Transcatheter aortic valve insertion: anaesthetic implications - 新青年麻醉论坛

Other approaches
If the femoral artery is significantly diseased but the transapical approach is deemed to be relatively contraindicated (for example if the patient has severe chronic lung disease and respiratory impairment), a number of other transarterial approaches have also been described. These are not in routine use owing to their relative complexity. They include the subclavian and iliac arteries. The CoreValve device may be currently more suitable for these approaches because of its smaller size when sheathed. If the size to which the valves can be reduced to during deployment continues to decrease as the technology is refined, then other approaches may be used more frequently, such as transbrachial or even radial.

Patient selection

Recent National Institute for Health and Clinical Excellence (NICE) guidelines17 and licensing regulations have restricted the use of TAVI to selected patients, who are either deemed to be at greatly increased risk of death or severe complications from conventional open surgery, or who are not suitable for surgical AVR

Patients previously turned down for surgery may be suitable for TAVI. Previous (or multiple) sternotomy is not a contraindication for either transfemoral or transapical approach, and indeed is regarded by most centres as a key indication, especially in the presence of patent coronary grafts. Redo-sternotomy in patients with a patent mammary artery graft is considered to be particularly risky because of the incidence of graft damage during surgical dissection of adhesions or sudden malignant arrhythmias owing to the transmission of diathermy current.18 There are also a number of patients not referred for surgery or turned down after surgical assessment because of medical conditions, especially chronic respiratory disease. These patients may be suitable for TAVI, with the transfemoral approach being particularly favourable because of the avoidance of postoperative hypoventilation owing to pain. Careful anaesthetic assessment of potential candidates in conjunction with further investigation may lead to successful management of patients who previously had no alternative to medical therapy.
There are a number of relative contraindications to TAVI, which may change as the technology develops. These include bicuspid aortic valve (because the altered anatomy makes secure placement of the transcatheter valve potentially unstable), previous mechanical AVR, endocarditis, recent myocardial infarction or cerebrovascular accident, moderate to severe mitral or tricuspid valve regurgitation, left ventricular or atrial thrombus, aortic annular dimensions outside the manufacturers' range (device-specific), ascending aorta >45 mm.
After referral for TAVI, detailed TTE is required to confirm the diagnosis, assess disease severity, and establish the annular and ascending aortic dimensions. If views are inadequate or the aortic valve annulus cannot be accurately assessed, transoesophageal study may be required. Coronary angiography is performed, and angioplasty may be indicated if proximal flow-limiting lesions are present to minimize the extent of non-revascularized myocardium. CT, angiography, or both are also required to allow detailed assessment of potential vascular access. In addition, comorbid conditions should be carefully assessed and optimized if necessary.
A team approach to patient assessment and investigation is essential.12 Comprehensive anaesthetic input is necessary; this should include preoperative assessment by the anaesthetist involved in the programme. Multidisciplinary meetings to plan the procedure should take place, and the anaesthetist should attend these as a matter of course.

Hybrid catheter laboratory

The ideal location for the TAVI is a hybrid location combining features of the catheter laboratory and operating theatre.27 High-quality fluoroscopic imaging equipment is required to facilitate precise device placement.
The room used must conform to operating theatre standards, including piped anaesthetic gases, vacuum and gas scavenging. In addition, a CPB machine should be in the room, ready for use with a dry circuit fitted. Other equipments required for the procedure includes cell salvage and proper surgical lighting (headlamps may be sufficient).

Anaesthetic management

Preoperative care
Baseline haematological and biochemical testing should be performed and 2 U of blood should be cross-matched. Aspirin 300 mg is given before operation. Consideration should be given to i.v. preoperative hydration, especially in patients with chronic renal dysfunction. This may reduce renal injury secondary to contrast administration during the procedure.
Intraoperative care
If general anaesthesia is chosen, a ‘cardiac’ type anaesthetic, aiming for haemodynamic stability, is appropriate. This should include large-bore i.v. and arterial access, usually placed under local anaesthesia before induction. Nitrous oxide should be avoided because of cardiac depression and potential expansion of intrathoracic air. Tracheal intubation and mechanical ventilation are necessary to facilitate passage of the transoesophageal echocardiography (TOE) probe. Central venous access and urinary catheterization are performed. Standard antibiotic prophylaxis for valve surgery should be administered according to local protocol. Continuous patient warming is used, including fluid warming, throughout the procedure, and the patients' temperature continuously monitored.
In some instances, transarterial AVR may be carried out under local anaesthesia and deep sedation. This may avoid complications potentially associated with general anaesthesia in patients with severe chronic disease, but may not provide ideal operating conditions. Patient movement may jeopardize the procedure leading to complications. Airway obstruction may occur and may be difficult to diagnose because of restricted access and environmental distractions. If open surgical transarterial access is required, local anaesthesia and sedation may be insufficient. In addition, TOE is not possible, which may make intraoperative echocardiographic assessment during the procedure more difficult or impossible. TOE is superior to TTE because it allows continuous visualization of the aortic valve during the procedure, assisting the operator in correct placement of the device.1 It can also be used to accurately measure the aortic annulus, essential for valve sizing (as opposed to open sizing in conventional AVR). In addition, it allows rapid diagnosis of complications and guides management of severe haemodynamic compromise. Newer three-dimensional technology may further improve the understanding of the dynamic anatomy, and is currently being evaluated for this procedure.
Cell salvage should be used; in the majority of cases blood loss will be minimal, but on occasion will be significant during vascular or left ventricular closure. Therefore shed blood should be collected in a heparinized custom reservoir, and processed for autotransfusion when an adequate volume is present.
Valve implantation procedure
After the stenotic valve has been crossed with a guidewire, balloon aortic valvuloplasty is carried out to dilate the native valve before deployment of the device. Rapid ventricular pacing is instituted via a temporary transvenous or epicardial ventricular pacing wire to reduce left ventricular ejection and cardiac motion, therefore stabilizing both the valvuloplasty balloon during inflation and the valve during deployment. TOE and arterial waveform observation are used to verify the lack of ventricular contraction and peripheral arterial pulse waves during testing of rapid ventricular pacing.2 After each episode, there may be considerable delay before optimum cardiac function resumes, accompanied by systemic hypotension. This period of haemodynamic instability is likely to be prolonged in patients with significant pre-existing left ventricular dysfunction. In such instances, the administration of vasopressors may be required, and very occasionally CPB will be necessary to allow resting of the heart. Catecholamine inotropic drugs such as epinephrine may worsen hypotension when administered to patients with left ventricular hypertrophy4 and should be used with caution. Echocardiographic assessment should be used to provide guidance for vasoactive drug use during the procedure.
Multiple imaging modalities are used to ensure optimal positioning of the device across the aortic valve including fluoroscopy, aortography, and TOE. After valve implantation, TOE is performed to assess the degree of paravalvular regurgitation, the patency of the coronary arteries, and to rule out haemopericardium and aortic dissection. Valve area and transvalvular gradient may be measured at this stage. Paravalvular regurgitation is often present immediately after valve deployment. This improves after 24–48 hours, as the valve morphology alters at body temperature.
Postoperative care
Tracheal extubation can usually be performed at the end of the procedure. Close postoperative monitoring is necessary, and admission to an intensive care or high-dependency unit is required, depending on institutional preference. Early critical care discharge is likely if the procedure was uncomplicated, and hospital discharge may be possible significantly earlier than after conventional AVR.
After wound infiltration with local anaesthesia, analgesia requirements after transfemoral AVR are minimal, and regular oral paracetamol is usually sufficient. However, the transapical approach is associated with more severe pain after operation. Intercostal local anaesthesia nerve block may be very effective, in combination with i.v. patient-controlled opioid analgesia and regular oral paracetamol. Regular aspirin and clopidogrel, starting soon after the end of the procedure, are recommended by the manufacturers unless contraindicated. These are normally continued for 3–6 months.
Patients who re-present after TAVI for non-cardiac surgery can be managed similarly to patients after conventional (pericardial) AVR. There is no evidence that discontinuing anti-platelet drugs increases the risk of valve thrombosis perioperatively, and full heparinization is not required.

Review of published data

After early experience in animal models, the first human percutaneous transcatheter aortic valve implantation was performed in 2002.8 Since then, equipment and techniques have evolved rapidly, and more than 1000 TAVI procedures have now been carried out.22 The paucity of published outcome data has, in part, been compromised by commercial sensitivities and protracted copyright legal cases.
Transvenous approach
Initially, transcatheter intervention procedures were carried out using a transvenous trans-septal approach to the aortic valve via the femoral vein.15 This route avoids the potential complications associated with arterial access, namely small vessel calibre, vessel tortuosity, and atherosclerotic occlusive disease. However, crossing the interatrial septum and mitral valve with a large device is technically challenging, risks damage to intracardiac structures, and may be associated with haemodynamic instability. The technique has been shown to be feasible but difficult to reproduce and its complexity has limited its widespread use.
Initial studies (I-REVIVE and RECAST trials) reported the successful use of transcatheter aortic valve implantation in 27 out of 36 high-risk patients deemed inoperable for conventional AVR.10 11 However, moderate or severe paravalvular leak occurred in 17 patients (63%). In addition, major adverse cardiac and cerebrovascular events occurred in seven patients (26%) at 30 days and in an additional 10 patients (37%) at 6 months. Major events within 30 days of the procedure included six deaths and one stroke. Deaths were caused by cardiac tamponade (two patients), sepsis (one patient), heart block (one patient), ventricular arrhythmia (one patient), and unknown aetiology (one patient).
Transarterial approach
The retrograde transarterial method of aortic valve implantation was developed as an alternative to the transvenous approach.29 This is now the method of choice for transcatheter AVR. Single-centre experience with a transarterial balloon-expandable aortic stent valve (Cribier-Edwards Valve) has been reported in 50 high-risk patients.30 Valve implantation was successful in 86% of patients, intraprocedural mortality was 2% (one patient), and 30-day mortality was 12% (six patients). The intraprocedural death was caused by aortic injury. The additional five post-procedural deaths occurring within 30 days were owing to ventricular arrhythmia, left main stem coronary artery occlusion, iliac injury, stroke and multiorgan failure (one patient each). Although the logistic EuroSCORE is not validated for transcatheter valve implantation, the estimated 30-day predicted mortality for this patient group for conventional surgery was 28%. After 1 yr, there were significant benefits in terms of valve area, left ventricular ejection fraction, mitral regurgitation, and functional status. There was no evidence of structural device failure during follow-up.
Multicentre experience with the device via the transfemoral route has been reported in 86 high-risk patients.13 Valve implantation was accomplished in 88% of patients and periprocedural mortality was 6% (five patients). Thirty-day mortality was 12% (10 patients) which compares well with the estimated logistic EuroSCORE of 22%. Serious morbidity was reported as occurring in 32% of patients. Multicentre experience of the transapical approach has also been published with similar results. Thirty-day mortality was 8% (four out of 50 patients), with serious in-hospital morbidity of 24%.28
The results of ongoing studies in Europe and Canada (REVIVE trial) and the US (REVIVAL II) are awaited. In particular, evidence about the long-term function of the valves is required. Additionally, there is anecdotal evidence that a relatively high number of patients are left with a degree of residual (paravalvular) aortic regurgitation. The significance of this is also not yet known.
The high rate of morbidity associated with both approaches to transcatheter AVR is obviously of some concern. The incidence of similar morbidity in comparable high-risk surgical patients is not clear. Randomized controlled multicentre trials of surgical and transcatheter AVR in high-risk patients are currently taking place.5 The PARTNER trial started recruiting patients in April 2007, randomizing them between surgical AVR and TAVI or medical management and TAVI if surgery is contraindicated (full details at http://clinicaltrials.gov/ct2/show/NCT00530894). However, final results will not be available until 2014.

Conclusion

TAVI offers the attractive possibility of valve surgery without sternotomy and CPB. However, the procedure is still in its infancy.20 A steep learning curve and further refinements are inevitable. As the technology continues to evolve, the devices are likely to become smaller and easier to deliver atraumatically. Experienced anaesthetic involvement is required, from inception and throughout the procedure itself. The results of ongoing trials are awaited, including randomized controlled trials.5 Morbidity and mortality is currently relatively high in the patient group receiving this treatment, and long-term outcomes are not yet known, therefore caution is required when discussing the implications of surgery with each individual patient.

Funding

Funding was restricted to institutional and departmental resources.

Acknowledgement

The authors wish to acknowledge the assistance of the Wythenshawe (Manchester) TAVI team in providing Figure 2 and some data for this article.