Cardiovascular Anesthesiology: Echo Didactics & Rounds
A 65-yr-old man with a medical history significant for coronary artery disease presented with aortic prosthetic valve endocarditis. Six months before admission, he had an aortic valve replacement for aortic insufficiency due to native aortic valve endocarditis. The preoperative transthoracic echocardiogram (TTE) demonstrated a “rocking” aortic prosthetic valve with severe periprosthetic regurgitation. No specific notation was made regarding mitral valve structure; however, a “wall-hugging” systolic jet in the left atrium was interpreted as mitral regurgitation. Based on the preoperative TTE, the surgical plan was to replace the infected prosthetic aortic valve. Mitral valve repair was considered based on the regurgitant jet.
The intraoperative transesophageal echocardiogram (TEE) confirmed the diagnosis of severe prosthetic regurgitation. A periannular abscess with involvement of the junctional zone between aortic and mitral valve annulus, also called “mitral–aortic intervalvular fibrosa” (Fig. 1) was noted. Color flow Doppler demonstrated two distinct perforations: First, through the posterior (superior) portion of left ventricular outflow tract, at the insertion of the anterior mitral leaflet. A second perforation was seen at the Sinus of Vasalva corresponding to the area of the noncoronary cusp (Figs. 2 and 3). On frame-by-frame analysis, it was apparent that regurgitant blood flow extended around the infected aortic valve prosthesis into the left atrium through these perforations. An eccentric jet parallel to the plane of the mitral valve was observed (video loop; supplemental data at www.anesthesia-analgesia.org). The mitral valve appeared to be intact, and only minimal mitral regurgitation was seen. Lastly, color flow Doppler also showed a bulging intraatrial septum with patent foramen ovale and left to right shunt.
The surgical procedure consisted of the removal of the infected valve and a replacement by a bileaflet mechanical valve. The fistula tracts were obliterated by sutures taken from the annulus of the anterior mitral valve leaflet exiting through the aortic side of the aortic annulus. The patent foramen ovale was closed by patch repair through a right atrial incision. Complete repair was confirmed by TEE. The patient recovered well and was discharged on the tenth postoperative day.
Endocarditis after prosthetic valve implantation occurs in 2%–4% of patients. In patients with aortic valve endocarditis, periannular abscesses have been reported in up to 80% and intracardiac fistula formation in 14% of patients, respectively (1). The junctional zone between the mitral and aortic valve annulus, also known as “mitral–aortic intervalvular fibrosa,” is relatively avascular and offers little resistance to spread of abscesses, aneurysm, and fistula formation (2). In a mixed series of 55 patients with native or prosthetic aortic valve endocarditis, 44% were found to have complications in that region, of which 13% were fistulae into the left atrium. Perforation of the anterior mitral valve leaflet also occurred in 13% of patients, and similar to this Echo-Rounds, an eccentric “mitral regurgitation-type” jet was observed in 15% of patients (2). Occasionally, aortic prosthetic valve abscesses involving the left ventricular outflow tract can lead to fistula formation into the right atrium (3).
Aorto–atrial fistulas involving the left atrium are better visualized by TEE because of the proximity of the transducer to the structures of interest (4). Technical limitations for the assessment of prosthetic valves, such as reverberation, attenuation, and other image artifacts, are diminished with TEE compared to TTE. For optimal imaging of a prosthetic aortic valve, the midesophageal short- and long-axis aortic views are preferred.
To optimize the accuracy of color flow Doppler, a Nyquist limit of 50–60 cm/s should be chosen (5). As pulse repetition frequency is inversely related to jet area, a substantial error in the size of the color flow Doppler jet can be introduced with higher or lower than the recommended settings. To maximize image quality and temporal resolution, the smallest color flow box size and minimal depth settings should be used (5).
In the case presented, a periannular aortic valve abscess had perforated into the left atrium, producing a systolic jet on color flow Doppler that was misinterpreted as mitral regurgitation on preoperative TTE. Intraoperative TEE established the correct diagnosis of aorto-left atrial fistula with a competent mitral valve. The fistula could be repaired through the aortic incision simultaneously with the aortic valve replacement. Intraoperative TEE diagnosis of an aorto–atrial fistula and documentation of normal mitral valve anatomy avoided opening of the left atrium and unnecessary inspection of the mitral valve.
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