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Troncone et al. Vessel Plus 2023;7:14 https://dx.doi.org/10.20517/2574-1209.2023.08 Page 5 of 15

distention is a universally present risk during all forms of extracorporeal circulatory support, including
cardiopulmonary bypass, primarily due to the nature of retrograde flow towards the aortic valve with
[27]
resultant higher afterload on the left ventricle, regardless of the cannulation strategy . In patients with
aortic insufficiency, the above situation is exacerbated by the incompetent valve yielding an elevated risk of
cardiac chamber distention due to regurgitant flow from bypass. Other sources of blood can also contribute
to left ventricular distention, including thebesian and bronchial vein flow, as well as incomplete cardiac
drainage from the venous cannula . All the above is present in the setting of a beating heart that can
[27]
actively eject blood and thus decompress the left ventricle. However, to achieve deep hypothermic
conditions to permit aortic surgery, the heart will experience spontaneous ventricular fibrillation, and all the
above factors that may lead to left ventricular distention will thusly be further aggravated by a now
fibrillating heart that can no longer eject, precipitating myocardial injury. There are numerous surgical
strategies to decompress, or vent, the left ventricle and prevent myocardial injury because of distention:
venting the left side of the heart directly, including pulmonary vein vent placement and left ventricular
apical vent placement; additionally, the left heart can be vented indirectly from the right heart by using
direct pulmonary artery vents, as well as percutaneously placed right sided vents into the pulmonary artery.
While the potential deleterious effects of cardiac distention and non-uniform myocardial blood flow during
hypothermic fibrillation are typically avoided by aortic cross-clamping and administration of cardioplegia,
this typically requires proximal aortic access which is not afforded by the incisions used for conventional
thoracoabdominal aortic surgery. Cardiac distention can be monitored for actively during surgery by using
pulmonary arterial pressures, as well as transesophageal echocardiography, providing information on the
necessity of left ventricular venting . Cardiac distention can be exacerbated by incomplete venous drainage
[28]
of the heart, particularly when femoral venous cannulation is employed. In the absence of direct
visualization of the heart given the surgical exposure from the left chest, transesophageal echocardiography
is crucial in ensuring adequate venous decompression of the right heart, which can be augmented by
addition of vacuum assistance, larger cannulas, addition of other venous drainage cannulas, or cannula re-
positioning. Additionally, some centers advocate administering a systemic dose of potassium chloride, from
40 to 60 mEq, into the CPB circuit to obtain diastolic arrest to maximize myocardial protection in addition
to profound hypothermia .
[29]

Cerebral protection remains one of the critical objectives of safe DTA/TAAA repair, as these procedures
continue to carry a 3%-8% perioperative stroke rate . In assessing the points of the procedure for repair of
[30]
DTA/TAAA that place the patient at risk of suffering neurologic complications, one can divide these into
atheroembolism during the cooling and rewarming phase, and both atheroembolism and hypoperfusion
during the proximal anastomotic phase. Patients with DTAs/TAAAs often have a high burden of
atherosclerotic debris in their entire aorta, and the classic approach of placing patients on partial femoral
cardiopulmonary bypass for cooling exposes the patient to the potential for retrograde atheroembolic debris
propagation into their cerebral vasculature. With the use of femoral arterial cannulation, the establishment
of cardiopulmonary bypass will initially be partial owing to both the incomplete decompression of the right
heart, as well as ongoing left ventricle ejection and native cardiac output. During cooling, prior to
hypothermic fibrillation, there will exist a duration of time with dual circulation, one being native antegrade
cardiac output, the other being femoral arterial pump flow. Depending on the amount of drainage and
subsequent femoral flow, as well as native cardiac output, there will be a varying location in the aorta where
blood mixing will occur. As detailed in peripheral extracorporeal membrane oxygenation [ECMO]
literature, the mixing point will typically be in the proximal aorta or aortic root at any ECMO flow rate in
the presence of severe myocardial dysfunction, whereas this point will migrate more distally into the aortic
arch as function improves . It has been previously shown almost two decades ago that with normal
[31]
myocardial performance, while the mixing point is beyond the aortic root even at maximal ECMO flows, it
is typically within the aortic arch . As such, it becomes clear that even at lower flows, there remains the
[32]