Equine Congenital Heart Disease

Congenital heart defects in Arabian horses and the prospects of genetic testing: A review

Congenital heart defects (CHDs) can have profound and potentially life-threatening consequences on horses' health and performance capability. While CHDs are rare in the general horse population, the Arabian breed is disproportionately overrepresented and thus is widely suspected to be genetically predisposed. This review discusses the most common CHDs in Arabian horses, including ventricular septal defect (VSD), tetralogy of Fallot (TOF), patent duct arteriosus (PDA), tricuspid valve atresia (TVA) and atrial septal defect (ASD). This review also explores how future research into the genetic factors that likely underpin many CHDs can revolutionise the way these disorders are managed in Arabian horses.

Echocardiographic Features of the Ductus Arteriosus and the Foramen Ovale in a Hospital-Based Population of Neonatal Foals

Simple Summary

In fetal circulation, the distribution of oxygenated blood from the maternal placenta is facilitated by two intracardiac shunts. Oxygenated blood flows from the right atrium to the left heart through the foramen ovale, which is formed by the septum primum and septum secundum. Less oxygenated blood is directed to the placenta through the ductus arteriosus, which connects the pulmonary artery and the aorta. The ductus arteriosus and foramen ovale should close after birth. However, knowledge about the exact time of closure of those structures in foals is limited. The current study investigates the ultrasonographical closure of both the ductus arteriosus and the foramen ovale in healthy and diseased neonatal foals. Cardiac auscultation and ultrasound were performed on fifty foals. Cardiac murmurs were common, and in some foals, the ductus arteriosus was still open at ten days of age. The foramen ovale was not open; however, a fluttering motion of the septum primum into the left atrium was a common finding in healthy and diseased foals. The exact clinical importance of those findings needs to be further elucidated.

Abstract

The ductus arteriosus (DA) and foramen ovale (FO), including the septum primum (SP) and septum secundum (SS), are important structures in fetal circulation and are unexplored in neonatal equids. The objective of this study is to describe echocardiographic characteristics in a hospital-based population of neonatal foals. On days 2, 5 and 10 after parturition, cardiac ultrasound was performed, and clinical data were collected in healthy and diseased Warmblood foals. Fifty healthy (n = 15) and diseased (n = 35) Warmblood foals were examined. A left-sided and right-sided holosystolic murmur was audible in 98% (n = 42) and 51% (n = 22), respectively, on day 2; in 81% (n = 25) and 19% (n = 6) on day 5; and in 44% (n = 4) and 11% (n = 1) on day 10. The median grade of the systolic murmurs was higher when the DA was open. Flow through the DA could be visualized with color flow and continuous wave (CW) Doppler from the left parasternal long-axis view of the pulmonary artery in 40/43 foals on day 2, 9/31 foals on day 5 and 2/9 foals on day 10. The DA diameter was 2 ± 1 mm on day 2, 2 ± 1 mm on day 5 and 1 mm on day 10. The thickness of both septa of the FO was similar. The SP fluttered into the left atrium at all ages, but the maximal distance between the SP and SS decreased over time. In conclusion, cardiac murmurs, a patent DA and fluttering FO are frequent findings in neonatal foals. While these findings are probably physiological, the clinical importance needs to be further elucidated.

Prevalence and characteristics of ventricular septal defects in a non-racehorse equine population (2008-2019)

BACKGROUND

Ventricular septal defects (VSDs) are the most common congenital cardiac defect in horses.

OBJECTIVES

To identify prevalence, age, breed, and sex distribution of VSD and to describe associated clinical and ultrasonographic findings.

ANIMALS

Hospital-based population of 21 136 horses presented to the equine internal medicine department.

METHODS

Medical records over a 12-year period were reviewed for VSD confirmed by ultrasonography. Age, breed, sex, sport discipline, murmur, clinical signs, outcome, VSD type, VSD size, shunt velocity, cardiac dimensions, concomitant cardiac anomalies, and valvular regurgitations were recorded.

RESULTS

From 1894 horses that underwent echocardiography, 54 had a VSD: 42 as an isolated lesion and 12 as part of complex congenital heart disease (CHD). Median age was 5 years (range, 0-26) and 1 year (range, 0-8), respectively. Warmbloods and males were overrepresented. In the isolated VSD group, only 15% had associated clinical signs and most horses had a perimembranous VSD (pmVSD; 36/42). Horses with a pmVSD and clinical signs showed a significantly lower maximal shunt velocity (3.77 vs 5.20 m/s; P < .001), higher VSD/Aortic root (Ao) diameter (0.52 vs 0.38; P = .05), higher left atrium/Ao diameter (1.94 vs 1.22; P < .001), and higher pulmonary artery/Ao diameter (1.15 vs 0.88; P = .005) compared to horses without clinical signs. All horses with complex CHD had clinical signs and abnormal cardiac dimensions.

CONCLUSION AND CLINICAL IMPORTANCE

Most isolated VSD were diagnosed only at a later age and were not associated with clinical signs. Horses with complex CHD were more likely to have or develop clinical signs at younger age.

Ascending aortic aneurysm associated with tetralogy of Fallot in an adult mare

Congenital heart disease is relatively uncommon in horses. Only three reports exist that describe a tetralogy of Fallot in adult horses. Whereas in humans the presence of congenital heart disease constitutes a risk factor for developing aortic aneurysms, their association has never been reported in horses. Here, we present a case with a large ascending aortic aneurysm as a complication of a tetralogy of Fallot in an adult mare. The mare was referred with sustained tachycardia and a 5 days history of mild intermittent colic, depression, inappetence and weight loss. Echocardiography was used to characterize the cardiac abnormalities and aortic root dilation. Due to the poor prognosis, the mare was euthanized and post‐mortem examination further characterized the abnormalities. At least four factors contributed in this case to the development of aortic haematoma: congenital disease, mucoid extracellular matrix accumulation vasa vasorum dysfunction and inflammatory/degenerative lesions in the aorta's intima. Although colic is primarily caused by gastrointestinal issues, cardiac disease should be suspected in cases with sustained tachycardia, even in absence of murmurs or arrhythmias. Despite the fact that congenital abnormalities are usually detected in foals, they may sometimes remain unnoticed for several years.