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Original Articles: Adult Cardiac

High-Risk Patients Referred for Transcatheter Aortic Valve Implantation: Management and Outcomes

^a Cardiopulmonary Research Science and Technology Institute, Dallas, Texas
^b Medical City Dallas Hospital, Dallas, Texas

Accepted for publication July 16, 2008.

^_* Address correspondence to Dr Dewey, 7777 Forest Lane, Suite A323, Dallas, TX 75230 (Email: tdewey{at}CSANT.com).

Presented at the Forty-fourth Annual Meeting of The Society of Thoracic Surgeons, Ft. Lauderdale, FL, Jan 28–30, 2008.

	Abstract

Top Abstract Introduction Material and Methods Results Comment Discussion References

 
Background: Aortic valve replacement (AVR) is the treatment of choice for critical aortic stenosis. Selected patients have not previously been referred for AVR because of excessive risk of mortality and morbidity with surgery. The option of transcatheter aortic valve implantation (TAVI) has increased referral of this high-risk cohort for therapeutic intervention. We report the management and outcomes of these patients.

Methods: Patients referred for TAVI from December 2005 to December 2007 were evaluated and followed up for intermediate-term all cause mortality. Patients received medical management, TAVI, conventional AVR, or balloon valvuloplasty (BAV) based on risk profile, hemodynamic and echocardiographic criteria, physician judgment, or patient choice. Patients were compared for demographics, Society of Thoracic Surgeons predicted risk of mortality score, and outcomes after AVR, TAVI, or BAV.

Results: One hundred five patients were referred for TAVI during a 24-month period. Fifty-two patients (49.5%) received medical management, 16 (15.2%) conventional AVR, 21 (20.0%) received TAVI, and 16 (15.2%) received BAV. Patients were classified as medical management because of physician or patient choice, not meeting TAVI criteria, or underevaluation for a possible procedure. For all patients the average length of follow-up was 159 ± 147 days. Patients receiving BAV had a Society of Thoracic Surgeons predicted risk of mortality score greater than those having medical management, AVR, or TAVI. Thirty-day mortality was 1 of 16 patients (6.3%) for AVR, 2 of 21 patients (9.5%) with TAVI, 2 of 16 patients (12.5%) for BAV, and 7 of 52 patients (13.5%) for the medical management cohort. Overall mortality during follow-up was 42.3% (22 of 52 patients) for medical management, 19.1% (4 of 21 patients) for TAVI, 12.5% (2 of 16 patients) for AVR, and 37.5% (6 of 16 patients) for BAV.

Conclusions: The population of patients screened for transcatheter therapy is complex and heterogeneous. Medical management alone demonstrates a high mortality rate, and BAV, although providing transient symptomatic relief, does not favorably impact survival. The majority of referred patients (65.7%), including those that declined intervention, were candidates for some form of valve replacement therapy, either TAVI or AVR. Transcatheter aortic valve implantation can be performed in appropriately selected patients with good early and immediate-term outcomes.

	Introduction

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Calcific aortic stenosis (AS) remains the most frequent valvular lesion in elderly patients with a prevalence of 2.5% by age 75, and up to 8% at age 85 years old [1]. Aortic valve replacement (AVR) remains the gold standard for treatment of critical AS, and numerous reports document the safety and efficacy of this approach even in elderly patients. A limitation of these studies, however, is their focus on preselected patients already having surgery, and not taking into consideration the outcomes of patients either not referred for surgical evaluation or refused surgical intervention. Frequently, the decision-making process with regard to which elderly high-risk patients are denied surgical intervention is not commented on. This population may in fact outnumber those receiving AVR, as several studies have shown that potentially between one third and two thirds of patients with critical symptomatic AS may not undergo either surgical repair or even referral for surgical consideration [2, 3]. Various reasons offered for refusal of either referral or intervention include advanced age, frailty, and the presence of significant comorbidities that would make patients a prohibitive surgical risk [4].

The development of transcatheter aortic valve implantation (TAVI) for the treatment of critical AS offers a viable option for patients at extreme or prohibitive risk with conventional approaches. Referrals of these high-risk patients to facilities providing TAVI provides an opportunity to evaluate outcomes for not only TAVI but also conventional AVR, and those refused surgical intervention. We report our experience with the management and outcomes of a high-risk group of patients specifically referred for TAVI.

	Material and Methods

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Patients
Between December 2005 and December 2007, 105 patients were referred for possible TAVI either having been refused surgical intervention, or considered to be at extreme risk with standard AVR. All patients had a calculated aortic valve area of 1 cm² or less, and velocities across the valve of 3.5 m/s or greater. This analysis of the collected patient data received exempt status from the North Texas Institutional Review Board at Medical City Dallas Hospital. Patient data were prospectively collected and retrospectively extracted from an STS (Society of Thoracic Surgeons) certified database maintained by the Cardiopulmonary Research Science and Technology Institute (CRSTI). The STS predicted risk of mortality (STS-PROM) for aortic valve procedures was calculated when patient data were entered into the STS database, and the logistic EuroSCORE was calculated according to published guidelines (http://www.euroscore.org/).

Patients were grouped according to their selected management plan. These plans were formulated after physical examination and review of the pertinent diagnostic data by a multispecialty team consisting of cardiac surgeons, interventional and noninterventional cardiologists, nurses, and research coordinators. Physician clinical judgment, as well as patient or family choice, also played a role in treatment plan selection. The therapeutic options ranged from (1) continued medical management (MM), (2) balloon aortic valvuloplasty (BAV) in addition to MM, (3) conventional AVR, and (4) TAVI. Eligibility for receiving TAVI included either compassionate use or meeting the inclusion criteria of current transcatheter valve trials.

Perioperative deaths were tracked from the STS database, and late mortality was obtained by searching the Social Security Death Index or direct phone contact. Long-term follow-up for mortality was available for all patients. All statistical analysis was carried out using SAS 9.1.3 (SAS Institute, Cary, NC).

Technique of Transcatheter Aortic Valve Implantation
Transcatheter valves are inserted using either a transfemoral or a transapical approach to the native aortic valve depending on femoral access. The valves currently come in two sizes, 23 mm and 26 mm, with corresponding 22F and 24F delivery sheaths. The valve platform is stainless steel, and requires balloon inflation for deployment. Leaflets are made of bovine pericardium with anticalcification mitigation. Femoral and iliac access generally should equal or exceed approximately 7.5 mm with noncircumferential calcification for the 22F sheath, and at least 8 mm for the 24F sheath. The current sizes can be implanted in native annuluses ranging from 18 mm up to 24.5 mm in size. Each approach begins by placing either an extra-stiff or super-stiff wire across the aortic annulus either by going retrograde from the femoral artery or antegrade from the left ventricular apex. A BAV is performed with a standard valvuloplasty balloon to facilitate crossing of the stenotic valve with the prosthesis. The valve is then directed to the aortic annulus under fluoroscopic guidance over the stiff wire. The transfemoral approach relies on the unique flexibility of the delivery catheter to navigate around the aortic arch and reach the aortic annulus. Less catheter flexibility is required for the transapical approach, but the increased stiffness of the delivery system provides one to one translation of movement to the end of the catheter, helping in positioning, and provides for little movement of the valve during deployment. Rapid ventricular pacing is instituted during deployment to decrease systolic blood pressure and significantly reduce cardiac output to prevent valve embolization into the aorta when the left ventricular outflow tract is occluded by the delivery balloon. Once deployed, confirmation of positioning is made by fluoroscopy and transesophageal echocardiography. A final aortic root angiogram is performed to ensure nonobstruction of the coronary ostia, valve position and function, and integrity of the aortic root.

	Results

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Of the 105 patients referred for transcatheter therapy, 52 patients (49.5%) received MM only, whereas 16 patients (15.2%) underwent BAV in addition to medical therapy. Patients were listed as MM if they or their family declined intervention (21 of 52 patients), they were considered too high-risk for conventional AVR and did not meet criteria for TAVI (18 of 52 patients), were not offered any intervention based on physician judgment (2 of 52 patients), or were waiting for intervention or in the process of work-up (11 of 52 patients). Twenty-one patients (20%) underwent TAVI, and an additional 16 patients (15.2%) had conventional AVR.

The demographics of the treatment groups are shown in Tables 1 and 2. Notably, there were no significant differences with respect to age, ranging from an average of 78.3 ± 8.9 years in the AVR group up to 81.3 ± 8.7 years in the TAVI patients. All groups had critical AS with valve areas averaging less than 0.65 cm² and maximum velocities across the valve of 4 m/s or greater; additionally, peak gradients ranged from 56.8 ± 23.3 mm Hg in the BAV patients up to 70.3 ± 21.4 mm Hg in the TAVI group. There were no differences among the groups with regard to ejection fraction, body surface area (BSA), percentage of female patients, and incidence of diabetes, hypertension, or cerebrovascular disease. There were significant differences in the frequency of previous coronary artery bypass grafting between the MM (34.0%), BAV (60.0%), and TAVI (52.4%) groups and the AVR cohort (12.5%; p = 0.02). Additionally there were intergroup differences that reached significance with regard to incidence of peripheral vascular disease (PVD; p = 0.02) and history of arrhythmias (p = 0.002). Mitral regurgitation was present in all groups, ranging from 1.73 ± 1.39 in the conventional AVR group up to 2.77 ± 1.09 in the BAV patients on a scale from 1 (mild) to 4 (severe).

There were significant differences among the groups with respect to predicted mortality by the STS-PROM with a predicted mortality of 11.8% ± 6.5% in the BAV cohort, and 11.3% ± 6.7%, 10.9% ± 3.5%, and 6.3% ± 3.5% in the MM, TAVI, and AVR groups, respectively (p = 0.019; Table 2). The logistic EuroScore estimate of mortality ranged from 19.0% ± 16.4% for the AVR patients up to a predicted mortality of 33.3% ± 23.2% for the BAV cohort. Actual 30-day mortality is shown in Figure 1. Mortality ranged from 6.3% in the AVR group to 9.5%, 12.5%, and 13.5% in the TAVI, BAV, and MM groups, respectively. The observed to predicted mortality ratios using the STS-PROM were 1.06 for the BAV group, and 1.19, 0.99, and 0.88, respectively, for the MM, AVR, and TAVI groups.

View larger version (29K): [in this window] [in a new window]   Fig 1. Thirty-day mortality rates. (AVR = aortic valve replacement; O/E = observed/expected ratio.)

View larger version (13K): [in this window] [in a new window]   Fig 2. Kaplan–Meier survival curves for treatment groups. (AVR = aortic valve replacement.)

	Comment

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Many unique variables such as femoral access, degree of peripheral vascular disease, orientation of the aortic annulus in comparison to the axis of the ascending aorta, and quantification of leaflet calcification become important when considering TAVI, and are best evaluated contemporaneously as a team. Additionally, evaluating the contribution of frailty to the symptom complex and the patients' ability to withstand even a catheter-based procedure becomes critically important. Measures used to quantify frailty include grip strength, the number of times the patient can rise from a chair without use of the arms, bowel and bladder continence, and maintenance of weight. A cognitive evaluation and quality-of-life scale is also used to decide which patients to offer intervention. For TAVI, there is a "sweet spot" of patients who are high-risk, but are not so debilitated as to be unsalvageable. The majority of patients referred for catheter-based intervention can appropriately be considered "end-stage" and require an accelerated workup and decision-making process.

Patients referred for TAVI constitute a heterogeneous population of patients, ranging from those too frail and sick to offer any intervention, to those who are operable but at increased risk compared with the standard patient referred for AVR. The majority of patients had either been refused surgical intervention or had never been referred to a surgeon. And as noted previously, those patients considered candidates for conventional AVR were at higher risk than standard-risk patients undergoing AVR during the same time frame (STS-PROM of 6.3 ± 3.5 versus 4.46 ± 4.4 for standard-risk patients; p = 0.08), and correspondingly had a higher mortality (6.3% versus 2.25; p = 0.35). Coexisting coronary artery disease was also common within this population. Although only 25% of the AVR group required concomitant coronary artery bypass grafting, 42.9% of the TAVI patients had coronary artery disease that required percutaneous coronary intervention, including left main stenting before catheter AVR. The prevalence of coronary artery disease in this cohort undoubtedly leads to underestimation of operative risk by the STS-PROM, as mortality risk is greater for AVR and coronary artery bypass grafting than isolated AVR given the same variables. Despite this, the 30-day mortality for TAVI showed an observed to expected mortality ratio of 0.88, confirming the safety of the procedure in a high-risk population. Additionally, a 6-month survival of 74.6% is notable considering that improvement in quality of life becomes the primary goal of surgical intervention as opposed to quantity of life in this elderly high-risk population. Placing these results in context requires keeping in mind the current restrictions regarding access to these devices, that generally being either nonoperative or at greatly increased with conventional surgery. Given the unknown in vivo durability of this novel prosthesis, the current patient cohort has been selected to mitigate against the possibility of the patients outliving these valves. Certainly, by implanting in lower-risk patients, improved mortality and morbidity would be expected to be observed, but the risk of possible repeat aortic valve intervention is then introduced.

Balloon aortic valvuloplasty was performed in the most symptomatic MM patients, and as a means of optimization in 8 of 21 patients before TAVI. The BAV patients not proceeding to TAVI had a lower ejection fraction, more severe mitral insufficiency, and the highest STS-PROM of any of the groups. Several studies have documented the poor outcomes in patients with AS and reduced ejection fractions who do not undergo operation [4]. Balloon aortic valvuloplasty provided symptom relief early after the procedure, but did not demonstrate long-term benefit with regard to survival. This corroborates many reports detailing the transient benefit of BAV in patients with critical AS [12, 13]. Long-term survival in the MM population was only 58.3% at 6 months, with the largest number of deaths in the groups that included those waiting during evaluation, and patients who were not candidates for AVR but did not meet inclusion criteria for TAVI. The fact that medically managed patients demonstrated worse survival than anticipated raises the question of whether TAVI provides a means to recruit and intervene in this population earlier in the disease process.

Given that the majority of patients in this series came to our attention solely because of the existence of a transcatheter aortic program, perhaps an analogy can be drawn between the introduction of another minimally invasive technique and TAVI. In the years after the introduction of laparoscopic cholecystectomy, many studies documented a rapid increase in the number of procedures performed, primarily owing to the fact that a true minimally invasive therapy was available [14, 15]. This new technology recruited a patient population not previously seen for conventional cholecystectomy, including not only those who did not want an open procedure, but also those patients believed to be too sick or high risk for standard surgery. This has been our experience as well after starting a transcatheter program. Provided TAVI continues to demonstrate efficacy, the ability to replace the aortic valve with a procedure that avoids cardiopulmonary bypass could also expand the indications for intervention in AS, before symptoms begin and left ventricular hypertrophy becomes irreversible.

In summary, the population of patients screened for transcatheter therapy for AS is complex and heterogeneous. Medical management alone demonstrates a high mortality rate, and the addition of BAV, although providing transient symptomatic relief, does not favorably impact survival. Transcatheter aortic valve implantation and AVR can be performed in appropriately selected high-risk patients with good early and long-term outcomes.

	Discussion

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DR LARS G. SVENSSON (Cleveland, OH): I would like to congratulate Dr Dewey and his colleagues for an excellent study and a very important one. It is important for a couple of reasons. Firstly, in these new percutaneous valve studies, particularly Evalve and the Edwards studies, the surgeons are the gatekeepers for these procedures. So as these studies get rolled out to more centers, this is something that more of you will be exposed to.

A more important question is what is going to happen once presumably the FDA approves these devices, and whether there are going to be inserts saying that a patient has to have a 15% predicted mortality rate or be inoperable to be included in the studies. The fear is that, as with drug-eluting stents, an inferior procedure, as witnessed recently in the New England Journal of Medicine, will take precedence over standards that we as cardiothoracic surgeons expect for our patients.

We did a similar study (Dr Kapdia) to Dr Dewey's with 92 patients earlier last year, and what is interesting is that approximately 21% of our patients went on to have regular surgery without being included in the study. One question I would have for Dr Dewey is what were the criteria for entering these patients into your study? We usually take patients who have an STS score of 10% or who are considered inoperable and then screen them.

Approximately 20% were able to be enrolled into percutaneous aortic valve procedures with a 30-day mortality rate of 5%. More recently, with some 200 patients, that rate of enrollment has declined to about 17%. Thus, many patients are not candidates for the procedure. In the medical intervention alone groups, our results are somewhat similar to yours, and, as you stressed, approximately 28% of our patients died before some percutaneous intervention could be undertaken, either balloon valvuloplasty or percutaneous valve insertion. As in your series, the patients who had a balloon valvuloplasty had a fairly low initial mortality rate of 4%, but 47% died if they did not undergo some other definitive procedure, and, in particular, a percutaneous valve procedure.

And similar to your study, the Kaplan–Meier curves here on the slide show an excellent survival for patients who had an aortic valve replacement, with no operative deaths; the percutaneous valve patients had a slightly greater risk of death; and the worst were the patients with balloon valvuloplasty.

I have a couple of questions for you as far as the STS scoring. As you know, the STS score correlation with your outcomes was excellent. Did you calculate the scores, I presume, in every patient, since that equation is not available? Perhaps you could also comment on why for aortic valve replacements, and it could be because of correlation with other variables, there appears that ejection fraction, patent coronary artery bypasses previously inserted, and other variables like peripheral vascular disease have no influence on the calculated STS score.

DR DEWEY: Well, thank you very much, Lars. I think our criteria are very similar to yours. We do an initial screening with the STS predicted risk of mortality looking for an STS risk of 10% or greater before proceeding on the rest of the workup to see if these patients may be candidates for a transcatheter procedure. We have found that the STS is a much more discriminating algorithm than the logistic EuroSCORE, which we find dramatically overestimates risk of mortality, especially in this high-risk sort of end of the curve population of patients.

To your question as to why there are some problems with the risk scoring, and I think you and I have talked about this, that of the 60 variables collected for the STS risk algorithm, only 24 are actually used to calculate a risk of mortality for isolated valve replacement. Surprisingly, ejection fraction is not one them, nor is peripheral vascular disease, and I think patent bypass grafts is not included in that risk calculation as well. It is not a weighted variable and so it doesn't really add to the risk factors of the patients.

DR CRAIG R. SMITH (New York, NY): I am required to disclose that I am the PI on the PARTNER trial. That is an unpaid position, and I have no financial interest in Edwards Life Sciences.

This is a very thought-provoking analysis of an increasingly important question, and I thank both the authors and the discussant for touching on this. There are probably those who have worked with us on PARTNER who are a little tired of hearing me make this point, but it may still be worth making for others. It is important to note that in the existing databases that are of any relevance to valve disease—that is STS, New York State, and the Ambler report from Europe—patients who have a predicted mortality greater than 10% are 8% or less of the populations analyzed. So we really don't have a lot of experience with that high-risk subset. And that small pool in our databases is a very small part of the larger pool of patients who haven't traditionally been offered AVR. Some of these patients are now being referred because the behavior of cardiologists is changing just with the suggestion that there might be a percutaneous alternative available. So we are entering a new era.

Why does this matter? Because it is very hard for us to know what to expect in this population. We may think we know because of our databases, but these are such a small fraction of our database populations that we really don't know. And despite what each of us may think about the accuracy of our personal protoplasmometers, we just don't have great tools for predicting outcomes in this group. So as we enter this new era, we have to keep a very open mind, and be prepared to rearrange some of our concepts about what to expect in these patients as experience from the trials we are talking about bleeds into practice.

So what should we conclude from this report? What we should not conclude is that AVR is a superior treatment in this population. You will notice the authors were scrupulous about avoiding that conclusion. The difference in STS score between the three groups should be enough to convince you that selection accounts for these results. It would be seriously misleading to proclaim that conventional AVR can be carried out with 0% mortality in high-risk patients who are candidates for transcatheter AVR. This is a period of shifting boundaries between the three patient subpopulations just presented, and we have to wait and see.

	References

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Todd M. Dewey David L. Brown William H. Ryan Syma L. Prince Michael J. Mack Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Dewey, T. M. Articles by Mack, M. J. Search for Related Content PubMed PubMed Citation Articles by Dewey, T. M. Articles by Mack, M. J. Related Collections Valve disease