Discussion

Aorto-left ventricular tunnel is a rare congenital cardiac defect which has an uncertain aetiology but is thought to evolve from a maldevelopment of the cushions which give rise to the aortic and pulmonary roots and abnormal separation of these structures. ^{Reference McKay3}

Hovaguimian et al. proposed a classification in 1988 as a way to guide the surgical strategy. ^{Reference Hovaguimian, Cobanoglu and Starr4} Type 1 is a simple tunnel with a slit-like opening at the aortic end and no aortic valve distortion. Type 2 is a large extracardiac aortic wall aneurysm of the tunnel with an oval opening at the aortic end, with or without valvular distortion. Type 3 has an intracardiac aneurysm of the septal portion of the tunnel, with or without right ventricular outflow tract obstruction. Type 4 is a combination of types 2 and 3. ^{Reference Hovaguimian, Cobanoglu and Starr4} In our series, two patients had a type 1 aorto-left ventricular tunnel (patient one and three) and two patients had a type 2 aorto-left ventricular tunnel (patient two and four). This classification has been used subsequently by some institutions in guiding which cases are best suited to transcatheter closure, ^{Reference Kathare, Subramanyam, Dash, Muthuswamy, Raghu and Koneti5} with recommendations for only closing type 1 aorto-left ventricular tunnel using a transcatheter approach.

The clinical presentation is variable with previous reports having demonstrated the heterogeneity of the presentations from asymptomatic patients referred with a murmur to acutely unwell neonates with complex cardiac anatomy. ^{Reference Kathare, Subramanyam, Dash, Muthuswamy, Raghu and Koneti5} This case series confirms the previous reports and also highlights the importance of the clinical examination prior to echocardiography. Patients with aorto-left ventricular tunnel will often demonstrate “to and fro” murmurs associated with thrills and bounding pulses. This can be difficult to distinguish from severe aortic regurgitation but in aorto-left ventricular tunnel the second heart sound will be normal. ^{Reference McKay3} The classic clinical examination findings complement the imaging modalities. Interestingly, one of our patients presented with ventricular noncompaction/hypertrophic cardiomyopathy phenotype in combination with dysplastic aortic and pulmonary valves which has been previously described in this setting. ^{Reference Vijayalakshmi, Chitra and Prabhu Deva6}

Echocardiography is the primary imaging modality and in the majority of cases is sufficient in making the diagnosis of aorto-left ventricular tunnel. ^{Reference Martins, Sherwood, Mayer and Keane7} We demonstrate (Fig 1 and 2) how useful echocardiography can be in establishing the diagnosis but also how important multi-modality imaging can be when presented with rare cardiac lesions. Trans-thoracic parasternal long-axis and parasternal short-axis views best demonstrate the location, size, and effect of the tunnel on the aortic valve. The use of contrast-enhanced CT in three of the cases (Fig 3) was helpful in outlining the tunnel further and clarifying its relationship to the coronary arteries prior to intervention.

Figure 1. Transthoracic echocardiography with a parasternal long- (left image) and short-axis (right image) views demonstrating the length of the aorto-left ventricular tunnel (ALVT)(*). Ao: aorta, LV: left ventricle, LA: left atrium, RC: right coronary cusp, LC: left coronary cusp, NC: non-coronary cusp.

Figure 2. Colour doppler imaging of the aorto-left ventricular tunnel (ALVT)(*) in a parasternal long-axis view. Ao: aorta, LV: left ventricle, LA: left atrium.

Figure 3. Computed tomography contrast image on aorto-left ventricular tunnel (ALVT) (*). Ao: aorta, LV: left ventricle, LA: left atrium, RV: right ventricle.

The mainstay of treatment is procedural with medical management reserved for the interim period prior to the tunnel being closed. Older reports focus primarily on surgical closure, ^{Reference Martins, Sherwood, Mayer and Keane7} with some more recent reports ^{Reference Diraneyya, Alhabshan, Alghamdi, Moafa, Alnasef and Kabbani8} describing successful surgical closure but the importance of long-term follow-up for aortic valve disease in a five patient data series. However, in more recent times, transcatheter closure has been described as a safe and feasible alternative. Chessa et al. first reported on the transcatheter closure using a Amplatzer patent ductus arteriosus occluder device (AGA Medical Corporation, Golden Valley, Minnesota) in a 14-year-old boy with a good outcome and no follow-up complications. ^{Reference Chessa, Chaudhari and De Giovanni9} A subsequent report has demonstrated the use of transcatheter closure in a child with left ventricular non-compaction cardiomyopathy who would not tolerate surgical closure. ^{Reference Vijayalakshmi, Chitra and Prabhu Deva6}

In this series, three of the four children underwent a transcatheter approach as first-line treatment strategy (Fig 4). The fourth case had multiple anomalies which required surgical repair. In the three cases, there were no peri-procedure complications and for the two patients who were asymptomatic, they were discharged 24 hours after admission. There were no cases of coronary artery compression or distortion of the aortic valve.

Figure 4. AP angiographic image demonstrating device position and occlusion of the aorto-left ventricular tunnel (ALVT).

Follow-up of the four patients revealed that patients one and four had mild aortic regurgitation before and after the procedure that has persisted at the most recent follow-up. Patient 2 had dysplastic aortic and pulmonary valves as well as the aorto-left ventricular tunnel and underwent a cardiac transplantation soon after surgical repair. Patient 3 had a complex background with hypoplastic left heart syndrome who had undergone a Norwood Sano operation and subsequently a bidirectional Glenn 2 years prior to the diagnosis. There was no aortic regurgitation before the aorto-left ventricle tunnel diagnosis or after its closure. They have subsequently undergone a cardiac transplantation for right ventricular failure.