Ann Thorac Surg 2004;77:523-526
© 2004 The Society of Thoracic Surgeons
Original article: cardiovascular
Usefulness of a multidetector-row computed tomography scanner for detecting pannus formation
Hideki Teshima, MDa*,
Nobuhiko Hayashida, MDa,
Shuji Fukunaga, MDa,
Eiki Tayama, MDa,
Takemi Kawara, MDa,
Shigeaki Aoyagi, MDa,
Masafumi Uchida, MDb
a Department of Surgery, Kurume University, School of Medicine, Kurume, Japan
b Department of Radiology, Kurume University, School of Medicine, Kurume, Japan
Accepted for publication August 6, 2003.
* Address reprint requests to Dr Teshima, Department of Surgery, Kurume University, School of Medicine, 67 Asahi-machi, Kurume 830-0011, Japan
e-mail: tesshi{at}med.kurume-u.ac.jp
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Abstract
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BACKGROUND: Prosthetic valve dysfunction (PVD) as a result of pannus or thrombus formation is an infrequent but serious complication. Currently available diagnostic tools, however, are insufficient to detect a minute pannus and thrombi. The use of a more advanced diagnostic image, multidetector-row computed tomography scanner, may enable us to determine the anatomic and functional causes of PVD.
METHODS: Patients who underwent aortic valve replacement with a St. Jude Medical valve were examined by transthoracic echocardiography and cineradiography to diagnose PVD. Sixteen patients with PVD (PVD group) and 12 patients with normal prosthetic valve function (control group) were studied using the multidetector-row computed tomography scanner. The multidetector-row computed tomography findings in 2 patients with PVD were validated by the observations during reoperation.
RESULTS: In 13 of 16 patients (81%) in the PVD group and 3 of 12 patients (25%) in the control group, multidetector-row computed tomography demonstrated that an abnormal small tissue, regarded as pannus, was found to extend from the left ventricular septum into the pivot guard. These findings were confirmed by the observations during reoperation in 2 patients in the PVD group.
CONCLUSIONS: Multidetector-row computed tomography can be a useful diagnostic technique for anatomic and functional evaluation of PVD as a result of pannus formation.
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Introduction
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Prosthetic valve dysfunction (PVD) as a result of pannus formation is an infrequent but serious complication [1–6]. However, the mechanism of pannus formation has not been fully proven yet. Multidetector-row computed tomography (MDCT) scanner has many detectors for the direction of axis from head to foot, and permits high-speed scanning of large volumes with a high resolution [7–9]. A combination of MDCT and gating electrocardiography may enable the detection of images without the unique artifacts that result from leaflet motion [10].
Many recent clinical and histologic studies have reported pannus formation related to prosthetic valve [1, 3, 4, 10–12]. Currently available diagnostic tools, however, are insufficient to detect a minute pannus and thrombi. Although cineradiography is essential in the diagnosis of obstructive leaflet movement [13], the method is unable to determine the cause. Although echocardiography is also a noninvasive and feasible diagnostic method, artifacts resulting from leaflet movement and lower resolution of the ultrasonic image may interfere with detailed observations of periannular morphology [12]. Magnetic resonance imaging also presents a problem; the prosthetic valve is detected as a defective image [14]. Recently we reported that the use of a more-advanced diagnostic image, MDCT, was useful in the diagnosis of PVD in a patient [15]. The technique, therefore, may enable us to elucidate the morphologic and functional cause of PVD.
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Material and methods
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Patients who underwent aortic valve replacement with a St. Jude Medical (St. Jude Medical Inc, St. Paul, MN) valve were examined by transthoracic echocardiography and cineradiography to diagnose PVD. Sixteen patients with PVD (PVD group) and randomly selected 12 patients with normal prosthetic valve function (control group) were studied. The diagnosis of PVD was determined by the deterioration of prosthetic valve function by transthoracic echocardiography and the obstruction of more than 20 degrees in the opening angle by cineradiography (the opening angle was calculated as the distance between the two leaflets in the fully open position) [13, 16]. Patients' profiles are summarized in Table 1.
The MDCT system was a Light Speed ULTRA (GE Medical Systems, Yokogawa Medical System, Tokyo, Japan) of the 8 slice/8 DAS type (20-cm field of view, 512 x 512 matrix, and 1.25-mm collimation of eight detectors' array scanner) with electrocardiographic-gated half reconstruction. We infused 120 mL of a contrast medium, using nonionic iodide, through an intravenous rapid injector. Scanning was started from 30 seconds after the beginning of contrast medium administration. Images were viewed using the workstation version of INTAGE RV version 1.3 (INTAGE RV, KGT Inc, Kubota, Tokyo, Japan) after being converted into DICOM data (Digital Imaging and Communications in Medicine; National Electrical Manufacturers Association, Rosslyn, VA). The images were described using the method of multiplanar reconstruction and three-dimensional technique. The conditions of multiplanar reconstruction were selected in optimal ranges from 100 to 200 in window level and 400 to 500 in window width. We measured the cardiac dimension for all cases viewed by the workstation version of INTAGE RV. The image was oriented to the corresponding transthoracic echocardiographic view. The variables measured were the diameter of left ventricular outflow tract, interventricular septum thickness, posterior wall thickness, and left ventricular end-diastolic dimension. When pannus was described in the long-axis tomographic section view of the MDCT image, we measured the length from the edge of pannus to the pivot guard.
The statistical analysis was performed with StatView software (SAS Institute Inc, Cary, NC). The data were expressed as the mean ± the standard deviation. Continuous variables were compared using the Student's t test, and categorical variables were compared by 
2 test. The statistical significance was assumed at a probability level of less than 0.05.
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Results
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Multidetector-row computed tomography clearly detected the aortic prosthetic valve in the closed position. However, artifacts associated with leaflet motion of the mitral prosthetic valve were demonstrated in cases with aortic valve replacement and mitral valve replacement.
The aortic prosthetic valve was located within the hypertrophic ventricular septum and narrowed left ventricular outflow tract, which was detected in the long left ventricular axis view by the two-dimensional technique of multiplanar reconstruction. Multidetector-row computed tomography demonstrated that a small tissue, regarded as pannus, extended from the left ventricular septum into the pivot guard (Fig 1).
This abnormal tissue was detected in 13 of 16 patients (81%) in the PVD group and 3 of 12 patients (25%) in the control group (Table 2).
The tissue was regarded as periannular pannus rather than prosthetic valve-related thrombus because the attenuation values on computed tomography were as same as that of the interventricular septum. The size of the tissue ranged from 1 to 4 mm (mean, 2.0 ± 1.0 mm) in the PVD group. The structural dysfunction of the prosthetic valve was not demonstrated in the images of three-dimensional technique (Fig 2).
Detectable thrombus was not found in all patients.
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Fig 1. (A) Aortic prosthetic valve was located within the interventricular septum, which was detected in the long-axis tomographic section view by the two-dimensional technique of multiplanar reformation. Multidetector-row computed tomography demonstrated that a small tissue, regarded as pannus (black arrow), extended from the left ventricular septum into the pivot guard. (B) Pannus (black arrow) was detected in short-axis tomographic section view. (AO = aorta; IVS = interventricular septum; LA = left atrium; LV = left ventricular.)
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Fig 2. (A) Pannus (black arrow) was detected in long-axis view in the images of three-dimensional technique. (B) Pannus (black arrow) was detected in short-axis view. The structural dysfunction of the prosthetic valve could not be demonstrated. (AO = aorta; IVS = interventricular septum; LA = left atrium; LV = left ventricular.)
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The diameter of the left ventricular outflow tract, interventricular septum thickness, posterior wall thickness, and posterior wall thickness measured with MDCT are summarized in Table 2. The interventricular septum thickness and posterior wall thickness were significantly greater in the PVD group (p = 0.02 and p = 0.01, respectively) than those in the control group.
Reoperation was performed in 2 patients with significantly deteriorated leaflet motion and pannus tissue detected by MDCT. Aortic root replacement was performed in these patients. Similar to the MDCT findings, pannus formation without thrombus was observed in the left ventricular aspect on the septum during the reoperations. The pannus had two linear prints, interfering with the straight edge of leaflet movement in the pivot guard (Fig 3).
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Fig 3. (A) Similar to the multidetector-row computed tomography findings, pannus formation (white arrows) without thrombus was observed in the left ventricular aspect on the septum intraoperatively. (B) The pannus had two linear prints, interfering with the straight edge of leaflet movement in the pivot guard (white arrows).
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Comment
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The major findings of this study were as follows: (1) MDCT demonstrated pannus formation into the pivot guard; (2) similar to the MDCT findings, pannus formation was observed during reoperation; and (3) the aortic prosthetic valve in patients with pannus was located within the hypertrophic ventricular septum.
The mechanism of pannus formation has not been fully proven yet. In particular we are concerned about the design of pivot guard systems in the St. Jude Medical valve [1]. The clearance between the edge of the pivot guard and the straight edge of the leaflet is very narrow in the fully open position [1]. Therefore, pannus overgrowth may easily extend into the pivot guard, with resulting PVD. Left ventricular hypertrophy, observed in pannus group, may also support this hypothesis.
Pannus was not detected in 3 of 16 patients in PVD group. Because leaflet motion of these 3 patients improved after thrombolytic therapy, the cause of PVD was assumed to be thrombosed valve in the hinge. Pannus was detected in 3 of 12 control patients. In our previous study, the opening angle of normally functioning aortic St. Jude Medical valves was 11.0 ± 1.4 degrees [13]. The opening angles of these 3 patients in cineradiography were 10, 13, and 15 degrees. We consider that opening angles between 12 and 19 degrees are borderline to making a diagnosis of PVD. Although the opening angle at present is not obstructed by more than 20 degrees, the leaflet motion in such patients, especially in the patient with 15 degrees in the opening angle, was interfered with as a result of pannus overgrowth. We believe that careful follow-up with echocardiography and cineradiography, and intensive anticoagulant therapy, is essential for these patients, even when they are asymptomatic.
Therefore, it is important to differentiate pannus from thrombus in the image of MDCT. The attenuation level, position, and size of abnormal tissue observed in MDCT may be important indices [15]. However, because the pannus is occasionally accompanied by secondary thrombi, careful inspection is required. To obtain an informative image, more sophisticated techniques that minimize artifacts associated with leaflet motion and optimize contrast enhancement are essential [7–10, 15]. Moreover, patient factors, such as regular sinus rhythm, low heart rate ranging from 60 to 70 beats/min, and negligible transvalvular leakage, are mandatory to obtain minute images without heart banding artifact. Further studies involving more PVD cases and improvement of MDCT are required to resolve these problems and to refine this diagnostic technique.
To determine an appropriate management strategy for PVD, whether thrombolysis or reoperation, it is useful to differentiate pannus from thrombus using the MDCT scanner. Although reoperation is considered as a general therapeutic method for symptomatic PVD, reported mortality rates of reoperation ranged between 0% and 69% [5, 6], largely depending on the severity of patient illness. Therefore, the indication for surgical treatment should be considered carefully in high-risk cases. Thrombolysis is also applied as an alternative therapeutic method for patients suspected of having PVD as a result of thrombosed valve [17]. However, reobstruction owing to thrombosis after successful thrombolytic therapy was reported when the primary cause was pannus formation [18]. Further studies involving more symptomatic or asymptomatic PVD cases are required to determine the indication for reoperation when the MDCT scanner reveals abnormal findings.
The MDCT scanner enabled clear detection of the prosthetic valve in the closed position. The MDCT scanner clearly demonstrated that abnormal tissue, regarded as pannus, extended from the left ventricular septum into the pivot guard, resulting in interference of leaflet motion. The tissue was observed in 81% of PVD cases. The MDCT scanner can be a useful diagnostic technique for anatomic and functional evaluation of PVD caused by pannus formation.
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Acknowledgments
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This work was supported in part by a Grant-in-Aid for Scientific Research, Japan Society for the Promotion of Science (grant C-14571290 and grant C-13671416).
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Abstract
Introduction
