4. Assessment of the ascending aorta and techniques to reduce
aortic manipulation
Recognizing patients with a calcified ascending aorta is essential to
preventing neurologic complications. In the era before routine use of
perioperative imaging, this diagnosis was made by visual inspection,
digital palpation or when the cross-clamp was found to incompletely
occlude the aorta (6). These methods have been largely replaced by TEE
and epiaortic ultrasound (EAU) (52,53). Katz (54) classified aortic
atheroma using intraoperative TEE in five different grades: I= no
disease or minimal intimal thickening, II = extensive intimal
thickening, III = sessile atheroma < 5mm thick, IV =
protruding atheroma ≥ 5mm thick, and V = mobile atheroma in the lumen
(Figure 3). Katz and Ribakove (54,55) demonstrated how careful aortic
assessment by intraoperative TEE guides the operative strategy in terms
of cannulation site, choice of aortic cannula and conduct of CPB. Their
results showed that the degree of aortic atheroma detected by TEE
correlated strongly with perioperative stroke (p=0.001) and that
modifications of surgical technique to avoid atheroma had a favorable
effect on patients with grade V disease (54).
Although intraoperative TEE is superior to manual palpation in detecting
advanced aortic arch atherosclerosis, visualization of the distal
ascending aorta can be suboptimal. To overcome these limitations
epiaortic ultrasound (EAU) is a preferable intraoperative imaging
modality to detect atheroma from the aortic root to the distal ascending
aorta and proximal arch (52,56).
Zingone (57) reported a significant reduction in postoperative
neurologic complications after the routine introduction of EAU.
Pathological findings at EAU guided changes in surgical strategies
including the aortic cannulation and cross-clamp sites, the use of DHCA
and off-pump techniques. Finally, pre-operative computed tomography (CT)
of the chest (with or without contrast) is a valuable tool to fully
characterize the degree of aortic atheromatous changes (2018 ESC/EACTS
Guidelines Class IIa, Level of Evidence C) (30). Lee (58) reported a
significant reduction in the rate of neurologic complications post
elective cardiac procedures after the introduction of a pre-operative
non contrast CT chest in high risk patients (3.04% pre-CT vs 0.73%
post-CT, p=0.05), thanks to ad hoc changes in operative strategy.
Similar results were described by Sandner (59): in 435 matched pairs of
isolated CABG postoperative stroke was significantly lower in the
preoperative CT cohort (0.92% vs 3.22%, p=0.017).
Once severe atheromatous changes of the ascending aorta are detected, a
variety of surgical techniques have been employed to minimize the
neurologic risk:
- aggressive aortic debridement or replacement under DHCA (55,60,61);
- imaging guided alternative cannulation, cross-clamping and proximal
anastomosis sites away from atheroma and use of a modified aortic
clamp (62-63);
- complete avoidance of aortic manipulation (“anaortic” technique).
Early reports by Ribakove (55) described aortic debridement under DHCA
via femoral cannulation in patients with grade V atheroma undergoing
isolated CABG; alternatively debridement and patch repair of the
ascending aorta has been reported by Robicsek (60) and Ott (61) to
perform proximal anastomoses. In a series of 500 patients by Wareing
(62) epiaortic ultrasound detected moderate to severe atheroma of the
ascending aorta in 68 cases. In the majority of patients an alternative
site for cannulation and clamping was sufficient to avoid overt
neurologic complications; otherwise when clamping wasn’t possible
hypothermic fibrillation was employed and very occasionally the
ascending aorta and proximal hemiarch needed replacement under DHCA
(64,65).
A valid alternative to these aggressive strategies is complete avoidance
of any aortic manipulation. Over the course of the last four decades
“no-touch” techniques have evolved from pump-assisted with peripheral
cannulation to totally anaortic off-pump grafting.
Mills and Suma (6,66) were among the first to describe and promote an
“aortic no-touch technique” for management of the severely diseased
ascending aorta during CABG. Although still utilizing distal arch or
peripheral cannulation to accomplish low-flow hypothermic cardiac
fibrillatory arrest, the authors successfully introduced the use of T or
Y grafts off the internal mammary artery (IMA) or the right
gastroepiploic artery to avoid manipulation of the ascending aorta (6).
Variations of the “no-touch technique” were described by Holland (67)
with the use of the innominate or carotid arteries as proximal inflow
for coronary grafts and by Murphy (68) with the idea of a composite left
IMA-saphenous vein extension graft to reach a distal marginal branch.
Finally, Hendel and Thomson (69) implemented “no-touch” strategies
with the adoption of femoral cannulation, fibrillation with venting and
core cooling to 25°C and construction of Y-vein-grafts from the left IMA
or extension grafts from the right IMA.
Avoiding both aortic manipulation and cardiopulmonary bypass adopting
off-pump techniques offer further neurologic protection when
intraoperative TEE shows extensive aortic atheroma (70-72). In a large
series of consecutive isolated CABGs, Grossi et al (70) selectively
performed OPCAB in patients with severe aortic disease detected by
intraoperative TEE with a significant reduction of both in-hospital
mortality (p=0.08) and perioperative stroke (p=0.01). Using propensity
score matching Mishra (71) and Sharony (72) showed significant survival
benefit (p<0.001 and p=0.01 respectively) and postoperative
stroke reduction (p=0.05 and p=0.03 respectively) when off-pumpvs on-pump coronary grafting was performed in patients with
severe aortic atherosclerosis documented by TEE.