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Clinical and echocardiographic features of aorto-atrial fistulas
© Ananthasubramaniam; licensee BioMed Central Ltd. 2005
Received: 19 December 2004
Accepted: 17 January 2005
Published: 17 January 2005
Aorto-atrial fistulas (AAF) are rare but important pathophysiologic conditions of the aorta and have varied presentations such as acute pulmonary edema, chronic heart failure and incidental detection of the fistula. A variety of mechanisms such as aortic dissection, endocarditis with pseudoaneurysm formation, post surgical scenarios or trauma may precipitate the fistula formation. With increasing survival of patients, particularly following complex aortic reconstructive surgeries and redo valve surgeries, recognition of this complication, its clinical features and echocardiographic diagnosis is important. Since physical exam in this condition may be misleading, echocardiography serves as the cornerstone for diagnosis. The case below illustrates aorto-left atrial fistula formation following redo aortic valve surgery with slowly progressive symptoms of heart failure. A brief review of the existing literature of this entity is presented including emphasis on echocardiographic diagnosis and treatment.
A 66 year old male with history of rheumatic heart disease and aortic valve replacement (AVR) (twice for severe native and subsequent prosthetic valve regurgitation) presented with progressive worsening fatigue, exertional dyspnea and paroxysmal nocturnal dyspnea. His other medical problems included poorly controlled hypertension and hyperlipidemia. Following his second AVR 4 years prior to this presentation, a routine follow-up 2-dimensional echocardiogram (TTE) had shown preserved left ventricular and prosthetic valve function and a aorto-atrial fistula with color flow between the aorta-and the left atrium. Notably, only a soft and short ejection murmur across the mechanical prosthesis was appreciated and no continuous murmurs were heard. This was felt to be a possible postoperative complication currently not of clinical significance given his asymptomatic status and he was treated medically and did well for the last 3–4 years.
In a large collection of about 4000 cases of thoracic aortic aneurysms, Boyd first reported AAF as an incidental finding on autopsy back in 1924 . Most of common etiologies of AAF are related to its occurrence as a result of bacterial endocarditis, paravalvular abscess, ruptured sinus of Valsalva, aortic dissection and possibly of congenital etiology [2–6].
Clinical presentation of AAF could vary from an acute presentation with acute chest pain syndrome due to rupture in the setting of dissection  or a refractory heart failure picture in the setting of endocarditis  and aortic dissection . In a previous report we have highlighted the fulminant course of prosthetic valve endocarditis due to Proteus mirabilis leading to aorto-right atrial fistula from rupture of a pseudoaneurysm secondary to prosthetic valve endocarditis . Isolated case reports of AAF as an immediate postoperative complication has also been reported .
Role of Echocardiography
TTE and TEE form an integral part of assessment of patients presenting with chest pain and heart failure symptoms particularly if audible murmurs or valvular pathologies are suspected. TTE is the intial test of choice in routine prosthetic aortic valve assessment and gradients estimation. Nevertheless TEE is superior to TTE in real time assessment of prosthetic valve function and morphology and for better delineation of intracardiac pathology such as complications of endocarditis namely root abscess and fistulas [7, 11, 12]. TEE has better signal to noise ratio and proximity of transducer to the heart leading to higher quality images with lesser attenuation. Furthermore since aorto-left atrial fistulas usually occur from the posterior aspect of the aorta, this area is better delineated with TEE than TTE. Turbulent flow of AAF can be mistaken on TTE particularly if near the prosthetic valve for prosthetic malfunction in the setting of endocarditis or heart failure. Inter-chamber communications and the fistulous tracts that are particularly small are best tracked by multiplane TEE. The exact origin, chamber communications and even the size of the fistulous opening can be well assessed by TEE. Furthermore, coexistent complications with AAF in the setting of aortic endocarditis such as presence of annular abscess, extension to the upper interventricular septum or the subaortic area and pseudoaneurysm formation are best seen by TEE. Nevertheless cases of underestimation of cardiac involvement also been reported with TEE . This reveals the limitations of viewing a three dimensional structure such as the heart in a two dimensional fashion, a void which may be filled by 3-dimensional (3-D) echocardiography.
This case highlights the importance of intraoperative TEE in guiding valvular surgery identifying potential intraoperative cardiac complications, which can be corrected in the same setting. Since repeat sternotomy and cardiac surgery by itself carries a higher risk of perioperative complications, intraoperative pre and post pump TEE play an integral role in guiding the surgeons as to any new complications which may have risen during surgery. This is more so in valve surgeries or aortic reconstruction surgery where a real time 2-D TEE with color assessment pre and post pump provides important information regarding success of surgical intervention and new complications.
Since clinical diagnosis of AAF is difficult, definitive diagnosis is by a thorough echocardiographic evaluation (TTE and TEE). Apart from antibiotic treatment for endocarditis, definitive treatment revolves around surgical correction. Since many of these patients may have had some form of surgical intervention in the past , reoperation is challenging. Mortality is high in patients who are continued on medical therapy particularly in the setting of aortic dissection [5, 7]. Surgical intervention consists of repairing the affected aortic segment, replacing prosthesis if the valve is destroyed, annular debridement in the setting of abscess and suture of the fistula.
Aorto atrial fistulas are rare but important complications of many disease processes of the aorta and aortic valve. Classical clinical signs of continuous murmurs may not be present and echocardiography forms the cornerstone of diagnosis. AAF should be suspected in patients with poorly controlled heart failure and prior aortic surgery. Prompt surgical repair is usually helpful in relieving symptoms and decreasing mortality.
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