A 6-year-old 430-kg (946-lb) Standardbred gelding with a history of intermittent upper airway noise was examined following completion of a race as part of a track safety initiative. The horse had just paced a mile in 1 minute and 53 seconds and finished in third place (crossing the finishing line 1 second after the winner). After the race, the trainer noticed no abnormalities except that the horse required more time than usual for cooldown. During the scheduled physical examination, the horse had a rapid regular cardiac rhythm with a heart rate of 200 beats/min and visible pulses in the jugular veins. The horse was tachypneic and hyperthermic, consistent with recent exertion. Electrocardiography was performed by use of a handheld clipless digital recording device.a
Vet Biolog II, QRS Diagnostic LLC, North Plymouth, Minn.
Stratus CS, Siemens Diagnostic Healthcare, Newark, Del.
Holter monitor, Impresario, Reynolds Medical Inc, Raleigh, NC.
Deem DA, Fregin GF. Atrial fibrillation in horses: a review of 106 clinical cases, with consideration of prevalence, clinical signs, and prognosis. J Am Vet Med Assoc 1982; 180:261–265.
Ohmura H, Hiraga A, Takahashi T, et al. Risk factors for atrial fibrillation during racing in slow-finishing horses. J Am Vet Med Assoc 2003; 223:84–88.
McGuirk SM, Muir WW. Diagnosis and treatment of cardiac arrhythmias. Vet Clin North Am Equine Pract 1985; 1:353–370.
Physick-Sheard PW, McGurrin MK. Ventricular arrhythmias during race recovery in Standardbred racehorses and associations with autonomic activity. J Vet Intern Med 2010; 24:1158–1166.
Reimer JM, Reef VB, Sweener RW. Ventricular arrhythmias in horses: 21 cases (1984–1989). J Am Vet Med Assoc 1992; 201:1237–1243.
Lindinger MI. Potassium regulation during exercise and recovery in humans: implications for skeletal and cardiac muscle. J Mol Cell Cardiol 1995; 27:1011–1022.
Bayly WM, Kingston JK, Brown JA, et al. Changes in arterial, mixed venous and intraerythrocytic concentrations of ions in supramaximally exercising horses. Equine Vet J Suppl 2006; 36:294–297.
Mogg TD. Equine cardiac disease: clinical pharmacology and therapeutics. Vet Clin North Am Equine Pract 1999; 15:523–534.
Estes NA III, Link MS, Cannom D, et al. Report of the NASPE policy conference on arrhythmias and the athlete. J Cardiovasc Electrophysiol 2001; 12:1208–1219.