Uhl's Anomaly

Uhl's anomaly, also known as "parchment right ventricle," is a rare congenital cardiac malformation. This condition is characterized by the congenital absence or hypoplasia of the myocardial layer of the right ventricular (RV) inflow myocardium. Due to this significant myocardial deficiency, the endocardium and epicardium of the right ventricle become opposed. Uhl's anomaly is often classified under hypoplastic right heart syndromes. In this condition, the RV free wall is extremely thin and largely replaced by fibroelastic tissue, giving it a “parchment-like” appearance. As a result, the right ventricle is dilated, poorly contractile, and unable to generate normal systolic pressure, leading to severe right-sided heart failure early in life. Henry S.D. Uhl first described this condition in 1952.

Pathology and Anatomy

The hallmark pathological feature of Uhl's anomaly is the complete or partial absence of the myocardial layer of the right ventricle. In affected hearts, the septal component, septomarginal trabeculation, and the papillary muscles of the tricuspid valve (TV) are typically muscularized normally, even with the widespread absence of other right ventricular myocardium. The right ventricular cavity is usually described as being greatly dilated.

Etiology and Embryology

The exact embryological mechanism leading to Uhl's anomaly is not fully understood. The myocardial absence may result from either a primary failure of myocyte development or a form of selective apoptosis. Most reported cases of Uhl's anomaly are sporadic. Vascular endothelial growth factor (VEGF) may play a role in the induction of this specific cardiovascular malformation.

Associated Conditions

Uhl's anomaly can occur in conjunction with other congenital heart defects, notably pulmonary atresia with intact ventricular septum (PA/IVS). Given its characterization by right ventricular hypoplasia, it is broadly grouped with other hypoplastic heart syndromes.

Clinical Presentation and Symptoms

The most common clinical manifestation of Uhl's anomaly is congestive heart failure, frequently accompanied by peripheral edema and pleural effusion. Clinically, affected infants or children present with cyanosis, failure to thrive, hepatomegaly, edema, and signs of right heart failure. 

Characteristic findings are observed through echocardiography:

• A notable contrast is seen between an akinetic right ventricular anterior wall and brisk paradoxic septal motion, alongside vigorous contractions of the right atrial wall.

• Unlike arrhythmogenic right ventricular dysplasia, arrhythmias and conduction disturbances are not common in Uhl's anomaly. This distinction is attributed to the absence of specific foci that typically transmit abnormal electrical activity in arrhythmogenic right ventricular dysplasia. Arrhythmogenic right ventricular cardiomyopathy (ARVC) involves fibrofatty replacement and has a strong arrhythmic component, whereas Uhl’s anomaly is typically present from birth, has minimal fatty infiltration, and is primarily a mechanical failure of the RV pump function rather than an arrhythmogenic disorder.

Management and Treatment

Management strategies for Uhl's anomaly encompass both medical and surgical interventions, aiming to alleviate symptoms and improve cardiac function:

• Medical Management: This primarily addresses symptoms of congestive heart failure and includes supportive measures such as the drainage of pleural effusions.

• Surgical Options:

  • Established surgical approaches include right ventricular (RV) exclusion with atrial septectomy, bidirectional cavopulmonary anastomosis (BDCPA), and closure of the tricuspid valve orifice.

  • One-and-a-half ventricle repair has also been reported as a surgical treatment for Uhl's anomaly.

    1. A one-and-a-half ventricle repair (1.5VR) is a specialized cardiac surgical procedure that combines intracardiac repair with a bidirectional cavopulmonary shunt (BCPS). This technique is typically employed when the left ventricle (LV) is functionally normal, but the right ventricle (RV) is insufficient to manage the body's entire cardiac output. It addresses "borderline right ventricles" – those considered too small for a complete biventricular repair, yet too substantial or functional to warrant a full single-ventricle Fontan circulation. Common indications include hypoplasia of the RV or tricuspid valve (TV), chronic RV dysfunction, acute RV failure, or to simplify complex repairs like those for double-discordance (congenitally corrected transposition of the great arteries (ccTGA)). The primary goals of a 1.5VR are to reduce the volume load on the compromised RV, ensure pulsatile pulmonary blood flow, achieve a near-equal balance between systemic and pulmonary blood flow, and maintain normal systemic oxygen saturations. By diverting a portion of the systemic venous return (e.g., from the superior vena cava) directly to the pulmonary arteries via the BCPS, the hypoplastic RV only handles the remaining (inferior) systemic venous return, thereby reducing its workload. This approach often leads to better exercise tolerance and avoids complications associated with high venous pressure in the lower body, such as protein-losing enteropathy or chronic liver congestion, which can occur with Fontan procedures.

  • For severe cases where other interventions prove insufficient, cardiac transplantation is considered the therapy of last resort.