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Fig 2: Base–apex surface electrocardiogram (ECG) recording showing atrial standstill in a 6-year-old horse with hyperkalaemia caused by digitalis intoxication (plasma K+ 7.5 mmol/L, reference values 3.0-4.9 mmol/L). Note the absence of P waves.
the presence of myocardial damage, but this may be due to primary or secondary cardiac involvement. Horses with colic showed increased cTnI levels and ventricular arrhythmias, most likely due to secondary myocardial damage caused by endotoxaemia (Diaz et al., 2014). Arterial and venous blood gas analysis and blood lactate measurements are necessary to evaluate pulmonary and renal function and to evaluate acid–base status. In exercising horses on a high-speed treadmill, hypercapnia and hyperlactataemia were positively associated with the presence of higher-grade arrhythmias (Reef et al., 2020). It is unclear whether there is a causative mechanism or whether these are merely co-markers of generalized muscle fatigue and hypoventilation. Urinalysis can be useful to identify renal injury caused by
heart failure or endocarditis and to determine fractional excretion of potassium. Blood culture is indicated if sepsis or endocarditis is suspected, while serum/plasma assays for digoxin and digitoxin should be performed in case of suspected intoxication with cardiac glycosides. Gastro- intestinal or feed samples should be collected for toxicology screening, for example ionophores. In horses with pericardial effusion, cytologic examination and culture after pericardiocentesis may provide additional information. Endomyocardial biopsies are also feasible in horses using a minimally invasive ultrasound-guided approach through the jugular vein and may reveal histological myocardial abnormalities (Decloedt et al., 2017). Despite the abundance of possible laboratory tests, the
aetiology of cardiac arrhythmias often remains unknown in horses. As a result, targeted treatment of the underlying disease is not always possible and the treatment mainly consists of rhythm control and general supportive care. If myocardial inflammation in absence of infection is suspected to be the primary cause of arrhythmia, a resting period combined with steroid treatment is often attempted.
Author’s declaration of interests No conflicts of interest to declare.
Ethical animal research None.
Source of funding None.
References
Broux, B., De Clercq, D., Decloedt, A., Van Der Vekens, N., Verheyen, T., Ven, S. et al. (2016) Atrial premature depolarization-induced changes in QRS and T wave morphology on resting electrocardiograms in horses. Journal of Veterinary Internal Medicine 30, 1253-1259.
Buhl, R., Meldgaard, C. and Barbesgaard, L. (2010) Cardiac arrhythmias in clinically healthy showjumping horses. Equine Veterinary Journal 42, 196-201.
Conze, T.M., Falkenau, A., Goehring, L.S. and May, A. (2022) Complete AV block in a neonatal foal suffering from nutritional myodegeneration. Equine Veterinary Education 34, 346, e282-e288.
Decloedt, A. (2019) Pericardial disease, myocardial disease, and great vessel abnormalities in horses. Veterinary Clinics of North America: Equine Practice 35, 139-157.
Decloedt, A., Borowicz, H., Slowikowska, M., Chiers, K., van Loon, G. and Niedzwiedz, A. (2017) Right ventricular function during acute exacerbation of severe equine asthma. Equine Veterinary Journal 49, 603-608.
Diaz, O.M.S., Durando, M.M., Birks, E.K. and Reef, V.B. (2014) Cardiac troponin I concentrations in horses with colic. Journal of the American Veterinary Medical Association 245, 118-125.
Jesty, S.A. and Reef, V.B. (2006) Septicemia and cardiovascular infections in horses. Veterinary Clinics of North America: Equine Practice 22, 481-495.
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