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Learning objectives
To review the indications for balloon aortic valvuloplasty (BAV) and how it fits into the treatment of aortic stenosis, and to consider which patients may benefit from the procedure.
To understand the technique and potential complications, including the variety of devices available.
To consider outcomes from the procedure and how BAV can be used in the future.
Introduction
Calcific, degenerative aortic stenosis (AS) is the the most common valve pathology in the ageing Western population.1 Prevalence increases with age, from 0.2% in those aged 50–59 years to 9.8% among those aged 80–89 years.2 AS is gradually progressive and can ultimately be fatal. Symptoms develop as the condition deteriorates, to the point where intervention is required either for symptoms, for prognosis or both.
The underlying pathology of senile, degenerative AS is an active inflammatory process akin to atherosclerotic vascular disease. Definitive treatments for AS include surgical valve replacement (sAVR) or transcatheter aortic valve implantation (TAVI). Both of these techniques are well proven and prominent in guidelines3 but are not suitable for all patients.
Balloon aortic valvuloplasty (BAV) has been in existence for over 30 years.4 After the initial enthusiasm was tempered by the finding of early restenosis, the treatment is often reserved for patients who are not physically strong enough to withstand more definitive therapy. Numbers of BAV procedures have increased with the widespread adoption and availability of TAVI.5 This article aims to discuss the role of BAV in current guidelines, which patients are most suitable for the procedure, how it is performed, and what outcomes and complications may be anticipated.
How does BAV fit into the guidelines?
Current European guidelines state that BAV has a IIb (level of evidence class C) indication for patients with haemodynamic instability as a bridge therapy to definitive treatment with either sAVR or TAVI,3 as a treatment for patients requiring urgent non-cardiac surgery and as a therapeutic trial in patients with confounding comorbidities.
American guidelines also give the same indication and evidence level for BAV as a bridging therapy to sAVR or TAVI in symptomatic patients, but do not consider BAV to have any role in patients who require urgent non-cardiac surgery. Certainly, the evidence that BAV has a role in this setting (as suggested in the European guidelines) is flimsy.
It is also widely agreed that BAV also has a role in palliation of patients for whom no reasonable options for definitive valve treatment are available but who are significantly affected by symptoms due to severe AS.
Patient selection and who might benefit
The decision to offer BAV in stable patients should be based on a heart team approach. Potential indications for BAV are given in box 1, and a decision-making algorithm as used in the Sussex Cardiac Centre is shown in figure 1. While most patients presenting with symptomatic severe AS will be offered sAVR or TAVI, some patients will be considered unsuitable for either of these approaches, and then a decision must be made about whether a BAV should be offered. It is the case, however, that as TAVI has evolved from general anaesthetic to a true percutaneous procedure under general anaesthetic, more frail and elderly patients are considered for definitive treatment, thus reducing the numbers of stand-alone BAV procedures in some centres.
Indications for stand-alone balloon aortic valvuloplasty
As palliation
In patients with severe aortic stenosis (AS) but multiple comorbidities precluding transcatheter aortic valve implantation (TAVI).
As a bridge to surgical valve replacement or TAVI
In patients where doubt exists as to the relative contribution of AS to the patient’s symptomatology.
To assess improvement in symptoms and improvement in left ventricular function in patients with severe left ventricular systolic impairment.
In patients with severe AS and acute decompensation.
Patients may also be offered BAV if they are technically unsuitable for TAVI (due to factors such as arterial access, an unusually large annulus or other unusual anatomy) or may be offered BAV as a standalone procedure if they have a life expectancy that is shortened due to other diseases.
Patients may have AS discovered during workup for surgery unrelated to cardiac disease. Intervention among this group of patients is frequently requested. There is, however, no evidence that BAV reduces perioperative risks to a degree commensurate with its own inherent major complication rate, and therefore, these requests should be resisted in most cases.6 In some cases, considering an urgent TAVI as destination treatment in these patients may be a better option, if a TAVI is indicated for the patient on its own merits.
In acute presentations, such as cardiogenic shock, BAV is a reasonable ‘bail-out’ treatment option, especially when clinical details or preprocedure imaging is not adequate to allow safe TAVI. Survival in this group, however, is poor compared with stable patients.7
Contemporary technique
Preprocedure considerations
Prior to the procedure, it needs to be established, in discussion with the patient, what level of care is appropriate for the patient, especially should a complication arise. This will include discussions regarding ceilings of treatment, resuscitation and expected life expectancy. Furthermore the goal of treatment needs to be clear, for example, palliative or as a bridge to further definitive therapy. Generally, BAV procedures are performed by interventional cardiologists in hospitals with cardiothoracic and vascular surgical teams to assist in the event of a complication.
Preprocedural imaging will usually take the form of echocardiography, with or without cardiac CT (more likely in the event the patient has been worked up for a potential TAVI procedure). Preprocedural imaging is important to assess the aortic annular size and therefore to select an appropriate valvuloplasty balloon. Echocardiographic balloon sizing leads to smaller balloon choices as the imaging diameter is made anteroposterior, in the minor axis of the annulus. If CT imaging is not available, arterial access may not have been assessed, but few patients cannot accept up to 12 F access from a common femoral artery.
Possible pitfalls to the procedure are also assessed prior to the procedure. This includes the degree of aortic insufficiency; severe aortic regurgitation (AR) may be a contraindication to BAV if the AS itself is not the dominant lesion.
BAV procedure
Procedures are almost universally performed via the femoral route, with vascular sheaths up to 12 F in diameter, depending on the choice of balloon, and often sheathes of 8–9 F are appropriate for most procedures. Procedures are usually performed under local anaesthesia, with conscious sedation. Although generally considered less invasive than a TAVI procedure, due to often greater comorbidity or worse clinical status in patients undergoing BAV, the procedure can be just as technically challenging, if not more challenging in some cases than a TAVI.
Historically femoral venous access was also required for placement of a temporary pacing wire into the right ventricle to allow rapid pacing during balloon expansion. More recently it has been shown that pacing can be achieved using the left ventricular 0.035” wire.8 Using the left ventricular wire has the obvious advantage of avoiding additional vascular access, reducing the risk of cardiac tamponade, and reducing the time, complexity and cost of the procedure. In patients with a pre-existing permanent pacemaker, this can be used for rapid pacing but must be checked first that this is possible, as some manufacturers have a limit to the length of rapid pacing allowed using pacemaker programmers.
Valvuloplasty balloons need 8–12 French arterial access sheaths, and therefore meticulous care in gaining vascular access is needed. For the smallest sheath sizes (8–9 Fr) it is usually possible to achieve closure with a single device such as Angioseal (Terumo, Japan) or ProGlide (Abbott, USA). For larger sheath sizes vascular preclosure is recommended, for example using the ProGlide or ProStar system (Abbott, USA). To ensure safe arterial access ultrasound should be used to find a puncture site in the common femoral artery, away from the bifurcation of the profunda femoris and superficial femoral. Other techniques can also be used, such as first inserting a 4 French sheath introducer and using a contrast injection through this under fluoroscopy to make certain that the puncture site is suitable between the femoral bifurcation and the inferior epigastric artery origin. In patients who have been worked up for TAVI, a CT demonstrating the peripheral vascular tree for TAVI planning may be available, which will help in selecting a suitable access site.
Once arterial access has been achieved, a pigtail catheter is advanced to the aortic root under fluoroscopy and an aortogram can be taken to allow visualisation of the anulus and help refine the projection angle. With the benefit of a CT scan the annular projection can easily be calculated; without this the best initial projection is AP caudal 15°. The aortogram also helps define the target crossing point where leaflet opening is seen, and contrast washout is greatest. The valve is usually crossed using a diagnostic coronary catheter, usually AL-1 (Amplatz left 1) or JR4 (Judkins right 4), floating the catheter tip in the aortic root and gently probing the valve with a soft-tipped straight 0.035” hydrophilic or Teflon-coated wire. Clockwise rotation of the catheter is necessary to direct the wire across the orifice and into the left ventricle (LV). Once the wire has entered the LV, the catheter is carefully advanced into the LV. At this stage, once pressure transduction demonstrates free connection to blood, an exchange wire can be used to allow introduction of a pigtail catheter. Transvalvular gradient measurement is taken from the pigtail and side-arm of the femoral sheath (figure 2)
Brief rapid pacing is initiated, aiming to drop the blood pressure to ≤60 mmHg for long enough to inflate and deflate the valvuloplasty balloon. Typically the pacing rate may be 180–220 bpm. The balloon is inflated by hand, which can generate up to 6atm load. Completeness of expansion is assessed fluoroscopically (figure 3). Balloon inflation is often repeated three times to achieve maximum effect - there is some evidence that a higher number of inflations leads to improved outcomes.9
The pressure gradient between the left ventricle and aorta is usually rechecked once the operator considers that enough dilatation has been done. AR can be assessed by aortography, left ventricular and aortic pressure waveforms and echocardiography. The haemodynamic aim is to reduce the peak or mean valve gradient by ≥50%. If this is not achieved, balloon upsizing can be considered but there is a balance to be struck between larger balloon diameters and the risk of complications.
Once the balloon apparatus is removed, haemostasis is achieved with the chosen closure system. If the procedure has been uncomplicated, an elective patient may be discharged later the same day provided support at home is in place. On clinical follow-up, symptom resolution can be assessed, along with the place of further definitive therapy.
Balloon selection and technology
Commonly used valvuloplasty balloons are shown in table 1, together with their characteristics and size ranges. A Z-Med II 23×40 mm valvuloplasty balloon is pictured in figure 4. Adult valvuloplasty balloons range from 16 to 30 mm diameter. Balloons may be semi-compliant or non-compliant. Semi-compliant balloons require smaller calibre vascular access but inflate and deflate more slowly, and are more prone to burst during inflation. Non-compliant balloons are preferred for post-dilation in TAVI.
Most balloons are cylindrical in shape and hourglass balloons offer no advantage. Longer balloon length can improve stability. The True Flow balloon (Bard, USA), is composed of multiple smaller balloons which allow flow in between, obviating the need for rapid pacing.
Specific clinical scenarios for BAV
Cardiogenic shock
Patients presenting with cardiogenic shock due to severe AS are a group with high mortality and poor outcomes. These patients are often too sick for any other treatment; BAV may be effective though procedural risks are high, with in-hospital mortality rates up to 50%.10
BAV in patients with low ejection fraction
In patients with low ejection fraction and apparent severe AS, balloon valvuloplasty is sometimes used as a diagnostic and therapeutic test where there have been difficulties differentiating to what extent poor left ventricular function reflects severe AS and to what extent aortic restriction is a bystander. This strategy is rarely helpful. Efforts should be made to distinguish true severe from pseudo-severe AS using dobutamine stress echocardiography (DSE) and cardiac CT, followed either by definitive therapy or medical management.
BAV in pregnancy
European Society of Cardiology guidelines recommend avoidance of conception in the context of untreated severe AS. However, this occasionally happens, as does diagnosis during pregnancy. BAV is potentially indicated in these patients if the AS is really severe and symptomatic.11
BAV during TAVI procedures
Pre-dilation with an aortic valvuloplasty balloon is an important part of many TAVI procedures, particularly for self-expanding valves with lower radial strength, although is being used less frequently with balloon expandable devices. Predilatation increases flexibility of the valve by calcium fracture, widens the orifice to allow the prosthesis to cross, and reduces the need for postdilatation.
Paravalvular leak (PVL) is important to recognise during TAVI.12 Factors contributing to PVL include annular calcification (both the degree of calcification and its pattern), prosthesis positioning within the annulus, valve underexpansion, and valve undersizing. Significant AR is associated with poorer outcomes both in terms of symptom relief and longevity.13 Balloon postdilatation after TAVI is not a risk-free procedure and may increase the risk of stroke. Techniques vary according to the valve type deployed. In the case of balloon expandable valves, it is usual practice to use the valve delivery balloon for further dilation, either with the same volume of fluid or with additional volume for greater expansion. Self-expanding valves are usually post-dilated with a balloon 2–4 mm smaller than the nominal diameter of the annular portion of the valve.14 15
Balloon dilation of surgical prostheses and valve ring fracture
An increasing role for TAVI is in the treatment of degenerative surgical bioprostheses.16 17 Valve-in-valve therapy however leads to small effective orifice areas, with high rates of patient-prosthesis mismatch.18 19 To overcome this problem there has been a move to “crack” the surgical valve with a balloon either immediately before or after implantation of the transcatheter valve.20 Surgical valve ring fracture is performed using high pressure non-compliant balloons (eg, True balloon or Atlas Gold (Bard)). A balloon up to 3 mm larger than the internal diameter of the relevant surgical bioprosthesis is taken and inflated to high pressure (eg, 16 atm) with an indeflator during rapid pacing in order to fracture the internal valve frame ring.21 This increases the effective area of the valve and decreases the residual valve gradient. It is expected that longer-term outcomes will be better as a result but data on this are awaited. A minority of surgical valves such as the Trifecta and Hancock II cannot be fractured.22
Outcomes from old and new data
Haemodynamic outcomes
Early BAV data came from two large registries, the NHLBI Registry23 and the Mansfield Registry,24 reporting outcomes from 674 and 492 patients respectively. Both reported an increase in valve area (from 0.5 to 0.8 cm2) and a reduction in peak AV gradient from 60 to 30 mmHg. The Mansfield Registry also examined variables that might influence outcomes and found that duration of balloon inflation was the only factor.
Since the introduction of TAVI, more recent studies reporting valve haemodynamic outcomes include 423 from the UK5 and 811 patients from a pan European registry25 reporting improvements in AVA from 0.58 to 0.8 cm2 and 0.61 to 0.8 cm2 respectively, very similar to results from registries in the pre-TAVI era. Despite changes in technology over more than 20 years this hasn’t translated into changes in acute haemodynamics.
Mortality outcomes
The NHLBI registry reported in hospital mortality rates of 3%, 30 day mortality of 14% and 1 year mortality of 36%.23 Khawaja et al reported an in hospital mortality rate of 2.5%,5 similar to that in a study of 472 patients conducted by Ben-Dor et al 26 in 2013. Higher in hospital mortality rates than this have been reported, however, for example Alkhouli et al retrospectively studied over 3000 procedures in the USA from 2004 to 2013 and found in hospital mortality rates of 8.5% across all patients.27 Procedural mortality was seen in 1.4% of these patients, with patients at higher risk of procedural and in hospital death if undergoing BAV for cardiogenic shock, if performed in the presence of a left ventricular assist device, or if undergoing BAV in centres performing only 1–2 procedures per year.
Longer term outcomes (1 year or more) in all patients undergoing BAV have been poor. Large early registries reported 1 year mortality of 36% in both NHLBI and Mansfield registries despite a number of these patients going on to have definitive treatment with sAVR. More contemporary data has done little to suggest an improvement in these outcomes longer term. In 415 consecutive patients Saia et al report 1 year mortality of 33% (and 57.4% at 2 years).28 Outcomes were worse for patients undergoing BAV as palliation (1 year mortality 44%) and better for those in whom it was a bridge to TAVI (1 year mortality 13%) and sAVR (0%).
In the initial PARTNER trial comparing TAVI to medical therapy (including BAV) follow-up extended to 5 years.29 At 5 year follow-up mortality in patients undergoing BAV was 94% compared with 72% in the TAVI arm, with similar poor long term survival from BAV reported in other studies.30 In shorter term follow-up of PARTNER, BAV in conjunction with medical therapy for severe AS did confer a survival benefit at 30 days over medical therapy alone.31
Restenosis and repeat procedures
Results from BAV are short lived32 and clearly this is reflected in the poor outcomes of BAV as a standalone treatment. Most valves will restenose by 6 months to 1 year, and some will require repeat procedures.
Repeat BAV procedures are safe and can potentially extend life expectancy33 but in practice are not undertaken lightly. Prior to an index procedure for AS it will have already been established what the ceiling of treatment for individual patients will be, and often this will have been BAV as a palliative procedure. If patients have made good recovery after BAV then definitive treatment should be considered, and therefore repeated BAV should be carefully considered.
Complications
Early studies reported high complication rates of up to 25%,23 with much of this driven by vascular complications. Other complications reported at varying rates in the literature include peri-procedural MI, development or worsening of AR, cardiac tamponade, death, ventricular perforation, stroke, systemic embolisation, and conduction abnormalities (table 2).
More contemporary data show a trend towards improving complication rates. Vascular complication rates, in particular, have fallen since earlier studies. Among the 811 patients reported by Moretti et al 25 major vascular complications were below 6%, using VARC definitions (41), a fall since the earlier published studies.
Stroke is a feared complication. In combined studies of over 5000 patients Alkhouli reported stroke and TIA in 2.2%,27 and Singh reported stroke in 3%.34
Bradyarrhythmias may occur during BAV procedures, but are reported less frequently than in TAVI with low permanent pacing rates.35 Transient heart block or bradycardia can be overcome with temporary pacing during procedures.
Acute AR is a rare but significant complication of BAV. Rates have changed little over time with the complication occurring in up to 3% of patients. In Saia’s large series it occurred in 2.6% of patients but was managed during the procedure in the majority of these by manipulating a catheter to mobilise a cusp that had become locked.28 In an early study the effect of BAV on worsening pre-existing AR was investigated,36 with no significant difference in worsening of AR compared with a group with no significant AR pre-procedure. Dall’ara et al in 2017 reported no change in AR in groups randomised to rapid pacing versus no rapid pacing,37 suggesting balloon movement during the procedure did little to affect the risk of AR.
Vascular complications remain the most common complication, but have decreased significantly since operators have become skilled in TAVI. The reduction in vascular complications is likely to arise from improved closure methods, more fastidious attention to haemostasis, and more advanced pre-procedure planning. Other complication rates, however, have changed little.
Future roles for BAV
Future prospects for BAV include a changing role with deployment during TAVI for both pre and post dilatation, and with an ageing population in the western world economic effects of BAV should be an area for investigation to ensure the correct treatments are used in suitable patients. Other new technologies may also expand the scope of BAV and make procedures more successful.
Novel technologies
Although not balloon based, the Leaflex system (Pi-Cardia, Israel) is an experimental device that in ex-vivo trials has shown promise at improving aortic valve area in severe AS.38 The device is designed to capture the aortic valve leaflets and mechanically score them thus increasing their flexibility and reducing stenosis. Currently Leaflex is being evaluated in clinical trials and is only available in this setting.
Intravascular lithotripsy is a relatively new area of development that has been used in calcific peripheral vascular disease and in calcified coronary disease.39 Its mechanism of action involves emission of pulses of sonic pressure waves to disrupt calcium and cause microfractures in calcified tissue to occur. Although available for use in coronary disease, feasibility studies are ongoing at an early stage for its use in AS and if successful will result in widening access to this technology for use in AS.
Timing of intervention
Timing of intervention for severe AS can be controversial,40 with the traditional approach being avoiding intervention in asymptomatic patients in the absence of left ventricular decompensation. Contemporary evidence, however, may point to a role of intervention for patients with severe AS while they remain asymptomatic.41 Although with safe and successful outcomes from definitive treatment being available, the role of BAV in these patients earlier will need to be assessed. It remains to be seen whether intervention with BAV at an earlier stage of disease would improve outcomes by preventing or delaying the onset of symptoms and the potential for left ventricular decompensation.
Economic considerations
TAVI, although cost effective in high income countries,42 is expensive and unaffordable for most in developing nations.43 Balloon valvuloplasty equipment is of course much cheaper than equipment for TAVI, and for sAVR. In developing countries it may therefore be a more attractive option. Even in affluent countries there is a finite amount of money available for healthcare, and so even in these nations where TAVI is cost effective on a population basis, there may be an argument in some patients that BAV, if effective, presents a more attractive use of resources.
BAV may be especially attractive in less affluent areas if it is able to prevent recurrent hospitalisations with symptoms of AS or heart failure and be performed safely with minimal complications.
Summary/conclusions
BAV still has an important role to play in the treatment of severe AS. Its use has increased over the years since the introduction of TAVI as a wider role has been recognised in bridging patients to definitive therapy, or in the treatment of patients in extremis with limited other options for treatment.
Complication rates have reduced over time, particularly with respect to vascular complications. Advances in technology supported by work in TAVI have improved planning of procedures in respect of vascular access, in addition to the use of modern vascular closure devices. Other advances in technology that have accompanied an upsurge in BAV procedures include the advent of pre-curved stiff guidewires that reduce the risk of trauma to the heart and can be used for rapid pacing in lieu of pacing via the right ventricle.
Despite advances in technology, the immediate haemodynamic benefit of valve dilatation has not changed since the procedure was first instigated. Long term mortality in the absence of definitive treatment also remains poor in patients undergoing BAV alone, although in hospital mortality and 30 day mortality rates have improved since the procedure was first used.
Investigation into the technique of BAV, including balloon sizing and inflation technique, would add valuable information for how to potentially improve the procedure with the long term aim of improving outcomes from BAV procedures alone. Future perspectives also include advancing technologies for valve modification and consideration of the economic impact of valve intervention, especially in less affluent areas.
Key points
Balloon aortic valvuloplasty (BAV) has a role for patients in extremis, or who are not suitable for definitive aortic valve intervention.
There is a wide range of equipment available with balloons demonstrating different characteristics for difference uses.
Despite advances in technology, long term outcomes from standalone BAV are poor and patients need to be aware of the limitations of the treatment.
BAV will continue to have a role in TAVI procedures.
Future technologies will build on balloon-only BAV and will look to generate more durable results without valve implantation.
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Footnotes
Contributors The authors contributed equally to the production of this work.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests None declared.
Patient and public involvement Patients and/or the public were not involved in the design, or conduct, or reporting, or dissemination plans of this research.
Patient consent for publication Not required.
Provenance and peer review Commissioned; externally peer reviewed.
Data availability statement There are no data in this work
Author note References which include a * are considered to be key references