 were found. The percentage error of 108% and precision of TD of ±18% resulted in an estimated precision of FloTrac of ±106%. Comparison of changes in COFloTrac with changes in COTD gave a concordance rate of 52% in the four-quadrant plot, and a mean polar angle of −11° with radial limits of agreement of ±61 ° in the polar plot. Mean arterial pressure ( MAP) and COFloTrac were positively correlated ( r = 0.5, p < 0.0001). No correlation of MAP with COTD was observed. Conclusions and clinical relevance The FloTrac system, originally designed for use in humans, neither measured absolute CO in standing horses accurately nor tracked relative changes in CO measured by TD correctly. The false dependence of COFloTrac on arterial blood pressure further discourages the use of this technique in horses. [ABSTRACT FROM AUTHOR]