Off-Pump Coronary Artery Bypass Grafting
◆ The
ability to perform coronary artery bypass grafting (CABG) competently without
the use of cardiopulmonary bypass is an important skill for all cardiac
surgeons. There are cases in which a safe coronary revascularization procedure
can only be performed as an off-pump procedure. Although off-pump coronary
artery bypass (OPCAB) has a steeper learning curve than on-pump
revascularization, there are clear benefits to it.
◆ After
an initial surge in popularity following its widespread adoption, the frequency
of OPCAB has declined. In 2012, only 17% of all coronary artery bypass surgery
was performed as an off-pump procedure.1 Much of this decline could be
attributed to the results of several cohort studies and clinical trials, which
showed no survival benefit for off-pump surgery.2,3 Despite this,
OPCAB has consistently been shown to decrease blood transfusions and lower the
risks of postoperative bleeding and renal and respiratory failure. OPCAB
performed with the aorta no–touch technique also seems to lower the risk of
postoperative stroke.4
◆ The
results of the initial large trials have also highlighted potential pitfalls of
OPCAB. Results suggested a higher proportion of incomplete revascularization
with off-pump cases and a lower graft patency rate.5,6 This
reinforces the notion that this procedure has a significant learning curve, and
surgeons must ensure that the choice to use an off-pump approach does not
affect the overall quality of the surgical revascularization.
◆ Understanding
when an off-pump approach is not in the patient’s best interest is also
critical; severe ventricular dysfunction, left main disease, ongoing ischemia,
and pulmonary hypertension are associated with poorer outcomes and the need to
convert to on-pump procedures.7
◆ To
perform OPCAB, a keen understanding of cardiac physiology is essential, because
it allows more careful positioning of the heart to visualize the targets
without affecting hemodynamics.
◆ In
this chapter, we describe a systematic, step by step approach to performing
complete myocardial revascularization using an OPCAB technique. We discuss and
illustrate key maneuvers, major pitfalls, and important strategic
considerations for off-pump coronary revascularization. We also highlight the
importance of total arterial revascularization and strategies to decrease
aortic manipulation.
◆ The
benefits of complete revascularization are well established, and surgeons
should bypass all vessels 1.5 mm or larger with stenosis of 70% or more. The
off-pump approach should never jeopardize the ability to perform complete
revascularization. Careful OPCAB planning should have a composite goal of a
safe, complete revascularization without the use of cardio- pulmonary bypass.
◆ Planning
an OPCAB begins at the time of the preoperative assessment. Patients presenting
for isolated CABG should be carefully and thoroughly examined and undergo a
complete diagnostic imaging workup. Particular attention should be paid to
congenital anomalies of the chest, such as pectus excavatum, which may affect
the feasibility of the operation.
◆ A
comprehensive preoperative assessment and diagnostic imaging workup should be
carried out, as with any cardiac operation.
◆ A
noncontrast computed tomography (CT) of the chest to rule out aortic
calcification is recom- mended for patients with advanced age (> 75 years),
chronic renal disease, severe vasculopathy, and a history of heavy smoking.
Ascending aorta calcification might make cross-clamping the aorta inadvisable
or, in the case of a porcelain aorta, impossible.
◆ Aortic
manipulation likely increases the risk of stroke,8-10 and an
off-pump approach allows myocardial revascularization without aortic
manipulation. The aortic no–touch technique should be strongly considered for
patients at increased risk for stroke.
◆ Aortic
calcification is one of the more common reasons to choose OPCAB, but there are
other indications. Patients who decline blood transfusions (e.g., Jehovah’s
Witnesses), and have borderline kidney and respiratory dysfunction likely
benefit from OPCAB.
◆ Just
as some preoperative findings might make OPCAB the preferred choice, other
findings, such as severe left ventricular dysfunction, ongoing ischemia,
pulmonary hypertension, and valvular heart diseases will strongly suggest an
on-pump approach to surgical revascularization. On-pump CABG is the safest
approach in these scenarios.
◆ With
any surgical coronary revascularization, the choice of conduits should be
tailored to the patient. In the case of OPCAB, careful consideration of the
patient’s coronary anatomy, targets to be grafted, and availability of conduits
is required.
◆ The
use of the left internal thoracic artery (LITA) to graft the left anterior
descending (LAD) territory has long been the standard of care for surgical
revascularization. For patients with multivessel coronary artery disease, the
remaining targets may be grafted with either arterial or venous grafts.
◆ For
patients younger than 75 years, the literature has demonstrated a survival
benefit for multiarterial revascularization.11-13 In general,
high-grade stenosis (> 80%) will be the preferred target for either radial
or gastroepiploic arteries due to their susceptibility to competitive flow.14
◆ The
internal thoracic arteries are less prone to competitive flow and can be
considered for stenosis of 60% to 80%.
◆ Venous
grafts will tolerate almost any degree of stenosis, although their suboptimal
durability and patency remain a major drawback, particularly in younger
patients.
◆ A
composite graft of a LITA with a radial artery grafting seems to confer the
same benefits as for a bilateral internal thoracic artery (BITA) and may be
preferable in diabetic patients, who may be at greater risk for sternal wound
complications.15-17
Step 3. Operative Steps
◆ OPCAB
is a team effort. The anesthesia team should be engaged prior to surgery for
better support of the patient’s hemodynamics during induction and conduit
harvesting and at the time of grafting.
◆ The
operating room should be kept warm during these operations, similar to the
practice in pediatric operating rooms. If this is not done, the patient’s
temperature can drop to a dangerous level, where spontaneous, malignant
ventricular arrhythmias, such as ventricular fibrillation and ventricular
tachycardia, could occur.
◆The
availability of pacing wires, atrial and ventricular, can help maintain normal
hemodynamics in patients with heart block or extreme bradycardia.
◆ Both
the surgical and anesthesia teams should carefully monitor hemodynamic changes
during heart positioning. If inadequate hemodynamics are observed, the best
course of action is to return the heart into the pericardium for optimal
functioning. The surgeon should then consult with the anesthesia team while the
heart is allowed to recover. Once hemodynamics stabilizes, an attempt may be
made to carefully reattempt the required positioning.
◆ Off-pump
CABG has been made possible by the development of many specialized tools. Two
of the most important tools are vacuum-based devices that are used to position
the heart or stabilize the segment of coronary artery to be anastomosed. For
the purposes of this text, the former will be referred to as positioning
devices, and the latter will be referred to as stabilization devices. In
addition to adequately placed pericardial sutures, these allow for optimal
exposure of the target vessels.
◆ Enhanced
visualization devices, such as the Blower/Mister (Clear View Misted Blower;
Medtronic, Minneapolis), have also been adopted, and they allow a safe
construction of the anastomosis. We routinely use a Blower/Mister to optimize
visualization. It delivers a jet of CO2 under pressure in the middle
of a jet of a pH-balanced saline solution, resulting in atomization of the
liquid. The resulting stream of mist and CO2, when directed over the
arteriotomy, clears the blood from the anastomosis without resulting in air
embolism because the CO2 is rapidly resorbed. The device does not
prevent blood loss but improves visualization during the anastomosis.
◆ Table
tilt maneuvers can aid with visualization and allow adequate filling of the
heart. If table tilting is not sufficient to correct preload, fluid infusion
should be initiated by anesthesia. The Trendelenburg position and rotating the
operating table toward the surgeon may also optimize lateral wall visualization.
Changes to the operating table should be performed slowly and incrementally to
allow the heart to adapt to different loading conditions.
 |
| Figure 4.1 Inverted-T pericardial incision. |
◆ Most
OPCAB procedures are performed through the standard median sternotomy.
◆ An
extensive inverted-T pericardial incision is usually required. The opening
should reach the cardiac apex on the left side and reach the pericardial
reflection on the right side (Fig. 4.1). This allows heart positioning without
any compressions or deformity.
◆When
harvesting the internal thoracic arteries, we strongly recommend complete
skeletonization. This approach decreases the rate of pleural effusions
postoperatively and decreases the incidence of ischemic injury to the chest
wall and subsequent mediastinitis. This is particularly important during BITA
harvesting.
◆ The
lie of the conducts is critical to avoid kinking and compression by the lungs.
An incision is made on the pericardium to accommodate the internal thoracic
artery (ITA). This pericardial incision starts at the edge and is located at
the level of the base of the left appendage for the LITA and at the level of
the transverse sinus for the right internal thoracic artery (RITA). It is
posteriorly directed toward the phrenic nerve. At 1 cm anterior to the phrenic
nerve, the incision extends 2 cm superiorly and inferiorly, creating a
T-inverted incision. This trench accommodates the in situ ITAs where they enter
the pericardium.
◆ The
radial artery can be harvested endoscopically or using an open approach, and
either pedicled or skeletonized, depending on the surgeon’s preferences. The
gastroepiploic artery should be harvested in a skeletonized manner for better
patency. Veins can be harvested endoscopically or using an open approach. Veins
harvested through an endoscopic approach have shown lower patency rates than
those harvested in an open manner.18,19
◆ There
are several possibilities for graft configuration, and the approach should be
tailored to the number and location of targets to be grafted:
1. In situ grafts do not require aortic
anastomosis, but they offer fewer distal anastomoses, and their length is
constrained.
2. Free grafts are less constrained by length but
require aortic manipulation for the inflow creation.
3.
Composite grafts pair an in situ graft, usually
a LITA, with another conduit branching in a Y or T fashion. Composite grafts
offer greater length and flexibility for grafting. In all cases, the graft
configuration should be planned to take into consideration the availability of
conduits and degree of stenosis in the target vessel.
§
For a full arterial revascularization in a
patient with multivessel coronary artery disease, the plan should almost always
include composite grafts due to the limited length of arterial conduits.
◆ Once
the surgical plan has been made, conduits harvested, and the pericardium
prepared, graft inflows should be considered.
◆ Lateral
pericardial sutures should be placed on each edge of the pericardium. These
should be attached to the drapes using hemostats to keep the lungs away from
the operative field and to expose the aorta for proximal anastomosis.
◆ Side-biting
clamping is safe for aortas with a wall thickness less than 3 mm throughout the
clamp length and the anastomotic site. Plaques that are more than 3 mm in
thickness increase the risk of adverse neurologic events during aortic
manipulaton20-22 (Table 4.1). We recommend
the use of epiaortic scanning to assess the quality of the ascending aorta.22,23
◆ When
manipulation of the ascending aorta is not advisable, the use of proximal
anastomosis sealing devices, such as the Heartstring Proximal Seal System
(Maquet Cardiovascular, Wayne, NJ), is recommended. They allow for minimal
manipulation of a severely diseased aorta.
◆ In
patients for whom this is not an option, and an aortic no–touch technique is
the only possible course of action, composite grafting allows for multiple
anastomoses.
◆ When
the aorta can be manipulated without concern, the standard sequence of events
is as follows: (1) blood pressure is brought below 90 mm Hg; (2) an atraumatic
side-biting clamp is applied; (3) small aortotomies are made with an aortic
punch, followed by direct anastomosis of each of the free grafts to the ascending
aorta; and (4) the partial clamp to fill the graft is released, avoiding a
purse-string effect of the proximal anastomosis as one ties the suture.
◆ If
the surgeon plans to use a composite graft approach, the ideal site of the Y-
or T-graft anastomosis is 1 cm distal the point of entry of the LITA into the
pericardial sac, at the level of the left atrial appendage. This can be
constructed in a Y or a T configuration, depending on which sequential
anastomosis will be constructed first. For high proximal branches, such as a
high diagonal (diagonal-LAD angle ≥ 90 degrees), ramus intermedius, or high
marginal, a T approach is ideal because it allows an optimal lie of conduct
once it is anastomosed in a diamond shape on those vessels (Fig. 4.2A). For
more distal branches of the circumflex and right coronary artery, either a Y or
a T graft will suffice, depending on the length of the available conduit (see
Fig. 4.2B).23
◆ Skillful
heart positioning is vital to maintaining stable hemodynamics while still
allowing visualization of target arteries. The heart should move freely inside
the pericardial sac and should not be squeezed or compressed against taut
pleurae and the sternal borders. This can be achieved by releasing some of the
pericardial sutures that hold the pericardial cradle up, specifically the
right-sided sutures.
◆ The
heart can be elevated using three methods: (1) pericardial stitches (Lima
stitch); (2) the deep stitch–sling technique; and (3) the use of suction-driven
positioning devices.
 |
| Figure 4.2 T and Y configurations of the composite graft. |
◆ Posterior
pericardial stitches (Lima stitches) can be used to enucleate the heart; the
number of stitches and location is a matter of surgeon preference. We place
three sutures to the posterior pericardium. The first suture is placed anterior
to the left superior pulmonary vein (LSPV) and below the phrenic nerve, the
second is anterior to the left inferior pulmonary vein (LIPV) and inferior to
the phrenic nerve, and the third suture is placed on the medial aspect of the
inferior vena cava (IVC; Fig. 4.3). A Rummel tourniquet is then passed through
each of these sutures to avoid injury to the epicardium. If each tourniquet is
sequentially put under tension, the heart will lift incrementally and rotate
medially. This will cause a broad posterior pericardial ridge, which helps
herniate the heart from the pericardial sac, with its apex pointing to the
ceiling. In most cases, these sutures allow for complete elevation of the heart
without hemodynamic consequences.
◆ An
alternative to the three-tourniquet approach described previously is the single
deep suture–sling technique, which is placed in the oblique sinus medial to the
right inferior pulmonary vein.24 In between the two ends of this suture, an
open 4- × 8-inch gauze is passed through the suture loop, and then a Rummel
tourniquet is applied, creating a sling. The deep stitch is put under tension
by pulling it inferiorly at the patient’s midline. This maneuver creates a
pericardial ridge deep in the oblique sinus. The two arms of the 4- × 8-inch
gauze work as a sling that rotates and lifts the heart by giving extra support
to the base of the heart. Different tension can be applied to either arm of the
sling, allowing variable heart exposures (Fig. 4.4).
◆ Suction-driven
heart positioning devices allow for complete enucleation of the heart. The
heart positioner is clipped onto the chest retractor, and the silicone cup is
applied to the epicardium, immobilizing an area of the myocardium approximately
3 × 2 cm in size. Once the cup has been applied, the heart can be slowly
displaced. When in the working position, the device arm is tightened, and it
becomes immobile. The ideal suction applied by these devices is 100 to 250 mm
Hg, and the silicone cup should be placed onto a smooth, fat-free region of the
pericardium to avoid epicardial avulsions and unnecessary bleeding.
◆ The
operator must never pull the suction cup off the epicardial layer while under
negative pressure; this will invariably cause an epicardial avulsion and
bleeding. To release the device, support the heart with one hand, and turn the
suction off by opening the stopcock to air. Then place the heart gently back
into the pericardial sac.
◆ During
heart positioning, particular attention should be given to patients with
enlarged hearts, decreased ventricular function, and pulmonary hypertension
because they are more likely not to tolerate aggressive displacement maneuvers.
A common mistake in OPCAB is to occlude inflow to the right-sided chambers due
to inadvertent tenting and occlusion of both venae cavae.
◆ Optimal
heart positioning can be achieved using more than one method that allows
herniation of the heart with normal hemodynamics. We favor a combination of
suction devices and pericardial stitches, which, when combined, seems to allow
for the maintenance of normal hemodynamics.
◆ In
the following, we describe different maneuvers to expose each wall of the
heart.
 |
Location of the three Lima stitches. (1) Anterior to the LSPV; (2)
anterior to the LIPV; and (3) halfway between the IVC and LIPV.
|
 |
The deep stitch–sling technique.
|
◆ These
are the most straightforward targets to expose, with minimal rotation of the
heart required. This can be easily achieved by applying traction on the first
and second Lima stitches. This pericardial traction brings the LAD and diagonal
branches anteriorly and superiorly (see Video 4.1 for anterior wall exposure).
◆ Alternatively,
one or two lap pads can be placed posteriorly to lift and rotate the heart,
moving the LAD toward the midline. Suction devices are not necessary to expose
these targets.
Lateral Wall
◆ Exposure
of the lateral wall poses a significant challenge during OPCAB. Proper heart
positioning technique is critical to allow optimal visualization without
hemodynamic instability. Many OPCAB surgeons advocate the use of a combination
of pericardial stitches and positioning device.
◆ The
pericardial retention sutures should all be relaxed to allow broad heart
mobilization toward the right side. A right pleural opening might be needed to
accommodate enlarged hearts.
◆ The
pericardial manipulation, in either form described previously, is the
cornerstone of this exposure if one seeks to maintain normal hemodynamics. For
the sling-aided method, the tourniquet is kept under traction at the midline,
attached to the drapes. The right arm of the rolled 4- × 8-inch gauze is put on
traction at the midline, and the left side is pulled slowly toward the
assistant’s side. This maneuver creates a platform to keep the heart chambers aligned
while it lifts the apex and rotates the heart simultaneously, exposing the
lateral wall. Once the lateral wall is exposed, the left arm of the gauze is
tethered on the drapes under traction (Fig. 4.5; see Video 4.2).
◆ For
the pericardial stitches method, the stitches are pulled under maximum
traction, allowing the heart to herniate superiorly through the mediastinum. We
favor the use of either a small lap pad or unfolded gauzes to protect the heart
against injuries when using this technique.
◆ At
the conclusion of either maneuver for lateral wall exposure, the base of the
heart is exposed, permitting the visualization of the atrioventricular (AV)
groove. As the heart is lifted and freely floats within the pericardial sac,
the suction positioning device is used to stabilize the most apical aspect of
the heart and elongate the cardiac chambers. This prevents inflow disturbances,
squeezing of the right ventricle, and bending of the heart. The positioning
device must be clipped on the right side of the chest retractor in the most
cephalad position. This allows ample manipulation of the heart within the
pericardial sac, without disturbing the surgeon’s movements.
◆ The
Trendelenburg position and table rotation toward the operators help optimize
target visualization and cardiac loading conditions. If positioning does not
correct preload, fluid should be initiated by anesthesia.
◆ At
this point, the surgeon should be able to see the targets and safely apply the
coronary stabilization device.
 |
| Sling-aided technique to herniate the heart for lateral wall exposure. |
◆ The
targets of the inferior wall can be separated into two areas: (1) the distal
right coronary artery (RCA); and (2) the posterior descending artery (PDA) and
posterolateral branches (PLB). Each of these requires a fundamentally different
exposure.
◆ For
the distal RCA, all that is required is tilting the table into the
Trendelenburg position and, if the surgeon wishes, use of the suction device to
rotate the free wall of the right ventricle. It should be noted that not all
surgeons use a suction device to graft this territory. If a suction device is
to be used, it should be positioned as cranially as possible on the right side
of the retractor. Cranial retraction is applied until the distal RCA is
optimally visualized and the working position is obtained. Whether or not a
suction device is used, the coronary stabilization device helps exposure. In
addition to stabilization of the segment of the coronary artery to be exposed,
it retracts the inferior wall superiorly, allowing visualization of the distal
RCA.
◆ For
the PDA or PL branches, a combination of table positioning, pericardial
maneuvers, and use of a positioning device may be required. The first step is
to place the patient in the Trendelenburg position. Then, the two arms of the
sling or the pericardial sutures are put under traction, toward the patient’s
left, to herniate the heart without medial rotation. The inferior wall is then
visualized; the positioning device must be applied to gain adequate exposure
and stabilization. The positioning device is applied adjacent to the apex,
never directly on the apex itself. For optimal epicardial suctioning, the
silicone cup fingers should be placed so that the three fingers are on the
anterolateral surface. No finger should be placed on the inferior wall because
it makes suctioning inefficient. Also, attention should be taken to avoid
suctioning on the LAD. Because the sling supports the heart inferiorly, a low
suction setting should (≤ 200 mm Hg) suffice. This maneuver allows for
elevation of the apex and traction of the heart toward the patient’s head (Fig.
4.6).
◆ Coronary
stabilizers have evolved tremendously, from first-generation stabilizers that
used compression as the method of stabilization to the latest generation of
suction-based stabilizers. Their primary goal is to decrease motion at the
anastomotic site.
◆ All
coronary stabilizers have flexible prongs in a fork-shaped configuration. Each
prong has four small silicone cups, connected to suction, that can be adjusted
as necessary. This suction- based stabilization allows OPCAB to be performed
with less aggressive fluid administration, which decreases volume overload and
reduces the need to open the right pleural cavity. Moreover, the malleable
prong allows for different shapes to mold the irregularities of the heart wall.
◆ Once
the heart is in the working position, the coronary stabilizer is applied over
the anastomotic site. The target coronary artery should lie in between the two
prongs. The suction prongs are applied first, and then the mechanical arm of
the stabilizer is tightened. The anastomotic site should not be compressed
because this might lead to a paradoxic increase in motion.
◆ Once
applied, the stabilizer prongs may be spread apart slightly to increase the
epicardial tension over the target. This facilitates coronary dissection with a
no. 15 blade.
◆ The
optimal heart rate during coronary anastomoses is controversial. Although
bradycardia leads to decreased visualization of the lateral wall by increasing
the heart size during diastole, the lower the heart rate, the more stable the
anastomotic site.
◆ Next
we will describe different maneuvers to achieve coronary stabilization on each
wall of the heart.
 |
Inferior wall exposure for the PDA and PL branches. Note the two arms of
the sling toward the left side and the proper position of the silicone cup.
|
s
The stabilizer is positioned on the right side
of the chest retractor, usually midway on the retractor arm. The prongs are
slightly bent inferiorly to create a convex shape. This allows for optimal
adherence of the stabilizer to the epicardium (Figs. 4.7 and 4.8).
◆ The
stabilizer is placed on either side of the chest retractor, per surgeon
preference. The prongs are left straight and facing down to optimize inferior
wall coronary stabilization ig. 4.9).
 |
Figure 4.7 The stabilizer is clipped on the right side. Note the
convex pod shaping for anterior wall vessel stabilization.
Figure 4.8 Right side stabilizer position and convex shape of the
stabilizer prongs to achieve optimal pericardial suctioning for lateral wall stabilization.
Figure 4.9 Coronary stabilizer on the right side (A) and
left side (B). Prongs are left straight and facing down.
|
Distal Right Coronary Artery
s
The stabilizer is usually placed on the left
side. The arm makes a curve superiorly, and the prongs are kept straight and
placed facing leftward (Fig. 4.10).
s
During OPCAB, the surgical team must pay extra
attention to hemodynamics and myocardial ischemia. Maneuvers to avoid
hemodynamic instability have been described previously. Prevention of
myocardial ischemia requires careful planning of the sequence of target vessels
to be revascularized and the use of ischemia prevention strategies, such as
shunts.
◆ The
sequence of revascularization is key to a successful OPCAB. It allows
optimizing blood supply to the myocardium during challenging heart positions.
◆ We
strongly recommend grafting the LAD territory first for a number of reasons.
Exposure of the LAD territory requires the least manipulation of the heart.
Revascularizing the LAD also protects the largest proportion of myocardium from
ischemic damage and improves blood supply to collateral territories in
subsequent repositioning. Finally, the LAD offers some of the most technically
straightforward anastomoses during OPCAB.
◆ It
should be noted, however, that grafting the LAD territory first is not always
the best approach; for example, when the LAD feeds occluded vessels through
collaterals. In this situ- ation, the choice to graft the LAD first may cause
extensive ischemia during the coronary arteriotomy, and it is preferable to
graft the occluded vessels before addressing the LAD.
◆ As
a general rule, we recommend revascularizing the inferior wall vessel (PDA or
PL branch) as the next step. The positioning of the heart required to expose
the inferior wall is less likely to induce hemodynamic instability than the lateral
wall. This anastomosis is also less technically challenging than those required
for more lateral exposures, such as the obtuse marginals (OMs).
◆ After
revascularization of the anterior and inferior walls, there is less risk of
hemodynamic instability when repositioning the heart to expose the lateral
wall. It is of paramount importance, however, to be aware of (and avoid) the
tension that may be applied to the LITA to LAD graft during this positioning
maneuver.
◆ When
constructing composite grafts, the LAD should be grafted first as well.
However, the sequence of anastomoses should be the ramus intermedius (RI), OMs,
PLB, and finally PDA. This approach precludes the need for intermittent
clamping of the graft, allowing immediate and continuous reperfusion of each
target vessel.
 |
Coronary stabilizer positioning for the distal RCA. Note the use of
positioning device to rotate the right ventricular (RV) free wall.
◆ The
use of temporary intracoronary shunts is the most reliable method to prevent
myocardial ischemia. These shunts allow distal perfusion of the coronary artery
while the anastomosis is being constructed. Shunts also improve the ability to
visualize the target and greatly facilitate the construction of anastomoses. We
recommend the use of shunts for every anastomosis.
◆ Shunts
are flexible, tubelike structures that permit the flow of blood when they are
inserted into a coronary artery. Shunts have a short tether attached
asymmetrically that can be used to remove the shunt prior to the completion of
the anastomosis. The asymmetric placement of the tether creates short and long
arms, and the long arm should be introduced into the artery first. Shunts range
in size from 1 to 3 mm. We recommend the use of silicone-based shunts, rather
than plastic, because they are more flexible and less likely to damage the
coronary wall.
◆ Care
should be taken not to oversize the shunt. An oversized shunt can damage the
coronary endothelium. It also can impair visualization and therefore the
construction of the anastomosis.
◆ The
shunt should be sized to allow smooth insertion, with minimal loss of blood
through the anastomosis. Adequate visualization should be maintained at all
times.
◆ Undersizing
is less of an issue with shunts. Visualization may be improved with smaller
shunts, keeping in mind that an element of benign coronary vasoconstriction
will likely occur.
◆ Coronary
arteriotomy usually requires proximal control for adequate visualization of the
anastomotic site after coronary opening. However, for severely stenotic
vessels, proximal control may not be necessary because the amount of blood
inside the vessel does not preclude visualization.
◆There
are different methods to occlude the coronary artery intermittently before the
arteriotomy. We use silicone (Silastic) tapes looped around the coronary artery
for blood flow control before opening and shunting the artery. Each arm of the
silicone tape is passed through one pledget, which works as an outside
occluder. Once the tape is put under tension, the pledget is pushed against and
occludes the coronary artery, with minimal trauma (Fig. 4.11).
◆ The
temporary occlusion of the coronary artery allows for a safe arteriotomy and
placement of a coronary shunt. After the shunt is inserted, the temporary
coronary occlusion should be reversed by the removal of the Silastic tapes or
the sutures.
◆ Distal
RCA grafting usually requires shunting because its occlusion frequently leads
to AV node ischemia and bradycardia. A jumper cable for ventricular pacing is
useful to overcome bradycardia should it occur during the temporary RCA
occlusion and shunting.
◆ Shunt
insertion follows several principles. It is performed using two forceps, with
the long arm inserted first, which allows more shunt mobilization during shunt
bending. The long arm should be inserted proximally in most cases, which
decreases the amount of blood in the anatomic field. After insertion of the
long arm proximally, blood control is achieved by pinching the shunt with one
forceps. Then the other forceps bend the shunt, and the short arm is inserted
distally. Final adjustments may be required (Fig. 4.12; Video 4.3)
 |
Figure 4.11 Coronary occlusion with silicone tape for proximal
blood vessel control.
Figure 4.12 Coronary shunt in place.
|
Step 4. Postoperative Care
◆ Patients
who have an uneventful OPCAB are extubated shortly after arrival to the
intensive care unit. Some centers even extubate patients in the operating room.
Because of less inflam- matory response and less blood loss, patients have a
smoother postoperative course, with less fluid and pressor requirements.
◆ Most
patients are transferred to the cardiac step-down unit the morning after the
surgery.
Step 5. Pearls and Pitfalls
◆The
anesthesia and surgical teams should work in close collaboration to anticipate
hemodynamic changes during heart positioning.
◆ The
pulmonary artery catheter is a useful adjunct to understanding loading
conditions and pulmonary pressures during OPCAB.
◆ The
combination of the deep stitch–sling technique and the use of suction-based
positioning devices allows for less hemodynamic changes during lateral wall
exposure. The sling prevents ventricular underfilling, and the suction-based
heart positioner elongates the heart, reshaping the cardiac chambers, which
improves heart performance.
◆ Common
mistakes during heart positioning and coronary stabilization include the
following:
1. Not
enough opening of the pericardium. The inverted-T pericardiotomy should
extend past the apex of the heart.
2. Taut
pericardium. The lateral pericardial stay sutures that create the initial
pericardial cradle should be taken down before manipulating the heart.
3. Impaired
right ventricular filling during lateral wall exposure. Suction devices and
deep pericardial sutures should be used to avoid distortion of the inflow of
blood to the heart. Do not bend or squeeze the heart. To this effect, the
Trendelenburg position and right lateral rotation are helpful maneuvers.
4. Compressing
the heart with the stabilizer. This is more common when the heart is
underfilled and may paradoxically increase the heart’s mobility. Before
applying any compression with a stabilization device, optimization of heart
filling pressures should be achieved. Do not push down on the stabilizer; this
will avoid impaired filling of the heart and hemodynamic collapse.
◆ The
sequence of the revascularization strategy should aim to decrease myocardial
ischemia and hemodynamic instability. The LAD territory should be grafted first
in most patients.
◆ The
use of intracoronary shunts is the safest approach to avoid ischemia and should
be used routinely in most cases. For severely stenotic and occluded vessels,
shunting may not be necessary. Shunts greatly facilitate the safe completion of
any anastomotic off-pump procedure.
◆ Myocardial
ischemia should be promptly corrected. If ischemia develops after coronary
occlusion, shunting is warranted. When myocardial ischemia secondary to
hemodynamic instability occurs, the heart back should be released into the
pericardial sac. The heart should be allowed to recover, and manipulation can
be reattempted in incremental moves.
◆ The
goal of CABG is to achieve complete revascularization with conduits that have
good long-term patency. OPCAB should not compromise the overall quality of the
revascularization procedure.
◆ Conversion
to an on-pump technique is sometimes needed, and the surgeon should perform it
electively. Emergency conversion to an on-pump procedure leads to increased
morbidity and mortality rates and therefore should be avoided at all costs.
◆ OPCAB
requires meticulous planning and evaluation of targets, distances, and angles.
If the operator feels that completing the operation will be compromised by the
use of a pumpless technique, a strong argument can be made to plan the
procedure, from the beginning, as on-pump CABG.
Keywords : OPCAG, coronary artery bypass surgery off-pump
surgery surgical technique, Operations for Coronary Artery Disease
◆ Bakaeen FG, Shroyer ALW, Gammie JS, et al. Trends in
use of off-pump coronary artery bypass grafting: results from the Society of
Thoracic Surgeons Adult Cardiac Surgery Database. J Thorac Cardiovasc Surg.
2014;148(3):856–864.e1.
◆ Lamy A, Devereaux PJ, Prabhakaran D, et al. Five-year
outcomes after off-pump or on-pump coronary-artery bypass grafting. N Engl J
Med. 2016;375(24):2359–2368.
◆ Diegeler A, Börgermann J, Kappert U, et al. Off-pump
versus on-pump coronary-artery bypass grafting in elderly patients. N Engl J
Med. 2013;368(13):1189–1198.
◆ Pawliszak W, Kowalewski M, Raffa GM, et al.
Cerebrovascular events after no-touch off-pump coronary artery bypass grafting,
conventional side-clamp off-pump coronary artery bypass, and proximal anastomotic
devices: a meta-analysis. J Am Heart Assoc. 2016;5(2).
◆ Hattler B, Messenger JC, Shroyer AL, et al. Off-Pump
coronary artery bypass surgery is associated with worse arterial and saphenous
vein graft patency and less effective revascularization: results from the
Veterans Affairs Randomized On/Off Bypass (ROOBY) trial. Circulation.
2012;125(23):2827–2835.
