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SECTION 7 Technical aspects ofcoronary artery bypass graft surgery338
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ready to begin coronary anastomoses. Concern over gra quality with
endoscopic vein harvest has prompted increased vigilance in an atraumatic harvest technique to ensure optimal conduits for bypass. We
use the same solution as described previously to store the radial artery
conduits from harvest until the time of graing. Vein gras are stored
in buered crystalloid solution (Plasma- Lyte®) at room temperature.
Cardiac positioners and stabilizers have greatly increased the
ability to manipulate the heart with minimal haemodynamic compromise. Although there are multiple alternatives commercially
available, two dierent systems are routinely used in our institutions: the Medtronic Octopus® Tissue Stabilizer and Starsh® or
Urchin® Heart Positioner (Medtronic, Inc., Minneapolis, MN, USA)
and the Acrobat® stabilizer and Xpose® positioner (Getinge, Sweden).
Pericardiotomy
Apical suction devices allow displacement and manipulation of
the heart by creating a vacuum- type seal to the epicardial surface.
ey are generally positioned on the apex to expose the anterior wall
Aer single or bilateral ITA harvest, the systemic heparin dose is
administered (1.5 mg/ kg or 180 U/ kg) and the arterial conduits are
divided distally. Once all conduits are obtained and checked, the
retractor is positioned inferiorly in the sternal incision. is placement reduces traction on the brachial plexus and generally facilitates
mobilization of the heart for positioning. Current retractors used
for beating- heart surgery accommodate attachable devices to aid in
positioning the heart as well as stabilizing the target artery. e pericardium is then incised in an inverted- T conguration, and then incised laterally along the diaphragm to facilitate cardiac displacement.
It is essential to free the le lateral pericardium from the diaphragm
to allow the pericardium to be retracted to displace the heart and
eectively expose the lateral wall of the le ventricle. Nonetheless,
the phrenic nerves must be identied and preserved during pericardial mobilization. Several pericardial traction sutures are placed
to assist with exposure and lateral displacement of the heart; these
stitches are positioned away from the opening margin of the pericardium rather deep in the lateral wall of the pericardium in order
to maximize the exposure and take advantage of the rolling ability of
the heart within the semicircular circumference of the pericardium.
To avoid compression on the right heart during lateral displacement,
the right pericardium can be dissected along the diaphragm or the
right pleural space opened widely to allow the heart to fall into the
right chest during lateral displacement; this manoeuvre is particularly useful in the setting of cardiomegaly. Additionally, one or two
rolled towels placed under the inferior aspect of the right side of the
retractor help to elevate the right side of the sternum to allow the
heart to be displaced towards or into the right chest. An important
traction suture is the deep stitch, which is placed approximately twothirds of the way between the inferior vena cava and le pulmonary
vein at the point where the pericardium reects over the posterior le
atrium. Care should be taken with placement of this suture to avoid
the underlying descending aorta, oesophagus, le lung, and adjacent
inferior pulmonary vein. While passing the deep stitch, the rightsided pericardial traction sutures should be relaxed to prevent compression of caval inow. e deep stitch should be covered with a so
rubber catheter to prevent laceration of the epicardium during retraction. Furthermore, the manual elevation and compression of the
heart required to take this stitch may be poorly tolerated in patients
with marginal haemodynamics or signicant le main coronary artery disease. In that case, graing and reperfusion of the LAD should
be accomplished before placing the deep pericardial traction suture.
(LAD territory) and inferior wall (posterior descending territory)
of the heart and may be placed on the acute margin to expose the
right coronary artery. ey are frequently placed o the apex, especially to the le of the apex, to expose the lateral wall and branches
of the le circumex coronary artery. Because these suction- based
cardiac positioning devices pull the heart in the appropriate direction rather than pushing it, the heart is not compressed, functional
geometry is maintained, and cardiac positioning is usually well tolerated. e coronary stabilizer devices consist of pods of suction
cups within the prongs of the stabilizer that immobilize the target
area by creating a vacuum between the epicardial surface and the
stabilizer arm. is allows for construction of the anastomoses to
take place in a relatively motionless eld, approximately replicating
the operative eld of an arrested heart. e anterior wall vessels
oen require only the coronary stabilizer for adequate exposure.
e stabilizer is positioned along the caudal aspect of the retractor
towards the le, with the retractor arm placed out of the way to
prevent interference during the anastomosis. e location of these
devices on the sternal retractor also requires consideration. For the
lateral and inferior wall vessels, the cardiac positioner is usually
placed on the surgeon’s side at the most cephalad location of the
retractor. e coronary stabilizers can then be placed on either side.
Ageneral rule is to place the stabilizer in the assistant’s way instead
of the surgeon’s in order to prevent these devices from obstructing
the surgeon’s view or interfering with hand positioning during suture placement.
In addition to the positioners and stabilizers, manipulating the
traction sutures can greatly enhance exposure. e purpose of the
‘deep stitch’ is to elevate the heart up and out of the pericardial well.
When this suture is retracted towards the patient’s feet, it elevates
the heart towards the ceiling and points the apex vertically with remarkably little change in haemodynamics. When retracted towards
the patient’s le side, the heart rotates from le to right, exposing
the lateral wall vessels. Variable tension on this stitch will enhance
exposure to both the anterior and lateral wall. During positioning,
the le- sided pericardial sutures should be pulled taut and the rightsided sutures completely relaxed to avoid compression of the right
heart during cardiac displacement. Pericardial sutures on both the
right and le sides are never under tension simultaneously when
displacing the heart to expose coronary targets, as this will generally lead to diminished venous return to the heart and subsequent
hypotension.
Manipulation of the operating table is also important to facili-
Exposure
tate exposure. Placing the patient in the steep Trendelenburg position exposes the inferior wall. Turning the table sharply towards
the right will aid with exposure of the lateral wall targets. Usually,
Optimal target- vessel exposure and three- dimensional stabilization
are essential for successful o- pump bypass surgery.
little manipulation is required for graing the anterior wall vessels.
Occasionally, a warm moist laparotomy pad can be placed adjacent
47 Off-pump coronary artery bypassgrafting 339
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to the ‘deep stitch’ to assist with elevating and rotating the heart out
of the pericardium.
In preparation for each distal anastomosis, a so silastic vessel
loop/ retractor tape mounted on a blunt needle (Retract- O- Tape®,
Quest Medical, Inc., Allen, TX, USA) is placed widely around the
proximal vessel for transient occlusion. For inferior wall vessels, this
suture can be displaced posteriorly and caudally by tying a more posterior pericardial suture loosely around the retractor tape. e pericardial retraction suture serves as a ‘pulley’ that not only enhances
coronary exposure and the surgeon’s view, but also keeps this retraction stitch from interfering with the sutures during the anastomosis.
Similarly, this manoeuvre can be done for some lateral wall targets.
Although a well- trained rst assistant is necessary for providing
an eortless anastomosis, the second assistant, oen the scrub
nurse, also plays a major role in exposure. e eld is kept free of
blood with a humidied carbon dioxide blower (DLP®, Medtronic,
Inc.) and Cell Saver® (Haemonetics Corporation, Braintree, MA,
USA), which are managed by the scrub nurse or second assistant.
e blower is used to keep the eld free of blood, but is also
used to open the target vessel and gra during suture placement
and can play a vital role in visualization during the anastomosis.
Occasionally, an epicardial fat retractor can be used to expose the
coronary target in patients with a large amount of epicardial fat. e
second assistant usually stands to the right of the surgeon, though
better exposure by this assistant standing at the head of the table, to
the surgeon’s le, may be achieved during anastomosis of inferior
wall or some lateral wall targets.
In chronically occluded vessels that have collateral and/ or
retrograde ow, bleeding into the anastomotic eld can be controlled with another retractor tape distally, a MyOcclude® device
(United States Surgical Corporation, Norwalk, CT, USA), or an
intracoronary shunt.
A nal preparatory measure is to place temporary atrial or ventricular pacing cables before positioning the heart if it seems likely
that intraoperative pacing will be useful. As the heart is rotated towards the right, visualization of the right atrium is more dicult,
making placement of temporary clip electrodes on the right atrium
challenging. (It may be necessary to pace the le atrial appendage
in rare circumstances; in this case, it is important to remember how
friable that structure can be.)
the LAD rst without an intracoronary shunt would not only leave
the anterior wall ischaemic, but also disrupt ow to the septum, inferior wall, and right ventricle during the LAD anastomosis. us,
a more prudent approach would be to use a shunt for the LAD or
to gra the posterior descending artery rst, then perform a proximal anastomosis to ensure adequate ow while the proximal LAD
is temporarily occluded for construction of the LAD anastomosis.
Another scenario that may pose problems is a large, moderately
stenotic right coronary artery. Not uncommonly, temporary proximal occlusion of this artery will result in profound bradycardia and
hypotension, due to acute ischaemia of the atrioventricular node. In
these circumstances, the surgeon must be prepared to pre- emptively
use an intracoronary shunt or promptly provide temporary epicardial pacing.
If the LAD and diagonal are generally considered easy to position, stabilize, and gra, an increased degree of diculty applies to
the main right coronary artery, posterior descending artery, proximal and lateral obtuse marginal, and ramus intermedius targets.
e ramus intermedius artery is challenging to expose and stabilize
due to compression on the right ventricular outow tract and pulmonary artery. Not infrequently this is an intramyocardial coronary
target, further increasing the technical diculty of graing. e
introduction of suction devices to position the heart has decreased
the haemodynamic alterations associated with exposing this difcult part of the heart. e apex of the heart is retracted towards
the patient’s right hip, and the table is rotated towards the surgeon.
is area of the heart tends to be tethered by the nearby pericardial reection, reducing its mobility and making exposure dicult.
Additionally, a large le atrial appendage can compromise visualization when graing near the atrioventricular groove.
Rapid recovery of regional myocardial function prior to subsequent occlusion of other target arteries is essential for successful
multivessel o- pump bypass graing. Additional options include a
‘proximals rst’ approach to allow adequate regional perfusion aer
completion of each distal anastomosis. Although concern for myocardial protection during OPCAB stems from the brief periods of
coronary occlusion necessary to visualize distal target vessels, adequate perfusion can be achieved by maintaining adequate systemic
perfusion pressure, selective use of coronary artery shunts, careful
use of traction sutures and stabilizers, and proper sequencing of
gra anastomoses.
Sequence ofgrafting
Intracoronaryshunts
Careful assessment of the preoperative cardiac catheterization is imperative. During on- pump cases, noting the location and number
of vessels requiring bypass usually suces during evaluation of the
catheterization lms. However, when planning for OPCAB, particular attention should be paid to the direction of collateral ow
between coronary vessels, the presence of intramyocardial vessels,
the size of the distal targets, the degree of stenosis, the complexity
of coronary disease, and the number of lateral wall vessels requiring
graing. Careful attention must be paid to the sequence of graing
because regional myocardial perfusion is temporarily interrupted
in the beating heart. As a general rule, the collateralized vessel(s) is
graed rst and the collateralizing vessel graed last. For example,
in patients with an occluded right coronary artery with a posterior
descending artery supplied by collaterals from the LAD, graing
Some experienced OPCAB surgeons use shunts routinely for every
anastomosis and insert the shunt as the rst step in distal graing.
is avoids regional ischaemia during construction of the distal
anastomosis and protects the back wall of the coronary artery from
inadvertent suturing. However, many surgeons nd the shunt obstructs and encumbers the actual suturing of the distal anastomosis
and prefer to use shunts selectively. We too prefer to use shunts selectively and nd they are most useful in graing a large coronary
artery with only moderate stenosis and in graing a coronary artery that provides collateral ow to a large myocardial territory.
ese are two scenarios in which occlusion of the coronary artery during graing may produce critical ischaemia that results in
haemodynamic compromise. Similarly, a large right coronary artery
SECTION 7 Technical aspects ofcoronary artery bypass graft surgery340
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may not tolerate proximal occlusion for o- pump graing without
bradycardia; early insertion of an intracoronary shunt will obviate
this important threat. Careful placement of intracoronary shunts is
important because at least one study demonstrated signicant endothelial injury with the use of intracoronary shunts. It is important
to ‘undersize’ the shunt relative to the target coronary artery, as the
shunt invariably causes spasm in the coronary artery leading to
vessel constriction that creates an adequate seal around the shunt to
provide haemostasis. Moreover, an oversized shunt can be dicult
and/ or traumatic to insert and extract aer completion of the anastomosis. e smaller shunt (typically the 1.75mm shunt) is more
exible, easier to manipulate to improve exposure of the coronary
intima during suturing, and easier to insert and remove.
partial- occluding clamp. In preparation for an aortic clamp, the
systolic blood pressure is lowered to less than 95mmHg. Once the
clamp is applied, aortotomies can be made with a standard aortic
punch device. Proximal anastomoses are then performed using 6- 0
polypropylene sutures with an RB2 needle. Before tying down the
most anterior proximal, the clamp is released and the aorta deaired
through the proximal anastomosis. Aer the suture is tied down, the
vein gras can be deaired with a 25- gauge needle before removing
their bulldog occlusion clamps. Arterial gras are not punctured but
are allowed to bleed backward before clamp removal.
Unlike on- pump coronary artery bypass, OPCAB provides the
opportunity to minimize or completely avoid manipulation of the
aorta. Avoiding partial clamping during proximal anastomoses
can be achieved by performing proximal anastomoses to in situ ar-
Distalanastomosis
terial gras, or using proximal automated anastomotic connectors
or facilitating devices. is may be particularly relevant in patients
with advanced aortic atheromatous disease detected by epiaortic
Aer cardiac positioning and coronary stabilization, the vessel loop/
retractor tape can be placed and the coronary artery dissected. If
there are concerns about haemodynamic stability during regional
ischaemia, the proximal vessel can be test occluded for 3– 5 minutes. During this time the gra can be prepared. is gives the
surgeon some assurance before committing to the anastomosis by
creating an arteriotomy. Aer a similarly brief period of reperfusion, the vessel can be reoccluded and the artery prepared for anastomosis. is form of transient ischaemic preconditioning may
render myocardium more resilient to subsequent more prolonged
ischaemia during suturing. e anastomosis is otherwise performed
in a manner identical to on- pump graing. It is essential to continue
communication with the anaesthesia team so that adequate steps can
be promptly taken if haemodynamic conditions deteriorate. For example, if pulmonary artery pressures begin to rise and mean arterial
pressures begin to fall during a lateral wall anastomosis, several steps
can be taken to avoid cardiovascular collapse. Gently relaxing on the
cardiac positioner or coronary stabilizer can oen improve haemodynamics. Optimizing table positioning, inotropes, vasopressors,
uid boluses, or pacing may also help. However, if it appears that
haemodynamic conditions are deteriorating despite these interventions, then the safe next step is to place an intracoronary shunt, release both the coronary stabilizer and cardiac positioner, return the
heart to the pericardial space, and allow haemodynamics to recover.
At this point, a decision must be made to either convert ‘electively’
to an on- pump procedure or complete the procedure o- pump.
With better preparation (e.g. uids, inotropes, vasopressors, pacing,
shunt), the anastomosis can usually be completed o- pump.
Another option that is frequently used in patients at high risk for
complications of cardiopulmonary bypass is the use of intra- aortic
balloon counterpulsation. An intra- aortic balloon pump can provide valuable mechanical support during cardiac displacement and
positioning to enable safe and controlled completion of a distal anastomosis or entire CABG case that would otherwise require cardiopulmonary bypass.
ultrasonography. Commercially available devices for clampless
proximal anastomoses include the Heartstring® III (Getinge/ Maquet
Cardiovascular LLC, San Jose, CA, USA) or PAS- Port® Proximal
Anastomosis System (Cardica Inc., Redwood City, CA, USA). e
Heartstring® device creates a nearly haemostatic seal with the inner
surface of the ascending aorta that allows the creation of a handsewn
anastomosis with a relatively bloodless eld. Aer completion of the
anastomosis, the device is removed by unwinding the sealing cup
from the aorta before tying down the suture; there is no foreign material other than suture material le in the anastomosis. However,
this device still requires a handsewn anastomosis to be performed
between the gra and the aorta and can be associated with some
blood loss.
e PAS- Port® Proximal Anastomosis System was specically designed to create a consistent anastomosis between a saphenous vein
gra and the aorta during either on- pump or o- pump coronary
bypass surgery. It is a fully integrated, automated system that cuts the
aortotomy and attaches the vein gra to the aorta in seconds, producing consistent, reproducible anastomoses. Compared with earlier
devices, the PAS- Port® system allows the endothelium of the vein
gra to be untouched during the loading and deployment process.
However, there is a small amount of metallic foreign material le
within the gra lumen.
A large network meta- analysis has shown that OPCAB without
aortic manipulation is associated with a strikingly decreased incidence of perioperative death or stroke compared to conventional
on- pump CABG and compared to OPCAB performed with a partial
clamp on the ascending aorta. Similarly, a single- centre institution
reviewed more than 12,000 patients who underwent primary isolated CABG and compared the incidence of stroke in patients with
a complete NAT manipulation technique (inow from the thoracic
arteries) versus patients who underwent proximal anastomosis with
a proximal facilitator device, versus patients where a proximal clamp
on the aorta was adopted. NAT technique and a proximal facilitator
device were associated with a statistically signicant reduction of
perioperative stroke when compared to a proximal side clamp.
Proximalanastomosis
us, a clampless OPCAB approach is our default operation for surgical coronary revascularization; a partial aortic clamp is virtually
never used in our coronary surgical practice. Moreover, whenever
Traditionally, in many institutions, proximal anastomoses
during OPCAB have been performed with the use of an aortic
the pattern of coronary artery disease and the available conduits
allow, we prefer a NAT approach, relying on bilateral ITA inow and
47 Off-pump coronary artery bypassgrafting 341
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construction of composite or sequential all- arterial gra outow to
completely revascularize the ischaemic heart.
Finally, in OPCAB we generally do not leave temporary epicar-
dial atrial and ventricular wires, unless the patient has required
completeness of revascularization and precision of anastomoses not
be compromised; this is achievable in most patients by scrupulous
attention to detail and experienced application of the technical prin-
ciples discussed herein.
pacing during surgery or has low le ventricular ejection fraction.
Any patient who develops new atrial brillation during OPCAB is
promptly cardioverted and receives le atrial appendage occlusion
with a commercially available clip (AtriCure, Cincinnati, OH, USA).
Conclusion
OPCAB avoids morbidity and mortality associated with aortic
manipulation and cardiopulmonary bypass, but is more technically demanding. In the hands of experienced surgeons and teams,
early clinical outcomes are equivalent to on- pump CABG for most
patients and superior for high- risk patients. Indeed, the relative
benet of OPCAB is greatest for those patients who are at greatest
risk of adverse events caused by conventional CABG on cardiopulmonary bypass. It is important to emphasize that OPCAB enables
NAT techniques and minimally invasive approaches that reduce
perioperative morbidity, and may be combined with multiple arterial or all- arterial graing to optimize long- term outcomes. e
authors believe that the current state- of- the- art in surgical coronary
revascularization for most patients is NAT OPCAB with multiple
or all- arterial gras. However, the benets of OPCAB require that
REFERENCES
1. Halkos ME, Puskas JD. Myocardial revascularization without
cardiopulmonary bypass. In:Cohn LH, ed. Cardiac surgery in the
adult. 4th ed. NewYork:McGraw- Hill; 2011, pp. 519– 38.
2. Hangler H, Mueller L, Ruttmann E, Antretter H, Pfaller K. Shunt
or snare:coronary endothelial damage due to hemostatic devices
for beating heart coronary surgery. Ann orac Surg. 2008;86(6):
1873– 7.
3. Guerrieri Wolf L, AbuOmar Y, Choudhary BP, Pigott D, Taggart
DP. Gaseous and solid cerebral microembolization during
proximal aortic anastomoses in o- pump coronary surgery:the
eect of an aortic side- biting clamp and two clampless devices. J
orac Cardiovasc Surg. 2007;133(2):485– 93.
4. Zhao DF, Edelman JJ, Seco M, Bannon PG, Wilson MK, Byrom
MJ, etal. Coronary artery bypass graing with and without
manipulation of the ascending aorta:a network meta- analysis. J
Am Coll Cardiol. 2017;69(8):924– 36.
5. Kempfert J, Opfermann UT, Richter M, Bossert T, Mohr FW,
Gummert JF. Twelve- month patency with the PAS- Port proximal
connector device:a single center prospective randomized trial.
Ann orac Surg. 2008;85(5):1579– 84.
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48
Intraoperative gra assessment
withtransit- time flow measurement
and epicardialultrasound
Teresa M. Kieser and Gabriele Di Giammarco
Introduction
Intraoperative quality assurance for coronary artery bypass gra
surgery (CABG) inuences both longevity and quality of life and is
increasingly becoming a standard of care. e technology of transittime ow measurement (TTFM) in coronary surgery was introduced in 1995 to validate o- pump CABG. Presently, it is used in
approximately 30% of CABG procedures worldwide, but with large
geographic variation. TTFM is a measure of the function of a bypass
and uses several indices which include:mean ow, pulsatility index
(PI), diastolic lling (DF), backward ow (BF), and visual evaluation
of the waveform (Table 48.1). Notably, a high PI has been associated
with adverse clinical outcomes.
Transit- time flowmeasurement
e following questions are oen asked by surgeons:
1. Why should a surgeon routinely check intraoperative gra ow during
CABG when it has rarely been done for 50years? Imperfection or even
failure of a bypass gra is oen not clinically obvious in the operating room and frequently occurs without haemodynamic changes
or changes in the electrocardiogram or wall motion abnormalities
on echocardiography. Intraoperative detection of problematic gras
oers the surgeon an opportunity to improve patient outcomes.
2. When should a surgeon perform intraoperative assessment of by-
pass gras? is can be answered two ways. First, gra assessment should be performed on every bypass gra for all patients.
is ensures discovery of an imperfect gra by providing the surgeon ample experience with many normally functioning gras.
TTFM may be dicult to interpret and even frustrating if only
used infrequently when an imperfect gra is suspected. Second,
each gra should ideally be assessed several times during the
operation at dierent stages of the CABG procedure whether
done o- or on- pump and especially aer any technical adjustments or revisions. At a minimum, TTFM should be performed
prior to and aer administering protamine to reverse systemic
heparin.
3. How should a surgeon perform intraoperative assessment of by-
pass gras? e TTFM probe should be used with acoustic
sterile gel on the double transducers (in the head of the probe)
to allow good contact with the conduit (see Acoustic Coupling
Index (ACI) in Table 48.1). Although technically easier to
measure gra ow proximally, the most accurate location for
gra ow measurement is near the distal anastomosis whenever
possible. Measuring gra ow at dierent locations on a conduit (i.e. near the anastomosis, midway, and near the proximal
inow) can result in quite dierent readings especially for in
situ right internal thoracic artery gras to the right coronary
artery system.
e ACI should be used at 20 MHz; although the waveform looks
‘smoother’ at 5 MHz, the tracing will not be as accurate or representative of actual gra function. One signicant factor that may be
masked by not measuring ow near the distal anastomosis with ACI
20 MHz is the amount of BF, which is reversal of blood ow back
into the gra from the native coronary artery. Measurement at a very
proximal location on the conduit may underestimate BF, which is an
important waveform characteristic useful in determining adequate
gra function. An acceptable amount of BF is less than 3– 4%; more
than this suggests competitive ow or technical problems with the
gra. Understandably, it is not possible to measure gra ow near
all distal anastomoses; a gra to a marginal coronary artery on the
posterior surface of the heart may be inaccessible when the heart is
in an orthotopic position. However, in case of o- pump procedures,
the ow may be measured with the stabilizer still in site aer the
completion of each anastomosis, while in case of on- pump procedures, ow can be checked aer completion of the anastomosis for in
situ gras.
SECTION 7 Technical aspects ofcoronary artery bypass graft surgery344
artery. BF should be <3–4%.
mL/min
–20
mL/mi
Q1
–20
mL/mi
(a)
(b)
Q1
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Table48.1 TTFM parameters and acceptable graft values
TTFM parameter Acceptable graft values
Flow >20 mL/ min
Pulsatility index (PI) <3.0 (ideal)
Diastolic filling (DF) 60– 70% (left- sided vessels)
Waveform:
Flow=45 mL/ min
PI=2.5
DF=80%
BF (backward flow)=1%
Green ‘100%’=‘Acoustic Coupling Index’ (ACI) and is best when >90%. The ACI
is a measure of the contact of the probe with the conduit. ‘Green’ and ‘yellow’
colours are acceptable. ‘Orange’ and ‘red’ are not; this can be corrected by
adding more gel to the probe
<5.0 (acceptable)
50% (right- sided vessels)
mL/min
45
150
100
50
0
Q1
3 mm LIMA-LAD
ACI
PI 2.5
80%DF
Backward flow: this is flow
reversing up the conduit, not flow
backward in the native coronary
e probe is held in a relaxed manner perpendicular to the conduit, waiting until the red line progressing through the wave form
from le to right (which is the mean gra ow (MGF)) is horizontal.
is takes approximately 7 seconds because ow, PI, and DF are calculated by measuring the dierence of the maximum and minimum
n
80
60
40
20
0
–20
(c)
n
80
60
40
20
3 mm
mL/min
4
RA–M2
mL/min
17
PI 21.7
22%DF
PI 1.4
ow divided by the mean cardiac ow calculated across ve cardiac
cycles. e slower the heart rate, the longer this takes.
Basic waveforms with which to become familiar include that of
gra occlusion (Fig. 48.1a), post- gra revision resolution of ischaemia, (Fig. 48.1b), and competitive ow (Fig. 48.1c). Surgeons
mL/min
Q1
–20
mL/min
80
60
40
20
0
80
60
40
20
3 mm
24
34
mL/min
mL/min
PI 1.3
DF
PI 0.8
66%RA–OM post-protamine
0
3 mm
Fig.48.1 (a) Occluded radial artery (RA) to second marginal (M2) graft due to twist at heel of the anastomosis. (b)Resolution of twist at the heel of
a RA graft to a marginal artery (OM) with augmented flow and low PI due to vasodilatation from ischaemia due to suboptimal graft. (c)Example of
competitive flow:image on the left shows an acceptable graft with flow of 17 mL/ min and PI of 1.4. However, with snaring of the proximal native LAD,
there is an augmented flow to 34 mL/ min and reduction of PI to 0.8 (right image). The level of stenosis in the LAD artery was 70%. LITA, left internal
thoracic artery.
DF
0
79%LITA–LAD
3 mm
DFQ173%LITA–LAD w/proximal snare
48 Intraoperative graft assessment withtransit-time flow measurement and epicardialultrasound 345
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Bypass graft
Narrowing at toe
Stenosis
of anastomosis
Blood flow
Fig.48.2 False- negative transit- time flow measurement (TTFM).
are oen reluctant to revise a gra when they feel that they ‘saw
every stitch’ and worry that they will make the situation worse.
However the measurement of a very low ow, especially in combination with a high PI, is a reliable indication of an imperfect gra and
should prompt a careful examination of the gra to detect a technical problem such as a kink in the gra, a defect in the conduit,
or a problem with the distal (or proximal) anastomosis. Very poor
run- o in a severely diseased coronary vessel may result in disappointing ow and high PI in the presence of a gra that has no technical problem, but this is a diagnosis of exclusion.
False negatives (when TTFM analysis suggests a good gra but the
gra is technically imperfect) are the ‘Achilles heel’ of using TTFM.
is usually occurs when the toe of an anastomosis is obstructed
but the heel is not (or vice versa). is most oen occurs in the le
internal thoracic artery to the le anterior descending artery (LAD)
because the retrograde ow in the LAD may have as signicant a
territory as the anterograde ow. e more proximal the stenosis
in the native LAD, the more important the retrograde ow will be
because of the rich septal perforator blood supply between the proximal stenosis and the anastomosis midway on the LAD (Fig. 48.2).
Other interesting ndings that can be examined with TTFM include increased arterial gra ow at reoperation (e.g. for postoperative bleeding), the dierence in the ow and PI when the intra- aortic
balloon pump is on or o, or the dierence in ow and PI when atrial
pacing is used compared with ventricular pacing. With constant use
a surgeon will recognize that TTFM measurement aer any repair
stitch is mandatory:a repair stitch may turn an excellent gra into a
suboptimal one. ere are other non- conventional uses, such as to
measure the ow of the native right coronary artery aer aortic valve
replacement because of a precariously low location of the native
right coronary artery near the aortic annulus. Aprotruding knuckle
of the right coronary artery on the epicardial surface lends itself to
be encircled with the TTFM probe to conrm ow.
It is also very important to remember that in animal studies, internal thoracic artery gra ow was only marginally decreased by a
75% mean luminal stenosis. is demonstrates the importance of
the second modality of intraoperative gra assessment— epicardial
ultrasound (ECUS).
equally important as TTFM if not more. is provides important information in addition to the gra function discerned by TTFM. One
of the most useful aspects of ECUS is that it greatly reduces unnecessary gra revision, which can be troublesome if TTFM is used alone.
First studies of ECUS began in 1985, correlating intraoperative
ECUS imaging verication of coronary disease with preoperative
angiography. Hiratzka etal. also reported the use of intraoperative
high- frequency ECUS to locate intramyocardial arteries. In 2002,
Haaverstad and colleagues reported the use of a designed sterilizable probe with epicardial colour Doppler ultrasound to ‘visualize’
coronary anastomoses. e commercial products, the VeriQC®
and subsequent MiraQ® were rst introduced by Medistim (Oslo,
Norway) in 2009 and 2014.
e use and interpretation of ECUS is technically more challenging than TTFM use. For the distal anastomosis, it is best performed
during the cross- clamp period for on- pump CABG and with the
cardiac positioner and coronary stabilizer in place for o- pump
CABG. e probe is placed obliquely overlying the anastomosis in
the long axis of the gra, using colour Doppler to rst locate the
gra. For best visualization of the actual anastomosis, colour ow
mapping may be removed leaving just the two- dimensional echo of
the walls of the conduit, anastomotic site, and the native coronary
artery. Several planes can be used, much the same way coronary
angiograms show multiple views to verify the presence/absence of
stenosis in any plane. is is not as easily done as in coronary angiography, but at the very least, two views should be recorded:longitudinal and a cross- section view of the actual anastomosis.
ere are at least two ECUS probes that may be used for
ECUS:the ECUS probe of the Medistim VeriQC® and MiraQ® devices and the L15- 7io® ECUS probe (Philips, Bothwell, WA, USA)
for the iE33® Philips transoesophageal echocardiography machine
already commonly used in cardiac surgery. Both have linear array
128- element transducers operating at frequencies of 8.0–18.0 MHz
for the Medistim probe and 7.0– 15.0 MHz for the Philips probe.
Both also have a two- dimensional- B mode, colour ow mapping,
pulsed wave Doppler, and colour Doppler. e main dierences are
that the Medistim probe is designed and approved for STERRAD®
sterilization 100 times, so it can be placed directly on the heart; its
Coronary artery
cord conguration is straight in line with the probe and is easier
Epicardialultrasound
to use on gras on the posterior heart surface. e Philips probe
must be used in a sterile sleeve and is hockey- stick shaped. Placing
ample sterile gel in the sterile sleeve and tying the sleeve around the
ECUS completes the intraoperative assessment of bypass gras by
clearly identifying the anatomy of the anastomosis ECUS and is
neck of the hockey stick allows for easier and more accurate placement of the transducer on the anastomosis and avoids air bubbles
SECTION 7 Technical aspects ofcoronary artery bypass graft surgery346
https://t.me/medicina_free
(a)
with high PI were patent and 10/ 16 gras with both high PI and
low ow were also open. erefore, strictly following only these cuto parameters can lead to unnecessary gra revision in many cases.
Niclauss etal. in 2017, in a literature review of nine TTFM studies
with postoperative imaging, found that a PI greater than 5 seemed
to have predictive value to exclude false positives, that higher mean
gra ow for saphenous vein gras (≥30– 40 mL/ min) than internal
thoracic artery gras (≥20 mL/ min) is associated with improved
long- term outcome, and that besides the three main parameters of
ow, PI, and DF, detailed analysis of the ow curve is important,
including the amount of BF, and should be part of TTFM analysis.
ey also stated that TTFM alone may be insucient to detect gra
failure.
ree consecutive sets of the European Society of Cardiology/
European Association for Cardio- oracic Surgery guidelines on
(b)
myocardial revascularization (2010, 2014, and 2018)– have included intraoperative gra evaluation with TTFM. e 2010 guidelines listed TTFM as a classIrecommendation, level of evidence
C with cut- o parameters as follows:‘Flow <20 mL/ min, and PI
>5 predict technically inadequate gras mandating gra revision before leaving the operating theatre’. In the 2014 guidelines,
the recommendation was changed to IIa C and in the recent 2018
guidelines, the recommendation has become IIa B.ese changes
in recommendation reect the increased interest worldwide for
intraoperative gra evaluation and studies questioning the absolute
eectiveness of TTFM.
e key to decision- making in the setting of equivocal TTFM
measurements is the use of ECUS. In 2014, Di Giammarco etal.
Fig.48.3 Examples of images using (a)a Medistim ECUS probe and
(b)a Philips L15- 7io® ECUS probe.
rst reported simultaneous use of TTFM and ECUS to evaluate the
addition of ECUS to the assessment of gra patency. In 333 patients with 717 gras from 2009 to 2012, the combined routine use of
both TTFM and ECUS provided a positive predictive value of 100%
that degrade image quality. Fig. 48.3a and Fig. 48.3b are examples of
ECUS images with these two probes.
ere are multiple possible applications for intraoperative ECUS
during coronary bypass surgery. ECUS can be especially helpful to
locate native coronary arteries in fatty hearts, during reoperative
surgery, or in the setting of intramyocardial vessels. Native coronary
arteries can be examined for ideal placement of the anastomosis and
surgical conduits may be analysed for damage or dissection (especially fragile internal thoracic arteries). Importantly, the ECUS probe
is ideally suited to examine the ascending aorta to detect intimal
thickening and endoluminal atherosclerotic debris (that is usually
not palpable) which may cause embolism with any aortic manipulation. is allows safe customization of surgical strategy to reduce the
risk of intraoperative/ perioperative stroke. ECUS can also be used to
interrogate the ascending aorta aer decannulation to detect or rule
out iatrogenic dissection.
and a negative predictive value of 99%, compared with TTFM alone
of 10% and 98% respectively. irty- nine gras were found to be
malfunctioning with TTFM, but in only two of these ECUS conrmed the failed gras. erefore, use of ECUS prevented 37 unnecessary gra revisions, a frequent concern regarding TTFM, that
can be almost completely avoided with ECUS imaging by its rening
and informing decision- making. Knowledge of the anatomy of the
anastomosis supersedes the TTFM functional assessment. TTFM
alone is not always accurate because numerous parameters combine
to aect ow in the coronary arterial system including the size of
conduit and native coronary artery, presence/ absence of distal or
diuse disease, spasm of the conduit or coronary bed, and diering
levels of stenosis leading to diering levels of competitive ow. Our
practice is to use TTFM and ECUS routinely in combination to
(1)completely evaluate a gra intraoperatively and (2)to avoid ambiguity of assessment, frustration of the surgeon, and unnecessary
gra revision.
Interpretation ofTTFM data and guideline
recommendations
Fig. 48.4 is an algorithm showing how to troubleshoot if the PI
is greater than 5.Use of TTFM and ECUS is especially useful for
training cardiac surgeons.
In addition, it is possible to further test the ow in conduits
e cut- o parameters of a PI greater than 3 or even 5 and mean
gra ows of less than 15– 20 mL/ min are not absolute. Jokinen etal.
in 2011, using cut- o values of a mean ow less than 15 mL/ min
and a PI greater than 3.0 and early postoperative angiography (up
to 6months) of 204 gras (75 patients), found that the 49/ 70 gras
that show suboptimal TTFM parameters (borderline mean gra
ow, high PI, and a BF >>3%) by using an intravenous bolus of
dobutamine (20 micrograms/ kg body weight) according to the ow
chart reported by Di Giammarco and colleagues. e normalization of parameters within the cut- o values conrms satisfactory
48 Intraoperative graft assessment withtransit-time flow measurement and epicardialultrasound 347
PULSATILITY INDEX (PI)
Good flow
pattern,
Little/no
backwar
fl
diastolic flo
Check proximal,
accuracy
https://t.me/medicina_free
PI<3
d
ow, mostly
Good graft
Leave alone
Use ECUS to
be sure
PI≤5
PI 3–5
w
Due to:
1) Competitive
Flow
2) Diffuse
disease of
coronary
artery
3) Poor graft
1) Snare test
2) Knowledge of
vessel grafted
3) If not either of
above, consider
revision, or use
ECUS
PI >5 PI>5
High
flow≥15
Likely
competitive
flow
Test with snare
on native
coronary
artery
proximal to
anastomosis
PI >5
Low flow<15
Normal DF (45–80)
Either poor
graft or
competitive
flow
Do snare test
to
differentiate,
or use ECUS
PI >5
Low
flow<15
Low DF <25
Likely bad
graft +/–
backward
flow
distal and
conduit, redo
graft, fix
something if
possible,
Use ECUS to
define with
Fig.48.4 Diagram of a troubleshooting algorithm if the PI is greater than 5.
gra function and helps to identify issues of possible competitive
ow, especially in the setting of Y- conduits.
Once the TTFM/ ECUS technique is mastered, it becomes an
essential ‘safety net’. TTFM and ECUS identify failed gras that
were otherwise undetectable. As emphasized previously, most
failed gras do not manifest themselves immediately in the operating room; rather, they become clinically apparent hours or days
later. e combined use of TTFM and ECUS has a strong positive and negative predictive value in identifying these infrequent
gra problems and allowing their correction before they cause adverse clinical events. Historically, CABG has been the only major
vascular surgical procedure that has not entailed a routine ‘completion angiogram’ to document adequacy of revascularization.
TTFM and ECUS provide a convenient way to routinely document
the quality of CABG gras.
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