The incidence of calcific aortic stenosis (CAS)
is increasing because of prolonged life expectancy.
A subset of elderly patients cannot undergo surgical
valve replacement, because of poor ventricular function
and comorbidities. Percutaneous balloon aortic valvuloplasty
(BAV) provides temporary improvement, but is associated
with a high mid-term restenosis rate. Hence, a percutaneous
bioprosthetic aortic heart valve is of interest. Cribier
described the experience at his institution with BAV,
the development of a percutaneous heart valve (PHV),
and the outcomes in the initial 14 patients with end-stage
CAS who received a PHV.
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Balloon aortic
valvuloplasty |
The limitation of BAV is the achieved final aortic
valve area is only 1.0 cm2, and on average is in the
range of 0.8-0.9 cm2. In 148 consecutive patients
over 80 years of age who underwent BAV, performed
by Cribier and colleagues, the complications were
in an acceptable range. Death occurred in 4 patients
(2.7%), stroke in 3 patients (2.0%), ventricular fibrillation
in 1 patient (1.0%), and surgical femoral complication
at the puncture site in 8 patients (5.0%).
The indications at Cribiers institution for
BAV are: Elderly patient (mean age 84 years) at very
high surgical risk due to severely depressed left
ventricular (LV) function or comorbidities; major
myocardial dysfunction (including cardiogenic shock)
to improve LV function before valve replacement (bridge
to surgery); urgent surgery for noncardiac disease;
and repeat BAV for symptomatic restenosis (up to 4-5
times).
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Lessons from
post-mortem studies |
Beginning in 1994, Cribier and colleagues examined
the use of implanted stents into the native valve
with CAS, which they considered the best way to address
the problem of restenosis to maintain an open aortic
valve. In 12 patients, a stent was implanted within
the valve, regardless of the degree of calcification,
without occluding the coronary arteries and impairing
function of mitral valve, and totally opened the valve.
Post-mortem studies showed that a 23 mm stent resulted
in an extremely large orifice, the best possible result
in patients with CAS.
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Cribier and colleagues worked with industry to develop
a PHV, with the idea of suturing the PHV with the
tricuspid valve using 3 anchoring struts. The concept
was to crimp the PHV over a balloon, go across the
native aortic valve and then inflate the balloon after
removing the sheath and deliver the PHV. The goals
were to develop a biologic valve mounted in a specific
stent that could be delivered percutaneously via standard
catheter-based techniques, within the diseases native
valve. The initial target population was patients
with severe CAS who are deemed inoperable or at unacceptable
risk for surgical valve replacement.
The first PHV was made in 1999 by Percutaneous Valve
Technologies, a US company. This 1st generation PHVs
was made of polyurethane, and were tested in animals.
The 2nd generation PHVs, made of bovine pericardium,
was tested extensively in vitro and was the first
one implanted in a human; it resulted in excellent
flow with parallel edges, which compared favorably
with the flow obtained with surgically implanted prosthetic
valves. In animals, a very good aortic valve area
(AVA) was obtained, the leaflets were very supple,
and the orifice was 1.7 cm2.
In 1999, Cribier and colleagues began PHV implantation
in animal models (> 100 implantations) in various
cardiac sites, including the native aortic valve,
native pulmonary valve, and the descending aorta.
Crossing the brachial cephalic trunk was possible,
introducing a 24 Fr introduce, when implanting in
the native aortic valve or descending aorta. Notably,
the diameter of the brachial cephalic trunk in sheep
is comparable to the femoral artery in humanswhich
allowed thinking about the concept of inserting the
PHV through the femoral artery in patients using the
same technique.
Notably, in the sheep model, at 1 month post-implantation
the PHV implanted in the pulmonary valve was working
normally. In 1 sacrificed animal, the PHV looked like
a native valve. In this model, it is not usual to
see the PHV functioning at 1 month because of the
well-demonstrated fast deterioration of a bioprosthesis
implanted in a pulmonary artery or venous blood of
animals. In their previous experience, a number of
animals were lost because of dysfunction of the bioprosthesis,
due to the valve becoming very thick and remaining
open. Therefore, implanting a bioprosthetic valve
in the pulmonary artery is not a good model to study
the long-term efficacy of a PHV.
So, implantation of the PHV in the native aortic
valve in the animal model was studied. In one
successful case, the PHV was implanted at the origin
of the aorta; the coronary arteries were patent and
LV function good. At post-mortem, the coronary arteries
were above the level of the PHV, with correction positioning
of the valve.
Two difficult problems in this model are ensuring
the correct position of the PHV and the risk of mobilization.
In the animal model, especially in sheep, the distance
between the ostia of the coronary arteries and the
insertion of the mitral valve is only 4-5 mm. So,
implantation is extremely difficult, as is the correct
positioning of the PHV. Also, when the PHV was
implanted, the risk of mobilization was very high,
because there was no calcium or fibrosis to maintain
the stent in place, in contrast to what would be seen
in patients. The number of migratory valves was very
high.
PHV implantation in the descending aorta was the
most interesting model, performed to determine the
6-months results. The PHV was implanted from the carotid
artery into the descending aorta, at 6 months it was
functioning well, without regurgitation, and at 6
months functioning ideally with excellent opening
of 1.7 cm2, no deterioration of the valve. To date,
in the animals in which the PHV has been implanted
in the descending aorta, the results show no or little
thickening of the leaflets, very clean aspect with
pannus or calcification possibly seen in just 1 case
for which confirmation is pending, and the 6-month
histopathology results are pending.
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PHV implantation
in humans |
In April 2002, PHV implantation in humans began.
The first person to receive a PHV was a 57-year-old
man, with severe CASand in cardiogenic shock. Surgical
valve replacement was declined by three surgical teams,
because of the patients hemodynamic status and
comorbidities. The patient had subacute ischemia of
the right leg (aorto-bifemoral bypass in 1996, recent
occlusion of right limb), and comorbidities included
silicosis, lung cancer (lobectomy in 1999), chronic
pancreatitis, and an LVEF of 10%. A BAV performed
by Cribier and colleagues failed and the patient returned
2 days later in cardiogenic shock. The PHV was implanted
using the antegrade approach, with no aortic regurgitation.
Hemodynamic results included decreasing gradient to
zero and no decrease in diastolic pressure. At day
8 post-implantation the patient was out of bed and
undertaking normal activities within the hospital.
The patient survived 4.5 months and died of leg amputation
complications.
After this first case, Cribier and colleagues worked
on improving the PHV for human implantation with the
company Percutaneous Valve Technologies. The latest
prototype has a tricuspid valve made of equine pericardium
and 23 mm stainless steel vent. The in vitro durability
is anticipated to be greater than 5 years based on
testing. Presently, there is only 1 size of stent,
with a maximum diameter of 23 mm, delivery pressure
of 4-5 Atm, crimped diameter 6 mm, and sheath 24-Fr
(compatible with 22-Fr or 20-Fr). It can also be used
for abdominal aortic aneurysms. Implantation of this
PHV within a diseased valve is possible without obstructing
the right coronary artery or left main artery, as
demonstrated by post-mortem studies.
The 2 methods for PHV implantation are the antegrade
trans-septal approach (ATSA), which is the gold standard,
and the retrograde approach. The steps in the ATSA
are: 1) pre-dilation of the native valve with 23 mm
balloon, 2) trans-septal catheterization, the lateral
view is best to cross the septum, 3) insert stiff
guidewire from the right femoral vein (RFV) to left
femoral artery (LFA), 4) trans-septal dilation with
10 mm balloon, 5) percutaneous introduction of a 24-Fr
sheath in the RFV, 6) PHV/balloon assembly advanced
to native valve, 7) PHV delivery within native valve
during brief rapid atrial pacing, and 8) supra-aortic
angiogram with or without a selective coronary angiography
to check exact position of the PHV. Local anesthesia
is used, the procedure duration is about 90 min, and
fluoroscopy time about 25 min. The limitation of this
approach is the learning curve, it is somewhat difficult
to learn, and particular attention must be paid to
achieving and maintaining an ideal loop when the guidewire
is advanced from the RFV into the left ventricle,
which requires 3 persons (1 for the valve and delivery
system, 1 for guidewire entering RFV, and 1 for guidewire
exiting femoral artery)all to maintain the loop
during the procedure. Not maintaining the ideal loop
could result in, for example, a position that pushes
away the anterior leaflet of the mitral valve, creating
an acute regurgitation, which could lead to transitory
collapse of the patient. The average time for femoral
puncture site compression is 15 minutes.
The retrograde approach is elegant, fast, and easier
to handle. The steps are: 1) pre-dilation of the native
valve with 23 mm balloon from RFA, with stimulation
of the heart in such a way that the balloon is not
moving during inflation, 2) introduce 24-Fr sheath
in the RFA (many limitations, especially in older
patients, who have vessel tortuosity and lots of atheroma;
the left femoral artery diameter must be above 7 mm),
3) PHV advanced to native valve, 4) PHV delivery within
native valve during brief rapid atrial pacing, 5)
supra-aortic angiogram with or without a selective
coronary angiography, 6) percutaneous closure of RFA,
with two 10-Fr Prostar. Retrograde approach
is performed under local anesthesia, procedure duration
60 minutes, and fluoroscopy time 20 minutes. Achieved
AVA is 1.6 cm2, which is larger than can be achieved
by surgery. The main limitation of the retrograde
approach is the difficulty of crossing the valve from
above, because the guidewire is crossing the valve
on the side, inside the commissure, and if the valve
is extremely calcific, the reduced diameter may make
it difficult to cross with the crimped valve on the
balloon. Cribier and colleagues experienced 3 failures
in crossing the valve in their series of patients.
Therefore, they are now working on improving the device
to avoid this problem.
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PHV experience
in 20 patients |
The feasibility of human implantation was studied
in compassionate cases, in which death was imminent.
To date, 20 patients have received a PHV (50% male).
Of these, 15 are in the prospective I-REVIVE study.
Patient characteristics include: Mean age 78 years,
range 57-91 years; NYHA class IV in all by inclusion
criteria; cardiogenic shock in 4 persons. All patients
were formally declined by 2 cardiac surgeons, according
to inclusion criteria, due to associated multiple
cardiac and non-cardiac factors. The Parsonnets
score was 52±7 (range 42-66) in these patients.
Associated cardiac factors in this population were:
severe CAD in 4 patients, recent AMI in 1, EF ú 25%
in 4, cardiogenic shock in 4, porcelain aorta in 4,
mitral stenosis in 2. Extra-cardiac factors were evolving
cancer in 5, recent stroke in 2, renal failure 6,
diabetes (insulin) 5, carotid dissection 5, COPD 8,
morbid obesity 1, liver cirrhosis 1, ongoing infection
1, thorax irradiation 1.
Procedural Results: Antegrade approach used in 13
cases, retrograde in 7 cases. Success was achieved
in 17 of 20 patients. Technical failures occurred
in 4 patients. In 1 patient, there was balloon/valve
assembly migration in a case of massive aortic regurgitation
post-BAV; the patient was in cardiogenic shock, early
death followed. There were 3 failures of retrograde
crossing of the native valve.
The hemodynamic results were very satisfactory.
Mean gradient (mm Hg) was 8.5 post-implantation, compared
to 4.3 pre-implantation (p=0.0076). The AVA was 0.56
cm2 pre-implantation and 1.69 cm2 post-implantation
(p=0.0076).
Procedural complications were: 1 stroke while crossing
the aortic valve with the guidewire; RV perforation
with the pacemaker lead and tamponade in a patient
under major steroid treatment for pulmonary fibrosis;
death during pre-dilation of the native valve in a
patient in cardiogenic shock; death after the end
of a successful procedure after removal of the RFA
sheath.
Aortic regurgitation of some degree seen in nearly
all patients, but it was grade 1 or 2 in most patient,
which is acceptable. In some patients, it was grade
3. In all of the cases, the aortic regurgitation was
coming from a gap between the stent and the distorted
native valve with lots of calcium deposit. One solution
is increasing the stent size. A 26 mm stent is nearly
ready for use. The LVEF nearly doubled in all patients
with reduced EF pre-implantation. At the time of this
presentation, 8 patients were surviving (1 to 6 months),
with no sign of heart failure. All of the deaths except
for one was due to a non-cardiac cause.
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