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Interact CardioVasc Thorac Surg 2008;7:195-200. doi:10.1510/icvts.2007.166587
© 2008 European Association of Cardio-Thoracic Surgery
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Work in progress report - Valves

Evaluation of biological aortic valve prostheses by dual source computer tomography and anatomic measurements for potential transapical valve-in-valve procedure{star}

Jürg Grünenfeldera,1,*, Andre Plassa,1, Hatem Alkadhib and Michele Genonia

a Clinic for Cardiovascular Surgery, University Hospital Zurich, Rämistr. 100, 8091 Zürich, Switzerland
b Institute of Diagnostic Radiology, University Hospital Zurich, Switzerland

Received 4 September 2007; received in revised form 19 December 2007; accepted 20 December 2007

1 Contributed equally to this paper. Back

{star} Presented at the 21st Annual Meeting of the European Association for Cardio-thoracic Surgery, Geneva, Switzerland, September 16–19, 2007.

*Corresponding author. Tel.: +41 44 2555 11 11; fax: +41 44 255 44 46.

E-mail address: jurg.grunenfelder{at}usz.ch (J. Grünenfelder).


   Abstract
Top
 Abstract
1. Introduction
 2. Methods
 3. Results
 4. Discussion
 5. Conclusion
 Conference discussion
 Acknowledgements
 References
 
Transapical aortic valve replacement has been introduced into clinical practice from which also patients with failing biological valves might profit: valve-in-valve procedure. The aim of the study was to determine the fate of biological valves in long-term follow-up (FU) and to evaluate topography and dimensions for transapical access via dual-source CT scan (DSCT). Fifty patients (mean age 76±13 years, range 38–87 years) underwent DSCT whereas the patients were followed for up to 13 years after porcine aortic valve replacement. Measurements of valve prosthesis and illustration of chest topography were done. Out of 46 evaluable patients, 34 showed no leaflet calcification and 12 minimally calcified. Seventeen valves (37%) showed no, 24 valves (52%) mild and 5 (11%) moderate-to-severe ring calcification. Three patients had moderate aortic stenosis, two patients showed mild insufficiency. The angle from the 4th ICS to apex to aortic valve annulus measured 80.3±11.1° compared to the angle from the 5th ICS which measured 101.6±7.2° (P<0.0001). Biological valves show good long-term results with minimal failure rate and limited calcification. Leaflet calcification might be problematic if unevenly distributed which can endanger the very close LCO. These measurements represent a prerequisite for preoperative planning and increase the awareness to detect potential procedural problems of the valve-in-valve concept.

Key Words: Biological valves; Long-term follow-up; Dual-source CT; Transapical valve-in-valve procedure


   1. Introduction
Top
 Abstract
 1. Introduction
2. Methods
 3. Results
 4. Discussion
 5. Conclusion
 Conference discussion
 Acknowledgements
 References
 
Life expectancy in the western world is continuously on the rise and therefore also the number of patients over 80 years who will need cardiac surgery in the future is growing significantly. Especially patients with a previously implanted biological aortic valve prosthesis (AVP) represent a patient population who will eventually need a second operation for failed aortic valve prosthesis. If reoperation is considered in these generally older patients a higher operative risk has to be taken into account. In line with the percutaneous valve replacement strategy, the transapical approach for a valve-in-valve procedure would be an attractive alternative for this high-risk patient group.

The durability of a biological valve prosthesis is known to be an average between 10 and 15 years depending on the valve type implanted [1–3]. To evaluate biological aortic valves, echocardiography has been the standard method for functional assessment. However, alternative imaging technologies have made rapid improvement in illustrating the morphology of cardiac structures so that the newest models of computer tomography might also be used for assessing aortic valve prostheses.

In this retrospective study, biological aortic valve prostheses have been assessed by dual-source computer tomography (DSCT) and echocardiography 6, 10 and 13 years after implantation at our institution. In addition, anatomic measurements were taken for a potential transapical valve-in-valve procedure.


   2. Methods
Top
 Abstract
 1. Introduction
 2. Methods
3. Results
 4. Discussion
 5. Conclusion
 Conference discussion
 Acknowledgements
 References
 
2.1. Patients

Fifty patients (39 male, 11 female) with previous biological aortic valve replacement at our institution were randomly selected and underwent DSCT and echocardiography examination and were retrospectively analysed from January to July 2007. All patients have been followed regularly by their cardiologists (Table 1).


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  		Table 1 Patient characteristics

 
Follow-up time point:Formula

2.2. Dual-source CT and image reconstruction

All CT-scans were performed on a DSCT scanner (Somatom Definition, Siemens Medical Solutions, Germany).

The following scanning parameters were used:

Slice collimation of 2x64x0.6 mm by means of a z-flying focal spot, Detector collimation of 2x32x0.6 mm, Slice thickness of 0.75 mm, Increment of 0.5 mm, Gantry rotation time of 0.33 s, Tube voltage of 120 kV, Tube current of 400 mAs (using ECG-pulsing for radiation dose reduction (22)), Pitch 0.22–0.46 (adapted to heart rate).

The cranio-caudal volume coverage included the level of the tracheal bifurcation down to the diaphragm. 80 ml contrast agent at a concentration of 320 mg/ml (Visipaque 320 mg/ml, GE Buckinghamshire, UK) was intravenously injected followed by a 30 ml saline chasing bolus at flow rates of 5.0 ml/s. The scanning delay was defined by bolus tracking in the ascending aorta.

2.3. DSCT image analysis

CT angiograms were reconstructed during mid-to-end diastole at following phase of the R–R interval depending on heart rate. In case of non-diagnostic image quality, additional reconstructions were performed in 5% steps of the R–R interval within the full tube current window.

2.4. Evaluation protocol

The evaluation protocol contains on one hand the measurement and assessment of the prosthesis (AVP evaluation) and on the other hand a planning protocol for potential transapical valve-in-valve procedure.

AVP evaluations:

  • Inner-diameter of prosthesis and valve orifice
  • Calcium distribution of valve leaflets and annulus and volumetric calcium score (VCS)
  • Valve function: insufficiency, stenosis
  • Pathologies: endocarditis, paravalvular leaks, thrombus on prosthesis

Planning protocol:

  • Measurements of the sinus of Valsalva (width/length)
  • Distances of right/left coronary ostium (R/LCO) to ring of prosthesis
  • Distance of 5th intercostal space (mid-clavicular) to apex
  • Distance of apex to aortic valve annulus
  • Distance of 5th intercostal space to aortic valve annulus (shortest distance)
  • Myocardial thickness at apex
  • Angle from 4th and 5th intercostal space (skin) to apex to aortic annulus

2.5. Echocardiography

Transthoracic echocardiography (TTE) was performed by using a multiplanar 2.5 MHz transducer (Sequoia 512; Acuson, Mountain View, USA) and results were interpreted by experienced echocardiographers. The examinations included M-mode, two-dimensional, continuous-wave, and colour Doppler echocardiography and were performed according to the international guidelines [4].

2.6. Image interpretation

Images were downloaded to dedicated workstations (Syngo InSpace 4D, Siemens Medical Solution, Germany) for subsequent analysis. All measurements were independently performed by two observers who were blinded to patient-identifying information and medical history. The degree of aortic valve bioprosthesis calcification at DSCT was semiquantitatively assigned a grade according to the classification system of Rosenhek et al.: grade 1, no calcification; grade 2, mild with small isolated spots of calcification; grade 3, moderate with multiple larger spots of calcification; and grade 4, severe with extensive calcification of the entire cusp [5]. The quantification of aortic stenosis was assessed through the calculation of the aortic valve area (AVA) by means of planimetry. The plane that demonstrated the orifice with the smallest opening during the phase of maximum valve opening was chosen on images obtained in double-oblique parallel planes through the aortic bioprosthesis. The plane was perpendicularly oriented to the left ventricular outflow tract across the aortic valve. The maximum AVA in systole planimetrically measured with CT was determined. For each patient the bioprosthesis was then semiquantitatively judged to be normal (AVA≥2.0 cm2), mildly stenotic (AVA 1.5–2.0 cm2), moderately stenotic (AVA 1.0–1.5 cm2), or severely stenotic (AVA<1.0 cm2). Identically the aortic valve regurgitation has been assessed semiquantitatively through the regurgitant orifice area: mild (ROA<0.10 cm2), moderate (ROA 0.10–0.29 cm2), severe (ROA≥0.30 cm2) [6]. The quality of the DSCT was graded by using a four-point ordinal Likert scale: grade 1 meant poor (non-diagnostic), grade 2, moderate (diagnostic, poor visibility of the anatomic details of the aortic valve cusps), grade 3, good (good visibility of the anatomic details of the aortic valve), and grade 4, excellent (excellent visibility and differentiation of the anatomic details of the aortic valve) [7].


   3. Results
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
4. Discussion
 5. Conclusion
 Conference discussion
 Acknowledgements
 References
 
Of the 50 patients studied, four patients could not be evaluated due to insufficient image quality (n=3) or other reason (n=1). Five patients (11%) showed moderate to severe calcifications at the ring of the prosthesis (Fig. 1a). No predominance was seen whether more porcine or more pericardial valves were affected by ring calcification. Twenty-four patients (52%) showed only mild calcification at the ring level. In 17 patients (37%) the ring was not affected at all. Regarding leaflet calcification only 12 patients (26%) showed some degree of calcium and these valves were mainly of porcine nature. All other patients had no calcifications at the leaflets of the bioprostheses (74%). Of the whole study group a total of 12 patients (26%) showed no calcifications at all on their bioprostheses (ring or leaflet) (Table 2, Fig. 1b).


Figure 1
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  		Fig. 1. (a) Mild to moderate calcifications of aortic valve prosthesis. (b) Normal aortic valve prosthesis.

 

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  		Table 2 DSCT assessment of calcification of aortic valve prosthesis

 
The analysis of function of the valve in the DSCT showed in three cases (7%) moderate stenosis of the aortic valve prosthesis with an AVA of <1.5 cm2. All three cases were consistent with the echo report, which confirmed a moderate stenosis by gradient (mean gradient between 25–40 mmHg). Eight patients (17%) showed a mild degree of stenosis by AVA in CT measurements. The remaining 35 patients (76%) had normal AVA by CT.

Regarding the detection of insufficiency, only two patients (4%) were found to have insufficiency (mild) of the aortic valve prosthesis in CT, whereas in echo seven patients (15%) showed an insufficiency (six patients with mild and one patient with moderate insufficiency).

The anatomic measurements from the sinus of Valsalva, the distances from RCA or LCA to annulus and the distances from the 5th intercostal space to the apex as well as the aortic valve annulus and the thickness of the myocardium taken by MSCT are depicted in Table 3. The angle from the skin of the 4th ICS to the apex and to the aortic valve annulus differed significantly to the angle of the 5th ICS (80.3±11.1° vs. 101.6±7.2°, P<0.0001).


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  		Table 3 DSCT measurements of anatomic structures

 

   4. Discussion
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
 4. Discussion
5. Conclusion
 Conference discussion
 Acknowledgements
 References
 
The durability of biological aortic valve prosthesis has been under debate for years. Reoperation following aortic valve replacement surgery is a relatively common event, particularly in patients with bioprosthetic valves. Freedom from reoperation for currently available mechanical valves is 95% at 10 years and 90% at 15 years. Bioprostheses, however, have a significantly higher rate of reoperation due to structural valve deterioration (SVD). In large series, freedom from reoperation has been >95% at 5 years, >90% at 10 years, but <70% at 15 years [2].

At present echocardiography still remains the gold standard to accurately evaluate the function of valve prosthesis. The feasibility of multidetector CT to image and perform planimetry of the aortic valve for measurement of aortic valve area has been shown in several studies [7, 8]. However, MSCT has, to our knowledge, never been used to systematically assess aortic valve bioprostheses. This study now clearly proves the suitability of the DSCT for evaluating the morphology of the valve prosthesis as well as the location and quantification of calcium on the valve prosthesis. Even to assess valve function DSCT is able to accurately detect aortic valve stenosis in most cases. However, in our study aortic insufficiency was missed in five out of seven patients who were diagnosed with aortic valve insufficiency by echo.

It is interesting to see that only 5 out of 46 patients (11%) showed moderate to severe calcification of the bioprosthetic ring in the CT which was consistent with moderate aortic valve stenosis regarding effective valve orifice in three patients. In these cases also echocardiography demonstrated moderate aortic valve stenosis by gradient calculation. If the ring of the prosthesis was severely calcified the calcium was more or less evenly distributed. This might be important for a future valve-in-valve procedure where evenly distributed calcium at the ring level probably would help anchoring the percutaneously implanted valve. On the other hand, leaflet calcification was seen much less than ring calcification. Only 12 patients showed a mild degree of calcification on the leaflets whereas the rest was free of calcium. In this respect, it was interesting to see that of the six pericardial valves implanted only one of them showed calcified leaflets. On the leaflets the calcium was located in half of the valves circumferentially on all leaflets, similarly to the calcification on the ring. In the same sense as for ring calcification this finding would be beneficial for a possible percutaneously or transapically inserted valve. A potential problem would be the presence of heavy calcification in front of the left or right coronary ostium if during the deployment calcium debris is being squeezed against the sinus portion and the ostium of the coronaries [9]. Our study showed that if the prosthesis is calcified it is mainly located on the ring. Another aspect is the danger of embolisation of calcium which can lead to neurological problems or even severe stroke. Therefore, an extensive preoperative planning with accurate images to define the location of the calcium is imperative to avoid potential hazardous complications.

The percutaneous antegrade and retrograde aortic valve implantation technique has already been introduced into clinical practice for selected patients [10–14]. However, the procedure including preparation as well as the selection of patients has to be optimized. Several imaging techniques – echocardiography, Multi-Slice CT, fluoroscopy – play an important role for diagnostic, preoperative planning, for intraoperative navigation and guidance of the surgical procedure.

Currently all patients who underwent a percutaneous aortic valve replacement belong to a high-risk population [15]. However, not only the equipment but also the technique needs to be improved and modified to be able to eventually treat less sick patients. We believe that the applicability and safety can be improved with a standardized and routinely performed preoperative planning through which the ideal device size for a specific patient can be defined before the procedure takes place. In addition, intraoperative guidance with all imaging techniques necessary for the implantation will make the procedure much more predictable than today. The data and measurements acquired in this study will help to design the perfect device for each patient individually. These measurements can primarily be used as a proof of concept that with DSCT accurate measurements of the topography of the heart in the chest are possible. Our data also show that the angle from the 5th ICS to the apex and to the aortic valve annulus is significantly bigger compared to the 4th ICS, which makes the delivery of a transapical valve almost straight shot. From the 4th ICS, however, the angle is <90° and therefore delivery might probably be more difficult.

In this context, an interesting patient population represent the patients with previously implanted biological aortic prostheses which eventually need to be replaced. In our study, we could demonstrate that approximately 75% of the patients with a biological valve show calcification of the valve during a follow-up of 6–13 years. Although surprisingly the degree of calcification is only mild and the number of patients with stenosis or insufficiency is low, still the valves eventually will fail at some point in time.

For these cases the proposed valve-in-valve concept will be a realistic option to treat these high-risk patients in the future less invasively. Especially these older patients who will have to undergo reoperation will profit the most from a percutaneous or transapical approach. Conventional surgery will pose a very high risk for these patients or otherwise they even will get refused from surgery.


   5. Conclusion
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
 4. Discussion
 5. Conclusion
Conference discussion
 Acknowledgements
 References
 
Biological valves show good long-term results with minimal failure rate and limited calcification which might be a limitation of the study. Valve function was accurately assessed for aortic valve stenosis but less for aortic insufficiency. Leaflet calcification might be problematic if unevenly distributed which can endanger the very close LCO. These measurements represent a prerequisite for preoperative planning and increase the awareness to detect potential procedural problems of the valve-in-valve concept.


   Conference discussion
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
 4. Discussion
 5. Conclusion
 Conference discussion
Acknowledgements
 References
 
Dr. D. Pagano (Birmingham, UK): Clearly this study, in my mind, is to be seen as an attempt to identify the best technique available in order to make safe the valve-in-valve deployment. It is rather unfortunate that you may have chosen the wrong population of patients, as most of these patients had a valve in for <10 years, and with modern valves that is probably a short time as illustrated by the fact that actually you did not see any leaflet problems. It would have been more interesting, and I am sure that you are thinking for the next study, to look at patients where there is actually a problem with the leaflets and to see how much of that is seen in the resolution of your technique. I suspect that none of these patients you studied actually needed any surgical intervention and they were just followed-up.

The second comment is your attempt to compare this technique with echocardiography, which I think does merit a little bit more comment from you. Firstly, 10% of your patients were not assessable by CT-scan. You see no aortic valve regurgitation, and that is probably a limitation of the technique. Could you give us a little bit more data on the echo findings on these patients?

And finally, it is a provocative question, if you had your life back again, which population of patients would you study?

Dr. Grunenfelder: Of course it is true, that it is actually a selected patient population we studied here because we wanted first to evaluate the feasibility and the possibility of DSCT in evaluating bioprostheses, because this has never been done so far to our knowledge. That was actually the reason for setting up a study like this. We just asked the patients who are alive, obviously, to come in and get a scan. These patients did fairly well. They had no symptoms, more or less. With a New York Heart Classification of 1.7, they were probably pretty asymptomatic. So, it is a selected patient population. These patients usually don't need a new valve, obviously, at that time. We just wanted to see if DSCT is a good tool in evaluating bioprostheses.

And the second question about the echoes, it is known in the literature that DSCT or CT is not very good in assessing aortic insufficiency and is not considered the gold standard, of course. Echocardiography was done in a transthoracic way, not only from our institution but also from outside hospitals. We asked the cardiologists who treated the patients to send us the patient for a new echo or give us the newest echo report. Therefore, it is not really randomized, not even with comparable patient population or treatment groups.

For the last question, I think if I had a patient who is very sick or I am very sick with a bioprosthesis, probably I would have a new valve implanted in the least invasive way, which probably is true for everybody here, I think.

Dr P. Kappetein (Rotterdam, The Netherlands): I think the longevity of the current bioprosthesis is so good that there will not be many patients. At Techno College last Saturday we were told that there would be a valve-in-a-valve demonstration, but a candidate was difficult to find. Thomas Walther, perhaps you could comment on this, also.

Dr. T. Walther (Leipzig, Germany): I was going to say that the good news is the bioprostheses are doing pretty well. We are looking for suitable patients for valve-in-a-valve for half a year. We have done the first one successfully. We looked at the CT. There was not very much calcification with the Perimount pericardial valve with stiffened cusps. However, if there would be a patient with very severe calcification, we probably would still go for it if the patient fulfills the inclusion criteria of a high perioperative risk, because we know that the coronaries are lateral from the conventional xenograft. We stay within, we squeeze the calcium aside, but it shouldn't touch the coronary ostia, and then we are probably safe. And that is what we saw in our first case, and I think we have to persuade patients to just go for it and pursue the surgical part and all experimental and clinical studies in that regard.

Dr. Kappetein: A question for both of you is that if the bioprostheses longevity is so good, and we cannot expect many patients from that cohort, could the patients with a failing homograft be suitable candidates for a valve-in-a-valve procedure? We do see that homografts fail quite early, but still sometimes you have to use them, for example, in patients with an endocarditis.

Dr. Walther: I personally think, yes, if there is calcification and you have a stiff enough annulus to squeeze a new valve in. In our center, we don't have so much homograft experience, so we didn't have a suitable candidate, but it is feasible.

Dr. Kappetein: What is your idea or comment on a valve-in-a-valve in a failing homograft?

Dr. Grunenfelder: Well, I think what the people say who do the transapical procedure for pulmonary valves, they have done that in homografts as well as in these Contegra grafts. I think as long as there are three leaflets more or less calcified, it is probably easier than in a pulmonary homograft, for instance, which has only one leaflet and the calcification is not really evenly distributed. It might be more of a problem.

Dr. Kappetein: You can perform a new study on that aspect.

Dr. Grunenfelder: Yes.


   Acknowledgements
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
 4. Discussion
 5. Conclusion
 Conference discussion
 Acknowledgements
References
 
We would like to thank Nadja Sommerhalder for her meticulous data collection and Dr. Lotus Desbiolles for her superb imaging preparation. H.A. was supported by the National Center of Competence in Research, Computer Aided and Image Guided Medical Interventions of the Swiss National Science Foundation.


   References
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
 4. Discussion
 5. Conclusion
 Conference discussion
 Acknowledgements
 References
 

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