Balloon aortic valvuloplasty as a treatment option in the era of transcatheter aortic valve implantation

Abstract

Aortic valve stenosis is the commonest encountered valvular pathology and a frequent cause of morbidity and mortality in cases of severe stenosis. Definitive treatment has traditionally been offered in the form of surgical aortic valve replacement in patients with an acceptable surgical risk and more recently with the less invasive transcatheter aortic valve implantation (TAVI) in those where surgery is not a viable option. Prior to the introduction of TAVI, inoperable patients were treated medically and where appropriate with balloon aortic valvuloplasty, a procedure which although effective only provided short-term relief and was associated with high complication rates especially during its infancy. Here we discuss whether balloon aortic valvuloplasty continues to have a role in contemporary clinical practice in an era where significant advances have been achieved in the fields of surgical aortic valve replacement, TAVI and postoperative care.

Keywords:

• aortic regurgitation
• aortic stenosis
• balloon aortic valvuloplasty
• surgical aortic valve replacement
• transcatheter aortic valve implantation

Degenerative aortic valve stenosis (AS) is the commonest valvular disease in the developed world, the incidence of which is increasing with an aging population. Severe AS is often associated with poor prognosis if left untreated with mortality rates approaching 50–60% at 2 years in patients with symptomatic disease [1]. Severe AS has traditionally been treated with surgical aortic valve replacement (SAVR), although up to 30% of patients have been precluded from this due to high surgical risk [2,3]. Balloon aortic valvuloplasty (BAV) offered an alternative treatment for inoperable patients, although this was confounded by a high complication rate and only a short-term improvement in aortic valve function [4]. With the recent introduction of transcatheter aortic valve implantation (TAVI), the incidence of BAV has been increasing as this had traditionally been performed as part of the TAVI procedure [5,6].

Balloon aortic valvuloplasty: the evidence

Most studies have demonstrated that BAV is associated with significant improvements in aortic valve area (AVA) and transaortic valve gradient as well as cardiac output in the immediate and early term post-procedure. In the multicenter case series by McKay, which included 492 patients with a mean age of 79 years, a mean AV gradient reduction of 30 mmHg was achieved (from 60 to 30 mmHg) with an 87% procedural success rate defined as at least 25% increase in AVA or at least 50% decrease in mean AV gradient in the absence of death or conversion to surgery in the first 7 days post-procedure. However, there was a 20% overall complication rate and an 8% mortality. Moderate or severe aortic regurgitation (AR) was noted in 2% of the cases [7]. In the National Heart, Lung and Blood Institute registry, which included 674 patients 80% of which were considered inoperable due to age or other co-morbidities BAV achieved a mean gradient reduction from 55 to 29 mmHg, with 86% of surviving patients (69% of group) noting significant symptomatic improvement. However, complication rate was high (31% prior to discharge) with a significant mortality risk at 30 days (14%) [8]. Predictors of poor clinical outcomes following BAV included poor pre-procedural clinical status, renal dysfunction, high pre-procedural right atrial pressure and low cardiac output [9]. In contrast to these early studies, recent studies have demonstrated acceptable early clinical outcomes with BAV. The study by Eltchaninoff et al., from a cohort of 323 patients treated between 2005 and 2008, reported much-improved major complication (6.8%) and mortality rates (2.5%). Complications were largely due to vascular injury or valve material embolization, whereas mortality was more commonly related to the occurrence of severe AR. Success rate defined as a decrease of mean aortic gradient of >50% and/or a final aortic valve area >1 cm² was achieved in 81% of the cases. With regards to long-term clinical outcomes, survival rates at 5-year were low at 3.3% in patients treated with BAV alone in contrast to patients who subsequently received more definitive treatment either in the form of SAVR or TAVI (40 and 22%, respectively) [10]. Similar results were noted from the UK experience comprising a cohort of 423 patients, where BAV was shown to offer good immediate hemodynamic efficacy at an acceptable risk of major complications but poor medium-term prognosis in the absence of more definitive therapy [11]. The poor long-term outcomes observed in these studies is a reflection of the high risk of restenosis in BAV-treated patients, which can approach to 60% at 6 months, as well as the extensive co-morbidity that makes BAV the only option for such patients. Consistent with this, the study by Otto et al. demonstrated that although AVA improves immediately post-procedure from a mean of 0.57 to 0.78 cm², this reduces to 0.65 cm² over the same 6-month interval [12].

BAV: its role in current practice

Currently, the European guidelines recommend BAV as a bridge to SAVR or TAVI in hemodynamically unstable patients who are at high risk for surgery or in patients with symptomatic severe AS who require urgent non-cardiac surgery (class IIb level of evidence C) [13]. The decrease in AV gradient and associated increase in cardiac output seen with BAV can provide an important time-window for such patients during which improved forward flow improves peripheral perfusion and decreased outflow obstruction, reduces pulmonary congestion, with associated improvements in clinical status. Such a stabilizing measure offers the opportunity for investigations to be completed in order to assess patient suitability for SAVR or TAVI as well as a period of hemodynamic improvement that can reduce the procedural risk of more definitive therapies, ‘bridge to therapy’. In the study by Saia et al., of the 210 consecutive patients referred for BAV, 78 underwent BAV as a bridge for TAVI of which 36 proceeded to receive TAVI and 22 improved sufficiently to undergo SAVR. The remaining surviving patients post-BAV did not experience any symptomatic improvement despite significant reductions in mean AV gradient and were thus treated medically as the cause of their symptoms was attributed to other factors [14]. It is important to note that when BAV is performed as a bridge to more definitive therapy that the latter takes place in a timely fashion. Evidence from the aforementioned studies suggests that success rates for BAV as a bridging measure can vary between 26.3 and 74%, with delays in destination therapy a major contributor toward poor mid-term outcomes [15].

BAV can, therefore, not only act as a bridge to TAVI or SAVR, but can also help to identify which patients are suitable for these therapies when other co-morbidities such as poor left ventricular function, concomitant chronic obstructive pulmonary disease and severe pulmonary hypertension raise concerns about symptom reversibility, ‘assessment of therapy’. In such a patient cohort, where symptom relief and not prognosis is the main issue, BAV can act as a gatekeeper to more definitive treatments sparing thus patients from the higher risks associated with these as well as healthcare systems from costly procedures that are unlikely to offer the desired symptomatic benefit.

Lastly, BAV can be a useful palliative ‘destination therapy’ in patients with severe AS but poor prognosis due to other co-morbidities, such as malignancy, as it often leads to significant clinical improvement often allowing hospital discharge.

The role of BAV in TAVI

BAV especially during the early TAVI era was an integral part of the procedure as this allowed easier valve delivery and helped to ensure complete valve expansion. More recently however, and especially after the introduction of self-expanding valves, TAVI is often performed without predilatation. Grube et al. demonstrated in a small study of 60 patients that TAVI with the self-expanding Medtronic CoreValve bioprosthesis (Medtronic, Minneapolis, MN, USA) without predilatation is feasible and safe with results similar to those with predilatation [16]. More recently, similar results were reported with the balloon expandable Edwards Sapien XT (Edwards Lifescience, Irvine, CA, USA) [17]. The currently recruiting randomized trial TAVI Without Predilation: SIMPLIFy TAVI and the observational prospective registry Balloon Expandable TAVI Without Predilation of the Aortic Valve: EASE-IT, a two-armed registry will provide more information regarding the need for balloon predilatation in TAVI. Irrespective of the results of these studies, BAV will continue to have a role in TAVI as a predilatation tool, especially in cases where valve area is particularly small and leaflet calcification is extensive as in such cases valve crossing may otherwise not be possible [18]. Finally, in cases of valve underexpansion or poor apposition to the annulus BAV is often required for postdilatation in an attempt to reduce paravalvular AR as this has been shown to impact on long-term outcomes [19]. Valve underexpansion is visible on fluoroscopy whereas paravalvular AR is usually evident either on TOE or on aortography. BAV in these cases requires a balloon of a smaller size as compared with that of the implanted valve as oversizing risks annular rupture. The aim of balloon postdilatation is not to completely abolish AR but to reduce this to a grade similar to that prior to TAVI in patients with pre-existing AR, whereas in ‘AR-naïve’ patients to minimal or trivial levels.

Expert commentary & future directions

Advances in the field of medicine throughout a range of specialties over the years have led not only to improvements in life expectancy but also an expanding aging population with multiple co-morbidities. As a result, a significant number of patients with severe symptomatic AS carry a high surgical risk for SAVR. The introduction of TAVI as a less invasive approach for the treatment of AS has allowed such inoperable patients to be successfully treated with improved outcomes as compared with medical therapy alone. BAV on the other hand, although providing only a temporary solution for such patients, continues to have an important role in the treatment of AS. It can be a ‘bridging therapy’, a stabilizing measure in acutely unwell patients offering a bridge to more definitive treatments, or ‘destination therapy’ for those with poor prognosis, but a need for palliative treatment. BAV can also help to identify which patients would benefit the most from definitive valve intervention when other pathologies make it difficult to assess whether symptoms are the result of severe AS. It is important here to note that careful planning is paramount to a successful BAV procedure. In particular, balloon diameter should not exceed aortic annulus dimensions as this risks annular rupture and increases the likelihood of significant AR. BAV should also be performed with caution in patients with more than mild AR as this can worsen the degree of AR, which in general is poorly tolerated as left ventricular compliance and relaxation is often impaired in these patients with severe AS. Finally, BAV will continue to be an important aspect of the TAVI procedure where required either as a pre- or postdilatation tool. Future directions in the field of BAV involve the development of drug-coated balloons with either paclitaxel or -limus drugs with early pre-clinical data suggesting that drug coating may reduce or at least delay valve restenosis.

Financial & competing interests disclosure

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending or royalties.

No writing assistance was utilized in the production of this manuscript.