Use of multidetector-row computed tomography scan to detect pannus formation in prosthetic mechanical aortic valves

Abstract

Aortic valve replacement (AVR) is the second most common cardiothoracic procedure performed in the United States (1) and Europe (2). Surgically or percutaneously implanted, the results of AVRs are uniformly good and the number of patients have been steadily increasing over the last decades (3). Although most of the newly implanted devices are tissue valves, yet a sizable number are mechanical especially in young patients with rheumatic disease. The latter group is predominant in non-Caucasian populations where the rheumatic disease is the most common aetiology (4).In parallel, during the same years computed tomography (CT) scan technology evolved substantially offering excellent resolution and the ability to identify the commonest and most challenging complications of AVR (5). In particular, ECG-gated CT scan proved to be more reliable than echocardiography in identifying pannus, the most insidious long-term complication of mechanical valves. CT scan techniqueImages are usually acquired using retrospective ECGgated protocols with cardiac phase reconstruction at 5% to 10% RR interval increments. Both systolic (at 20% to 40% of RR interval) and diastolic phase (at 70% to 90% RR interval) are usually necessary. With these modalities, more than 90% of the valves can be accurately evaluated (6). As opposed to retrospective triggering, prospective ECG-gated protocols tend to generate less artifacts and require lesser radiation doses. However, they can be used only in patients with regular heart rate. When the patients are in atrial fibrillation, short acting beta-blockers can be used during the acquisition phase. However, with faster heart rates best results are obtained with dual source CT scan.CT data are reconstructed by a separate workstation for post-processing where oblique coronal or oblique sagittal images of the aortic root are assembled (Figure 1). By using a multiplanar image technique, profile and enface views of the prosthetic aortic valve showing the least amount of motion artifacts are generated. The presence or absence of a subprosthetic pannus is determined by the examiner as the appearance of a low-attenuation lesion or a calcified lesion Abstract: Obstruction of a mechanical aortic valve by pannus formation at the subvalvular level is a major long-term complication of aortic valve replacement (AVR). In fact, pannus is sometime difficult to differentiate from patient-prosthesis mismatch or valve thrombosis. In most cases cine-angiography and echocardiography, either transthoracic or transesophageal, cannot correctly visualize the complication when the leaflets show a normal mobility. Recent technological refinements made this difficult diagnosis possible by ECG-gated computed tomography (CT) scan which shows adequate images in 90% of the cases and can differentiate pannus from fresh and organized thrombus.

Challenging Cases of Aortic Prosthesis Dysfunction, the Importance of Multimodality Imaging, a Case Series

“…The distinction between a pannus and a thrombus may be challenging [ 3 , 12 ]. It has been shown by recent studies that MDCT is a very sensitive technique capable of differentiating a pannus from a thrombus by detecting its exact location and measuring its attenuation [ 14 , 15 ]. A pannus usually affects the ventricular side of the PHV and has attenuation similar to myocardium [ 12 ]; on the contrary, a valvular thrombus usually has lower attenuation and preferentially involves the aortic side of the prosthesis [ 12 ].…”

The Role of Multimodality Imaging in Left-Sided Prosthetic Valve Dysfunction

“…The use of cardiac CT for the assessment of possible prosthetic aortic valve dysfunction has risen rapidly over the past 10 years. One important reason for this is that CT can differentiate between thrombus and fibrotic pannus ingrowth based on Hounsfield units, with thrombus having lower attenuation than fibrotic pannus ingrowth [20]. CT can also help in the identification of premature bioprosthetic leaflet degeneration, in the assessment of mechanical leaflet motion and in the assessment of aortic root abscess formation [14,21].…”

“…Once again, CT images, which can be reconstructed in any desired imaging plane after acquisition, could provide an accurate definition of PVL due to endocarditis and root abscess and their relationship with the Valsalva sinus and the coronary artery [13,20,21].…”

Extent of Subprosthetic Pannus after Aortic Valve Replacement: Changes Over Time and Relationship with Echocardiographic Findings

“…However, as it is often difficult to visualize the exact cause of prosthetic valve dysfunction even by TEE, cardiac CT can be used as a complementary method to more clearly evaluate the dysfunction of the prosthetic aortic valve (2,(7)(8)(9)(10)(11)(12)(13)(14)(15)(16).…”

“…A 42-year-old female who underwent aortic valve replacement using a 21-mm St. Jude valve 5 years ago.A. Initial CT image shows pannus formation (arrowheads); maximal width, 2.7 mm; pannus area, 40.16 mm 2 ; and effective orifice area, 275.84 mm2 . B.…”