Aorto-ventricular tunnel

What is Aorto-ventricular Tunnel (AVT)?

Aorto-ventricular tunnel (AVT) is an extremely rare congenital heart anomaly. AVT is an extracardiac channel connecting the ascending aorta above the sino-tubular junction to either left or right ventricular cavity.

Embryology

It is considered that the formation of AVT is associated with congenital thinning of the anterior wall of the left ventricular outflow where the right aortic sinus contacts the membranous septum. 

Antenatal diagnosis is reliable after 18 weeks gestation; however, in this period it is difficult to suspect it. Most often, this defect is diagnosed between the 22 and 24 weeks gestation.

Anatomy

Aorto-left ventricular tunnel is more common.



The ascending aorta is extended. A tunnel, covered with an epicardium, passes from the anterior- left or anterior-right surface of ascending aorta above the level of the coronary arteries. AVT may be tubular or have an aneurysmatic shape. The aortic opening of the tunnel is usually located at the level of the commissure of the valve and is separated from the right sinus of the Valsalva by a protruding transverse ridge. The tunnel is located outwards from the fibrous ring, to the right of the pulmonary trunk, where it immerses into the myocardium near the interventricular septum.

The tunnel can displace the outflow part of the interventricular septum to the right, creating subpulmonary stenosis. Occasionally, the tunnel opens into the infundibular part of the right ventricle. At different levels along the tunnel, its wall may form aneurysms.

AVT can be associated with VSD, aortic stenosis or aortic atresia with left ventricular hypoplasia and pulmonary valvular and subvalvular stenosis.

Classification

1. AVT from the right sinus of Valsalva;
2. AVT from the left sinus of Valsalva.

Hemodynamics

Hemodynamic disturbances are associated with blood regurgitation from the aorta to the ventricle. Hemodynamic changes depend also on association of AVT with other congenital heart defects.

The tunnel does not create obstacles to the free blood flow in all phases of the cardiac cycle. A certain amount of blood flows back into the ventricle during systole. The ventricle is experiencing volume overload. In these patients cardiomegaly and heart failure develops quickly. As these changes occur already in the prenatal period, heart failure may occur soon after the birth. 

Without concomitant CHD, hemodynamic changes are associated also with permanent insufficiency of blood flow from the aorta while the aortic valve cusps are intact.

Workup

• ECG. Hypertrophy of the left ventricle and left atrium.
• Doppler echocardiography, CT. Visualization of the AVT and DDx.
• Chest X-ray. Signs of congestive heart failure, increased heart shadow, enlargement of the ascending aorta, bulging aortic sinus.
• Cardiac catheterization with aortography. To exclude concomitant intracardiac anomalies.
• Echocardiography, Doppler-cardiography and aortography make it possible to distinguish this defect from:
• the aortic valve insufficiency due to the absence of retrograde blood flow through the aortic valve;
• the presence of a coronary fistula opening into the left ventricle due to the presence of normal right and left main coronary arteries; 
• the concomitant VSD due to the absence of a blood shunt through a defect; 
• the rupture of SVA due to the anterior arrangement of AVT and the absence of dilatation of the aortic sinuses. 

Clinical presentation

As the presence of AVT affects hemodynamics already in the prenatal period, heart failure may occur soon after the birth. Clinical presentation of volume overload: tachycardia, dyspnea, enlarged liver.

In general, the clinical picture resembles aortic insufficiency. Continuous murmurs are heard to the left of the sternum and at the apex of the heart. The pulse is high, the diastolic blood pressure is low.

Treatment

Confirmed diagnosis is an indication for surgery. It should be performed as soon as possible.



Surgical approaches involve closure of the aortic and/or ventricular opening of the tunnel. Closing the two ends is preferable as it prevents further dilatation of the tunnel. Special attention must be paid to the coronary arteries and the aortic valve to prevent its damage. 

In the late postoperative period, some patients can develop aortic valve deformity, and later plastic surgery or prosthetics can be required. Early operations lead to rapid recovery of heart function and aortic valve dysfunction.