As you know, the SCCT is the global professional medical membership organization dedicated to ensuring patient access to the appropriate use of cardiovascular CT. In keeping with SCCT's educational mission, this Case of the Month series showcases cardiovascular CTA in various clinical scenarios. This series is spearheaded by the the Fellow and Resident Leaders of SCCT (FiRST) committee. Please provide feedback or forward any questions to info@scct.org 
Evaluation of Mechanical Prosthetic Aortic Valve by Cardiac CT:
Between Redo Valve Replacement and Medical Therapy: Cardiac CT is the Judge.
Thura T. Abd, MD, MPH (1), Hayder S. Yasir, MD (2), Richard T. George, MD (1)
  1. Division of Cardiology, Department of Medicine, Johns Hopkins University, Baltimore, MD
  2. Baltimore Medical System, Baltimore, MD
  3. Division of Cardiology, Department of Medicine, Johns Hopkins University, Baltimore, MD
Corresponding Author:
Thura. T. Abd, MD, MPH
1800 Orleans Street,
Zayed 7125
Baltimore, MD 21286

History

The patient is a 49 year-old man with history of hypertension, end stage renal disease and pulmonary embolism on chronic Warfarin therapy. In late 2014, he was diagnosed with severe symptomatic aortic stenosis and underwent mechanical aortic valve replacement (19 mm On-X valve). About 6 months later, the patient was diagnosed with cervical spine stenosis secondary to cervical spine spondylosis. Surgical intervention for his cervical disease was deemed necessary. Pre-operative evaluation with transthoracic echocardiogram (TTE) revealed elevated pressure gradients across the prosthetic aortic valve, mean pressure gradient (PG) of 53 mmHg, peak PG of 87 mmHg and poorly visualized prosthetic valve leaflets (Figures 1&2). His peak and mean aortic valve gradients immediately post valve replacement surgery were 40 mmHg and 28 mmHg, respectively. Valve fluoroscopy showed that one of the leaflets was fixed in the closed position (Figure 3). The patient has been maintained on adequate anticoagulation. His International normalized ratio (INR) was 3.1 at presentation. However, he has history of subtherapeutic INR in the past. The patient was taken to the operating room the next day for a redo-aortic valve replacement. However, a pre-sternotomy intraoperative transesophageal echocardiogram (TEE) showed a much reduced PG across the valve with peak and mean PG of 52 and 28 mmHg, respectively (Figure 4). The valve leaflets could not be well-seen (Figure 5). The patient was transported to the cardiac CT scanner for mechanical aortic valve evaluation by Cardiac CT imaging. A non-contrast cardiac CT was performed with 120 kVp for one full cardiac cycle (0-100% of R-R interval).  

Figure 1: Short-axis view on a transthoracic echo showing mechanical valve in aortic position with leaflets are not well-seen.

Figure 2: Prosthetic valve pressure gradients from the 5-chamber view of the transthoracic echo showing markedly elevated pressure gradients across the prosthetic valve and reduced aortic valve area.
















Figure 3A: Figure 3B fluoroscopy of the mechanical aortic valve showing only one mobile leaflet.



Figure 4: Prosthetic valve pressure gradients from the deep gastric view of the intraoperative transesophageal echo showing mildly elevated pressure gradients across the prosthetic valve with peak velocity of 3.3 m_sec_ mean PG 28 mmHg_ Peak PG 52 mmHg.

Figure 5: Long axis view of the prosthetic aortic valve with Doppler color compare image of the intraoperative transesophageal echo showing prosthetic leaflets poorly visualized with flow turbulence across the valve
Findings

Functional cardiac CT evaluation of the prosthetic aortic valve showed a well-seated valve in aortic position without any evidence of dehiscence. Additionally, there was normal and symmetric movement of the valve leaflets throughout the cardiac cycle (Figures 6-7). Therefore, redo-aortic valve replacement surgery was aborted.  A few days later, the patient had his cervical spine surgery successfully and uneventfully and had a complete and unremarkable recovery. 

Figure 7: A CT image of the long axis of the prosthetic aortic valve showing the two leaflets with normal opening and closing. Also seen are calcification of the ascending aorta and surgical clips.
Figure 6: A CT image of the prosthetic aortic valve showing bileaflet prosthetic valve with both leaflets freely mobile.


Discussion

In this case, we present a complicated clinical scenario where the diagnosis of mechanical aortic valve dysfunction was not clear despite evaluation with TTE and TEE.  The Cardiac CT scan was able to define the condition of the valve very easily and quickly that resulted in a major change in clinical decision appropriately saving the patient a potentially unnecessary major cardiac surgery.

Echocardiograms provide valuable information regarding transarortic valve gradients; however, anatomical evaluation can be difficult at times. In those settings cardiac CT scan can delineate the valve leaflets anatomy and motion accurately producing a 3-dimentional, high resolution image of the mechanical valve. 

Although, the use of cardiac CT as a way to evaluate prosthetic valve function is not routine in daily clinical practice, the 2009 and 2014 guidelines for evaluation of prosthetic valves recommend cardiac CT as a method to evaluate prosthetic valve function when evaluation with TTE and TEE are inconclusive (1,2). Additionally, the 2010 appropriate use criteria for cardiac CT considers the use of cardiac CT for evaluation of prosthetic valve dysfunction as appropriate (3).
 
The discrepancy of results between the fluoroscopy findings and the CT results cannot be explained with certainty in our case. However, one possible explanation is false positive fluoroscopy result or, more likely, the patient did have a temporary valve dysfunction by a small thrombus that has resolved in the interval timing. However, the patient did not have other features suggestive of valve thrombosis. 

Conclusion

Cardiac CT should be considered as part of the diagnostic armamentarium during evaluation of prosthetic valve dysfunction especially when other imaging modalities (TTE, TEE or fluoroscopy) results are inconclusive or discrepant.
References

1. Nishimura RA, et al. AHA/ACC guideline for the management of patients with valvular heart disease: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines. JACC 2014;63(22):2438-88.

2. Zoghbi WA, et al. Recommendations for Evaluation of Prosthetic Valves With Echocardiography and Doppler Ultrasound. J Am Soc Echocardiogr. 2009;22(9):975-1014;

3. Tayler, AJ, et al. ACCF/SCCT/ACR/AHA/ASE/ASNC/NASCI/SCAI/SCMR 2010 Appropriate Use Criteria for Cardiac Computed Tomography. JACC 2010;56(22):1864-94)


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