11.5.7 Endoprosthetic heart valves

The positioning of the prosthesis is controlled by radiological and echocardiographic visualisation; the use of TEE alone reduces the rate of postoperative renal insufficiency as it avoids the need for contrast injection [12]. It is replaced by the less effective transthoracic exam in cases where sedation and analgesia are used (see Chapter 10, Aortic valve implantation technique).

A comparison between TAVI and AVR in high-risk patients shows that 1-year mortality is lower with TAVI (14.2% vs 19.1%), the complication rate is also lower (20% vs 27%), and the stroke rate is not increased [1]. Compared with surgical AVR, TAVI showed no significant difference in mortality and stroke rates at 2 years (19.3% vs 21.1%), with a reduction in rates of renal failure, AF and bleeding; however, surgical AVR had fewer vascular complications, residual AF and permanent pacemakers [16]. Survival after TAVI is 37% at 5 years (31% at 6 years); one third of patients are in NYHA class I or II; the cumulative stroke rate is 16%. The prosthesis shows no signs of deterioration, with a mean gradient of 10.7 mmHg and a mean surface area of 1.6 cm² [4]. Despite the advances in prostheses and the remarkable success of the technique, TAVI is limited use for a young, low-risk population and do not yet make it a full equivalent to surgical AVR [18,25].

• The average rate of permanent pacemakers for complete AV block varies between 5% and 25% of cases, depending on the type of prosthesis;
• The rate of significant residual AI (paravalvular and intravalvular leak) remains high (12%) and worsens the prognosis when the insufficiency is grade ≥ 2;
• The rate of stroke is 3-5.5%;
• The long-term durability of prostheses is largely unknown.

 Figure 11.62: Three examples of transcatheter aortic valve implantation (TAVI). A: Corevalve™ (Medtronic, Minneapolis, MN, USA); the biological valve is placed inside a self-expanding nitinol stent. B: Sapien™ (Edwards Lifesciences, Irvine, CA, USA); the valve, mounted in a flexible stainless steel stent, is inflated with a balloon during deployment C: Valve Acurate TA™ (Symetis SA, Lausanne, Switzerland), mounted in a self-expanding nitinol stent and used only transapically; it can be repositioned during the procedure, leaving the coronary ostia accessible.

 Progress in clinical results is leading to the extension of TAVI to intermediate-risk patients, where the results of AVR in ECC are excellent. At present, there are only a few studies in this category of patients. They tend to show equivalent results with TAVI and AVR in terms of mortality and stroke, but with a higher incidence of residual AI and permanent pacemaker with TAVI, but fewer transfusions, atrial fibrillation and renal failure than surgery [16,30]. The transvalvular gradient is lower with TAVI than with AVR (8 vs 12 mmHg) and the orifice area is larger (2.2 vs 1.8 cm²) [26]. Interim results already show that in moderate-risk patients aged > 65 years operated in experienced centres, the 1-month mortality of TAVI is 1.1-4.4%, which is encouraging and supports the comparison with the mortality of conventional AVR, which is 2.4% > 75 years and 1.3% < 70 years [17]. Long-term follow-up is not available as the longest one for TAVI is 8 years [4].

 Percutaneous repair of mitral regurgitation

Mitral regurgitation can be treated percutaneously with various types of bioprosthetic and prosthetic devices [28]. Transcatheter mitral valve repair using the MitraClip™ system (Abbott Laboratories) is the most widely used technique. It involves end-to-end suturing of the distal ends of the two mitral leaflets using a clip introduced via the femoral venous route and transeptal access to the LA. The system is based on the Alfieri technique, in which the mitral orifice is transformed into two half-orifices by suturing A2 and P2 together (edge-to-edge repair).

Video: Image of a MitraClip in place in a 70° bi-commissural view.

Video: Three-dimensional view of a MitraClip in place from the LA; the valve opens through two holes on either side of the clip, which joins the central portion of the two leaflets.

Le clip possède deux bras en alliage chrome-cobalt de 8 mm de longueur recouverts de tissu polyester, et deux bras secondaires ou éléments de préhension ; ces derniers permettent d’immobiliser les feuillets au moment de leur accrochage. Le système peut s’ouvrir et se fermer lorsqu’il est monté sur son guide (Figure 11.63) [10,11].  The clip has two 8mm chromium-cobalt alloy arms covered with polyester fabric and two secondary arms or grasping elements; the latter are used to immobilise the leaflets when they are attached. The system can be opened and closed when mounted on its guide (Figure 11.63) [10,11].

 Figure 11.63: Percutaneous mitral valve repair using MitraClip™.) A: Suture of the medial end of the two leaflets with a clip; in diastole the orifice is transformed into two hemi-orifices of limited size [11]. A number of conditions must be met for successful mitral clip implantation. B: The width of the prolapse must be < 15 mm (double green arrow) and the prolapse must be located at A2 or P2 (A2 prolapse). C: the height of the coaptation must be > 2 mm and the distance between the coaptation point and the plane of the ring (tenting distance) ≤ 11 mm. D: in the case of prolapse, the gap between the lamellae (interstice) must be < 10 mm. These measurements are made in the mid-esophageal 4-cavity 0-20° and long-axis 120° views of the LV, except for the width of the prolapse, which is more accurate in the full-volume 3D reconstruction. E: The width of the base of the prolapse should not exceed 15 mm in the 60° bicommissural view.

 This technique is preferably reserved for situations where the regurgitation is caused by a coaptation defect in the medial region of the leaflets (A2-P2) in symptomatic patients with a very high surgical risk.

• Localised prolapse of P2 or A2;
• Functional MI due to LV dilatation (ventricular failure) or parietal akinesia (ischaemia);
• Elderly or debilitated patients with a predicted mortality rate of more than 15-20% when undergoing PVM in ECC and with a reasonable life expectancy.

To achieve good results, certain conditions must be met; these are well defined for TEE [3,6,23,32].

• Moderate to severe central MI of non-rheumatic or non-endocardial origin;
• Valve orifice area at least 4 cm², mean gradient ≤ 4 mmHg;
• Coaptation height > 2 mm;
• Distance between the point of coaptation and the plane of the ring ≤ 11 mm (tenting height);
• In case of prolapse, the lesion should be concentrated on a single festoon, preferably A2 or P2; the flail gap should be < 10 mm and the flail width < 15 mm;
• Posterior leaflet length > 10 mm;
• Free edges of flexible, non-calcified leaflets to which the clip is to be applied.

 To date, more than 50,000 patients have been treated with MitraClip™. The technical success rate (reduction of MI by ≥ 2 degrees) exceeds 95%, 1-month mortality ranges from 0% to 7.8%, and 1-year survival is between 75% and 90% [20,29]. At 1 year, the incidence of stroke is 1.6% and the reoperation rate is 1.3% [24]. When compared to surgical repair, MitraClip™ has a higher technical failure rate (3.2% vs 0.6%, 25-33% residual MI), but significantly lower operative mortality (3.3% vs 16.2%), stroke rate (1.1% vs 4.5%) and bleeding risk (4.2% vs 59%) in high-risk categories [24,28]. According to international recommendations, the MitraClip™ is indicated for symptomatic patients with severe primary or secondary MI despite optimal medical therapy, who are considered too high risk for surgery (mortality > 8% for MVR and > 6% for MVP) and who have a life expectancy of at least 1 year (class IIb, level of evidence C) [2,22].

Echocardiography plays a crucial role in all percutaneous valve procedures, whether TEE under GA or TEE under sedation, and if involved, the anaesthetist must be familiar with the various plastic or prosthetic devices [13]. For a detailed description of the insertion technique and TEE monitoring, see Chapter 10, MitraClip™ Technique/Imaging and Valvular Interventions.

 Anaesthesia for non-invasive valve procedures

The haemodynamic constraints are those of the respective pathologies, essentially aortic stenosis (TAVI) and mitral regurgitation (MitraClip™). They are identical to those encountered in conventional valve surgery, but there are two major differences compared to conventional procedures: 1) no ECC and 2) high-risk patients. For the anaesthetist, these data have two implications for the anaesthetic technique: 1) rapid circuit (extubation on the op table), and 2) rigorous haemodynamic monitoring, invasive monitoring, support as needed. In these procedures, anaesthesia and analgesia need not be deep, as there is no pain stimulation other than that required if resuscitation manoeuvre [15].

For TAVI, the choice of anaesthetic is less important than the way it is administered, which must be very careful: reduced doses, slow induction, immediate correction of any circulatory deviation. Coronary perfusion pressure must be maintained (MAP ≥ 75 mmHg) with a vasopressor (phenylephrine, norepinephrine); this does not mean an increase in LV afterload, as this essentially depends on the degree of aortic stenosis. The greatest haemodynamic stability is achieved with a combination of etomidate/propofol and fentanyl/sufentanil for induction and sevoflurane or propofol for maintenance. The most commonly used technique is total intravenous anaesthesia (TIVA): induction with propofol (2-3 mg/kg) and remifentanil (0.15-0.3 mg/kg), supplemented by rocuronium (0.3 mg/kg) for intubation, followed by continuous infusion of the same agents (propofol 3 mg/kg/hour, remifentanil 0.2 mcg/kg/min) [8,9,15]. Alternatively, induction with etomidate (0.3 mg/kg) or propofol (1-2 mg/kg), sufentanil (0.5-1 mcg/kg) and rocuronium (0.6 mg/kg) followed by maintenance with sevoflurane (1%) and remifentanil (0.2 mcg/kg/min) [7]. In very frail patients, etomidate is preferred to propofol for induction.

While GA is required for thoracic (apical), sternal, axillary or subclavian access, sedation-analgesia is well suited for femoral access. Puncture/arteriotomy is performed under local anaesthetic (infiltration) and/or ilioinguinal or iliohypogastric block. Several methods of sedation/analgesia are available.

• Midazolam: repeated boluses (1-3 mg), possibly combined with nalbuphine (5 mg); risk of delirium (inappropriate > 75 years), prolonged sedation.
• Propofol: infusion (1 mg/kg/h), possibly combined with remifentanil (0.03 mcg/kg/min); reduced preload, risk of respiratory depression.
• Remifentanil: infusion (0.03-0.5 mcg/kg/min) for levels of 1-3 ng/mL; risk of bradycardia and respiratory depression.
• Dexmedetomidine (Dexdor® ): infusion (0.5-1.0 mcg/kg/h); risk of bradycardia and hypotension (hypertension with bolus), contraindicated in AV block.

Sedation-analgesia appears to reduce mortality (RR 0.73), the need for vasopressors (RR 0.45) and length of hospital stay (-2 days), but the incidence of paravalvular leak is higher than with GA (RR 1.2) [31]. There was no difference in the incidence of stroke, renal failure, cardiovascular complications, bleeding or the need for a pacemaker. Anatomically simple cases in co-operating patients in good general condition are performed under LA with the support of transthoracic echocardiography and radiology. GA is reserved for patients in whom implantation may be difficult, who require TEE monitoring due to unfavourable anatomy, or who suffer from renal failure and must avoid contrast product [21]. The trend is certainly towards sedation-analgesia techniques, which are less invasive and more attractive to the patient. Their popularity goes hand in hand with the miniaturisation of the implantation systems, the reduced need for rapid pacing with the new prostheses, the precision of 3D reconstructions and the experience gained in high-volume TAVI centres. Sedation-analgesia is currently used in an average of 60% of cases [5].

After mitral repair, the loss of the low pressure valve, represented by the leak into the LA in systole, is equivalent to an increase in afterload mismatch for the LV as it leaves the bypass graft. In addition, the preload is reduced with the reduction in mitral regurgitation. This situation is particularly worrying in the context of secondary MI, ventricular dilatation and low preoperative EF. This mismatch between afterload and ventricular function is less frequent and less severe with the MitraClip™ technique than with mitral plasty or replacement in ECC, probably because the latter has a deleterious effect on ventricular function [19]. The choice of anaesthetic technique is determined by the patient's condition (extent of MI, ventricular function, comorbidities) and the low invasiveness of the procedure (see Chapter 10, Anaesthesia for MitraClip™).

• Induction: propofol (stable cases) or etomidate (decompensated cases);
• Maintenance: Propofol/remifentanil infusion (stable cases) or isoflurane (decompensated cases); modest doses given the lack of stimulation;
• Curarisation: for intubation only;
• Strict normothermia;
• Heparin 100 IU/kg (ACT 250-300 sec), reversed with protamine;
• Recovery and extubation on the op table or within the first hour.

Valvular stent patients receive lifelong aspirin and dual antiplatelet therapy for 3-6 months.