Aorto-Ventricular Tunnel

Summary: It is a rare congenital malformation characterized by an abnormal extracardiac channel connecting the ascending aorta to a ventricle, most commonly the left. This section includes high-resolution CT reconstructions showing the tunnel’s origin from the aortic root and its termination in the ventricle, as well as echocardiography clips with color Doppler demonstrating continuous turbulent flow from the aorta into the ventricle throughout the cardiac cycle. Aorto-ventricular tunnel is distinct from aortic regurgitation and ruptured sinus of Valsalva aneurysm because it bypasses the aortic valve, resulting in continuous runoff from the aorta, diastolic volume overload, progressive ventricular dilation and dysfunction, and potential coronary flow steal if the tunnel is close to the coronary ostium. Early recognition is critical, as surgical or transcatheter closure in infancy can prevent heart failure and long-term morbidity.

Aorto-ventricular tunnel (AVT) is characterized as a congenital, extracardiac channel that establishes a communication between the ascending aorta, specifically above the sinutubular junction, and the cavity of either the left or, less frequently, the right ventricle. It is identified as an abnormal, non-valved, extracardiac channel. This malformation is distinct from a ruptured sinus of Valsalva aneurysm or an aortopulmonary window. Aorto-left ventricular tunnel (AoLVT) is the most common manifestation, accounting for over 90% of reported cases. This is an extremely rare diagnosis, representing less than 0.1% of congenitally malformed hearts observed in clinico-pathological series, with estimates ranging as low as 0.05% among patients undergoing cardiac catheterization. Approximately 130 cases have been documented in the medical literature (See below Mackay R. et al.). A higher incidence is noted in males, with about twice as many cases reported in males compared to females, and the condition is infrequently observed in individuals of Asian, Oriental, or African descent.

Anatomic Characteristics and Etiology

The aorto-ventricular tunnel originates in the tubular portion of the ascending aorta, superior to the sinotubular junction. For AoLVT, nearly 80% of the aortic orifices are situated centrally above the right coronary sinus of Valsalva. The size of these orifices can vary; most are large (Hovaguimian type 2 or 4 - the four types are described here), but some tunnels feature smaller, elliptical orifices (Hovaguimian type 1 and 3) that may restrict flow. The tunnel follows an extracardiac course, passing through the tissue plane located between the aortic and pulmonary roots. It traverses outside the heart, running between the aortic sinuses and the muscular subpulmonary infundibulum, notably without passing through any ventricular myocardium. The ventricular orifice of the AoLVT is usually positioned on the septal surface of the left ventricular outflow tract, located beneath the left–right coronary commissure. The AoLVT is characterized by having a single entrance orifice and a single exit orifice. Histological examination reveals that the arterial end of the tunnel resembles the aorta, containing fibrous tissue, elastic fibers, and smooth muscle cells, while the ventricular end is composed of hyalinized collagen and muscle, reflecting the structures through which the tunnel passes. The exact etiology of AVT remains uncertain, but it appears to result from a combined failure in the development of the cushions that form the pulmonary and aortic roots, along with an abnormal separation of these structures. The defect has not been linked to any specific described genetic syndrome.

Pathophysiology and Clinical Presentation

The AoLVT allows continuous blood flow between the aorta and the left ventricle during both the systolic and diastolic phases of the cardiac cycle. During ventricular systole, ejection occurs through both the aortic semilunar valve and the tunnel itself. However, the critical hemodynamic effect occurs during diastole, when blood flow reverses from the high-pressure aorta back into the left ventricle. This mechanism causes rapid runoff of blood from the aorta, and consequently, the pathophysiology of AVT closely resembles severe aortic valve regurgitation. Large tunnels typically result in significant ventricular volume overload, leading to the onset of congestive heart failure, usually manifesting within the first year of life. Less commonly, patients may present asymptomatically with only a heart murmur and cardiac enlargement. If the AoLVT orifice is restrictive, symptom severity may be reduced or delayed. In the very rare cases of aorto-right ventricular tunnel (AoRVT), a large shunt would produce physical findings and hemodynamic consequences similar to an aorto-pulmonary window, including prominent aortic diastolic run-off and signs of severe right ventricular and/or pulmonary artery hypertension. Both ventricles are subject to volume overload with AoRVT. Associated defects, which typically involve the aortic or pulmonary valves or the proximal coronary arteries, are found in nearly half of the cases. Of particular note, the anomalous origin of the right coronary artery arising from the distal aspect of the AoLVT has been observed. Furthermore, if the ventricular end of an AoLVT is not closed during repair, the ensuing residual high pressure in the blind-ending tunnel pouch may cause compression of the right ventricular outflow tract.

Diagnosis and Management

Echocardiography is regarded as the diagnostic investigation of choice. Antenatal diagnosis of AoLVT is possible via fetal echocardiography after 18 weeks gestation, and the presence of ALVT may cause congenital heart failure and fetal hydrops. Imaging typically shows the AoLVT body as a vascular space located anterior to the aorta, which penetrates the basal portion of the interventricular septum to empty into the left ventricular cavity. Color flow Doppler studies clearly demonstrate the prominent diastolic flow running from the aorta through the tunnel into the ventricular outflow tract. AoRVT, conversely, is often better visualized using the short-axis view. Cardiac catheterization may be employed as needed to clarify associated defects or the origins of the coronary arteries. Optimal management for symptomatic AVT involves prompt surgical repair following diagnosis. Medical therapy provides only temporary palliation for heart failure symptoms. Early surgical intervention is highly recommended, even in asymptomatic patients with significant blood flow, as the risk of long-term ventricular dysfunction increases if repair is delayed past six months of age.

The surgical repair aims to close the tunnel while simultaneously ensuring support for the aortic valve and preventing obstruction of ventricular outflow or compromise to the coronary circulation. In most AoLVT repairs, this is achieved by performing a transaortic closure of both the aortic orifice and the ventricular orifice using patches. Closing the ventricular orifice is important because it supports the right coronary leaflet, which is thought to reduce the incidence and severity of late regurgitation. Although closing the aortic orifice by direct suture sometimes yields good results, it carries a higher risk of tunnel recurrence or progressive aortic regurgitation due to an unsupported or distorted right coronary leaflet, potentially requiring later valve replacement. The tunnel wall itself can sometimes be utilized to achieve an equivalent anatomical outcome. For the rare instance of an associated anomalous coronary artery originating directly from the tunnel, the complex repair often involves surgically transferring and reattaching the coronary artery to the ascending aorta, similar to the technique used in the arterial switch operation. Transcatheter closure has been reported using devices, but this approach is generally less favoured than surgery because devices do not provide the necessary support to the aortic valve. Long-term, life-long follow-up is necessary for all patients to monitor for potential issues such as tunnel recurrence, aortic valve incompetence, left ventricular function, and aneurysmal enlargement of the ascending aorta; cystic medial degeneration was noted in an ascending aortic aneurysm fifteen years after a tunnel repair.