Download Mitral valve implantation using off-pump closed beating intracardiac

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doi:10.1510/icvts.2007.154567
Interactive CardioVascular and Thoracic Surgery 6 (2007) 603–607
www.icvts.org
Work in progress report - Experimental
Mitral valve implantation using off-pump closed beating intracardiac
surgery: a feasibility study夞
Gerard M. Guiraudona,b,h,*, Douglas L. Jonesa,c,d, Daniel Bainbridgee , Terry M. Petersf,g,h
Canadian Surgical Technologies and Advanced Robotics (CSTAR), Lawson Health Research Institute, CSTAR Legacy Building, LHSC-UC,
339 Windermere Road, London, Ontario, N6A 5A5, Canada
b
Department of Surgery, London, Ontario, N6A 5A5, Canada
c
Department of Physiology and Pharmacology, London, Ontario, N6A 5A5, Canada
d
Department of Medicine, London, Ontario, N6A 5A5, Canada
e
Department of Anesthesiology, London, Ontario, N6A 5A5, Canada
f
Department of Medical Biophysics, The University of Western Ontario, London, Ontario, N6A 5A5, Canada
g
Department of Radiology and Nuclear Physics, The University of Western Ontario, London, Ontario, N6A 5A5, Canada
h
Imaging Research Laboratories, Robarts Research Institute, London, Ontario, N6A 5A5, Canada
a
Received 22 February 2007; received in revised form 23 May 2007; accepted 24 May 2007
Abstract
We have developed the Universal Cardiac Introducer䊛 (UCI) with the aim of modernizing the off-pump, closed, beating, intracardiac
approach. This paper reports our ongoing experience with positioning of a prosthetic MV, under image-guidance, substituting for direct
vision. The UCI is comprised of two detachable parts: an attachment-cuff and an airlock-introductory chamber for bulky tools. A prosthetic
MV was introduced into the left atrium in 12 pigs via the UCI (LA appendage). Transesophageal and 4D epicardial ultrasound were used for
guidance. Limitations of ultrasound imaging prompted the development of a multimodality virtual reality (VR) system introduced in the
last three animals. There were no complications associated with cardiac access, while achieving proper valve positioning. TEE contributed
to navigating, while 4D epicardial ultrasound was adequate for positioning the prosthesis into the MV orifice. VR provided a 3D context for
real-time US imaging with precise navigation and positioning using augmented reality representation of the valve. We demonstrated the
feasibility of positioning MV prostheses via the UCI. These results suggest the tremendous potential of virtual reality in making access safe
and effective for many intracardiac targets, with the ultimate goal of a safe, versatile, clinical application.
䊚 2007 Published by European Association for Cardio-Thoracic Surgery. All rights reserved.
Keywords: Experimental surgery; Mitral valve surgery; Off-pump surgery; Image-guidance; Virtual reality guidance; New technologies
1. Introduction
Current cardiac surgery uses either open-heart techniques, which are associated with significant morbidity and
mortality w1x, or a closed, beating heart, epicardial
approach, with or without cardio-pulmonary bypass w2x.
Since 2003, our group has revived and modernized offpump, closed, beating, intracardiac surgery w3x using a new
device for access and image guidance for substitution for
direct vision w4–7x. This approach could be an alternative
to open heart surgery and catheter-based intracardiac
interventions w8–10x.
1.1. The Universal Cardiac Introducer
Our goal was to develop a device providing safe intracardiac access. The Universal Cardiac Introducer䊛 (UCI) w11,
夞 Supported in part by the Canadian Institutes for Health Research,
Canadian Foundation for Innovation and the Ontario Research Development
Challenge Fund, and a grant from the Department of Surgery at UWO. No
conflict of interest with industry.
*Corresponding author. Tel.: q1 519-685-8500 (ext 32645)yq1 519-6438610; fax: q1 519-663-2930.
E-mail address: [email protected] (G.M. Guiraudon).
䊚 2007 Published by European Association for Cardio-Thoracic Surgery
12x was developed for access to any cardiac chamber. The
UCI is composed of two components: an attachment-cuff
(cuff), and an introductory-airlock chamber with 1–4
sleeves for introduction of tools and devices.
The cuff controls the port access, and has a secure
attachment to the heart chamber. It is made of a soft,
collapsible material that is easily and quickly occluded by
a vascular clamp. The cuff has a safe connection with the
introductory-airlock chamber.
The introductory-airlock chamber is impervious to prevent
bleeding and air embolism. The sleeves fit snugly to the
holders or handles to avoid blood leakage and air suction.
The airlock chamber acts as a bubble trap, with its upper
sleeves well above the heart port access, allowing venting
of air before opening the UCI to the cardiac chamber. The
design also allows for the introduction tools or devices in a
retrograde fashion, to accommodate larger tools or devices
through the heart port access, while having the handles as
narrow as possible. The connecting system between the
cuff and the airlock chamber should be tight, resilient, and
easy to release (Fig. 1).
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The lack of direct vision of the intracardiac target was
substituted with ultrasound (US) imaging alone w12x. Later,
tracked US imaging was integrated with tracked instruments in a virtual reality (VR) environment (Atamai
Viewer).
Implantation of an unmodified mitral valve (MV) prosthesis
was selected to document that the UCI can accommodate
bulky devices. The study focused on the introduction and
positioning (implantation) of the prosthetic MV, to test the
introducer and image-guidance system.
2. Methods
2.1. Animal experiments
2.1.1. Surgical protocol
The protocol was approved by the Animal Care and Use
Committee of the University of Western Ontario and followed the Guidelines of the Canadian Council on Animal
Care. A total of twelve pigs were used.
2.1.2. Surgical preparation
Animals were tranquilized with Telazol and Rompun before
transportation to the laboratory. After intubation, they
were ventilated mechanically and anesthesia was maintained with nitrous oxide and Isoflurane. Surface EKG,
arterial pressure, end tidal carbon dioxide and pulse
oximetry were monitored continuously throughout the
procedure. The heart was exposed via a left anterior
thoracotomy. The pericardium was opened and the left
atrial appendage was exposed.
2.1.3. The Universal Cardiac Introducer䊛
The UCIs were custom-made with vascular graft material.
A UCI with four sleeves was selected and preclotted. The
left atrial appendage was excluded using a large Satinski
vascular clamp. The LAA was opened with a straight incision. Trabeculations were divided when necessary for unobstructed access. The cuff was attached to the appendage
using 4y0 Prolene running suture.
Then, the MV prosthesis and its holder were introduced
in a retrograde fashion into the airlock chamber. The
connecting orifice of the airlock chamber was connected
to the cuff using 4y0 Prolene running suture. The pressure
line was introduced into the airlock chamber and used for
instilling saline to assist with de-airing; thereafter the line
was connected to a transducer for monitoring left atrial
pressure. The two other sleeves were occluded with small
tourniquets and used later for introduction of the anchoring
system, if needed. The animal was fully heparinized, and
the UCI was opened into the left atrium by releasing the
clamp occluding the cuff. De-airing was completed by
evacuating the air bubbles by puncturing the UCI roof. The
UCI was now ready for assisting in introducing the prosthesis
into the left atrium, and positioning into the MV orifice.
The MV prosthesis used was a porcine heart valve (Mosaic,
Medtronic Inc, Minneapolis, MN). The prostheses were used
more than once, with the risk of becoming stenotic. We
used a custom made valve holder, which was non-stenotic
and self-releasing (Fig. 1).
2.1.4. Image guidance
Initially, ultrasound (US) was the sole image guidance. US
imaging was used for the pre-implantation measurement of
the native MV annulus diameter (Table 1). A transesophageal echocardiography (TEE, Paediatric omniplane, Philips
Medical) was used to navigate the prosthesis into the left
ventricular MV in-flow tract. Then an X4 3D probe (Philips
Medical), applied directly onto the UCI, was used for
positioning the prosthesis within the MV annulus and to
address the following questions: (1) Was the valve axis
parallel to left ventricle? (2) Was the insertion cuff in
contact with the MV ring without perivalvular flow? (3) Was
the prosthetic valve functioning well?
Virtual reality was developed and tested on a cardiac
phantom in the imaging laboratory w13, 14x (Fig. 2).
3. Results
Twelve pigs had MV prostheses positioned into their native
MV orifices without complications. In seven animals, the
valve was positioned only; in the remaining five, positioning
of a clip applier was attempted. The implantation was
discontinued in one pig because the prosthesis had become
too stenotic after multiple uses.
The Universal Cardiac Introducer䊛 could be easily
attached to the LAA in approximately 30 min. It proved
safe and effective for introducing MV prosthesis into the
left atrium, without complications. De-airing was made
easy by filling in the air-lock chamber with saline, venting
the air via one sleeve, and then opening the cuff that is at
the bottom of the UCI, the final de-airing was done by
inserting small needles through the roof of the UCI. The
pre-clotted material proved tightly hemostatic and the
sutures tight. There was little blood loss via the UCI. The
flexibility and pliability of the UCI made manipulation easy
without mechanical stress on the heart attachment. No
tears were observed. The UCI is designed for easy changing
of tools. In two cases, the MV prosthesis was replaced
without complication. After occluding the cuff, a partial
and temporary separation of the cuff from the introduction
chamber, allowed removing and replacing the prosthesis,
before closing the UCI as described.
The introduction of the prosthesis across the LAA ostium
was performed with great care but without complication
(valve sizes up to 31 mm were introduced). When too
large, the prostheses were changed. The valve size calculated by TEE was used to select a prosthesis fitting snugly
into the MV annulus. Prosthesisyorifice mismatch did not
preclude testing the positioning of the prosthesis using
image-guidance.
3.1. Image-guidance
The 2D TEE field of view displayed only a cross sectional
view. However, without the 3D global anatomical context,
the orientation of the valve holder, or the direction to
move the valve into MV orifice could not be determined.
‘Trial and error’ method was used to place the prosthesis
into the MV orifice. However, when the prosthesis was
within the MV inflow track, it could be visualized by the
4D epicardial US transducer for fine positioning. The pros-
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Fig. 1. Sequential synoptical views of the Universal Cardiac Introducer䊛 (UCI), its attachment and left atrial access for mitral valve (MV) prosthesis introduction.
(a) A schematic representation of the UCI. The mitral valve with its holder is within the introductory chamber inserted through one of the sleeves. One sleeve
will admit the clip applier and the other the left atrial pressure line. (b) A diagram of the thoracic cavity during positioning of the UCI and its contents as well
as the TEE probe in the esophagus. LV: left ventricle. (c) Photograph of the attachment-cuff which has been sewn over the cardiac port access opening in the
left atrial appendage that has been occluded with the Satinski clamp. (d) Photograph of the UCI with the valve holder and the tracking system. The sensor is
buried at the tip of the holder and taped in place. (e) Photograph of the UCI with the MV prosthesis inside before being attached to the cuff. (f) Photograph
of the airlock-introductory chamber being connected to the cuff. (g) Photograph of the UCI after completion of the attachment with the MV holder and additional
sleeves occluded with snares. The prosthetic MV and its holder are inside the left atrium and being navigated towards the native MV orifice. (h) Photograph of
post mortem examination showing the prosthetic MV snugly inside the native MV orifice. Two attachment clips are in place.
thesis was positioned inside the native valve, without
negative effects, in a fashion accepted in clinical practice.
Manipulation of the clip-applier was not intuitive, particularly as the orientation of the tip and the clips could not
be visualized using US. As the unmodified tools were quite
bulky, they often collided with each other, making positioning very difficult or impossible except in one case (Fig. 1).
Virtual augmented reality was introduced in the last three
pigs. The VR system impacted the procedure: the magnetic
field generator for the 3D tracking system needed to be
placed close to the chest incision but otherwise was not
obstructive. In general, equipping the various tools with
tracking sensors required significant modifications of the
tools, making them bulkier, and thus limiting their move-
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Table 1
Weight of the pigs and the mitral valve annular diameter
Pig No.
Weight
(kg)
MV
annulus (cm)
LA dimension
(short axis)
Mean LA
pressure
(mmHg) pre-implant
Mean LA
pressure
(mmHg) post-implant
Prosthetic
valve size
1
2
3
4
5
6
7
8
10
11
12
50
52.6
52
100
49
69
63
60
52
61.6
73
3.07
2.39
2.23
3.65
2.87
2.87
2.64
2.8
2.28
2.78
3.1
2.74
2.95
2.58
3.88
2.06
3.41
2.92
2.92
2.89
2.90
3.41
16
7
10
11
19
–
19
8
–
–
13
32
20
19
Arrested
41
–
37
13
–
–
28
25
25
25
25
29
29
25
29
29
27
29
ment. These last experiments stressed the need for redesigning the tools to adapt to the new environment,
before going further. In the test phantom, without access
limitations, VR guidance allowed precise positioning of both
the prosthetic device and attachment clips with an accuracy of 0.99"0.29 mm (Fig. 3).
4. Discussion
Comments will focus on the limitations and future developments of this multidisciplinary project, that is more
challenging and exciting than anticipated, and may require
revisiting not only access and visualization but also the
surgical techniques, as experience suggests.
The Universal Cardiac Introducer䊛 implantation using graft
material does not require special techniques. The UCI has
been used in 47 animals, in addition to this series: for LV
assist device implant, creation and closure of ASD, and
surgery for atrial fibrillation, using this closed, off-pump,
beating, intracardiac surgery. Closure of the UCI for chronic
Fig. 2. Photograph of the computer screen during Virtual Reality using the
phantom. The image is taken from the Atamai䊛 viewer that can integrate
different image modalities and augmented reality. The screen shows the CT
scan of the phantom, with the chamber wall, the partition, and the Cryogel
membrane with a hole simulating the mitral valve. The structures are displayed in various shades of gray or color for easy interpretation. The 2D
probe that was used for the phantom study is represented with its field of
view. The cuff of the valve with its holder is displayed. The pointer that was
used to track the phantom 3D position is also displayed in its 3D position.
study is easy, using the cuff for pledgetted suture and then
ligation of the LAA. The UCI was used in a chronic study
for atrial fibrillation in 17 long-term animals, clinical follow
up and autopsy did not document complications associated
with the UCI closure or air-embolism. The UCI proved safe,
versatile and effective. An approved medical grade UCI is
needed to conduct a safety and effectiveness trial. Recently, we have successfully modified the cuff of the UCI for
implantation over the right atrial interatrial sulcus for more
conventional and user-friendly access to the left atrium.
This right-sided access requires opening the left atrium
under the protection of the UCI, as was done for the left
ventricle. It also avoids the narrowing of the LAA neck.
4.1. Image guidance
US imaging has significant limitations for navigating,
because of its only 2D display or restricted 3D view.
However, US imaging has two critical advantages: (1) it is
readily available in every cardiac operating room, without
Fig. 3. Photograph of the results of clipping the valve on the phantom Cryogel
membrane using only Virtual Reality for positioning. The most striking feature, besides the accurately positioned mitral valve and clips on the cuff, is
the good radial orientation of the clips.
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interfering with the procedure, and (2) it provides tracked
real-time dynamic imaging that is the indispensable ‘reference’ for integrating preoperative and intraoperative
other 3D modalities for virtual stereoscopic vision augmented by virtual representation of tracked tools. The
combination of VR and augmented reality (AR) provided 4D
visualization for navigation and the positioning of tools and
devices, and made important details visible (e.g. size,
orientation, position of the effective tip, etc.), which are
not visible using 2D or 3D US alone. The virtual vision
platform is making intracardiac access via the UCI independent of direct vision but with excellent visualization,
with the additional possibility of testing while doing. The
three last pigs were only used to identify the problems
associated with the operative setting. Very important progress is being made. We can now envision a VR platform
that will display more information than direct vision.
Mitral valve surgery was used as a major test for the UCI
in introducing bulky devices. This experiment also suggested that the design of current tools is inadequate. This
observation is consistent with the finding that design of
tools depends on access and visualization and can only be
correctly designed after the latter have been established.
When adequate tools are available with support of robotics
w15x, we are confident that most current interventions
would be duplicated and translated to clinical use.
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