ECG of the month

A 14-year-old 18-kg (39.6-lb) sexually intact male German Shorthaired Pointer was evaluated because of severe weakness and inability to maintain a standing position. The owner had found the dog outdoors in lateral recumbency, after it had been outside for several hours during the winter season. It had been recently determined that the dog had vestibular syndrome. On physical examination, the dog was in lateral recumbency and had dull mentation. The dogâs rectal temperature was 33.8°C (92.84°F); oral mucous membranes were pale pink, and capillary refill time was 2 seconds. The femoral pulses were weak and irregular, and the heart rate was variable (120 to 200 beats/min). A grade 2/6 left apical midsystolic heart murmur was auscultated. Bradypnea (10 breaths/min) with deep breaths and expiratory apneas were observed. The initial diagnostic evaluation included hematologic and serum biochemical analyses, blood gas analyses, blood pressure measurement, thoracic radiography, ECG, and echocardiography. The CBC revealed mild leukocytosis (18,200 WBCs/μL; reference range, 5,000 to 17,000 WBCs/μL) with neutrophilia (15,400 neutrophils/μL; reference range, 3,700 to 12,000 neutrophils/μL). Venous blood gas analysis revealed metabolic acidosis (pH, 7300 [reference range, 7360 to 7.410]; HCO3-concentration, 15.3 mEq/L [reference range, 20 to 24 mEq/L]; pCO2, 36 mm Hg [reference range, 40 to 50 mm Hg]; base excess, -5.7 mmol/L [reference range, -4 to +4 mmol/L]) with hyperlactatemia (4.1 mmol/L; reference range, 0.5 to 2.5 mmol/L). Results of serum biochemical analyses were within reference ranges. Systolic blood pressure measurement revealed systemic hypotension (70 mm Hg). No abnormalities were detected on thoracic radiographs. Echocardiography revealed a mild thickening and prolapse of the mitral valve leaflets, with mild mitral valve regurgitation and normal heart chamber dimensions. Electrocardiography was performed to evaluate the arrhythmia