Hematuria and a complex congenital heart defect in a newborn foal

Abstract

A 16-hour-old foal was referred for evaluation of hematuria. A pansystolic heart murmur and left thoracic thrill were detected; laboratory diagnostics and ultrasonography identified a complex congenital heart defect. The diagnosis was confirmed at postmortem.

A farm call was made to a 16-hour-old female paint foal with hematuria and colic. Although the client had not been present during foaling, she had observed the foal nursing and passing meconium; however, hematuria was noted during the first urination. At 15 h of age, the foal developed clinical signs of colic, evidenced by rolling and tail swishing. When examined, the foal appeared strong, stood and moved normally, and was interested in her surroundings. Rectal temperature, pulse, and respiration were within normal ranges, and no abnormal findings were detected on auscultation of the heart and lungs. Mucous membranes were slightly pale and the capillary refill time was < 2 s. The foal's navel was dry and did not appear inflamed. The abdominal contours appeared normal. The perineal region and hind legs were blood stained. Frank blood was present in the urine throughout micturition, and approximately 750 mL of clotted blood was expelled from the vulva immediately after urination. A soapy water enema was administered, and the foal was treated with ceftiofur (Excenel; Pharmacia and Upjohn Animal Health, Orangeville, Ontario), 2.2 mg/kg body weight (BW), IM. As there were signs of colic, flunixin meglumine (Banamine; Schering Canada, Pointe-Claire, Quebec), 1.1 mg/kg BW, was administered, IV. Ancillary diagnostic tests were required to determine the source of the hematuria, and the foal was referred to the Veterinary Teaching Hospital, University of Guelph, for further evaluation.

On general physical examination, findings included a grade VI/VI pansystolic heart murmur, audible mainly on the left side, with referred sound on the right side, and a point of maximal intensity at the base of the heart on the left side. A palpable thrill over the left thoracic wall was evident, indicating a probable right-to-left shunt. The foal was in thin body condition and weighed 50 kg. There were no other abnormal findings.

Differential diagnoses for the hematuria included ruptured bladder, ruptured urethra, severe omphalitis, and severe nephritis. Although a ruptured bladder was a possibility, it is less common in females than in males, and in this case, urine flow appeared normal and abdominal distention (indicating uroperitoneum) was not apparent. Differential diagnoses for the heart murmur included a simple or single congenital defect (ventricular septal defect (VSD)) and a complex congenital heart defect or multiple defects, such as VSD and patent ductus arteriosus (PDA) or pulmonic stenosis.

A complete blood cell (CBC) count, blood biochemical profile, and blood gas analysis were carried out. The hematocrit and total plasma protein were slightly below normal range. An arterial blood sample revealed a very low PaO₂ of 45.8 mmHg (reference range, 90 to 100 mmHg). Oxygen therapy was not provided, as the foal appeared clinically stable, and management of oxygen therapy would have been difficult because of the mare's temperament. Although an immunglobulin G test (CITE Foal IgG test; Idexx Laboratories, Toronto, Ontario) indicated adequate passive transfer of maternal antibodies, prophylactic antibiotics were administered, IV, by catheter. Treatment was initiated with sodium penicillin G (Marsam Pharmaceuticals, Cherry Hill, New Jersey, USA), 25 000 U/kg BW, and amikacin (Amiglyde-V; Fort Dodge Animal Health, Fort Dodge, Iowa, USA), 7.5 mg/kg BW. Oral ranitidine (150 mg, q12h) was prescribed for prevention of gastric ulcers, and boluses of lactated Ringer's solution were administered, IV, intermittently to maintain hydration. No pathogens were identified in a fecal sample submitted for culture for Salmonella spp. and assay for Clostridium difficile toxin.

An ultrasonographic examination performed on the foal at 2 d of age revealed a complex congenital heart defect, including an atrial septal defect (ASD), a VSD, and a PDA. The mucous membranes were bluish, and arterial blood gas showed a slight increase in PaO₂ (58 mm Hg). As there was no evidence of pulmonary disease, the combination of low arterial oxygenation, and the heart murmur and the left point of maximal intensity suggested right-to-left shunting in the heart, and since there was no structural reason for right-to-left shunting (pulmonic stenosis), pulmonary arterial hypertension was suspected. The foal was given a very poor prognosis and was euthanized.

On postmortem examination, the heart was of normal size and shape, and positioned normally in the thorax. The presence of a large ASD II, a VSD in the infundibular region below the right and left coronary cusps of the aortic valve (Figure 1), and a PDA were confirmed. The ASD II was 1 cm × 4 cm, and the VSD was 2 cm × 3 cm. The 5-mm diameter PDA was smaller than expected on the basis of ultrasonographic observations. This was attributed to partial closure during the 9 h between ultrasonography and euthanasia. Slight cranial displacement or dextrorotation of the aorta was evident. The epicardium, endocardium, and myocardium appeared normal, but the free wall of the left ventricle was about 3 times thicker than that of the right ventricle. This 3 to 1 ratio is typical of mature cardiac conformation; the ratio in neonates is usually 1 to 1. Hemorrhage extended from the urachus to the urinary bladder. Hematuria was attributed to hemorrhagic omphalitis and cystitis.

Figure 1. Heart of a 2-day-old paint foal at necropsy showing a ventricular septal defect (2 cm × 3 cm) in the infundibular region (arrow). This foal also had an atrial septal defect II and a patent ductus arteriosus (not shown).

Congenital heart disease is not a common diagnosis in the horse (1). There is no known cause for complex heart anomalies, but oxygen deficiency, viral infections in early pregnancy, nutritional and genetic factors, and teratogenic exposure are suspected causes (2). Simple VSDs are most commonly reported and have varying degrees of clinical significance (3). Complex anomalies, although rare, must be distinguished from simple anomalies, as they usually carry a poorer prognosis (4). Small, solitary VSDs may go undetected in a horse throughout a performance career, but horses with complex anomalies usually die prematurely or are euthanized at an early age (3).

Congenital heart defects cause cardiovascular dysfunction through a variety of pathophysiological mechanisms (5). During fetal circulation, the ductus arteriosus allows shunting of maternally oxygenated blood away from the fetal pulmonary circulation to the descending aorta and systemic circulation, as the lungs are inadequately developed and nonfunctional (4). Shortly after birth, with the commencement of respiration, functional closure of the ductus arteriosus occurs, as pulmonary vascular resistance decreases and oxygen tension, systemic vascular resistance, blood volume, and left ventricular pressure increase (6). When PDA occurs in the absence of pulmonary hypertension, blood is shunted from the aorta into the main pulmonary trunk, increasing the volume of blood in the left atrium and ventricle (4). Pulmonary hypertension in the presence of congenital heart defects involving abnormal communication between the systemic venous and arterial circulation (including PDA, ASD, and VSD), as in the case of this foal, may be associated with flow from the systemic venous to systemic arterial circulation (a right-to-left shunt) (5). In the case of a simple PDA, deoxygenated blood is shunted into the descending aorta. Because the PDA is located distal to the brachiocephalic trunk and left subclavian artery, the head and forelimbs receive normally oxygenated arterial blood, while the abdomen and hindquarters receive a combination of arterial and deoxygenated blood (5).

Atrial septal defect II involves the ostium secundum, which is located in the central region of the atrial septum at the fossa ovalis (6). An ASD is usually detected as part of a complex defect, in conjunction with other congenital heart anomalies (6). When a VSD is also present, its clinical significance depends on its size and location and the resistance of the pulmonary circulation (7). The resistance of the pulmonary vasculature is normally lower than that of the systemic circulation, and a VSD causes a left-to-right shunt across the defect (8). Pulmonic stenosis and pulmonary vascular disease increase pulmonary vascular resistance, causing a reversal of blood flow (right-to-left shunt) (8). The long-term effects of excessive pulmonary blood flow due to left-to-right shunting may be irreversible pulmonary vascular lesions and permanently increased vascular resistance (9). As reversal of blood flow occurs, there may be a period when a previously audible murmur becomes inaudible.

Medical management of the heart defect in this foal would have required close monitoring of the respiratory and cardiovascular systems. Large congenital cardiac defects may cause pulmonary congestion and, therefore, predispose the animal to pneumonia (7). Congestive heart failure resulting from congenital defects has been reported in foals and horses with VSD (7,10). Bronchodilators, diuretics, and oxygen therapy are indicated for increasing PaO₂. The antiprostaglandin action of nonsteroidal anti-inflammatory drugs, such as indomethacin, may aid in PDA closure. Indomethacin (Indocin; Merck Frosst Canada, Kirkland, Quebec) may be administered at 0.2 mg/kg BW, q12h, for initial treatment of a PDA. Congenital defects should be included as a differential diagnosis for foals or horses showing cardiovascular abnormalities, heart murmurs, pulmonary hypertension, general unthriftiness, or weakness. Results of physical examination, such as location of the point of maximal intensity associated with a heart murmur, presence and location of a thrill, capillary refill time, and color of mucous membranes, often provide useful information as to the nature of the defect. Ancillary diagnostic tests, including blood gas analysis and echocardiography, should also be done for a more specific diagnosis.