Aorta-right atrial tunnel is a rare congenital condition. Its incidence is unknown, because most patients are asymptomatic with only a continuous murmur on examination. Symptoms, when present, are usually due to significant left-to-right shunt, pulmonary overcirculation, arrhythmia, and heart failure due to volume overload.1 A review of published reports showed that patients may present at any age, from neonates2 to young adults.1 Our patient was unusual in his advanced age at presentation because there is only 1 previous report of aorta-right atrial tunnel in a septuagenarian.3 Furthermore, in this case, the tunnel was undiagnosed despite a previous transthoracic echocardiogram.
A number of conditions can lead to an abnormal blood return to the RA (Table 1). Coronary-cameral fistula occurs when an aberrant branch of coronary artery drains directly into one of the cardiac chambers causing ischemia and heart failure, usually in utero. Adults with aneurysmal coronary arteries have also been described, either causing external compression of the heart4 or forming a fistula that drains into the RA.5 In our patient, the RCA was of normal caliber and followed a normal course. However, we cannot dismiss the possibility that this was a very proximal fistula originated at the RCA ostium. Also in older patients, a sinus of Valsalva aneurysm and subsequent rupture into the RA is more common than aorta-right atrial tunnel. One institution reported 9 cases of aorta-right atrial tunnel compared with 66 cases of ruptured aneurysm during a 10-year period.1 The key distinction between the 2 is the extra-cardiac location of aorta-right atrial tunnel and its tortuous course. Other causes include trauma, endocarditis, and complications from surgeries involving the aortic valve, ascending aorta, and ventricular and atrial septal defects. A fistula between a saphenous vein graft and RA have also been reported in patients who had coronary bypass surgery.6 One clinical scenario worth mentioning is the Cabrol shunt. For ascending aorta surgeries with difficult hemostasis, the Cabrol shunt is a perigraft space-to-RA conduit used to decompress the perigraft space. This shunt is expected to close spontaneously but may remain open for some time.7
To our knowledge, this is the first published report of TEE images of aorta-right atrial tunnel. Compared with a transthoracic echocardiogram, TEE is more sensitive due to the probe’s proximity to the relevant structures and freedom to optimize echographic windows with distorted anatomy. While the aorta-right atrial tunnel in our patient originates from the right sinus and is anterior to the aorta, most originate from the left sinus and take a retro-aortic course. We were able to demonstrate the proximal origin of the tunnel from the sinus of Valsalva, its extra-cardiac location, and its termination into the RA near the SVC. Two-dimensional TEE cannot capture its tortuous course in entirety. However, by focusing on the region and using a small adjustment of probe depth and multiplane angles, we were able to capture the tubular tunnel in its short axis. Last, the case highlights that not all left-to-right shunts are necessarily intracardiac, and the continuous Doppler signal suggests the arterial origin of the shunt.
The differential diagnosis of abnormal fistulous connection between the aorta and the RA should include the aorta-right atrial tunnel. Its complex anatomy requires multiple imaging modalities including TEE. Sometimes, as in this case, the distinction between aorta-right atrial tunnel and a coronary artery fistula remains unclear. The need for and timing of surgical intervention of patients with this pathology should be based the severity of symptoms.
Clinician’s Key Teaching Points
By Nikolaos J. Skubas, MD, FASE, Donald Oxorn, MD, and Martin J. London, MD
- An extra-cardiac communication between the left (more commonly) or right sinus of Valsalva and the right atrium (RA) is a rare congenital defect known as an aorto-RA tunnel. It usually presents in younger patients with a continuous murmur. Over time, the left-to-right shunt results in pulmonary volume overload. The first echocardiographic sign is often an abnormal color flow signal into the RA.
- The differential diagnosis of an abnormal color flow signal in the RA includes a congenital fistula between a coronary artery and a cardiac chamber, an iatrogenic communication between the ascending aorta and the RA (as in a Cabrol shunt), and aneurysms of a coronary artery, a saphenous vein bypass graft, or a sinus of Valsalva, all of which may develop fistulous tracts into the RA. In addition, these pathologies may cause extrinsic compression to neighboring structures.
- In this case of an elderly patient with multiple regurgitant valves, an arteriovenous fistula between the sinus of Valsalva and the RA was diagnosed with angiography. With intraoperative transesophageal echocardiography (TEE), a large tortuous vessel with an anterio-posterior course, abutting the right coronary artery and draining into the RA, was imaged in the midesophageal aortic valve long-axis, short-axis, and bicaval views. Its extra-cardiac course, anterior to the aorta, was verified by slowly withdrawing the TEE probe to the midesophageal ascending aorta short-axis view. Examination with color Doppler imaging revealed continuous, left-to-right flow between the aorta and the RA.
- The proximity of the TEE probe to the atria may enable the correct diagnosis of rare, abnormal communications between cardiac structures. It may be possible to follow the tortuous course of an abnormal communication by using appropriate multiplane rotation of the transducer and making small adjustments in probe depth. Doppler color flow imaging should be used to determine the direction and duration of the abnormal flow.
Name: Ali Salehi, MD.
Contribution: This author helped write the manuscript.
Attestation: Ali Salehi approved the final manuscript.
Name: Wilson W. Cui, MD, PhD.
Contribution: This author helped write the manuscript.
Attestation: Wilson W. Cui approved the final manuscript.
This manuscript was handled by: Martin J. London, MD.
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