Perspective Chapter: Transcatheter Aortic Valve Implantation (TAVI)-Anesthetic Considerations

Abstract

Aortic valvular stenosis remains the most common weakening valvular heart lesion. Many high-risk patients cannot tolerate surgery. Transcatheter aortic valve implantation (TAVI) is an emergent alternative technique. General and local anesthesia plus sedation are both valid alternative techniques that can be titrated according to patient characteristics. Hemodynamic management is the main concern of intraoperative anesthesiological management. Preprocedural, multidisciplinary assessment of the patient is essential prior to TAVI and should include a full anesthetic evaluation. TAVI offers a number of advantages to patients and medical teams, but there are still accompanying important complications and anesthesiological risks.

1. Introduction

Aortic valve stenosis is described as the most common heart valve disease. Reportedly 2–4% of patients over 65 years of age develop aortic valve stenosis [1]. The increase in survival along with the comorbidities of these patients led to the development of intravascular aortic valve replacement (TAVI), a procedure suitable for intermediate- or high-risk patients with severe aortic valve stenosis. It is described that more than 1/3 of patients with severe aortic valve stenosis are patients at high surgical risk [2]. It is important to note that since the introduction of the technique in 2002, more and more patients are undergoing TAVI [3]. The criteria under which patients are selected play an important role as does the preoperative assessment. Various access routes are described, with trans-femoral access being the preferred route in the vast majority of TAVI patients. The anesthesia plan and the type of anesthesia depend on the access route, the patient’s medical history, the training and experience of the center where the procedure is performed, the surgical team’s preference and the possible hemodynamic, respiratory and procedural complications that the anesthesiologist may encounter. General anesthesia (GA) was initially preferred especially in patients with coexisting diseases such as heart failure, obesity, and pulmonary disease. During GA, transesophageal echocardiography (TEE) may be used as an intra-procedural monitoring tool to provide feedback during the procedure, to assess prosthetic valve function, and to detect complications rapidly. Other anesthesia techniques include local anesthesia (LA) with or without conscious sedation (CS), a technique that is increasingly used as it allows for hemodynamic stability and immediate detection of complications that may arise from the procedure. Furthermore, cases of epidural anesthesia have also been described for intravascular aortic valve replacement [4, 5]. Reported complications of the procedure include stroke, kidney damage, conduction abnormalities, pacemaker implantation, vascular access damage, hemorrhage, and even death. A coordinated multidisciplinary approach, including a cardiologist, cardiothoracic surgeon, perfusionist, and cautious anesthetic management, is essential for the success of TAVI [6, 7].

2. The history of transcatheter aortic valve implantation (TAVI)

The idea of intravascular aortic valve replacement emerged by clinicians Anderson and Cribier in the early 1990s. However, the lack of funding and the skepticism of heart surgeons at the time, who argued that a calcified valve should be removed, delayed the development of this new therapy.

Heining Anderson, in 1989, envisioned placing a valve on a balloon and positioning it through a stent. The idea arose from watching a speech by Julio Palmaz about coronary stents. Anderson began by constructing and placing a porcine aortic valve on a balloon catheter. In 1989, the first implantation attempt on a porcine model failed, creating more obstacles in his pursuit of funding and support.

Alain Cribier, on the other hand, had become a pioneer in balloon valve surgery, but noted high rates of restenosis. According to Cribier, a calcified valve could be used to anchor a new valve [8]. The cardiologists of the time had the same opinion, that is, that a calcified valve can be used as a lumen without any problems.

At the end of the twentieth century and the beginning of the twenty-first, the valve was designed by Cribier with the contribution of heart surgeons and a company called Percutaneous Valve Technologies (PVT) [9, 10]. In due time, in vitro experiments proved that the valve remained stable. In 2000, the first experiments on healthy (non-atherotic) animals were performed but failed since there was no atheromatic valve and aortic annulus to provide anchoring.

Cribier used the technique in 2002 when he came across a 57-year-old man with heart failure and an ejection fraction of about 10%. This was also the first application of the TAVI technique. The development of the technique required the pairing of surgical teams, their training in addition to the recording and collection of as much data as possible. Despite the difficulties in the development of the TAVI procedure, its rapid progression and minimally invasive technique have replaced open heart surgery and have provided a solution for high-risk patients with severe stenosis. In addition, the results of the procedure, the continuous training of medical teams, the evolution of the valves, and the improvement of the anesthesiologic approach have increased the survival rate of the patients and have significantly reduced hospital stay [11]. In the future, TAVI is expected to substitute the surgical replacement of the aortic valve [12].

2.1 Patient’s selection

The TAVI procedure, despite its minimally invasive technique, is often associated with complications that may affect surgical and patient outcomes. The appropriate selection of patients involves clinical and anatomical assessment, surgical risk assessment, and evaluation of the feasibility and safety of the procedure for each patient individually. The selection is made by a team of experienced interventional cardiologists, cardiac surgeons, and anesthesiologists. The patients selected are mainly elderly with an estimated life expectancy of >1 year, deemed inoperable (high risk) and presenting with complications from aortic stenosis, such as left ventricular dysfunction, or with comorbidities that affect their quality of life. Surgical risk is determined by the logistic EuroSCORE or the Society of Thoracic Surgeons (STS) score. Euroscore II has now been introduced, which also incorporates patients’ muscle weakness [13]. There are studies that claim that Euroscore II has a better prognostic value than the other two, but even so we cannot predict mortality at 30 days or even 1 year [14].

In patients referred for TAVI necessary measurements include identification and quantification of aortic stenosis, number of valve cusps, extent and distribution of calcification, sinus dimensions, effective annular diameter, height of the coronary ostium above the valve annulus, basal septal hypertrophy, and presence and severity of mitral valve disease. Transesophageal and transthoracic echocardiography assessments show that prospective patients have a low ejection fraction and reduced diastolic flow. In such cases of low-flow and low-gradient aortic valve stenosis, it is difficult to delineate the degree of stenosis, and if the patient is expected to benefit from an intervention, therefore the implementation of dobutamine stress test is indicated.

TAVI is being increasingly utilized, and we are given the opportunity to successfully treat high-risk patients with severe aortic valve stenosis. Despite the rapid progression of this procedure and its impact on aortic stenosis prognosis, a percentage of individuals show low long-term improvement from the procedure or even mortality within a year. Thus, further research is needed with focus on the selection and outcome of TAVI patients. For example, in the case of patients undergoing TAVI and suffering from chronic severe lung disease (CLD), studies have shown that they show earlier mortality than TAVI cases without CLD. It is necessary to quantify the severity of CLD and to analyze the relationship between the disease and the poor outcome of the procedure [15, 16]. Similarly, renal function is affected during the procedure. A recent report notes that patients with severe kidney disease undergoing TAVI have an increased risk of mortality within a year [17].

2.2 Preoperative anesthesiologic assessment and preparation

Preoperative assessment is the foundation in the management of patients undergoing intravascular aortic valve replacement and contributes greatly to reduce morbidity and improve their outcome. The main purpose of the preoperative assessment is to obtain information about the patient’s medical history in addition to performing a clinical assessment. This way intraoperative risk can be more accurately estimated and minimized. As mentioned, aortic valve stenosis is the most common valvular disease. More specifically, 2–4% of the population over the age of 65 has aortic valve stenosis. In the case of severe aortic valve stenosis, intravascular valve replacement is the best treatment option since these patients have a high surgical risk [18]. The predominant symptoms of severe aortic valve stenosis observed during the preoperative assessment are angina, heart failure, stroke, fatigue, and shortness of breath. During the clinical examination, a distinct auditory finding is the mid-systolic ejection murmur, heard best over the “aortic area” or right second intercostal space, with radiation into the right neck. Echocardiography is the main method to assess aortic stenosis (AS) severity and is crucial for patient management and risk stratification. It relies on three parameters: the peak velocity (Vmax), the mean pressure gradient (MPG), and the aortic valve area (AVA). The peak velocity and mean pressure gradient increase as the stenosis becomes severe, while the aortic valve area decreases. With these parameters, severe aortic stenosis is defined by a Vmax >4 m/sec, an MPG >40 mmHg, and an AVA <1 cm².

Guidelines regarding medical management suggest that serial Doppler echocardiography should be performed every 6–12 months in those with severe aortic stenosis, every 1–2 years in those with moderate stenosis, and every 3–5 years in those with mild stenosis [19].

The anesthesiologist as well as the interventional cardiologist should be aware and should inform patients with severe aortic valve stenosis, who fulfill clinical suitability and are about to undergo intravascular valve replacement, that they are at increased risk of sudden death due to arrhythmias, heart failure, myocardial infarction, and/or coexisting congestive heart failure.

Intravascular replacement of the aortic valve is associated with lower risk of infection, reduced blood loss, less metabolic stress for the patient, and fewer hemodynamic fluctuations. It is important, however, for the team of specialists to be prepared in the event of an aortic rupture to modify this minimally invasive procedure into an emergency open heart surgery.

Anesthesia options for this procedure include both general anesthesia and local anesthesia with or without conscious sedation. Standard monitoring includes an electrocardiogram, pulse oximetry as well as capnography monitoring. It is necessary to secure a venous access for the administration of drugs as well as artery catheterization for invasive blood pressure measurement. Arterial blood gases and activated clotting time (ACT) can be monitored when necessary. Premedication in these patients can diminish stress and help reduce anxiety and tachycardia. In general, the management of patients scheduled for intravascular aortic valve replacement consists of a coordinated multidisciplinary approach with primary focus being the minimization of complications.

2.3 Procedural considerations

TAVI techniques are based on the main principles of percutaneous interventions, which are commonly used for cardiac and vessel diseases. In most cases, reaching 80–85%, the access site for the procedure is the femoral artery [20]. This approach is feasible with both types of anesthesia, general anesthesia and regional anesthesia with or without conscious sedation. Additionally, the operation can be performed with surgical cutdown or percutaneous techniques and devices. The transfemoral approach is the preferred one except for cases that a serious contraindication is present, including small diameter or tortuosity of the femoral artery, presence of serious atheromatous disease in the iliac arteries, abdominal aorta or the aortic arch, former aortic dissection, or any other cause that increases the risk of rupture or thromboembolic events. Alternatively, other vascular access sites can be utilized including the axillary artery, carotid artery, transaortic approach, or transapical approach [21]. All the alternative vascular access sites require general anesthesia.

The procedure is usually performed by 2–4 cardiac interventionists and cardiac surgeons. All attendants in the operative theater must wear protective gear that shields from radiation. The initial step of the operation is accessing both the femoral arteries. Most often the TAVI device is positioned through the right femoral artery, and the left femoral artery is used for the positioning of the pigtail catheter used for the administration of the contrast. Subsequently, the electrode of a temporary transvenous pacemaker is placed in the right ventricle through the left femoral vein. The function of the pacemaker should be carefully checked before the intervention. After this setup, the main part of the procedure begins with the placement of a wire into the left ventricle with a manipulation called crossing of the aortic annulus. This is followed by a subsequent dilation of the vessel with sheaths of increasing diameter. Before the implementation of the TAVI device, unfractured heparin is administered at a dose of 100 IU/kg with a goal Activated Clotting Time (ACT) of more than 250 or 300 s depending on the center [17]. When the necessary ACT is obtained, the TAVI device may be positioned on both sides of the aortic annulus. Depending on the type of bioprostheses used, balloon-expandable or self-expandable, the balloon expansion is performed before the valve implantation. Most types of valves require rapid ventricular pacing during the balloon expansion and the valve implantation, which causes blood pressure collapse. The position and the function of the implanted bioprosthesis are checked for regurgitation and paravalvular leakage with repetitive angiography. The procedure is completed with the removal of the TAVI device and the closure of the femoral artery access site. It is prudent to keep the temporary pacemaker in standby mode with low pulses and low pacemaker sensitivity and output for a few hours after the intervention.

2.4 Anesthesia techniques

General anesthesia was initially preferred by anesthesiologists and the surgical team during TAVI. However, the creation of specialized teams, the reduced time, and the familiarization of the anesthesiologists with the procedure led to the application of local anesthesia with or without conscious sedation. In both techniques, there are advantages and disadvantages, and the anesthetic management during TAVI is still considered controversial. Depending on the type of anesthesia, the time of hospitalization is affected, postoperative pain, tissue damage as well as identification of procedural complications. Optimal method of anesthesia and good preoperative risk evaluation should be provided by the anesthesiologist to reduce the morbidity and mortality risk associated with TAVI.

All patients should receive antibiotic prophylaxis (piperacillin-tazobactam and/or vancomycin, dosage according to renal function) 1 hour before the procedure and are on dual antiplatelet treatment (acetylsalicylic acid 100 mg and clopidogrel 75 mg daily).

2.5 General anesthesia

Anesthesiologists that take part in TAVI procedures should be knowledgeable of cardiothoracic anesthesia in cases the procedure is converted to surgical aortic valve replacement (SAVR) due to complications. Therefore, the anesthesiologist needs an understanding of physiology, pharmacology, circulatory pathophysiology, esophageal echocardiography, and even cardiopulmonary bypass. Preparation, organization, and meticulous attention to detail actually help in dealing with intraoperative events. As soon as the patient is positioned on the operating table, it is important to secure two peripheral venous lines (preferably with 18- or 17-gauge cannula). Usually, the placement of a double or triple lumen central venous catheter is required. An initial dose of midazolam may then be administered to produce sedation and preoperative impairment of memory. In addition to standard monitoring, which includes ECG, oximetry, and capnography, catheterization of an artery is utilized, before or immediately after induction to anesthesia, for continuous measurement of blood pressure. Intraoperative monitoring of arterial blood gas (ABG) and activated clotting time (ACT) are necessary during these operations as ACT is used to direct heparin anticoagulation [22, 23].

Drugs used for induction of general anesthesia include intravenous anesthetics, opioids, and muscle relaxants while maintenance of anesthesia is achieved through the use of volatile anesthetics or by total intravenous anesthesia (TIVA). Intubation is a painful stimulus, which requires the administration of opioids such as Fentanyl at a dose of 1–2 mcg/kg. Propofol has a loading dose of 0.5–1.5 mg/kg and an infusion rate of 10 mg–20 mg/kg/h. Remifentanil can also be used, in combination with other hypnotics or alone, for maintenance of anesthesia with an infusion rate of 0.25–1 mcg/kg/h. A targeted controlled infusion (TCI) pump can be utilized to achieve a controlled concentration of a drug in the blood. *Hypnomidate is a hypnotic agent frequently used in hemodynamically unstable patients with a bolus dose of 0.1–0.3 mg/kg. Finally, Rocuronium is the most common neuromuscular blocker of choice at a bolus dose of 0.6–1.2 mg/kg.

Maintenance of anesthesia is usually achieved using a volatile anesthetic with a concentration flow that allows for a minimum alveolar concentration (MAC) of 0.5–1. The third and final way to maintain general anesthesia is a combination of volatile anesthetic and TIVA [24].

The choice of drugs for induction and maintenance aims to ensure the depth of anesthesia and hemodynamic stability. Studies have shown that the use of the aforementioned drugs during general anesthesia increases the use of inotropic and vasoconstrictor drugs intraoperatively [25].

One of the advantages of general anesthesia during TAVI is the use of transesophageal echocardiography (TEE). It provides valuable information about the anatomy and function of the heart during the procedure. The pressure gradients can be determined as well as the diameter of the valve ring [26]. Morphology of the valves can be visualized in addition to the function or malfunction of the new valve.

At the end of the procedure, most patients are transferred to the cardiac ICU sedated and mechanically ventilated for 1 or even up to 12 hours. Particular consideration is given to the hemodynamic stability of patients postoperatively, while hospital stay ranges an average of 5 days.

2.6 Local anesthesia with conscious sedation (LACS)

Conscious sedation in combination with local anesthesia in the access site is increasingly preferred in the vast majority of TAVI procedures. The anesthesiologic approach is no different from that of general anesthesia. Standard monitoring includes an electrocardiogram, pulse oximetry, capnography, invasive blood pressure monitoring, and a Venturi mask that delivers a controlled percentage of oxygen.

Lidocaine Hydrochloride 2% solution is injected into the access site, femoral access is usually preferred, by cardiologists or cardiac surgeons. Conscious sedation is achieved by intravenous administration of drugs, including but not limited to propofol infusion, midazolam, remifentanil, ketamine, and dexmedetomidine. The dosage and rate of administration of the drugs as well as their combined administration should be individualized and titrated to attain the desired result. To perform conscious sedation, the anesthesiologist should take into consideration the age of the patient, the classification of AS, comorbidities as well as any previous interventional procedures. The objective is to secure hemodynamic stability and to be aware of complications such as bleeding and arrhythmias. In addition, it is important to have access to ventilation throughout the procedure and to be prepared for LACS failure, defined as the conversion to GA from LACS during TAVI.

Studies have shown that LACS compared with general anesthesia results in reduced total procedure time, length of hospital stay, and length of ICU stay [27, 28]. Hypotensive episodes associated with general anesthesia during TAVI procedures affect renal function more in comparison to LACS [29]. Another complication of TAVI is the occurrence of a stroke during the procedure. This can be immediately perceived during LACS as there is constant communication and contact with the patient [30, 31]. Based on the available data, there is no difference in mortality depending on the type of anesthesia [32]. In Table 1 the main anesthetic and analgesic drugs used for such procedures are presented.

Drugs	General anesthesia	Sedation
MIDAZOLAM	0.01–0.1 mg/kg	0.1–0.4 mg/kg
DIAZEPAM		0.04–0.2 mg/kg
PROPOFOL	1–2.5 mg/kg; 50–200 μg/kg/min	25–100 μg/kg/min
KETAMINE	1 mg–2 mg/kg	2.5–15 μg/kg/min
HYPNOMIDATE	0.2–0.5 mg/kg
DEXMEDETOMIDINE	1 μg/kg bolus dose (10 min) and 0.2–0.7 μg/kg/h infusion rate
ALFENTANYL	Bolus dose: 8–100 μg/kg; 0.5–3 μg/kg/min
REMIFENTANIL	Bolus dose: 1.0 μg/kg; 0.5–20 μg/kg/min
FENTANYL	2–50 μg/kg
ROCURONIUM	Intubation dose: 0.6–1.2 mg/kg; The onset of action is dose-dependent 45–120 seconds, with a duration of action 30–90 minutes.
CIS-ATRACURIUM	Intubation dose: 0.2 mg/kg (40 min–75 min)
SUCCINYLCHOLINE	Intubation dose: 1.0 mg/kg (5 min–10 min)
The dose and rate of administration of drugs as well as their combined administration should be individualized and titrated to attain the desired result

Table 1.

The main anesthetic and analgesic drugs with the associated dosages used in TAVI procedures are presented for both methods (general anesthesia and sedation).

3. Complications

Even though TAVI is a reliable alternative for high-risk patients, the associated complications are not negligible. On the contrary, the mortality rate is 8.1% for this category of patients [33]. During the procedure and after the completion, there is a high incidence of vascular complications, which reaches 17.3% for major complications and is correlated to increased 30-day mortality [34]. Other life-threatening complications include cardiac tamponade, aortic dissection, aortic rupture, malposition or migration of bioprosthesis, or heart rhythm disturbances, such as atrial fibrillation or complete atrioventricular block [35]. These complications require urgent surgical intervention, and the implementation of cardiopulmonary bypass (CPB) may be necessary. Moreover, CPB machine and cardiac surgeon must be standby for the treatment of such complications.

Another serious complication after TAVI is the stroke with a rate of 3.3%, despite the fact that the subclinical incidence of cerebral infraction is very high. It is of great significance to highlight that the patient should be closely monitored during the procedure for signs of stroke, and the conscious sedation offers a clear advantage on this field. Renal failure is also common after TAVI with contributing factors including preoperative impaired renal function and the amount of contrast used [36]. Additionally, the presence of acute renal injury is a negative prognostic factor in patients undergoing TAVI [5]. The placement of permanent pacemaker is very common after TAVI as its incidence reaches 20.5% [37].

4. Studies comparing general anesthesia versus sedation

More than 35 studies regarding the choice of anesthesia during TAVI were performed from 2002 to 2021. According to a relatively recent meta-analysis of Cheng on this field, sedation can reduce the length of hospitalization, procedural time, 30-day mortality, cardiovascular drugs administration, while there was no statistical difference detected between general anesthesia and sedation in permanent pacemaker placement, shock, myocardial infraction, acute kidney injury, and the procedural effectivenes [37]. The SOLVE-TAVI is a completed trial including 447 patients undergoing TAVI who were randomized according to the type of anesthesia. The results of the study suggest that the primary composite endpoint (consisted of mortality, stroke, myocardial infraction, infection requiring antibiotic treatment, and renal failure within 30 days) was similar between the two groups (conscious sedation 27.2% versus 26.4% for general anesthesia) [38]. Another review of 13 studies with 6718 patients indicated that the outcomes remain similar between the two groups after 1 year [39]. In the same line, studies showed that there is no difference regarding acute kidney injury and neurocognitive outcome [40, 41].

A randomized study performed between 2014 and 2018 in two centers consisted of 477 consecutive patients, which was published in 2020, and suggests that the conscious sedation group was associated with higher efficiency compared with general anesthesia group while the safety was similar for both groups [41]. More specifically, reduced length of stay (2 vs. 3 days, p < 0,001), inotropes (13% vs. 32%, p < 0,001), blood transfusions (10% vs. 22%, p < 0.0008), contrast volume (50 vs. 90 ml, p < 0,001), fluoroscopy time (20 vs. 24 minute, p < 0,001) were found for the sedation group compared with general anesthesia group respectively. According to the authors of this study, these findings, which are considered as efficiency parameters, suggest that sedation is a more efficient method than general anesthesia. As regards the safety of each strategy, the primary endpoints for mortality, ischemia, cerebral events, renal dysfunction, procedural complications, permanent pacemaker placement, and mid-term survival (1 year) were similar [41]. Another study in which 204 patients were studied showed that the sedation group received less catecholamines, less intravenous fluid during the procedure, while the conversion rate was 4.6% [42]. There are many data and publications in this field, which indicate that both strategies are acceptable. The choice of the one or the other method is mainly related to the anesthesiologist’ and the patient’s preference in practice, but more randomized trials may delineate the parameters that should be calculated for the correct choice while the increasing experience is expected to improve the clinical outcomes.

5. Conclusions

Severe aortic stenosis is an acquired valvular disease with a poor prognosis, especially when symptomatic. Diagnosed patients have a high mortality rate for open heart surgery and are therefore given certain criteria, referred for a less invasive transcatheter aortic valve implantation. The TAVI procedure is rapidly displacing surgical aortic valve replacement due to its favorable outcome, minimalization of complications, reduced hospital stays, and reduced use of resources. Anesthetically, high-risk patients who undergo TAVI appear to have similar outcomes regardless the type of anesthesia they receive. General anesthesia or local anesthesia with conscious sedation can be successfully utilized in patients undergoing TAVI. The first step to selecting the most appropriate anesthetic technique is a thorough preoperative assessment from all members of the procedure team. No matter what technique is used, the anesthesiologist should maintain optimal hemodynamic stability during the procedure and be cautious of possible complications.