A word of caution: Spontaneous rupture of the noncoronary sinus of the Freestyle xenograft: Two cases and review of the literature

From the Departments of Cardiac Surgery, Radiology, and Anesthesiology, Centre Hospitalier Universitaire Vaudois, Lausanne University, Lausanne, Switzerland. Disclosures: The authors reported no conflicts of interest. The Journal policy requires editors and reviewers to disclose conflicts of interest and to decline handling or reviewing manuscripts for which they may have a conflict of interest. The editors and reviewers of this article have no conflicts of interest. Received for publicationMarch 7, 2022; revisions receivedMay 19, 2022; accepted for publication June 14, 2022; available ahead of print July 19, 2022. Address for reprints: Ziyad Gunga, MD, Department of Cardiac Surgery, Centre Hospitalier Universitaire Vaudois, Lausanne University, Lausanne, Switzerland (E-mail: ziyad.gunga@chuv.ch). JTCVS Open 2022;11:59-61 2666-2736 Copyright 2022 The Author(s). Published by Elsevier Inc. on behalf of The American Association for Thoracic Surgery. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). https://doi.org/10.1016/j.xjon.2022.06.012 Endovascular virtual reality angiography highlighting the fenestration (arrow) of the noncoronary sinus seen from the inside (case 2).

Video clip is available online.
The porcine stentless Freestyle xenograft (Medtronic Inc) has proved to be an ideal substitute for aortic root replacement (ARR) as it provides excellent hemodynamics and durability. 1,2 Nonetheless, like other bioprostheses, structural valve deterioration is observed in the long term, mostly due to aortic cusp tears. However, spontaneous rupture of the Freestyle xenograft aortic wall has also been reported. 3,4 We present 2 patients who developed pseudoaneurysm after ARR using a Freestyle xenograft, related to spontaneous rupture of the noncoronary sinus (NCS) of Valsalva.

CASE 1
In November 2018, an 80-year-old male patient with a history of aortic root dilation had a complete ARR using a 25-mm Freestyle xenograft. In August 2020, the patient was hospitalized for acute lung edema related to massive aortic valve insufficiency due to deformation of the xenograft by a pseudoaneurysm. Intraoperative findings noted a tear of the upper portion of the NCS of the Freestyle xenograft. This part was trimmed, and a reconstruction of the sinotubular junction was achieved using a 24-mm Dacron graft, strengthened by an extraluminal pericardial patch.
In October 2020, a computed tomography scan highlighted a recurring pseudoaneurysm, triggering a third operation. A 1-cm rupture of the NCS was identified, without sign of infection. The Freestyle xenograft was trimmed, leaving the annulus, and a redo ARR was performed using a 23-mm Freestyle xenograft. The patient died 1 week later due to sudden cardiac arrest secondary to acute hypoxemia following bronchoaspiration. Transthoracic echocardiogram confirmed the absence of pericardial tamponade.

CASE 2
A 72-year-old female patient with a history of aortic valve replacement in 2018 was admitted emergently for type A dissection in February 2020. ARR using a 25-mm Freestyle xenograft was performed, associated with hemiarch replacement.
In November 2020, the patient was reoperated for severe tricuspid insufficiency, and operative findings pinpointed a small pseudoaneurysm on the suture line between the distal Endovascular virtual reality angiography highlighting the fenestration (arrow) of the noncoronary sinus seen from the inside (case 2).

CENTRAL MESSAGE
Freestyle bioprosthesis is an ideal substitute for aortic root replacement. Rupture of the Freestyle has been rarely described. We present 2 cases of spontaneous rupture of the noncoronary sinus.
portion of the Freestyle xenograft and the Dacron prosthesis. This 2-mm orifice was sutured and strengthened with heterologous pericardium and BioGlue (CryoLife, Inc).
In October 2021, an acute thoracic pain triggered a computed tomography scan that showed a large circulating pseudoaneurysm of the aortic root originating from a tear in the NCS of the Freestyle xenograft ( Figure 1). Intraoperative findings confirmed the rupture in the central part of the NCS, without sign of infection (Video 1). A redo ARR using a 25-mm Freestyle was performed. The patient had an uneventful recovery. Both patients gave written informed consent for the use of their data for publication use.

COMMENT
The Freestyle xenograft is the only currently commercially available aortic root xenograft. It provides excellent hemodynamic results in terms of postoperative transvalvular gradients, effective orifice area, and regression of left ventricular hypertrophy. Furthermore, excellent durability has been reported by several studies, with 1-year freedom from reoperation rates of more than 90%. 1,2 However, early-and mid-term structural valve deteriorations have been outlined. In addition to cusp tears, the aortic wall of the Freestyle xenograft seems also vulnerable, as highlighted by the present cases. Six similar cases of spontaneous rupture of the Freestyle xenograft wall have been previously reported, and are summarized in Table 1. Interestingly, the rupture occurred most frequently in the noncoronary sinus of the xenograft.
Since neither of the cases has been related to an infectious origin, we retain 3 hypotheses to explain these clinical observations. Ozaki and colleagues 3 suggested a weakness in the transitional zone between annular collagen fibers and the aortic elastic wall. Similarly, using biomechanical analyses, Takaya and colleagues 4 noted that NCS was significantly thinner and less elastic than the other sinuses, hence inherently more vulnerable and at greater risk of tissue failure.
Alternatively, traumatic manipulation of the Freestyle xenograft, such as pinching of the prosthetic wall, could contribute to its subsequent failure. In our practice, we used to invaginate the Freestyle into the left ventricular outflow tract to facilitate tying of the proximal suture line. In view of the present cases, this practice cannot be recommended anymore.
Finally, a toxic factor could also be incriminated. Indeed, Kazui and colleagues 7 have reported that BioGlue surgical adhesive might occasionally cause severe injury to aortic tissue, such as excessively thinning of aortic tissue at the site of adhesive application, hence inciting pseudoaneurysm formation.
We underline the importance of additional multidimensional imaging in the follow-up to depict structural aortic abnormalities after Freestyle implantation, insufficiently unveiled by TEE as suggested by Dagneg ard and colleagues. 8

CONCLUSIONS
Spontaneous rupture of the NCS constitutes a rare hazard after ARR using the Freestyle xenograft. Atraumatic handling of the bioprosthesis and avoidance of potentially toxic surgical adhesives should be recommended. Meticulous follow-up should be devised to detect this potential complication.