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The British Journal of Radiology logoLink to The British Journal of Radiology
. 2013 Dec 13;87(1033):20130595. doi: 10.1259/bjr.20130595

Transcatheter aortic valve insertion (TAVI): a review

B Clayton 1,, G Morgan-Hughes 1, C Roobottom 2
PMCID: PMC3898978  PMID: 24258463

Abstract

The introduction of transcatheter aortic valve insertion (TAVI) has transformed the care provided for patients with severe aortic stenosis. The uptake of this procedure is increasing rapidly, and clinicians from all disciplines are likely to increasingly encounter patients being assessed for or having undergone this intervention. Successful TAVI heavily relies on careful and comprehensive imaging assessment, before, during and after the procedure, using a range of modalities. This review outlines the background and development of TAVI, describes the nature of the procedure and considers the contribution of imaging techniques, both to successful intervention and to potential complications.

AORTIC STENOSIS

Aortic stenosis (AoS) is a common disorder in which the narrowing of the aortic valve orifice leads to an obstruction of left ventricular (LV) outflow. In the general population, the prevalence is in the order of half a percent but increases greatly above the age of 65 years,1 such that a slim majority of patients with it are aged over 70 years. Importantly, it is therefore associated with significant comorbidities in more than one-third of cases.2

AoS in a population aged over 70 years is usually due to age-related calcification, but in younger patients, bicuspid valve is the primary cause.3 The disease seems to be mediated by an inflammatory process, similar to that of atherosclerosis,4 and calcific deposition may occur at the final stage in the healing process, akin to coronary atheroma. Progressive deposition and valvular thickening results in the obstruction of the LV outflow tract. Initially, the LV hypertrophies in an attempt to overcome this, but, over time, the myocardium becomes less compliant with a rise in LV end-diastolic pressure and impairment of relaxation (diastolic dysfunction).

Increased chamber filling pressures and reduced cardiac output lead to dyspnoea, which is the commonest symptom of AoS. Angina is common in severe disease and may occur because of increased LV mass, poor coronary filling5 and reduced coronary flow reserve.6 Exertional pre-syncope and syncope also occur, probably owing to the fixed cardiac output at times of increased demand and vasodilatation or to arrhythmia. Unsurprisingly, the risk of sudden cardiac death increases with the severity of disease.

Without intervention, the prognosis of patients with symptomatic severe AoS, where the aortic valve area is <1 cm2 or <0.6 cm2 m−2,7 is poor. The onset of symptoms heralds a rapid decline, and mortality in patients with heart failure symptoms is around 50% in the first year.8 Patients with other symptoms do only slightly better, with 50% survival up to 3 years once syncope occurs and up to 5 years following presentation with angina.9

SUITABILITY FOR SURGICAL AORTIC VALVE REPLACEMENT

Even elderly patients do surprisingly well following surgical aortic valve replacement (AVR), with the survival in one large population of patients older than 80 years at 89% and 69% after 1 and 5 years, respectively,10 and octogenarians require similar levels of post-operative care and resource as do younger patients.11 Indeed, the European Society of Cardiology recommend that transcatheter aortic valve insertion (TAVI) be offered to patients who are unsuitable for conventional surgery on the basis of comorbidities12 rather than age. Nonetheless, elderly patients do have more comorbidities and are more likely to be denied conventional surgery.13

Major factors contributing to poorer outcomes in aortic valve surgery include moderate to severe heart failure (New York Heart Association Stage III or IV), pre-operative atrial fibrillation10 and concomitant coronary artery disease.14 LV function per se does not predict survival in large analyses,14 probably because a significant proportion of patients with systolic impairment will experience some degree of recovery once the outflow obstruction is relieved. However, patients with so-called “low-flow/low-gradient”, where the aortic valve is severely stenosed but the transvalvular pressure difference is low owing to poor ventricular contraction, have worse outcomes.15 Despite this, the prognosis of untreated AoS is so poor that intervention is still recommended in many such patients.

Finally, conventional AVR is sometimes recommended but is technically challenging or prohibitive, for example, in patients with mediastinal fibrosis or adhesions following radiotherapy or previous surgery. Patients who have previously undergone coronary artery bypass grafting (CABG) have a higher risk of death than both those who have never had surgery and those undergoing a combined valve and graft operation.16 In all, up to one-third are denied conventional aortic valve surgery because of the perceived operative risk.13,17

DEVELOPMENT OF TRANSCATHETER AORTIC VALVE INSERTION

With preliminary animal studies and temporary palliative devices being developed as early as the 1960s and 1970s,18,19 it has been a quarter of a century since the concept of a permanent “stent valve”, catheter-mounted, balloon-deployable valve prosthesis was first described.20 It was a decade further, however, before the first human received a prosthetic valve in this fashion, in this case in the pulmonary position,21 and 2002 before the first TAVI was performed.22 Since then, the rate of TAVI has risen enormously, with >50 000 having been performed worldwide, the vast majority in Europe.23

The procedure has revolutionized the care of patients with “inoperable” AoS. It is less limited by patient frailty and surgical considerations such as mediastinal adhesions or a porcelain aorta.24 Compared with standard medical therapy, including the use of balloon aortic valvuloplasty (BAV), mortality in 1 year has significantly improved (50.7–30.7%), hospitalizations have reduced and functional capacity has recovered.8 The PARTNER A cohort compared TAVI with surgical AVR in a high-risk population and found that the outcomes were broadly similar, although there were more vascular complications, more paraprosthetic regurgitation and more strokes with TAVI.25

DEVICES AND PROCEDURE

Approach

The first TAVI was undertaken from the right femoral vein, with a transseptal puncture required to access the left ventricle.22 This higher risk and technically demanding procedure was soon replaced with arterial access, crossing the aortic valve with a retrograde approach from the femoral or subclavian artery, or even with direct aortic puncture.26 These methods, particularly those using more peripheral arteries, require favourable anatomy, with small calibre, heavily calcified or tortuous vessels proving problematic.

Because of this, antegrade techniques were also developed to provide access through the apex of the heart, directly into the left ventricle, via a mini thoracotomy. This procedure obviates the need for sternotomy and cardiopulmonary bypass, but is somewhat more invasive than the femoral approach. The latter is preferred as it is less invasive and carries a lower risk of mortality, although other outcome measures appear equivalent between the two methods.27 Perhaps unsurprisingly, it remains the most common technique, with use in approximately 80% of cases.28

Devices

Five types of valves have Conformité Européene (CE) mark approval for use, with two in widespread clinical use,29 and there are at least three more in development. Most use a catheter-mounted valve constructed of a metal alloy frame, with leaflets cut from animal pericardium. Manufacturers must balance the security and robustness of the device with its insertion technique and cross-sectional profile when mounted on an introducer. For example, equine or bovine pericardium is generally considered to be harder wearing than porcine material30 but is bulkier, requiring larger sheaths for vascular access. Modern devices also attempt to limit paravalvular leak and to preserve the ability to reposition the device in the event of inaccurate deployment.

The Edwards devices (Edwards Lifesciences, Irvine, CA) are of cobolt-chromium construction with bovine pericardial leaflets, and are deployed over an expandable balloon. Three sizes (23, 26 and 29 mm) are available, with a recommended modest oversizing of 1–5 mm.

The Medtronic CoreValve® (Medtronic, Inc., Minneapolis, MN) system uses a self-expanding Nitinol (nickel-titanium) frame with porcine leaflets, which extend to form a lip at the base of the valve intended to minimize paravalvular leak. A large flare sits in the aortic root to minimize ventricular migration, although this also imposes anatomical prerequisites for patient selection—the trans-sinus diameter must be at least 27 mm and the ascending aortic diameter must be <43 mm.31 The risk of coronary occlusion is possibly greater;30 particularly, if deployment is high,32 as although the mid section of the frame is concave, intended to sit proud of the coronary ostia, it does extend further into the root than other prostheses. The flexibility of the frame and thinness of the porcine leaflets permit delivery of all four sizes (23, 26, 29 and 31 mm) transfemorally, although theoretically reduces the robustness of the device compared with bovine tissue.30

The Symetis Acurate™ (Symetis, Lausanne, Switzerland) is a newer valve, combining a self-expandable Nitinol frame with a trans-apical delivery system.33 The distal stent has a lip to reduce leak, and, at the other end, stabilization arms improve anchorage within the aortic root. A novel delivery system opens the arms, against which gentle traction is applied, before the device is released during rapid pacing. The valve is available in 23, 25 and 27 mm annular diameters. There is little clinical data to support its use.

The JenaValve™ (JenaValve Technology GmbH, Munich, Germany) incorporates a low-profile Nitinol frame with a standard porcine tissue valve. It, too, has a lip (of porcine pericardium) to minimize leak and three projecting arms above the valve to facilitate positioning. It is delivered via the apex and released in alignment with the native valve cusps, during ventricular pacing. 23, 25 and 27 mm prostheses are available but again there is a paucity of data at present to evaluate this device.

The latest prosthesis to receive European approval is the Direct Flow Medical® Transcatheter Aortic Valve System (Direct Flow Medical, Santa Rosa, CA), which uses bovine pericardial leaflets on a plastic polymer frame, secured in place with an injectable resin.29 The prosthesis is designed to be repositioned, up to the point that it is secured in place with the resin. There are no published trials using this device at present.

Technique

Most procedures are performed using a retrograde approach. Femoral, or alternative arterial, access is achieved using a standard Seldinger technique,34 with retrograde puncture and a vascular sheath. This is most commonly achieved percutaneously, although cut-down procedures may be useful, particularly where the target vessel is calcified or stenosed. Venous access is also obtained for the purposes of a right ventricular temporary pacing wire. Once access is achieved, the patient is anticoagulated with unfractionated heparin or bivalirudin.35

The aortic valve is crossed using a guide wire, followed by a diagnostic coronary catheter to undertake transducer assessment of the aortic valve gradient. BAV is then undertaken.

The use of an inflating balloon to overcome the stenosis of a valve was originally conceived to correct congenital AoS in children,36 and was later applied to degenerative AoS.37 Ballooning the calcified aortic valve is believed to fracture the calcific deposits but has very limited short- to medium-term efficacy.38 Having fallen out of favour as a stand-alone therapy, it has had a renaissance for TAVI, even postulated as a pre-procedure test of likely response,7 and is also used as a bridging therapy, allowing short-term improvement in symptoms and ventricular recovery. The procedure is performed during a brief period of rapid ventricular pacing, in the order of 160–220 beats per minute, or adenosine-induced asystole28 to reduce LV outflow, minimizing the chances of ejection of the balloon from the outflow tract or rupture.

Prior to undertaking BAV, the TAVI prosthesis is prepared. BAV is performed using an undersized balloon, to minimize trauma to the aortic annulus and reduce the likelihood of paravalvular leak.28 Care should be taken to avoid coronary occlusion, although this procedure also provides an opportunity to ensure that the prosthesis will not encroach on the coronary ostia. Following successful dilatation, the balloon is exchanged for the TAVI prosthesis. If the balloon-expandable prosthesis is used, it must again be deployed during the iatrogenic reduction in LV output (Figure 1). The aortic valve gradient is then remeasured, and there is an assessment of valve flow, either by fluoroscopy or, as in our institution, using transoesophageal echocardiography (TOE). The catheters and guidewires are withdrawn, and vascular closure is achieved, either surgically or using a percutaneous closure device. The patient is recovered and will be ambulatory within 24–48 h. Many centres prescribe a combination of aspirin and a thienopyridine before and, for 3 months, after TAVI12 or lifelong aspirin,39 although there is little evidence to support either practice. Ongoing anticoagulation is not required unless there are additional indications for its use.39

Figure 1.

Figure 1.

Insertion of an Edwards valve via the apical approach. (a) Collapsed stent over a guidewire via the apical introducer (AI). A pigtail catheter (PC) can also be seen in the aortic root, in addition to a right ventricular, temporary pacing wire (TPW) and a transoesophageal echo (TOE) probe. (b) The expanded prosthesis in place.

Alternative access and approach

For apical access, the patient is positioned on the operating table, and the LV apex is identified using transthoracic echo. An anterolateral mini thoracotomy is performed at the fourth to sixth intercostal space.28 Pericardotomy is achieved, and the epicardial surface is visualized, to which pacing wires are attached. The apex is then punctured, and a guidewire is passed antegradely across the aortic valve. The delivery sheath is advanced to just below the valve, the dilator is removed and balloon valvotomy, followed by valve insertion, is performed as before.

A number of other methods have been explored for vascular access. A subclavian approach40 may offer improved device control and angulation in some patients,28 while bleeding complications can be managed percutaneously from the femoral artery if required. This route may risk injury to the left internal mammary artery, particularly important to patients who have undergone CABG using this vessel. Direct aortic access has also been attempted in some cases,41 via a mid-clavicular or right parasternal incision, having pre-screened the vessel for calcification, using pre-operative imaging, real-time ultrasonography or direct palpation.28 The procedure then follows the same course as for other retrograde methods, and the wound is closed under direct visualization. This technique avoids myocardial puncture, potentially reducing ventricular aneurysm formation, delayed rupture or arrhythmogenesis from scar tissue. However, the paucity of data on this method renders it largely experimental at this time.

IMAGING

Annular sizing

Assessment of the aortic annulus, paramount to the success of a TAVI, relies entirely on pre- and periprocedural imaging. This is in stark contrast to surgical AVR, where the surgeon has an opportunity to directly size the annulus using a probe.32 For TAVI, it is measured using echo, predominantly TOE [two dimensional (2D) or three dimensional (3D)], or multiplanar imaging. One downside to the use of 2D echo is the complexity of the aortic annulus. Rather than forming a flat circular shape, in fact, it is often oval and considerably larger than it appears in single-plane imaging.42,43

Importantly, the differences between echo and CT are such that they may modify the operative approach in up to 42% of patients.44 While proponents of CT may suggest that the vastly superior spatial resolution makes measurement accuracy far better with CT, good clinical outcomes continue with widespread use of echo.31 Nonetheless, echocardiography underestimates the annular size43 in about half of all patients42 compared with both CT and intraoperative findings,45 with a mean difference of 3 mm (±1.9).42 Cardiac magnetic resonance (CMR) imaging permits simultaneous anatomical and functional assessment of the valve, but usually in a 2D plane. Although this may achieve better morphological evaluation of the valve, CMR is poor at the delineation of calcified tissue, and there is a paucity of data as to its accuracy for TAVI assessment.32 Some experts suggest that, at least, discrepancies between modalities highlight a need to revisit the imaging, potentially reducing error.31

The assessment of annular size needs to consider these features, which, although well described anatomically, have only recently been fully appreciated with cardiac imaging.31 The annular size is obtained by creating a plane cutting through the LV outflow tract along the basal attachment of the aortic valve leaflets. The lowest hinge point of the leaflets must be measured to accurately delineate the annulus.46

Coronary ostia and the hinge point

The proximity of the coronary ostia may present further problems for TAVI operators. Particularly with the longer CoreValve prosthesis, the geometry of the aortic root is paramount to procedural success and to ensuring the coronaries are protected. Obstruction by the prosthesis is important, but the effacement of the heavily calcified native valve cusps against the coronary origins must also be considered.47 A distance of >14 mm between the cusp hinge point and the associated coronary ostium has been recommended,47 and some experts go further than this, measuring the cusp length and assessing the distribution of calcification.31 In our institution, we consider 10 mm to be the minimum distance possible for TAVI and between 10 and 14 mm as a caution, which is reassessed in real time during balloon valvuloplasty.

Vascular tree

As will be discussed later, vascular injuries are the commonest procedural complications during TAVI.8 Originally, assessment for vascular suitability was performed using single-projection angiography at the time of coronary evaluation,31 but the use of multidetector CT has superseded this. The appreciation of not only luminal size but also vessel tortuosity and calcification is straightforward with CT (Figure 2). The latter is particularly important, as circumferential or “horseshoe” calcification has been implicated as a cause of increased risk of vessel dissection or catheterization failure.31 This information not only assists decision making regarding the choice of approach but may also facilitate arterial puncture, avoiding areas of calcification or areas distal to important stenoses. That said, undesirable vascular features do not always preclude the use of an arterial approach, and a range of techniques, such as vascular cut down or the surgical placement of temporary grafts to facilitate access, are used.7 Because of these varied options, it is difficult to provide absolute parameters, which would render a transfemoral approach impossible, although increasing calcification and the ratio of vascular sheath to femoral artery diameter >1.05 seem predictive for important complications.48 The smallest delivery catheter was previously 18 French gauge (6 mm), and the largest 24 French (8 mm), such that vessels of these sizes are considered to be the limits for a transfemoral approach by many authorities,49 although smaller sheaths are now available. At our centre, we report vessels of <6 mm as being unlikely to be suitable for transfemoral approach, 6–8 mm as possibly suitable and >8 mm as usually suitable, dependent on vessel calcification and tortuosity. We provide 3D volume rendered and maximal intensity projection images of the entire tree alongside our measurements to allow the operators to decide on their operative approach.

Figure 2.

Figure 2.

Pre-assessment of peripheral arterial access with CT can identify where the vascular tree is too narrow (a), too tortuous (b) or otherwise undesirable [(c) demonstrating an infrarenal aortic aneurysm].

Projection angle

The opportunity for 3D image manipulation also allows CT to evaluate the aortic root projection, or axis, relative to the body. The valve prosthesis must be deployed coaxially to the centreline of the aorta, perpendicular to the annulus, to minimize the risk of maldeployment and stent embolization.50 Pre-assessment of the optimal C-arm angle with which to achieve in-line visualization can reduce fluoroscopy screening time and contrast volume,51 along with procedure time.

Imaging protocol

At our institution, patients undergo both CT and TOE assessment prior to TAVI. We undertake CT using prospective electrocardiographic gating, whereby image acquisition occurs only at a pre-selected phase of the cardiac cycle. Many centres prefer retrospective gating,31 where data are acquired continuously throughout a number of cycles, with retrospective selection of the required phases. This provides multiphase data, but at the expense of a high radiation dose, perhaps more justifiable in the TAVI population who are older and with more comorbidities.

No intravenous beta-blockers are given owing to the risk of haemodynamic compromise—coronary evaluation is usually undertaken with invasive angiography and so aggressive heart rate control is less important. This practice is similar to other expert centres.31 We use systolic triggering for all patients, acquiring images at end-systole (i.e. 45% of the R-R interval), which maximizes image quality at higher heart rates and provides aortic valve area and annular measurements at maximal stretch, in comparison with echo. Owing to the large volume acquired, breath-hold is initiated with the scan (rather than early, as for coronary assessment), and patients are permitted to breathe gently once the thoracic volume is acquired, as the abdominal imaging continues in a craniocaudal direction.

Method

We analysed all TAVI studies on a dedicated workstation, and the valve and annulus are examined first. Various techniques are used to ensure assessment of the true annulus.31 We start from an axial view, identifying the centre of the mitral valve, through which an oblique plane is generated, perpendicular to a line from the valve to the apex (Figure 3a). This results in an oblique view through the aortic valve and a second oblique view is created, perpendicular to the valve plane, along the centre of the aortic root (Figure 3b). This plane effectively provides a three-chamber view comprising the left atrium, left ventricle and LV outflow tract (Figure 3c). A final oblique line is drawn through the hinge point of the non-coronary cusp, perpendicular to the aortic root (Figure 3c), to give a cross-section through the valve (Figure 3d). The oblique plane should be rotated (Figure 3c, white arrow) until all three valve cusps appear equally visible (Figure 3e). The plane can be adjusted longitudinally (Figure 3c, black arrow) until the valve is just in view (Figure 3f), which provides the location for annular measurement. Generating the views in this manner avoids the use of the coronal plane, which is automatically generated and can be affected by abnormal cardiac morphology or variable patient positioning on the scanner table.

Figure 3.

Figure 3.

Sizing the aortic valve annulus. (a) From the axial views, identify the centre of the mitral valve, through which an oblique plane is generated (solid line), perpendicular to a line from the valve to the apex (broken line). This results in (b) an oblique view through the aortic valve and a second oblique view is then created, perpendicular to the valve plane, along the centre of the aortic root (solid line). (c) This plane effectively provides a 3-chamber view comprising the left atrium, left ventricle and left ventricular outflow tract. A final oblique line is drawn through the hinge point of the non-coronary cusp, perpendicular to the aortic root (solid line), to give (d) a cross-section through the valve. The oblique plane should be rotated (c, white arrow) until (e) all three valve cusps appear equally visible. The plane can be adjusted longitudinally (c, black arrow) until (f) the valve is just in view, which provides the location for annular measurement.

The longest and shortest cross-sections of this orifice are measured, and the area is calculated by drawing around the circumference. The area and mean dimension can then be referenced to the manufacturer's sizing recommendations. The distance from the coronary ostia to the cranial aspect of the valve hinge point are also measured (Figure 4).

Figure 4.

Figure 4.

The right coronary artery in this patient was <10 mm from the insertion of the right coronary cusp. The artery was temporarily occluded during the balloon inflation for balloon aortic valvuloplasty, leading to inferior electrocardiographic changes. Ultimately, transcatheter aortic valve insertion was not completed. 2D, two dimensional.

Finally, suitability for access is assessed. The lumenal diameter of the arterial system cranially, from below the femoral heads, is evaluated, along with an impression of its tortuousity and the presence of any adverse features such as heavy calcification or aneurysm. The minimum permissible arterial diameter is dependent on the device being used. The apex of the heart can also be assessed for myocardial pathology, likely ease of access and potential risk from overenthusiastic apical puncture.

Procedural imaging

High-quality imaging during TAVI is also paramount to its success, usually using a combination of echo52 and fluoroscopy.7 The latter is more readily matched with tomographic imaging, and some systems can overlay CT or MRI images onto the fluoroscopy screen.32 Balloon positioning and subsequent inflation can be easily studied, akin to angioplasty.

Many centres, including our own, utilize adjunctive TOE. This provides the advantages of continuous real-time assessment without radiation and accurate evaluation of haemodynamic performance, at the expense of spatial resolution and the preference for general anaesthesia. Transthoracic echo is utilized for verification of the true apex,7 and both echo techniques can facilitate the avoidance of the mitral valve apparatus when an apical approach is selected.

BAV offers an opportunity for a “test run”, prior to prosthesis deployment.32 Annular or leaflet calcification (which may limit complete circumferential expansion), prosthesis sizing, risk of coronary occlusion and likelihood of aortic regurgitation can all be checked with the valvuloplasty balloon. Imaging angles can also be verified to ensure the prosthesis is being seen in-plane during expansion.52

Once the prosthesis is in situ, the technical result can be immediately evaluated. This ensures that there is minimal aortic regurgitation (AR) and presents an opportunity for remedial action. Of course, utilizing both imaging modalities also ensures that rapid identification of procedural complications can occur.

POTENTIAL COMPLICATIONS

Stroke

Although low (a large meta-analysis suggests a rate of 3.3%53), the risk of periprocedural stroke during TAVI is widely recognized, predominantly caused by mechanical trauma of the calcified valve and surrounding structures. Simply crossing a calcified aortic valve with a catheter increases the risk of cerebral embolism,54 and carotid Doppler studies during TAVI illustrate that valvuloplasty and prosthesis positioning generate substantial microemboli.55 Subclinical intracranial lesions can be demonstrated with diffusion-weighted MRI in 68–84% of patients post-procedure,56 although interestingly no association has been found between these findings and the rate of clinical stroke.57 The incidence of clinical stroke is greatest in the first 24 h following implantation, but there remains an elevated risk for up to 2 months.58 Stroke is commoner with TAVI than with surgical AVR7,25 and adversely affects survival.59

Despite the apparent logic of calcific emboli causing cerebral injury, there is also evidence of thrombotic aetiology, with thrombin deposition and inflammation preceding endothelialization of valve prostheses within 3–6 months.59 For this reason, along with the regular coexistence of coronary atheroma and aortic calcification, antiplatelet therapy is recommended for all patients with valvular prostheses.

Atrial fibrillation (AF) is a major risk factor for stroke in any population and remains an independent risk factor in TAVI patients,60 along with embolization or post-dilatation of the prosthesis. Although the rate of new-onset AF is lower than that of surgical AVR and the duration shorter,61 patients undergoing transapical access or with an enlarged left atrium remain at considerable risk of AF following TAVI, with an increased risk of stroke at both 30 days and 1 year.62 The mechanism of AF in this context is poorly understood, although may be related to inflammation in response to injury.63 It is a common occurrence following all cardiothoracic surgery and confers a significant risk of morbidity and mortality.64,65

Coronary obstruction

As with the subclinical neurological findings following TAVI, subclinical evidence of myocardial damage can be demonstrated in almost all patients, with elevation of troponin T.66 The level of elevation correlates with longer term LV impairment and cardiovascular mortality. This is likely to be owing to a range of factors, including direct myocardial trauma from balloon expansion, obstruction of the LV outflow tract, rapid ventricular pacing or coronary embolization.28

In some cases, inflation of the valvotomy balloon or deployment of the prosthesis results in the occlusion of a coronary artery (Figure 4). Displacement of a heavily calcified valve cusp over the coronary ostia may also cause obstruction.28,47 Myocardial ischaemia with catastrophic haemodynamic instability can follow, with percutaneous coronary intervention or even CABG required. A number of case reports now describe such events, which appear commoner in women and in patients receiving a balloon-expandable prosthesis.67

Vascular complications

Complications arising from injury to the vasculature or access site are the commonest encountered, and increase mortality by two- to three-fold.8 The risk is proportional to the size of the delivery catheter,68 and as technological improvements reduce the size of these the risk continues to fall. The 30-day rate of major vascular complications in the 2010 PARTNER B trial was 16%,8 whereas a retrospective analysis of a service 2 years later had improved this by just 1%, with more rigorous pre-operative assessment and improved procedural skills.69 Other risk factors include female gender, concomitant peripheral vascular disease, the need for valve retrieval and percutaneous access.68,70

Conduction disturbance

Surgical AVR and, indeed, AoS itself predispose patients to atrioventricular conduction disturbance. The proximity of the intraventricular conduction system to the aortic valve leaves it vulnerable to disease progression and to local trauma. Such disturbance is extremely common (approximately 80%) after TAVI, with balloon valvuloplasty responsible for the greatest proportion. The permanency of these sequelae is not clear, with one study suggesting that almost two-thirds of patients with complete (third degree) AV block will recover normal conduction.71 This presents difficulties when considering the timing of any pacemaker implantation with a need to provide prompt efficacious prophylaxis for asystole but with the potential to avoid long-term pacing and the small risks of device implantation.

Pacemaker implantation rates following TAVI range from 5% to 40% and are higher with the CoreValve than with the Edwards,72 probably owing to the former's large profile and incursion into the LV outflow tract.7

Valve malpositioning and sizing

Regurgitation through and around the valve prosthesis is common following TAVI, and occurs in up to 85% of patients post-procedure.7 Mild AR is expected and usually is inconsequential. Moderate AR was seen in around 15% of patients in the PARTNER studies,8,25 although the incidence of this appears lower subsequently, particularly since routine oversizing of prostheses has been undertaken.46 Severe AR is rare,7 but when seen, is predictive of mortality.73 The overall incidence of moderate or severe AR has been reported as 15–20%.74

A variety of problems contribute to prosthetic leak. If the annulus is calcified, this may leave irregularities or debris between it and the prosthesis.75 However, the most frequent causes for severe AR are owing to the malpositioning with infra- or supra-annular implantation and the undersizing or underexpansion of the prosthesis.28 The commonest of these is undersizing.76

Suboptimal positioning of the valve prosthesis occurs in about 5% of cases, irrespective of which type of valve is used.77,78 In addition, a valve may be undersized, or underexpanded, leading to either paraprosthetic regurgitation or so-called patient–prosthesis mismatch, where the valve orifice area is too small for the size of the patient. This results in a high transvalvular gradient and persistence of symptoms.

Most self-expanding prostheses can be retrieved and even removed, provided the valve remains attached to the delivery device.78 Once disconnected, or if a balloon-expandable valve is used, more radical methods must be used to correct malpositioning. Valves deployed too high risk aortic trauma, regurgitation or embolization into the aorta.77 If this occurs, the valve can sometimes be grasped and pulled into the aorta, away from branches, and overexpanded into the vessel wall.31 This appears to be remarkably safe. Valves that are positioned too low down in the left ventricle increase the risk of mitral valve dysfunction or heart block and may embolize retrogradely into the LV cavity.79 This usually necessitates urgent surgical removal79 (Figure 5).

Figure 5.

Figure 5.

This prosthesis migrated into the left ventricular cavity (a) and had to be surgically removed via the apex (b), unfortunately leaving a traumatic ventricular septal defect (c, arrow).

Inadequate deployment or positioning can sometimes be remedied with further balloon dilatation, often with an oversized balloon. Alternatively, a second prosthesis can be deployed inside the first, providing further stability and paravalvular seal.47

Mitral valve injury

Mitral valve injury is an unusual complication but has been reported, particularly with the apical approach. This technique risks ensnaring the mitral valve chordae with a wire or device, with the potential for distortion of the mitral apparatus or complete avulsion, leading to acute mitral regurgitation.47 Alternatively, a subannular deployment of the prosthesis may extend into the left ventricle and interfere with the mitral valve leaflets (Figure 6).

Figure 6.

Figure 6.

A Medtronic CoreValve® (Medtronic, Inc., Minneapolis, MN) in the aortic position. The metallic stent framework can be seen extending into the aortic root. There is a St Jude metallic mitral valve (St Jude Medical, St Paul, MN) replacement adjacent to this, highlighting the close proximity of the two valves. Excessive caudal positioning of the transcatheter aortic valve insertion prosthesis therefore risks impinging on the mitral valve.

Annular rupture and aortic dissection

Although rare, dissection and rupture of the aorta or aortic annulus are catastrophic, life-threatening events. Mortality for aortic dissection is around 50% following surgical AVR.80 The aortic root and ascending aorta can also be injured by the expanding balloons, catheters or guidewires. In TAVI, aortic dissection usually occurs because of the migration of the balloon into the aortic root.

Rupture of the aortic annulus may occur because of oversizing of the valvuloplasty balloon or prosthesis, compounded by severe calcification of the tissues28 (Figure 7). It can occur when the balloon retropulses into the left ventricle. Contained ruptures are possible and may lead to some considerable diagnostic delay,81 although the usual consequence is the rapid development of haemopericardium and pericardial tamponade.

Figure 7.

Figure 7.

Contrast extravasation highlighting rupture at the aortic root (arrow).

Myocardial trauma

This is a rare but important complication of TAVI, which can occur in a variety of ways. Wire perforation is a well-described complication of many interventional cardiac procedures, including TAVI. J-ended guidewires are widely recommended28,47 to minimize LV injury. The right ventricular wall can also be perforated with the temporary pacing wire. Overall, the incidence of cardiac tamponade following TAVI has been reported as 0–7%.47

Traumatic complications may be increased using the apical approach, where greater tissue dissection is required, and apical pseudoaneurysms have been described.47 A ventricular septal defect can also arise (Figure 8) following a tear at the aortic valve inflow, usually because of overdilatation during BAV or valve deployment.

Figure 8.

Figure 8.

A traumatic ventricular septal defect following repair with an occluder device (arrow).

Low cardiac output, cardiogenic shock and cardiac arrest

As described previously, patients with severe AoS are often highly premorbid. They may have poor LV reserve, not least because the noncompliant hypertrophied myocardium is highly susceptible to ischaemia.7 Balloon occlusion followed by BAV also stretches the haemodynamic performance, particularly in conjunction with rapid ventricular pacing. Arrhythmia is often poorly tolerated by patients with severe AoS, and iatrogenic arrhythmia is no different.

The result of these features is that poor cardiac output and shock are not uncommon during TAVI.7 Vasopressors,82 emergency (femoral) cardiac bypass or intra-aortic balloon counterpulsation7 have all been used and should be anticipated. The need for chest compressions is possible and should prompt valve re-evaluation of the valve prosthesis, which can become misshapen.47

SUMMARY

The use of TAVI is increasing rapidly, and all specialities are likely to encounter patients who have undergone this procedure (Figure 9).

Figure 9.

Figure 9.

Ungated CT pulmonary angiogram demonstrating a distinctive Edwards SAPIEN (Edwards Lifesciences, Irvine, CA) transcatheter aortic valve insertion prosthesis.

It requires meticulous preparation, which is heavily dependant on accurate imaging, and inaccurate pre-operative assessment can severely impair the success of the procedure. While reducing, the risk of complications in this group of potentially frail patients with complex medical needs remains, and an understanding of the procedure and its potential sequelae is essential.

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