Discussion

Mitral regurgitation in the neonatal period is relatively rare and can be a result of a congenital malformation or deformation secondary to volume load of the ventricle. ^{Reference Carpentier, Branchini and Cour1,Reference Shah, Zhong and Minutello2} Less commonly, it can be due to coronary artery abnormalities. ^{Reference Memon, Amanullah and Atiq3,Reference Ahmad, Haw and Vettukattil4} The mitral valve has two papillary muscles that connect to the leaflets via the chordae tendineae. The anterolateral papillary muscle typically receives blood supply from the left circumflex and left anterior descending artery. The posteromedial papillary muscle is supplied by the right coronary artery in a right dominant system (most common) and by the left circumflex artery in a left-dominant system. ^{Reference Rajiah, Fulton and Bolen5} The papillary muscles play an important role in valve function and are the last portion of the heart to be perfused, resulting in a higher risk for ischaemia. ^{Reference Rajiah, Fulton and Bolen5} Ischemia of these papillary muscles results in mitral valve dysfunction and subsequent regurgitation. Although this is a well-established phenomenon, our case describes a particularly unusual mechanism for the development of mitral valve dysfunction: ischaemia occurring as a result of intermittent obstruction of the left coronary os by a dysplastic left aortic valve cusp. More commonly described mechanisms for this echocardiographic finding, albeit still very rare, include anomalous left coronary artery from pulmonary artery and left main coronary artery atresia.

This rare finding of left coronary artery occlusion by an aortic valve cusp has been described in the literature, primarily in older children and adults. To the best of our knowledge, there has been only one previously reported case of this finding in the neonatal period. However, ours appears to be the only case that presented primarily with progressive mitral valve insufficiency. Samuel et al. described a case of a 15 days old with a known dysplastic aortic valve with moderate aortic regurgitation who presented in cardiogenic shock with ischaemic changes on EKG. Both a cardiac MRI and cardiac catheterisation were performed to delineate coronary artery anatomy, neither of which provided a clear aetiology for this presentation. In the operating room, direct surgical inspection revealed obstruction of the left coronary os by the left coronary leaflet. ^{Reference Samuel, Dhanantwari and Meyer6} The other cases found in the literature describe older children and adults, who presented with syncope, shortness of breath, angina, or sudden death. On echocardiogram, they commonly had aortic regurgitation or supravalvular aortic stenosis. ^{Reference Ahmari, Schaff, Click and Chandrasekaran7–Reference Waxman, Kong, Behar, Sabiston and Morris9}

The aortic valve is typically well-visualised by transthoracic echocardiography, allowing for delineation of the morphology of the commissures and fusion of leaflets. In addition, transthoracic echocardiography with colour Doppler is an important tool for evaluation of the coronary arteries and can reliably image the proximal coronary arteries. ^{Reference Lai, Mertens, Cohen and Geva10} In our case however, echocardiography did not serve as a reliable tool for diagnosis. On this patient’s echo, the left coronary artery had a normal origin with antegrade flow and no stenosis of the vessel itself. Thus, although echocardiography is useful for diagnosis of coronary artery abnormalities, this unique abnormality of the aortic valve cusp with subsequent left coronary artery occlusion was not able to be visualised. This case demonstrates the utility of cardiac catheterisation in the functional assessment of both the aortic valve and the coronary arteries.