Different Sites of Vascular Access for Transcutaneous Aortic Valve Implantation (TAVI)

Aortic valve stenosis is a common valvular heart disease and its incidence is increasing day by day as the life expectancy is increasing gradually. It can be of congenital or acquired variety but in old ages aortic stenosis is acquired mostly and main reasons rheumatic heart disease or senile calcification of aortic valve. Aortic valve replacement with mechanical tissue valves is the surgical management of aortic valve stenosis but some of the patients are not suitable for the surgery based on their physical status and associated comorbidities. These patients are high risk for surgical complications or they have prohibitive risks for surgery. Transcutaneous aortic valve implantation is the new technique developed to implanting aortic valve mostly without opening the sternum and without using cardiopulmonary bypass machine. This procedure is mostly done via transfemoral access but in case of contraindications to use femoral artery for access some other different accesses are used to implant the aortic valve, that is, transsubclavian/transaxillary access, transapical access, transaortic access, transcarotid and transcaval accesses. In this chapter we are going to discuss all accesses in details.


Introduction
Aortic valve is present between left ventricle and aorta. It opens during ventricular systole and closes at ventricular diastole.
Aortic stenosis (AS) represents obstruction of blood flow across the aortic valve due to congenital or acquired narrowing. Etiology can be bicuspid aortic valve, rheumatic aortic stenosis and senile aortic stenosis due to calcification of aortic valve.
It is a progressive disease that presents after a long subclinical period with symptoms of decreased exercise capacity, exertional chest pain (angina), syncope, and heart failure.
Echocardiography helps in diagnosis and grading of the aortic stenosis ( Table 1).
Most of the patients usually undergo open surgical aortic valve replacement with mechanical or bioprosthetic aortic valve, but some patients may not be suitable Vascular Access Surgery -Tips and Tricks candidate for the open surgical aortic valve replacement because of their associated comorbidities or risk of adverse outcome.
Transcatheter aortic valve implantation (TAVI) is the procedure of implanting the prosthetic aortic valve through intravascular route. First transcatheter aortic valve implantation was done by Cribier et al. [1].
It is the preferred procedure for the severe aortic stenosis patients who are being considered as non-operable [2] or high risk procedure [3] for open surgical aortic valve replacement.
It has become a well-established procedure over the years and since its invention over hundreds of thousands of valves has been deployed. This number is gradually increasing day by day.
There is a basic idea of a crimped aortic bioprosthetic valve and its transcatheter implantation in aortic valve position.
Followings (Table 2) are the aspects to be considered by the heart team to take decision for management of severe aortic stenosis in high risk patients for surgical aortic valve replacement or TAVI.
There are many ways of implanting the aortic valve (Figure 1) by TAVI but most commonly used route is retrograde transfemoral arterial access. This is less invasive and the only percutaneous way of implanting the aortic valve. Even it can be done without general anesthesia. Other routes need surgical cut down for the arterial access.
Peripheral vessels must be assessed for the size, tortuosity, and calcification of the iliac and femoral arteries. Vascular assessment is most commonly performed using contrast angiography or CT angiography. By default transfemoral access is considered to be vascular access site for TAVI.
Other retrograde transcatheter aortic valve implantation (TAVI) is currently performed through an alternative access in 15% of patients. Existing data does not favor one route over another one. All the routes have different advantages and disadvantages. This chapter will review the different accesses for aortic valve implantation. Most common vascular access for TAVI is transfemoral artery by default. As the technology has improved, the options for the vascular access for TAVI has increased and may include transfemoral, transsubclavian (transaxillary), transapical, transaortic, and transcaval.
With the availability of the lower profile aortic valves for implantation, these valves are mostly deployed via transfemoral route but in case of contra-indication to use femoral artery for TAVI other vessels are used for access; as in case femoral arteries are of small size, tortuous or heavily calcified.
Before proceeding for TAVI, patient should undergo full work up with coronary angiography, CT angiography scan of heart, aorta and peripheral vessels, transthoracic and transesophageal echocardiography, lab investigations and other radiological investigations.  Although in most of the TAVI procedures, Cardiopulmonary bypass (CPB) is not required but patient should have a full informed consent with possibility of emergency midline sternotomy and use of CPB in case of complications.
While it is difficult to predict which patients will need temporary CPB support during or after valve deployment, usually patients with ejection fraction (<25%) with severe pulmonary hypertension, especially those requiring significant inotropes during and after anesthetic induction are at higher risk.

Preoperative assessment and planning
Potential TAVI patients must undergo full evaluation with Patients with severe coronary artery disease and lesions which are treatable by percutaneous coronary intervention should get stents prior to the procedure. We keep patients on dual anti platelets therapy for about 6 weeks and then take them for TAVI.
The aortic annulus is sized at mid-systole, and the valve size is selected based upon 10% over-sizing of the annular diameter.
If the annulus is not adequately sized, there would be risk of improper valve size selection that could lead to paravalvular leak, valve embolization, coronary obstruction if the sinus of Valsalva is small or the distance between the annulus and the coronary ostia is less (<10 mm).

Introduction
Transfemoral access (Figure 2) is the most preferred route in majority of the TAVI procedures world over [4] unless there is an increased risk of vascular complications depending on vascular size, tortuosity and calcification [5].

Planning
• All patients should undergo a CT-angiographic scan with 3D reconstruction of aorta and femoral vessels • Aorta should be assessed for tortuosity, presence of aneurysms, atherosclerotic plaques and aortic arch calcifications • Minimum size of femoral and iliac arteries should be more than 5.5 mm (ideally more than 6.5 mm) and it should be free of calcification • A circumferential calcification could be a potential contraindication for transfemoral approach • Some studies shown that a sheath to femoral artery ratio of greater than 1.05 is predictive of a vascular complication [6] • Bifurcation of femoral artery and its relation with the femoral head should be evaluated properly • Site of needle entry may be altered based on CT scan or ultrasound findings of high bifurcation of the common femoral artery and presence of significant calcium.  • 6Fr sheath is inserted in one femoral artery and then a 5 Fr pigtail catheter is placed in non-coronary sinus of aorta as a marker for aortic valve placement and positioning.
• These days routinely we are using right radial artery for placing Pigtail catheter in non-coronary sinus of aorta instead of femoral artery • IV heparin is given to keep activated clotting time (ACT) around 200-250 s.
• Another femoral artery is used to insert 18 Fr valve deployment sheath. First a 6 Fr sheath is inserted and then a soft, J-tipped wire is placed into the descending thoracic aorta (DTA).
• Two percutaneous sutures based vascular closure devices (Per close devices) are placed, which are used to control the bleeding after the procedure.
• The soft J-tipped wire and an exchange catheter are inserted into the aorta

Transsubclavian/axillary access 4.1 Introduction
The subclavian artery has recently become a site of access for TAVI [7]. Right axillary or subclavian artery is rarely used for TAVI because of anatomic restrictions and unfavourable angle for valve implantation. The proximal third of the left axillary artery (between the lateral border of the first rib and the medial border of the pectoralis minor) represents the ideal target for both surgical and percutaneous approaches.
A study suggested that subclavian access is not advisable in patients with subclavian artery diameter <7 mm, significant tortuosity, or prior coronary artery bypass grafting (CABG) and patent in situ internal mammary artery grafts [8].

Disadvantages
There is a higher risk of stroke due to interruption of blood flow to the vertebral arteries in patients with carotid disease who depend on the vertebral arteries for cerebral perfusion.

Planning
• CT angio scan with 3D reconstruction of the subclavian and axillary arteries.
• Vessel size should be >6.5 mm without calcifications and tortuosity • It is more prone for vascular complications (especially in old age) because of anatomical differences between subclavian/axillary (more elastic fibers and less muscular wall) and femoral arteries.
• Post CABG patients in whom LIMA was used for LAD anastomosis, this approach can be lethal due to acute graft occlusion.

Technique
• A femoral artery and vein access is obtained, 6 Fr sheath is inserted and then pigtail catheter is placed in the aortic sinus and a femoral transvenous temporary pacing lead inserted through femoral vein.
• Surgical cutdown for the left axillary artery is done in deltopectoral groove (6-7 cm in size and 1 cm below and parallel to the clavicle from the mid clavicular line to the axillary line) (Figure 3) • Axillary artery is exposed by dissection of pectoralis major and lateral retraction of the pectoralis minor • A fully percutaneuos approach was described in 2012 as the "Hamburg Sankt George Approach" [9] • Once the sheath is in place, aortic valve is deployed in same manner as for previously described transfemoral access • Heparin reversal, sheath removal and control of vascular bleeding are done in same way as transfemoral approach.

Introduction
Transapical access (Figure 4) is the alternative approach for TAVI in patients in whom transfemoral or transsubclavian/transaxillary approach is not feasible.

Advantages
The transapical approach has the following advantages over other approaches: • Access to femoral vessels must be done in beginning of case, if femoral vessels are supposed to be used as a bailout CPB cannulation (on the contra lateral side, other than from the femoral arterial access for pigtail aortogram and venous access for ventricular pacing • Axillary artery can also be cannulated in case femoral artery is small in size • A final bailout for CPB is transapical cannulation itself putting a long arterial cannula across the aortic valve. The obvious advantage of this approach is that area will already be readily accessible. The disadvantage of the transapical CPB cannulation is that it gives up the site of access for valve deployment • It need to be careful while tying the sutures as LV can tear due to friable myocardium

Introduction
The transaortic approach was originally reported by Bapat et al. [12,13]. The concept behind this first report was the use of the short transapical TAVI delivery system for the retrograde TAVI implant through the ascending aorta. Since then it has become a valid option in case of severe peripheral vascular disease [14].

Advantages
It has many practical advantages compared to other approaches: 1. It avoids thoracotomy which could potentially impedes pulmonary function in COPD patients

It avoids cannulation of the left ventricular apex
3. It is easier to achieve hemostasis in aorta than in LV due to fragile myocardium 4. If needed, direct visualization of the aorta permits rapid cannulation and initiation of cardiopulmonary bypass for support

Disadvantages
1. It is technically challenging in case of previous sternotomy and internal mammary artery or saphenous vein grafts for CABG 2. It cannot be used in patients with porcelain aorta [15]

Planning
• Preoperative CT scan is done to shows the relationship of the distal ascending aorta to the sternum, calcification, and the distance from the distal aortic cannulation site to the aortic root • This distance should be ideally >7 cm allowing enough space for the valve implantation.
• CPB should be standby for any intra operative complication

Technique
• It needs a hybrid operating room where fluoroscopy and TEE • Supine position with the lower neck remaining exposed for a counter incision for the delivery sheath • Femoral arterial access is obtained as routine for placing a pigtail catheter in the aortic sinus • A femoral transvenous pacing lead is placed in the right ventricle • It can be performed by two approaches. The first is through mini-sternotomy ( Figure 5) and the second is by a right mini-thoracotomy (Figure 6).
• An upper ministernotomy is performed with extension to the second intercostal space, where the "J" is completed • The pericardium is opened • Pericardial stay sutures are placed for retraction. The aorta is then inspected to find a suitable place for catheter insertion • It should be free from calcification and at least 6-8 cm from the aortic valve for valve deployment • Two aortic purse strings are placed

Transcarotid approach 7.1 Introduction
This approach is used rarely and required in only for the patients who have contraindications to all other accesses. Modine reported a successful series of 12 patients who underwent CoreValve TAVI with no access site complications, no stroke, and only 1 TIA contralateral to the accessed side [16].
Mylotte et al. [17] reported the feasibility and the safety of this transcarotid approach in 96 patients enrolled in 3 different French sites. In their series, no major bleedings nor vascular complications related to the access site occurred, while only three transient ischemic attacks and no strokes were reported.

Planning
• Common carotid artery diameter must be >8 mm without any calcification, stenosis or tortuosity • CT angio carotid and brain to rule out significant atherosclerotic disease and to assess patency of the circle of Willis and cerebral circulation • MRI brain is done assess the patency of circle of Willis.

Technique
• A 6-F sheath is placed in the femoral artery and an angled pigtail catheter is utilized for ascending aortography • A transvenous pacing lead is placed via the femoral vein • The right common carotid artery is exposed by vertical lower neck incision • After proximal cross-clamping of the common carotid artery, it is opened longitudinally for 2.5 cm • The de-aired bypass shunt is placed through the arteriotomy into the distal carotid to maintain cerebral perfusion • Cerebral oximetry is monitored for both the cerebral hemispheres during the whole procedure • Through the proximal portion of the arteriotomy, a 0.035-inch J-tipped wire and 7-F introducer are placed in the ascending aorta • A multipurpose catheter is then inserted and a straight wire is used to cross the aortic valve • The straight wire is exchanged for an Amplatz extra-stiff wire • Under TEE and fluoroscopic guidance bioprosthetic valve is deployed as in other approaches • After the procedure the wires, catheters, and sheath are removed, and the carotid artery is repaired with a pericardial patch. The transcaval approach, described by Greenbaum et al. [18] is considered as the last resort in patients not qualifying for any other vascular access. In the transcaval approach (Figure 7), the delivery system is inserted through the femoral vein and crossed to the arterial system by creating an aortocaval fistula, which is closed with an Amplatzer device after the valve is deployed.
A case series demonstrated the feasibility of the transcaval TAVI, revealing a successful valve deployment in 17 of 19 patients despite a 79% rate of transfusion and a 33% rate of vascular complications [18].

Planning
The location of the fistula is determined by a careful evaluation of the CT abdomen and pelvis prior to the procedure.

Technique
• A baseline CT-scan to identify a calcium free target on the right abdominal aortic wall allowing for a safe passage from the inferior vena cava to the aortic lumen of the large bore sheath • After having obtained a femoral venous access, the inferior vena cava is punctured by means of a stiff CTO wire mounted over a microcatheter and a standard RCA or IMA guiding catheter • The caval and aortic walls are perforated by using electrocautery applied at the distal end of the wire.
• Once the access is obtained to the aortic lumen, the wire is snared and both the microcatheter and the guiding catether are advanced into the abdominal aorta. • This allows for the placement of a stiff "0.035" wire and the advancement of a large introducer sheath from the femoral vein into the aortic lumen for conventional retrograde aortic valve replacement • At case completion, heparin is reversed, and the aortic perforation is closed using a conventional vascular, duct or ventricular septal defect occluder device.

Author details
Mohd Shahbaaz Khan Cardio-vascular and thoracic surgeon, King Fahad Medical City, Riyadh, Kingdom of Saudi Arabia *Address all correspondence to: mohdshahbaazkhan@yahoo.com