Download Feasibility of a Technique for Branch Pulmonary Artery Stent

Technical Developments and
Instrumentation
Feasibility of a Technique for Branch Pulmonary
Artery Stent Implantation1
Olga H. Salazar, MD
Kimberly A. Krabill, MD
David W. Hunter, MD
Michael 5 . Vance, MD
Albert P. Rocchini, MD
Index terms: Children, cardiovascular system,
59.1552,944.7229 Interventional procedures, in
infants and children, 944.1268 Pulmonary arteries, stenosis or obstruction, 59 1552,944.7229
Stents and prostheses
JVIR 1996; 7:41-46
'
From the Divisions of Pediatric Cardiology
(O.H.S., K.A.K.,M.S.V.,A.P.R.)and Radiology
(D.W.H.), University of Minnesota Hospital and
Clinic, Box 94-UMHC, 420 Delaware S t SE, Minneapolis, MN 55455. Received March 29, 1995; revision requested May 24; revision received July
17; accepted July 20. Address correspondence
to O.H.S.
O SCVIR, 1996
BALLOON-expandable stainless steel
stents have become a n important tool in
the treatment of stenosis in branch pulmonary arteries. Previous reports have
described the safety and efficacy of use
of these stents (Palmaz stent; Johnson &
Johnson Interventional Systems, Warren, N J ) in the treatment of congenital
heart disease (1-6). The current delivery
technique is complicated by the inability
to advance a large sheath or stent across
branch pulmonary arteries that are severely stenotic. I t is also complicated by
kinking of the sheath during stent passage, which results in a long procedure
time and may cause premature dislodgment of the stent from the balloon catheter. The use of a 10- or 11-F sheath precludes stent placement in many small
children.
This study describes a n alternative
method of endovascular stent implantation t h a t can help resolve some of these
technical difficulties. This method is especially useful in smaller patients, in
whom venous access is frequently a
problem. The purpose of this study was
to evaluate the efficacy and safety of a
method of endovascular stent implantation in a dog model and to determine the
feasibility of using this alternative technique in children with stenosis of a
branch pulmonary artery.
METHODS
The method presented here and old
methods of stent delivery initially were
assessed in nine mongrel dogs that
weighed 12.9-20.2 kg. Isolated stenosis
of the left pulmonary artery was created
by placing two pieces of 2-0 Vicryl suture
(Davis & Geck, Wayne, NJ) around the
branch pulmonary artery (3). The sutures were tightened so that the pulmonary artery was narrowed 40%-50%.
After surgery, all dogs were given intramuscular antibiotics for 3 days to prevent infection, and they were given morphine sulfate to prevent pain. Cardiac
catheterization was performed 3-6
months after the creation of t h e stenosis,
with the dogs under anesthesia. After
the stenosis was hemodynamically and
angiographically assessed, stent placement was attempted (Fig 1). Five dogs
were randomly assigned to treatment
with the old method, and four were assigned to the new method. The animal
component of this study conformed to
the guiding principles of the American
Physiological Society (7).
In determining the efficacy of the
method, two factors were evaluated: The
first was the ability to place a stent. The
second was the time required for stent
placement, which was defined as the
time that elapsed from the placement of
a n exchange guide wire in the branch
pulmonary artery to the expansion of the
stent across the stenotic lesion.
Old Method of Stent Delivery
In the old method, a 0.038-inch Amplatz Superstiff Teflon-coated exchange
wire (Medi-tech/Boston Scientific, Watertown, Mass) was positioned in the distal branch pulmonary artery. An 11- or
12-F long sheath (Mullins sheath; USCI
Angiographic Systems Division, C R
Bard, Billerica, Mass) and a dilator were
advanced beyond the stenosis, and the
dilator was removed from the sheath.
The P308 Palmaz stent was mounted on
a n 8-10-mm polyethylene balloon catheter ( ~ e d i - t e c h b o s t b nScientific) and
was advanced through the sheath until
it reached the site of stenosis in the
branch pulmonary artery. An 11-F
sheath was used for the 8-mm balloon
catheter, and a 12-F sheath was used for
the 10-mm balloon catheter. The balloons selected were the same size a s or
slightly larger than the diameter of the
pulmonary artery distal to t h e stenosis.
The sheath was partially withdrawn
over the stent, and centering of the stent
across the stenosis was confirmed by
means of a small injection of contrast
material into the sheath. The sheath
was then withdrawn completely from the
stent, and the balloon was inflated until
the stent was fully expanded. The balloon was withdrawn, and if necessary, a
42
Journal of Vascular and Interventional Radiology
January-February 1996
Figure 1. Angiograms show
(a) isolated left pulmonary artery
stenosis (arrowhead) surgically
created in a dog and (b) a stainless steel stent (arrowhead) placed
at the site of a previously created
left pulmonary artery stenosis.
r,
a.
Table 1
Patient Demographic and Technical Data
Patient
No./Sexl
Age (y)
Weight
(kg)
Diagnosis
Approach
Type of
Sheath
Size of
Olbert Balloon
l"M2.3
1*M2.5
2M3.0
3M3.5
4M4.5
10.2
10.6
13.4
13.5
16.3
TOF PA
TOF PA
PO Glenn anastomoses
PO Glenn anastomoses
PO Glenn anastomoses
RFV
RFV
RIJ
LIJ
RIJ
8-F Mullins
8-F Mullins
7-F Cordis
7-F Cordis
7-F Cordis
81415.8190
81415.8190
81415.8190
81415.8190
81415.8190
5Fl15.5
6M15.0
51.3
56.5
PPS
PO HT
RFV
RFV
8-5' Mullins
8-F Mullins
81415.8190
81415.8190
Size and Type of
Redilation Balloon
101417175VC
1014/7/75 VC
101417175VC
1014/7/75 VC
1214171100 BX
1214/7/100 BX
1214171100 BX
Note.-BX = Blue Max, HT = heart transplant, LIJ = left internal jugular vein, PA = pulmonary atresia, PO = postoperative, PPS = peripheral pulmonary stenosis, RFV = right femoral vein, RIJ = right internal jugular vein, TOF = tetralogy of
Fallot, and VC = Vast-cath.
*Data in regard to stent placement in the right (row 1)and left (row 2) pulmonary arteries in patient 1 are given.
larger angioplasty balloon was used to
further dilate the stent. The balloon was
then deflated and exchanged for an endhole catheter, and the expanded stent
was left across the area of stenosis. Repeated hemodynamic and angiographic
evaluations were performed.
New Method of Stent Delivery
In the new method, a 0.035-inch
Superstiff exchange guide wire was positioned in the distal pulmonary artery
well across the narrow area. The Palmaz
stent was mounted by hand onto an 01bert 81415.8190 (balloon outer diameter
[millimetersl/balloon length [centimeters1French sizelusable length [centimeters]) balloon catheter (Meadox Medicals, Surgimed, Oakland, NJ) and was
pressed firmly onto the middle of the
balloon. The Olbert balloon catheter is
made of a material that allows a tight
bond to be formed between the stent and
the balloon and thus makes premature
dislodgment of the stent from the balloon almost impossible. The Palmaz
P308 stents were 3 cm long with a 3.4mm nominal outer diameter (Table 1). A
Touhey-Borst type of adapter (Intenentional Medical, Subsidiary of Medtronic,
Danvers, Mass) was Luer-locked to the
sheath hub to prevent movement of the
balloon catheter and to permit injection
of the contrast medium into the sheath
to confirm stent position (Fig 2). The
stent mounted on the Olbert balloon
catheter was preloaded into an 8-F long
sheath (Mullins sheath), and this unit
was advanced into the stenosis in the
distal pulmonary artery. The sheath was
withdrawn and the stent was deployed
in a fashion similar to that used in the
old method. If the pulmonary artery distal to the stent was greater than 8 mm
in diameter, then the stent was dilated
further by advancing a 10-mm balloon
catheter (Opti-Plast; Vas-Cath, Mississauga, Ontario, Canada) over the exchange guide wire.
After we had demonstrated its efficacy in the dog model, we used this
method to place seven stents in six children (five boys, one girl) with stenosis of
a branch pulmonary artery. The patients
were aged 2.3-15.5 years (mean, 6.6
years f 5.9 [standard deviation]), and
weighed 10.2-56.5 kg (mean, 24.5 kg
20.2). Informed consent was obtained
from all patients (Table 1). The study
protocol was approved by the institutional committee on human research.
All patients who had stenosis or hypoplasia of a branch pulmonary artery
*
Salazar et a1
-
43
Volume 7 Number 1
Statistical Analysis
All data are presented as the mean f
standard error. Statistical analysis was
performed with the unpaired Student t
test.
I RESULTS
Figure 2. Photographs of the Palmaz stent mounted on an 8-mm Olbert angioplasty balloon catheter. (a) Combination of preloaded Olbert balloon, Palmaz P308
stent, and 8-F sheath is shown. A Y hemostatic valve was attached to the sheath hub
to prevent movement of the catheter. (b) Palmaz P308 stent is mounted on an 8 mm
x 4 cm Olbert balloon catheter on a 5.8-F shaft.
were considered eligible. Diagnoses included tetralogy of Fallot with pulmonary atresia, univentricular heart physiology and a previous caval-pulmonary
anastomosis, isolated branch puln~onary
artery stenosis, and in one patient
branch pulmonary artery stenosis after
heart transplantation (Table 1). Patients
1 , 4 , and 5 underwent numerous procedures during which both balloon and
surgical angioplasty were used to try to
enlarge and unifocalize their hypoplastic
pulmonary arteries before stent placement. Patients 2, 3, and 4 had surgically
induced stenoses of branch pulmonary
arteries after aortopulmonary shunt
placement and had previously undergone unsuccessful attempts to enlarge
their stenotic pulmonary arteries with
both balloon and surgical angioplasty.
The patients were examined clinically
and appropriate laboratory studies were
obtained before cardiac catheterization.
Right heart catheterization was performed from the femoral approach in
four patients and from the left internal
or right internal jugular vein in three
patients with Glenn anastomoses (Table
1). The areas of stenosis were defined
with angiography. Systemic anticoagulants were administered routinely by
means of a heparin bolus (100 Ukg). After stent placement, all patients were
given 80 mg of aspirin per day for 1
month.
A specially ordered 8-F Mullins long
sheath (80 cm long) was used when the
femoral vein approach was employed.
When the internal jugular vein approach
was used (patients with Glenn anastomoses), a 7-F, 23-cm-long Cordis Plus
sheath (Cordis, Miami, Fla) was used
(Table 1). Redilation was performed with
a balloon catheter with a larger diameter when indicated. Opti-plast 10/4/7/75
and BlueMax 12/4/7/100 balloon catheters (Medi-tech/Boston Scientific) were
used for redilation to 10 and 12 mm, respectively (Table 1).When redilation
with a larger balloon catheter was required, the long sheath was exchanged
for a balloon catheter with a larger diameter; this catheter was advanced directly through the skin, without a
sheath. All stents were dilated to a size
equal to or slightly greater than the diameter of the pulmonary artery distal to
the stenosis. In patients 1 and 2, the
stents developed stenoses because of patient growth and were successfully redilated to a larger size 2-3 years after the
original stent placement.
Experimental Data
Before stent placement, the peak systolic gradients across the stenoses were
similar in the two groups of dogs (Table
2). Stents were placed successfully in
three of five dogs with the old method
and in four of four dogs with the new
method. The old method failed in one
dog because we were unable to advance
the large sheath from the right ventricular outflow tract and across a distal pulmonary artery stenosis; it failed in the
second dog because we were unable to
advance the stent through the sheath at
the level of the stenotic pulmonary artery, despite previous dilation with an 8mm angioplasty balloon catheter. In
both of these dogs, the stents were successfully placed by means of second
catheterization with the new method. In
all cases in which stent delivery was successful, the gradient across the stenosis
was abolished. They were no major complications associated with stent placement with either method.
Significantly less time was required
for stent placement with the new
method (13 minutes k 3) compared with
the old method (39 minutes k 5) ( P =
,009). Dogs in whom the stent could not
be placed with the old method were not
included in this analysis of time.
Patient Data
Seven stents were successfully delivered in six patients with stenoses of
branch pulmonary arteries by using the
new method. Stent placement resulted
in a significant reduction in systolic gradient across the stenosis (from 37 mm
H g k 3 9 to l l m m H g + 1 6 ) a n d a
marked increase in vessel diameter
(from 3 mm + 1 to 9 mm f 2) ( P < .001).
The time required to place the stents in
these children ranged from 7 minutes f
18 to 13.5 minutes 2 (mean, 13 minutes f 4) (Table 3). There were no complications related to the procedure.
+
I DISCUSSION
In 1985, Julio Palmaz and colleagues
(8) developed an expandable intraluminal graft in an attempt to overcome the
elastic recoil that occurs in lesions refractory to balloon dilation. Balloon-ex-
44
Journal of Vascular and Interventional Radiology
January-February 1996
pandable intravascular stents were initially used to support vessel walls in
coronary arteries in adults (9). In 1988,
Mullins et a1 (1)and Charnsangavej et a1
(10)
. . evaluated the efficacv of im~lantinn
expandable stents in pulmonary arteries
and systemic veins. Twenty-seven balloon-expandable stents were placed in 13
mongrel dogs with good results and few
complications. In 1991, O'Laughlin et a1
(2) described the successful placement of
36 stents in 23 patients with stenoses of
branch pulmonary arteries and reported
a substantial reduction in the pressure
gradient and an increase in vessel diameter.
The feasibility of repeated dilation of
the Palmaz stent in growing pulmonary
arteries was recently studied by Trerotola et a1 (6). They placed 23 stents in 20
newborn lambs and redilated the Palmaz stents after 4 months, when vessel
growth had created a stenosis. The process of repeated dilation of stents in pulmonary arteries proved to be relatively
straightforward, without major complications.
A more recent report on intermediate
follow-up after endovascular stent placement in patients with congenital heart
disease described a combined experience
in 85 patients in Houston and Boston
who underwent placement of 121 stents
(5). Follow-up revealed stent fracture in
one patient, restenosis in one patient,
and sudden death in one patient. There
was no statistically significant change in
luminal diameter or pressure madient at
follow-up catheterization (average of 8.6
months after stent placement) compared
with findings at immediate postimplantation catheterization. Redilation was
performed in 14 patients (mean of 10.2
months after implantation) who had stenoses with a residual waist or who
needed a larger arterial diameter, with
good results.
Some of the problems associated with
the current technique of stent placement
are related to technical difficulties in delivering the stent to the area of stenosis.
These problems are also related to the
large size of the sheath required, which
results in limitations on venous access in
smaller patients. In the past, patient selection has been important, with the
most favorable candidates being adults
or adolescent-sized patients because of
technical ease of implantation and ability to dilate the stent to,a size appropriate for an adult (5).
We conducted the animal study to determine the feasibility of this new technique of stent placement, and we com-
Table 2
Experimental Results in a Dog Model
Old Method
New Method
P
16f2
25f 2
16f3
26 2
+
NS
NS
0.3 f 0.6
0.3 f 0.5
NS
60% (3 of 5)
38.3 f 6
100% (4 of 4)
12.3 3
,009
L,
Mean weight of dogs (kg)
Gradient before stent
placement (mm Hg)
Gradient after stent
placement (mm Hg)
Success rate
Time ( m i d *
+
...
Note.-NS = not significant.
*The time required, after placement of a Superstiff exchange guide wire into
the branch pulmonary artery, to position the expanded stent across the stenotic
lesion.
pared our ability to place the stent and
the time required for stent placement
with each method. We chose a randomized study design to eliminate investigator bias in the selection of animals for
each group and to ensure that the experience of the cardiologist with the various stent-placement techniques did not
bias the results. All stents were positioned by one primary operator (A.P.R.)
with an assistant (O.H.S., D.W.H., M.V.,
or K.A.K.). Until 1991 when we completed the animal component of this
study, the old method was the standard
technique used for endovascular stent
implantation at our institution. We did
not perform a randomized trial comparing the old and new methods in patients
because of the success of the new
method in our animal studies and the
small number of patients who undergo
this procedure. The new technique was
especially advantageous in smaller patients, in whom the low-profile balloon
catheter permitted the use of a smaller
sheath. The use of the smaller sheath
was especially desirable in the patients
with a Glenn anastomosis in whom
placement of a P308 stent from an internal jugular approach was required.
The results of this method of placing
stents in branch pulmonary arteries appear to be encouraging. By using the
stent-mounted balloon catheter as the
"dilator" for the sheath and simultaneously advancing the sheath, balloon,
and stent into the branch pulmonary artery, the time required for the procedure
is decreased and stent delivery to even
severely stenotic vessels is facilitated.
Problems such us kinking of the sheath
during stent passage and dislodgment of
the stent from the balloon catheter are
essentially eliminated. We have not en-
countered any stent-related complications such as distortion fracture or
stress fatigue as a result of reexpansion
of the stent after it has been crimped
onto the 8-mm, 5.6-F-shaft Olbert balloon catheter. The use of a smaller balloon did not interfere with our ability to
redilate the stent up to 12 mm when indicated.
In older patients in whom redilation
of the stents to 15 or 18 mm may be indicated, the 8-F long sheath can be exchanged for a larger-diameter balloon
catheter, which is advanced directly
through the skin without a sheath. One
disadvantage of our method is that when
the final desired stent diameter is
known to be greater than 10 mm, redilation of the stent is required after initial
placement. In some such patients, a
modification of the new method of stent
placement in which the appropriate-size
balloon is used as the dilator for a larger
sheath may be preferable. Given the limited amount of data available in regard
to stress fatigue and stent integrity with
overexpansion of the Palmaz stent, as
well as the continued advice from the
manufacturer that the stent not be expanded more than 12 mm, such overdilation should be performed with caution
until more data are obtained or larger
stents become available.
We used the Cordis Plus 7-F sheath
in patients with a Glenn anastomosis in
whom the internal jugular approach was
used. The Cordis Plus sheath is used
with the 8-mm Olbert balloon and stent
but is only 23 cm long. Because the 8mm Olbert balloon and stent will not fit
through a 7-F Mullins sheath and a n 80cm-long sheath is necessary when the
leg approach is used, the Cordis sheath
could not be used. The preferred ap-
Salazar et a1
45
Volume 7 Number 1
Table 3
Results in Patients
Pressure Gradient (mm Hg)
Patient
No.
Site
1
1
2
3
4
5
6
RPA
LPA
RPA
LPA
RPA
LPA
LPA
Mean
+ SE
Note.-LPA
*P < .05.
= left
Before Stent
Placement
After Stent
Placement
Change in
Gradient
(mm Hg)
89
92
2
4
4
41
25
36.7
39.4
44
20
0
0
0
4
9
1l *
16.6
45
72
2
4
4
37
16
25.7
26.6
Stenosis Diameter (mm)
Before Stent
Placement
After Stent
Placement
Change in
Diameter
(mm)
Time
(min)
2.3
2.4
2
3.9
3.2
4
4
3.1
0.88
7
8.9
9
8
11
12
8.2
9.2*
1.8
4.7
6.5
7
4.1
7.8
8
4.2
6.0
1.7
14
13
18
7
10
14
17
13.3
3.8
pulmonary artery, RPA = right pulmonary artery, and SE = standard error.
proach for stent implantation in the pulmonary artery is from the right femoral
vein to facilitate catheter manipulation
and provide a more straight catheter
course. This approach also avoids the
need for general anesthesia in smaller
children.
The Olbert balloon has several
unique features (low profile before and
after deflation and balloon material)
that make it ideal for placement of the
Palmaz stent. The low-profile characteristics of the Olbert balloon allow delivery
of the balloon and stent into the branch
pulmonary artery with only a 7-8-F
sheath. The Olbert balloon catheter is
constructed of a material that allows formation of a tight bond between stent
and balloon; we have found that this
bond makes premature dislodgment of
the stent from the balloon uncommon.
Finally, unlike other angioplasty balloons that develop "wings" after deflation, the Olbert balloon retains its low
profile after deflation, and inadvertent
dislodgment of the expanded stent during balloon removal is virtually eliminated.
Because of its coaxial design, the
Olbert balloon inflates by shortening as
the tip of the catheter retracts. At the
time of inflation, the leading edge of the
balloon (and therefore the stent) is
moved 5-8 mm back toward the catheter
hub. To compensate for this movement
the stent should be positioned 5-6 mm
above the final desired position, and the
position of the stent should be corrected
a t a partially inflated state (4-6 atm)
(11). If the stent is crimped onto the balloon near its trailing edge, the stent will
move less (1-3 mm) as the balloon in-
flates, but this implies that the balloon
catheter must be advanced farther past
the lesion, and advancing the catheter
may be difficult.
We have found the use of a TouheyBorst type of adapter, Luer-locked to the
sheath hub and holding firm to the shaft
of the balloon catheter, to be helpful in
preventing dislodgment of the stentmounted balloon catheter from the
sheath before crossing the stenosis. Use
of this adapter also obviates the need for
a second catheter for confirmation of
stent position because the adapter allows
injection of contrast media through the
sheath.
Bjarnason et a1 (11)recently described
placement of 19 Palmaz P308 stents by
using the same size balloon and a similar
method in 11patients with atherosclerotic lesions in the iliac arteries. They reported no complications or difficulties
with the technique. In their series, the
Palmaz stent was also crimped onto the
balloon by means of only finger pressure,
and there were no reported instances of
distorted slits or asymmetric expansion.
We believe that this new method of
stent placement represents a useful alternative for endovascular stent implantation in smaller patients. The use of a
smaller sheath and a single-unit delivery
system allows adequate stent positioning
and redilation to up to 12 mm in diameter when indicated. This technique also
may prove advantageous when a difficult
catheter course is anticipated because it
allows simultaneous passage of sheath,
balloon, and stent across the stenotic lesion.
In our experience, this new method of
stent placement decreases the time re-
quired for the procedure and improves
the ease and success rate of stent placement in stenoses of the branch pulmonary artery. It has become our method of
choice, especially in young children.
Acknowledgments: We are grateful
to J u a n Salazar, MD, and Kurt Amplatz, MD, for their technical assistance.
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Journal of Vascular and Interventional Radiology
January-February 1996
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