19 декабря 2001 00:00 |
Coronary Artery Exposure in Off-Pump CABG: A Word of Caution
ABSTRACT
Coronary exposure and stabilization have focal importance in
off-pump coronary surgery. Off-pump complete myocardial
revascularization can be performed safely in the majority of the
patients whenever strict surgical protocols are followed. Although
new devices may be used to facilitate the performance of this
demanding operation, technical pitfalls should be recognized to
ensure the success of the procedure. We herein report our timely
experience with the Xpose device (Guidant Corp., Cupertino, CA).
INTRODUCTION
The increasing popularity of off-pump coronary artery bypass
grafting (OPCAB) has stimulated interest and concerns about
different techniques of coronary exposure and stabilization. In our
experience, complete myocardial revascularization may be performed
safely without cardiopulmonary bypass (CPB) and via median
sternotomy if strict surgical protocols for coronary exposure and
stabilization are followed in order to maintain adequate
hemodynamics during the entire procedure. Since March 1998, the
introduction of the «single suture» technique [Bergsland 1999] has
drastically changed the applicability of beating heart coronary
surgery. A single heavy suture is placed in the oblique sinus of the
pericardium after having elevated the heart from the pericardial
cradle. The suture is then passed through a double-armed vaginal
tape and is snared down to the posterior pericardium [Bergsland
1999]. Different degrees of traction on the suture and different
positioning of the vaginal tape allow adequate exposure of the
different coronary branches including the topographically more
difficult circumflex coronary artery. Our experience has shown that
normal hemodynamic values can be maintained during lateral
revascularization in the majority of the patients with the «single
suture» technique [D'Ancona 2000].
Recently a new device (Xpose, Guidant Corp., Cupertino, CA.) has
been developed to enrich the surgical armamentarium for complete
myocardial revascularization off-CPB. The Xpose device consists of
a suction cup system that is placed at the apex of the left
ventricle. The cup is connected to an articulated arm that is fixed
to the sternal retractor. Once suction is applied, the tip of the
heart can be gently elevated and different positions of the arm
allow for exposure of different coronary artery branches. The
clinical applicability of this device has been recently demonstrated
in an elegant study [Dullum 2000]. Although the Xpose is a unique
and user friendly system, some associated technical pitfalls should
be recognized. We herein summarize a timely case report.
CASE REPORT
class I angina pectoris, and preserved ejection fraction. OPCAB was
scheduled electively. After induction of general anesthesia and
endo-tracheal intubation, a median sternotomy was performed. The
left internal mammary artery (LIMA) was harvested together with
saphenous vein conduits. After systemic heparinization, the
pericardium was opened using an inverted T incision. The heart was
normal in size with preserved global contractility. The coronary
targets were adequate for OPCAB [Bergsland 2000]. The Xpose
the left anterior descending coronary artery (LAD). The LAD was a
2−mm vessel with 80% proximal stenosis. The vessel extended to the
apex of the ventricle. After mechanical stabilization, placement of
a 4−0 polypropilene pledgetted suture, the coronary was opened and a
2−mm intracoronary shunt was placed to maintain adequate distal
perfusion. The proximal snare was released and 7−0 continuous
polypropilene running suture was used to anastomose the LIMA to the
LAD.
During the procedure, multiple premature ventricular contractions
with ST segment elevation in the anterior leads were noted. At the
end of the anastomosis, intraoperative graft patency verification
was performed using transit time flow measurement (TTFM) (Medi-Stim,
Oslo, Norway). A 2−cm segment of the LIMA was skeletonized and a
3−mm flow probe was placed around the LIMA, with the Xpose in
place. The TTFM curve showed an adequate diastolic pattern with a
relatively low absolute flow value [Figure 1 :1791:]. Initial TTFM
analysis suggested patent LIMA to LAD anastomosis.
While measuring flow, ST segment elevation was accompanied with
sudden hemodynamic impairment. At closer inspection, the Xpose
suction cup seemed to compress the distal segment of the native LAD.
We immediately released the tip of the heart from the suction cup
and reassessed flow within the LIMA graft. Transit time flow
measurements were repeated and a significant increase in the
absolute flow value was noted [Figure 2 :1792:]. The EKG tracing
reverted to normal and the systemic hypotension resolved. After
that, we used the «single suture technique» to achieve adequate
exposure of the remaining coronary targets. The operation was
successful, without perioperative morbidity or mortality.
DISCUSSION
OPCAB is performed successfully using different techniques of
coronary exposure and stabilization. In our experience, simple,
standardized, and reproducible protocols have been used to ensure
satisfactory technical results and postoperative outcomes. Minimal
changes in the surgical routine can drastically compromise the
success of the operation and, for this reason, should always be
adopted cautiously. The «single suture» technique enables coronary
exposure while different degrees of traction are placed on the
pericardium. In theory, no compression on the heart and the
epicardial vessels is utilized with this technique.
Although the Xpose can achieve adequate coronary exposure, direct
snaring of the apical vessels with the suction cup should be
avoided. As documented in this case report, compression on the
coronary artery branches not only reduces native flow causing
regional ischemia, but also limits actual flow through newly
constructed anastomoses. As a consequence, erroneous revisions of
patent grafts can be avoided if the pitfall is recognized. This case
report also documents the wide applicability of intraoperative
flowmetry [Canver 1994, Louagie 1994, Walpoth 1996, Canver 1997,
Jaber 1998a, Jaber 1998b, Louagie 1998, Walpoth 1998, Cerrito 1999,
D'Ancona 1999, Di Giammarco 1999, Walpoth 1999]. This technology may
be useful in detecting anastomotic imperfections [Canver 1994,
Louagie 1994, Walpoth 1996, Canver 1997, Jaber 1998a, Jaber 1998b,
Louagie 1998, Walpoth 1998, Cerrito 1999, D'Ancona 1999, Di
Giammarco 1999, Walpoth 1999] and in identifying modifications in
graft flow during the different phases of the operation. Proper
function of coronary grafts should always be ensured at any time to
maintain adequate hemodynamics during off-pump coronary surgery and
to prevent emergent conversions to CPB.
REVIEW AND COMMENTARY
1. Editorial Board Member SC389 writes:
There are no values such as PI shown with Figure 1. There should be
a picture or diagram of placement of the Xpose device on the heart
so that the location of the device and also the placement of the
heart can be visualized so as to assess incorrect displacement, such
as RV or LV compression.
I am concerned about the conclusion from this case report. I do not
have the familiarity and experience with the TTFM that the authors
obviously have, but just looking at the absolute numbers of flow in
Figure 1 and Figure 2 -- Figure 1 is 33 ml/min and Figure 2 is 7
ml/min. I have significant experience with off pump cases with and
without the Xpose and have seen these changes occur from many other
reasons with spontaneous resolution and feel very strongly that this
conclusion can not be drawn from this case.
I would be interested in knowing if the authors have ever had these
changes occur in any of their prior cases without the Xpose. I am
also interested in exactly where the Xpose was placed to be able to
compress the distal LAD and how much of the LAD was compressed. In
the early Octopus experience, it was shown that a suction device
could be placed directly over a coronary vessel without damage to
the vessel.
Authors' Response by Giuseppe D'Ancona, MD:
PI values were adequate in both measurements. The suction cup was
placed on the apex of the heart and was compressing the terminal
portion of the LAD (last 3 cm). The right pleura was fully opened to
prevent compression on the right ventricle. Measurements were done
after removing the coronary stabilizer to prevent compression on the
left ventricle.
We usually test graft flow many times (an average of 20 times/case)
during the same operation to detect any possible kinking,
compression, or excessive tension on the newly constructed grafts,
especially when the heart is elevated and rotated to expose the
lateral coronary targets. If the heart stays in a fixed position and
there are no sudden changes in blood pressure, we very seldom see
drastic changes in the flow curves and values.
As already proven in the Octopus experience, direct suction does not
cause any sort of endothelial lesion on the coronary vessels. On the
contrary, no one has ever shown any data about how coronary flow may
change during the use of these suction devices. It is logical to
believe that, although the suction cup will not cause any sort of
permanent damage of the vessel, its compressing effect may
temporarily deform the coronary artery and consequently reduce the
blood flow.
2. Editorial Board Member MN393 writes:
The original work on suction stabilization (Grundeman, Borst, et
al.) showed no ill effect of 400 mmHg suction applied directly to
the epicardium over a coronary artery. The present case report
strongly suggests coronary compression. Could this be related to the
design of the Xpose device? I have observed that this draws the
whole apex of the heart into the cup (i.e., curving around the outer
lip). Clearly this increases the amount of traction one can obtain.
However, I can see how a relatively unsupported epicardial coronary
artery (lying in epicardial fat) could be kinked around this edge.
Authors' Response by Giuseppe D'Ancona, MD:
Yes, we believe that a direct compression of the LAD and the
surrounding tissue may be the explanation for our findings. A
suctioning cup with a smaller design may be an option.
3. Editorial Board Member EE455 writes:
To me ischemia to the distal LAD, though likely, has not definitely
proven to be the origin of the problem. In this case report, the
fact that removing the Xpose system improved the situation is of
course convincing in its role as a trigger of hemodynamic
instability, but other factors may have been involved. Further
details should be provided, if available (e.g., TEE findings,
hemodynamic measurments, etc.).
ECG changes are not interpretable and some ESV when the heart is
tilted are frequent; there are no definitive proofs of severe
ischemia. Authors should provide further data about the acute
hemodynamic intolerance that happened after completion of the
anastomosis. In my experience, compression of the LAD with the
Xpose system, if any, is very distal and would be unlikely to
provoke major ischemia. Could any other factor have been an issue,
such as inappropriate twisting of the great vessels, or compromise
of the RV function?
Authors' Response by Giuseppe D'Ancona, MD:
Grafting of the LAD requires only minimal displacement and
manipulation of the heart and, for this reason, hemodynamic
impairment due to compression of the ventricles and twisting of the
great vessels is very seldom. On the contrary, we have often noted
sudden instability for ischemic reasons, for example, when the LAD
is not properly shunted or the vessel is excessively compressed by
the stabilizer foot. In this case report, signs of ischemia were
noted after some minutes from the placement of the Xpose, during
construction of the LAD anastomosis. The coronary was shunted and
there were no evident causes of ischemia. At the end of the
anastomosis, the coronary stabilizer was removed, the mammary was
opened to reperfuse the distal LAD, and the heart was almost back to
its initial position. In spite of this, EKG changes persisted and
were accompanied by low-graft flow and then by sudden hypotension.
Because there were no other explanations, we suspected the Xpose to
be the cause of our findings. Immediately after removal of the
suction cup, the situation reverted to normality. This should be
enough to justify our reasonable doubts.
4. Editorial Board Member PB44 writes:
Was the distal LAD visible epicardially and could this have been
anticipated from the angiogram? The LAD usually needs minimal
displacement to perform an anastomosis, thus a stitch usually is
more than adequate. Should one not reserve devices like this to when
they are best needed?
Authors' Response by Giuseppe D'Ancona, MD:
The LAD was visible epicardially.
We agree that exposure of the LAD and other coronary artery branches
can be easily achieved using different strategies.
AUTHOR/ARTICLE INFORMATION
Address corespondence and reprint requests to: Hratch Karamanoukian,
MD, 100 High Street, Buffalo General Hospital, Buffalo, NY, 14203,
Phone: (716) 859−2248, Fax: (716) 859−4697, EMail: lisbon5@yahoo.com
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