Leveraging Color M-Mode to Diagnose Aorto-Atrial Fistula as a Complication of Infective Endocarditis

Abstract

Aorto-atrial fistula is a rare and life-threatening complication of infective endocarditis, classically diagnosed by visualizing a connection between the aorta and atrium with associated continuous flow. A patient presented with bioprosthetic and native valve enterococcal endocarditis with multiple complications, including an aorto-atrial fistula that was diagnosed by color M-mode on transesophageal echocardiography. We review the features of aorto-atrial fistula and utilize this case to demonstrate how M-mode can be leveraged to provide improved temporal resolution in the setting of diagnostic uncertainty.

Figure 1

Select images from the (a, b) initial transesophageal echocardiogram performed upon admission to the referring hospital and (c, d) follow-up transthoracic echocardiogram performed upon transfer to our tertiary academic medical center. (a) Midesophageal short-axis view demonstrating thickened bioprosthetic aortic valve leaflets with vegetation (arrow). (b) Midesophageal four-chamber view showing large vegetation along the anterior leaflet of the mitral valve. (c) Parasternal short-axis view of bioprosthetic aortic valve in diastole with color flow suggestive of aortic valve regurgitation (arrow). (d) Apical five-chamber view in diastole showing high-velocity flow in the left ventricular outflow tract consistent with aortic valve regurgitation (arrow).

Figure 2

Transesophageal echocardiogram obtained approximately two weeks into hospital stay. (a–c) Bulky vegetation on the mitral valve extending along the aorto-mitral curtain with associated mitral regurgitation and possible leaflet perforation that are not well-characterized. (d) High-velocity flow in the LVOT concerning for regurgitation, as well as (e) an abnormal lucency along the aorto-mitral curtain consistent with abscess and possible fistula (yellow arrow). (f) There was high-velocity flow associated with the abscess by color Doppler (white arrow); however, in the context of tachycardia and adjacent LVOT flow, it was difficult to discern the timing of flow in the cardiac cycle.

Figure 3

Color M-mode was used to differentiate flow along the aorto-mitral curtain from aortic regurgitation in the LVOT. The temporal resolution from M-mode clearly defines continuous, turbulent flow within the space adjacent to the aorto-mitral curtain, consistent with fistula between the aorta and left atrium. Flow within the LVOT occurs predominantly in systole, which is inconsistent with aortic regurgitation.

Figure 4

Three-dimensional transesophageal echocardiography. (a) Reference three-dimensional echocardiography showing thickened aortic valve leaflets (∗). (b, c) Three-dimensional color Doppler images suggesting continuous flow across the aorto-mitral continuity in both systole ((b) color denoted by a white arrow is multifactorial from mitral regurgitation and fistula flow) and diastole ((c) yellow arrow) supporting the diagnosis of aorto-atrial fistula.