Cardiovascular findings in ponies with equine metabolic syndrome

• Autores: Natalie Heliczer, Vinzenz Gerber, Rupert M. Bruckmaier, Johannes H. van der Kolk, Cristóbal Navas
• Localización: JAVMA: Journal of the American Veterinary Medical Association, ISSN-e 0003-1488, Vol. 250, Nº. 9, 2017, págs. 1027-1035
• Idioma: inglés
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• Resumen

  • OBJECTIVE To determine whether hypertension, high sympathetic tone, resting and exercising arrhythmias, and echocardiographic changes consistent with hypertensive cardiomyopathy were associated with equine metabolic syndrome (EMS) in ponies.

    DESIGN Prospective case-control study.

    ANIMALS 19 privately owned ponies with a diagnosis of EMS (history of laminitis, body condition score ≥ 7/9, cresty neck score ≥ 3/5, and abnormal oral sugar test result; cases) and 20 healthy control ponies.

    PROCEDURES Heart rate (HR), noninvasively measured arterial blood pressure (BP), markers of autonomic tone (splenic volume and HR variability), 24-hour and exercising ECGs, and echocardiograms were compared between cases and controls.

    RESULTS Compared with controls, cases had a higher mean ± SD HR (44.5 ± 7.5 beats/min vs 38.6 ± 6.8 beats/min) and median mean left ventricular wall thickness (2.0 cm vs 1.8 cm). No differences were identified between groups in BP, splenic volume, HR variability, and number of premature complexes in ECGs. Mean wall thickness was correlated with BP (r = 0.54), high-frequency power (r = −0.71), and ratio of low-to high-frequency power (ϕ = 0.66). Relative wall thickness was correlated with serum insulin concentration (r = 0.71).

    CONCLUSIONS AND CLINICAL RELEVANCE Ponies with EMS had myocardial hypertrophy that was correlated with insulin response to an oral sugar test, sympathetic and parasympathetic tone, and BP. The heterogeneity and limited sample size of this preliminary study should be considered when drawing conclusions. Cardiovascular changes associated with this syndrome deserve further attention.

    Equine metabolic syndrome is characterized by regionalized or generalized obesity, insulin dysregulation, and an increased risk of laminitis, compared with the risk in unaffected horses.1 Other potential components include changes in the plasma lipid composition,2 alterations in reproductive cycles of mares,3 and hypertension.4 The recent increase in the number of horses in which EMS has been diagnosed may be attributable to changes in their activities and management as well as increasing awareness of owners and veterinarians regarding this condition. This metabolic syndrome in horses is similar in many respects to that in humans but differs in that laminitis is the main component for horses, and a broad spectrum of cardiovascular disease and diabetes mellitus are the main risk factors for humans. In humans, metabolic syndrome is diagnosed on the basis of obesity, dyslipidemia, hypertension, and fasting hyperglycemia5 and is associated with an increase in the risk of cardiovascular abnormalities, including atherosclerosis, endothelial dysfunction, myocardial infarct, stroke, supraventricular and ventricular arrhythmias, cardiac failure, and sudden cardiac death.6 Horses with EMS are suggested to be less prone than humans to development of vascular complications, including atherosclerosis and coronary artery disease, because of differences in lipoprotein metabolism, diet, and lifespan.1,7 The pathophysiologic mechanisms underlying the association of EMS with insulin dysregulation and laminitis in horses are incompletely understood. Various mechanisms have been investigated, including the effects of low peripheral glucose metabolism on lamellar tissue, accumulation of glycation end products, insulin resistance-associated proinflammatory status, effects mediated by insulin-like growth factor, and vasoactive properties of insulin and subsequent development of hypertension or endothelial damage.4,8 Dysfunction of the vascular endothelium is likely to be important in the development of laminitis,8 but whether laminitis in the presence of EMS should be interpreted as a cardiovascular, metabolic, or inflammatory condition or a combination of all of these conditions is debatable.

    The ANS and cardiovascular system are closely interrelated. Horses intrinsically have high resting parasympathetic tone, and imbalances in autonomic regulation could cause detectable changes. Autonomic imbalances precede insulin resistance in humans with metabolic syndrome,9 and overactivation of the sympathetic nervous system has been suggested as one of the possible underlying causes of arrhythmogenesis10 and insulin resistance in those affected.11,12 In horses, myocardial hypertrophy and hypertensive heart disease in association with laminitis have been reported,13,14 and seasonal increases in blood pressure have been identified in prelaminitic ponies, concurrent with increases in serum insulin and plasma triglycerides concentrations.4 However, no studies have been reported that specifically address the cardiovascular components of EMS.

    The purpose of the study reported here was to explore the cardiovascular component of naturally occurring EMS in ponies to determine whether equine clinicians and researchers should consider this aspect of the syndrome. Such information could lead to investigations concerning early recognition, more sensitive diagnostic and monitoring approaches, and more comprehensive therapeutic and preventive strategies. In addition, characterization of cardiovascular abnormalities and ANS dysregulations in affected ponies could be useful from a comparative and translational perspective, providing information regarding whether research findings on exercise, dietary, and pharmacological interventions in affected equids might be applied to affected humans. The hypothesis was that EMS would be associated with hypertension, an increase in sympathetic tone (as evidenced by changes in HRV), a decrease in splenic size, an increase in the frequency of resting and exercise arrhythmias, and echocardiographic changes consistent with hypertensive cardiomyopathy (ie, an increase in MWT, RWT, or LVM).