A Novel Device for Intraoperative Direct Visualization of a Pressurized Root in Aortic Valve Repair

Abstract

PURPOSE

One major challenge in generating reproducible aortic valve (AV) repair results is the inability to assess AV morphology under physiologic pressure. A transparent intraoperative aortic valve visualization device was designed and manufactured.

DESCRIPTION

This device is comprised of an open proximal end, a cantilevered edge to allow attachment of the device to the aorta or graft, a distal viewing surface, and two side ports for fluid delivery and air removal.

EVALUATION

The performance of the device was evaluated ex vivo using normal porcine AV in situ (n=3), AV after valve-sparing aortic root replacement (VSARR, n=3), and porcine pulmonary valve in Ross procedure (n=3), and in 3 patients who underwent VSARR. AV morphology was clearly visualized using the device in all experiments. In human, the use of this device successfully illustrated cusp prolapse after the initial VSARR and effectively guided additional cusp repair.

CONCLUSIONS

This device successfully allows for direct visual assessment of the AV apparatus under physiologic pressure. The use of this device can potentially increase the adoptability of AV repair in clinical practice.

Aortic valve (AV) repair is recognized as a durable treatment in select patients with aortic regurgitation (AR) or root aneurysm [1]. It avoids the disadvantages associated with replacement [2]. However, AV repair is technically challenging, and outcomes largely depend on surgeon experience. One of the major challenges in generating reproducible results is the inability to assess AV morphology after repair under physiologic aortic root pressure. Additionally, although transesophageal echocardiogram (TEE) evaluation remains the primary mode of intraoperative assessment of the AV, the results are highly operator dependent and do not provide direct visualization of the AV. Furthermore, if significant AR is found based on TEE assessment after coming off cardiopulmonary bypass, additional AV repair can only be performed after re-cross clamp, cardiac re-arrest, and aortic reopening, all of which could negatively impact postoperative outcomes. Therefore, we sought to design an intraoperative AV visualization device that allows for direct evaluation of the AV under physiologic pressure without the need to come off bypass.

TECHNOLOGY

An intraoperative AV visualization device must allow direct assessment of the AV under adequate pressurization and be easily integrated with the aorta or interposition graft. An ideal device should be small and portable, allow for reversible attachment and detachment to the aorta or graft, not rely on additional instruments to function properly, be inexpensive to manufacture, and easily scaled for mass production. To meet these design goals, we invented a transparent device that can be used intraoperatively to subject the aortic root to diastolic aortic pressure, thereby allowing direct visualization of the AV in its physiologic state (Figure 1). This device takes a conical form with an open proximal end for placement above the AV. Just above the open proximal end of the device, a cantilevered edge was designed such that a suture or sterile zip tie can be used to wrap around the aorta or graft over the device above the cantilevered edge to create a secure, water-tight, pressure-resistant seal. The distal surface allows for a bigger visualization field. Two orthogonal, lateral ports at the top of the device allow for fluid infusion into the device via one port while removing air via the other port. Once de-airing is complete, the de-air port can be closed to allow pressure in the device to increase to reach physiologic pressure. To ensure appropriate fitting of the device above the AV inside the aorta or graft, different sizes of the device were also designed. The final design was 3D printed using a U.S. Pharmacopeial Convention Class IV clear polycarbonate material (Protocafe, Newark, CA).

Figure 1:

Computer-aided design rendering of the intraoperative aortic valve visualization device. This device is placed above the aortic valve and comprises of an open proximal end, a cantilevered edge to allow secure attachment of the device to the aorta or graft, a transparent viewing surface, and two side ports for fluid delivery and air removal.

TECHNIQUE

Device Use

Supplemental Video illustrates the general steps to use this device. The open proximal end is inserted into the aorta or graft above the AV. Using a 2 nylon suture or a zip tie placed just above the cantilevered edge, the device was secured. Note that the suture can also be tightened using a plastic tourniquet commonly used to secure cannulas in large vessels in open cardiac surgery cases. An infusion line or syringe was attached to the fill port to enable fluid delivery and pressurization. The de-air port was connected to a stopcock to allow air removal. Once the air in the device was removed, the stopcock was turned to the closed configuration to allow pressure inside the device to increase to physiologic pressure. The morphology of the AV can be evaluated from the distal viewing surface. After the assessment was complete, the stopcock was opened to allow the pressure to be released. The device was then carefully detached from the aorta or graft by removing the suture.

Ex Vivo Evaluation

To evaluate the efficacy of the device, 3 ex vivo testing were completed: normal AV in situ (n=3, Figure 2A), valve-sparing aortic root replacement (VSARR) specimens [3] (n=3, Figure 2B), and pulmonary valves prepared using the inclusion technique in a Ross procedure [4] (n=3, Figure 2C). Detailed sample preparation and experimental set up is provided in the Supplementary Materials.

Figure 2:

A) Demonstration of the use of the device to assess a normal porcine aortic valve in situ. B) Demonstration of the use of the device to assess a porcine aortic valve after valve-sparing aortic root replacement repair. C) Demonstration of the use of the device to assess a porcine pulmonary valve in ross procedure using the inclusion technique. D) Visualization of the same normal aortic valve as shown in (A). E) Visualization of the same aortic valve as shown in (B). F) Visualization of the same pulmonary valve as shown in (C).

Human Intraoperative Testing

The device was brought to the operating room for evaluation in 3 VSARR cases. Preoperatively, patients were consented for use of the device. Prior to the operation, newly manufactured devices of all sizes were sterilized using ethylene oxide. The detailed clinical device use is provided in the Supplementary Materials. Patient data were prospectively collected. The use of this device in humans was approved by the Institutional Review Board at Stanford University.

CLINICAL EXPERIENCE

The device easily and reversibly attached to the aorta and graft without leakage. Clear valve morphology and suture lines were observed in all samples ex vivo (Figure 2D–F). Note that the graft’s pliability did not affect the visualization of the AV after VSARR.

Patient preoperative demographics and diagnoses are shown in Supplemental Table. All 3 patients had aortic regurgitation with aortic aneurysm. Patient 2 was also diagnosed with bicuspid aortic valve. In addition to VSARR, patient 1 also underwent atrial septal aneurysm and patent foramen ovale closure. The use of the device was highly effective in illustrating AV morphology after VSARR. Specifically, in patient 1 and 2, additional aortic cusp repairs using the free margin plication technique were performed, guided by the AV appearance and cusp prolapse as visualized via the device. After additional repair, the AV symmetries were obtained for both patients with proper leaflet coaptation without any prolapse (Figure 3). No adjacent intra-thoracic structure was damaged during the use of this device. On average, the cardiopulmonary bypass time was 167.3±25.7 minutes, and the aortic cross-clamp time was 133.3±12.5 minutes. Postoperatively, no patient experienced myocardial infarction, cerebral vascular accidents, atrial fibrillation, pacemaker implantation, reoperation due to hemorrhage or cardiac tamponade, respiratory failure requiring re-intubation or ventilation for more than 48 hours, or renal failure requiring dialysis. The average ICU length of stay was 1.7±1.2 days, and the hospital length of stay was 5.3±0.6 days. No patient required blood transfusions. Postoperative echocardiogram demonstrated no AR for all patients. The hospital and 30-day mortality were 0%.

Figure 3:

Intraoperative use of the aortic valve visualization device in a patient undergoing valve-sparing aortic root replacement. Additional aortic cusp repair was successful using the free margin plication technique was performed. This was guided by the aortic valve morphology and cusp prolapse as visualized via the device under physiologic pressure.

COMMENT

An intraoperative AV visualization device was designed and manufactured to allow direct visual assessment of the AV under physiologic pressure. This device was designed for intuitive operation, allowing for reversible attachment to the aorta or graft, enabling surgeons to assess AV morphology, cusp symmetry, and coaptation before and after AV repair in an iterative process without the need to come off bypass. From our ex vivo evaluation, Dacron grafts were not needed to use this device. 2 Nylon sutures were adequate to provide a fast, water-tight, pressure-resistant seal to connect the device onto an aorta or Dacron graft. By combining the plastic tourniquet system, the connection could be easily adjusted if needed.

A similar valve competency testing methodology had been adopted many years ago in mitral valve (MV) repair where saline was injected into the left ventricle using a bulb syringe to pressurize the left ventricle and test for mitral regurgitation [5,6]. Unfortunately, for AV repair, surgeons have to rely on assessment of AV morphology under non-physiologic pressure prior to definitive yet indirect evaluation of AV competency using TEE, which requires coming off cardiopulmonary bypass. Although injection of normal saline onto the AV could allow cusps of the AV to come together for visual assessment, this methodology does not generate adequate pressure, and therefore may miss pathologies that become prominent under physiologic pressure. In some centers, intraoperative evaluation of repaired AV geometry is performed by angioscopy under pressure [7]. However, this technique cannot be applied to AV repair cases without the use of grafts, and the need of a flexible autoclavable videoscope and the cumbersome set up may prohibit the adoption of this approach. Another similar intraoperative AV testing device has also been previously described, but it is significantly larger in profile compared to our device and similarly requires endoscopic instruments and equipment [8]. Our device, as a stand-alone instrument, can hopefully help increase the rate of AV repair by providing a better tool for intraoperative visual assessment of the AV.

The ex vivo experimental results demonstrated the excellent performance of the device by allowing clear visualization of the entire AV apparatus. In our clinical experience, this device easily fits into the thoracic cavity through a standard sternotomy incision given its small profile and clearly assisted in identifying subtle AV asymmetry and cusp prolapse in 2 of the 3 patients, which helped guide the surgeon to further repair the AV cusp [2,9]. Furthermore, the use of this device was not associated with any postoperative morbidity or mortality in this investigation, and its ease of use was reflected in comparable cardiopulmonary bypass and cross-clamp times similar to what have been reported in previous studies [10].

One potential limitation of the device is the level of insertion into the aortic root. At a minimum, the device should be inserted above the level of the sinotubular junction, since securing the device below such level would inevitably distort the AV geometry. Another limitation is the potential need to snare down the coronary arteries to minimize fluid leakage to ensure adequate pressurization. However, in our clinical experience, we used the device after the right coronary button was already anastomosed to the Dacron graft. Without clamping the right coronary artery, we did not notice any issue with pressurization. We suspect that if continuous fluid infusion could be delivered at an appropriate speed, the physiologic pressure in the aortic root can be maintained. Lastly, 2 nylon sutures were used to secure the device onto the aorta in this study. However, detailed analysis should be performed to investigate if any endothelium damage occurs with the current attachment mechanism.

In conclusion, an intraoperative AV visualization device was successfully designed and manufactured to enable direct visual assessment of the AV under physiologic pressure to evaluate AV morphology, cusp symmetry, and coaptation both ex vivo and in human open cardiac operations. This device has tremendous potential to enhance intraoperative assessment of AV repair, providing a tool that could help to ease the adoptability of AV repair in clinical practice.