A condition resembling hypoplastic left heart syndrome in a foal

The Equine Neonatal Cardiovascular System in Health and Disease

The neonatal foal is in a transitional state from prenatal to postnatal circulation. Healthy newborn foals often have cardiac murmurs and dysrhythmias, which are usually transient and of little clinical significance. The neonatal foal is prone to infection and cardiac trauma. Echocardiography is the main tool used for valuation of the cardiovascular system. With prompt identification and appropriate action, dysrhythmias and other sequel to cardiac trauma can be corrected. With infection, the management and prognosis are driven by concurrent sepsis. Congenital disease represents an interesting diagnostic challenge for the neonatologist, but surgical correction is not appropriate for most equids.

Congenital cardiac defects in neonatal foals: 18 cases (1992-2007)

BACKGROUND

Literature available regarding congenital cardiac defects in foals is limited to reports of individual cases or small case series.

OBJECTIVE

To describe the clinical, echocardiographic, and necropsy findings and breed predilection of congenital cardiac defects in neonatal foals.

ANIMALS

Eighteen foals < 15 days of age with 1 or more congenital cardiac defects.

METHODS

Medical records of foals diagnosed with congenital cardiac defects at the William R. Pritchard Veterinary Medical Teaching Hospital were reviewed. Data collected included history, signalment, clinical signs, laboratory data, diagnostic and necropsy results, and outcome.

RESULTS

Arabian foals represented 39% of cases with congenital cardiac defects and were significantly (P = .004) overrepresented (OR = 4.7 [CI: 1.8-12.4]) compared with the general hospital population. Ventricular septal defect (VSD) (14/18), tetralogy of Fallot (5/18), and tricuspid valve atresia (4/18) were the most common defects identified. A > or = 3/6 heart murmur (14/ 14) accompanied by tachycardia (14/17), tachypnea (17/17), and cyanosis of mucous membranes (7/16) were the most common clinical signs. Concurrent congenital defects were common (9/18). Two foals, both with VSD, survived for > or = 8 years after diagnosis and 1 was a successful performance horse.

CONCLUSIONS AND CLINICAL RELEVANCE

Arabian horses appear to have a predisposition for cardiac defects. The presence of a loud murmur (> or = 3/6), cyanotic membranes, and tachycardia or tachypnea in a neonatal foal should warrant thorough evaluation of the heart for congenital defects. Foals with cardiac defects should be closely evaluated for concurrent congenital defects in other body systems.

Hypoplastic left heart syndrome: Rheumatic heart disease of the fetus?

Hypoplastic left heart syndrome (HLHS) accounts for nearly 25% of deaths among neonates with congenital heart disease. The essential feature of HLHS is a small left ventricle (LV) incapable of supporting the circulation. The etiology of HLHS is unknown. A hypothesis is proposed implicating an immune mechanism involving maternal antibodies produced in response to pharyngitis caused by group A beta-hemolytic streptococci (GABHS) ("strep throat"). After crossing the placenta, the antibodies injure the developing fetal heart, leading to HLHS either because of direct injury to the LV or secondary to reduced blood flow through affected aortic and mitral valves. Analogy is drawn to rheumatic heart disease (RHD), a known sequela of strep throat. In RHD a misdirected immune response originally intended for GABHS leads to cardiac injury through "molecular mimicry"; the normal heart antigens supposedly mimic the GABHS antigens. A similar pathogenesis is proposed for HLHS and related heart defects. HLHS may represent an extreme form of injury, while a milder insult may present as only mild aortic stenosis or a bicuspid aortic valve, conditions with wide prevalence among the general population. The injury may indeed superimpose on many other congenital heart defects, leading to a variable presentation of these other diseases. Beside remarkable likenesses between HLHS and RHD, the hypothesis is also supported by increasing evidence for the role of deleterious transplacental antibodies in the pathogenesis of other fetal diseases. Implications for other congenital heart diseases and the broader picture of global public health are discussed.