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The “frozen elephant trunk” (FET) technique was developed by Karck et al., who modified Borst's ET technique by using a stent graft to secure the distal ET section. Working in collaboration with Vascutek Terumo, we in Hannover Medical School introduced the 4-branched hybrid FET graft In 2012 (Thoraflex Hybrid). However, the results after open aortic arch repair mainly depend on perioperative management and patient factors. Over the years, peri-operative management and operative techniques have evolved greatly contributing to better results. We describe our surgical technique of implantation of this hybrid graft in acute aortic dissection Stanford type A, DeBakey type I (AADA DeBakey I) patients.
The 4-branched Frozen Elephant Trunk Graft facilitates total aortic arch replacement. Continuous myocardial perfusion helps to decreases the myocardial ischemia time during complex aortic arch surgery, thereby allowing arch replacement in elderly and high-risk patients.
The original Elephant Trunk technique was first described by Borst et al. in 1983, in order to facilitate the second stage operation after initial total aortic arch replacement in patients with complex pathologies of the thoracic aorta.
Initially, the FET was used to treat patient having complex thoracic aneurysms with a distal so- called “landing zone” so that these patients could be treated in “single stage”. Over time, indications have expanded and the FET procedure has been used to treat acute aortic type A dissection as well. Nevertheless, performing total aortic arch replacement with FET in acute aortic dissection patients is controversial.
Nevertheless, it may be helpful in the following conditions: (1) In patients with distal malperfusion, FET has the potential to expand the true lumen in the descending aorta, thus restoring visceral/lower body perfusion.
(2) In patients with rupture of the distal aortic arch or the proximal descending aorta, FET may be the only way to save the patient. (3) FET implantation in AADA DeBakey I patients reduces the risk of bleeding from the false lumen in the distal aortic arch and proximal descending aorta. (4) FET implantation in AADA DeBakey I reduces the risk of future surgical interventions of the aortic arch and proximal descending aorta and facilitates (as the classical ET) a second stage procedure, either as a endovascular or open procedure. A FET may be a superior landing zone for secondary endovascular procedures.
which was and still is the only commercially available 4-branched FET graft in Europe and the U.S. At our institution, the Thoraflex Hybrid has become the preferred FET graft to treat complex thoracic aneurysms and aortic dissections. Over the years, our results have proven that total aortic arch replacements with 4 branched FET can be performed with excellent results in patients with AADA DeBakey I.
In this manuscript, we present our technique of total aortic arch replacement with the FET technique.
Main Section (Surgical Technique)
Direct aortic cannulation using the Seldinger technique under transesophageal echocardiography (TEE) guidance is our standard method for arterial access, even in acute dissection cases (Fig. 1B). If the true lumen cannot be cannulated safely via direct needle placement for the Seldinger technique (e.g. in complete circular aortic dissection), “direct open cannulation” after venous drainage and transection of the aorta at the level of the ascending aorta is our preferred option (Fig. 1C).
For additional cerebral protection, temporary retrograde cerebral flush perfusion (flush RCP) via the superior vena cava is an option to reduce the risk for cerebral embolization during cannulation and surgical dissection of the aortic arch (see also below). Axillary or femoral cannulation is only used in selected patients in our institution (eg, for peripheral ischemia or a circular thrombosed false lumen of the ascending aorta). The left heart is vented through the right superior pulmonary vein. The surgical field is flooded with CO2.
In AADA DeBakey I cases the patient is cooled down to a core temperature of 20-22°C. Lower temperatures may be used in malperfusion cases.
If the aortic valve is pathological, we perform Bentall operation. In case of an intact aortic valve and normal-sized aortic root, we prefer glue-repair with insertion of a Dacron strip to stabilize the aortic wall.
Both the cardiac perfusion pressure and coronary flow are controlled (target pressure: 60-80 mm Hg, target flow: 150-250 mL/min). Flow can vary significantly depending on cardiac size, pathologies and perfusion temperature. Cardiac perfusion is achieved via the cardioplegia pump. Cardiac perfusion temperature is initially kept as low as the core temperature (20-22°C). After circulatory arrest, both cardiac perfusion and core temperature are gradually increased. Typically, cardiac perfusion pressures are not increased over 80 mm Hg. During cardiac perfusion, the left ventricle is thoroughly vented through the right upper pulmonary vein. After initiating the noncardioplegic, continuous cardiac blood perfusion the aortic arch is then replaced on an empty “beating heart.”
In this way, the myocardial ischemia time is reduced, as well as the re-perfusion time and consequently, the total operation time. After rewarming the patient can by directly weaned from ECC. The technique results in a reduced cardiac morbidity and mortality.
In order to do this, we selectively cannulate the superior vana cava with a 90° steal cannula. The cannula is connected to the arterial line with a Y-connector to allow for rapid transition between retrograde and antegrade perfusion. The aortic arch procedure starts with clamping of the arterial line to the aortic arch. Thereby lower body HCA is initiated and the aorta is opened. With an open aortic arch the SVC is clamped by placing a straight vascular clamp between the retrograde perfusion cannula and the right atrium. Retrograde cerebral flush perfusion with cold blood (20°C) is initiated. The perfusion pressure is monitored via the central venous line and kept at ≤ 40 mm Hg. Target flow is 500-1000 cc/min and retrograde flow from the supraaortic vessels is confirmed. Cold blood cardioplegia (Buckberg) is our preferred method of myocardial protection, and is given every 30 minutes.
Retrograde cerebral perfusion helps in retrogradely flushing out possible debris from the aortic dissection itself, aortic cannulation or aortic manipulation. During open surgical preparation of the non-clamped supraaortic vessels flush RCP prevents air embolization. The surgical aortic dissection for implantation of the 4 branched FET prosthesis includes isolation of the supraaortic vessels as buttons and establishment of a distal aortic anastomosis site in zone 2 (proximal to the left subclavian artery [LSA]). After isolation of the innominate artery (IA) and the left common carotid artery (LCCA) catheters (Medtronic, USA; DPL retro-cardioplegia catheters with pressure monitoring line) are placed under direct vision into boththe IA and LCCA. After stopping the flush RCP and declamping the SVC, selective bilateral antegrade cerebral perfusion (SACP) is started at a rate of approximately 10 mL/kg/min. SACP perfusion pressure is kept at ≤65 mmHg at 20°C.
The left subclavian artery (LSA) is clamped or occluded with a Fogarty catheter (Baxter, USA).
The aorta is transected between the LCCA and the LSA (zone 2).
This novel hybrid graft has the following novel features:
Consists of unstented Dacron & a stented parts(polyester and nitinol stent)
Un-stented part has 4 branches (3 for the supra-aortic arteries and one for the arterial cannulation),
The length of the stented part: 10 & 15 cms.
The proximal unstented & distal stented parts are available in different sizes
a sewing collar for the suturing of distal anastomosis.
Radio-opaque markers in the stented part.
Fully Sealed Device
We measure the total diameter of the Descending aorta at the site of “Landing Zone” of the distal end of the stent. We use the FET hybrid graft with 10 cm length.
After the distal anastomosis is completed, the perfusion to the lower part of the body is restarted via the fourth branch of the graft.
The venous and arterial cannulae are removed and the fourth branch of the arch graft used for ECC is ligated.
Short Closing Section
Performing a total aortic arch replacement with FET in acute aortic dissection patients was and remains controversial.
Nevertheless, the FET procedure may be helpful in the following situations:
In patients with distal malperfusion, FET can expand the true lumen in the descending aorta, thereby restoring visceral/lower body perfusion. This hypothesis has also been addressed in the position paper of the EACTS published in 2015.
Although true lumen expansion can sometimes be observed after proximal aortic arch replacement or conventional total aortic arch replacement as well, we believe that the FET's stent graft in the descending aorta has higher capacity to stabilize the true lumen of the dissected aorta.
In patients with rupture of the distal aortic arch or the proximal descending aorta, FET may be the most expeditious way to save the patient. Bilateral anterior clamshell thoracotomy is technically another approach.
Rupture of the aortic arch may be treated with conventional total aortic arch replacement, but rupture of the proximal descending aorta cannot be repaired through a median sternotomy. Repositioning the patient to perform a lateral thoracotomy to reach the descending aorta is not an option in this emergent setting, thus, the FET may be the only way save the patient.
FET implantation in AADA DeBakey I patients reduces the risk of bleeding from the false lumen in the distal aortic arch and proximal descending aorta. The dissected aorta remains fragile and continous oozing from the distal aorta can often be observed. By reexpanding the true lumen and by stabilizing the dissected walls of the aorta, the FET has the potential to reduce the risk of bleeding.
FET implantation in AADA DeBakey I patients reduces the risk of future surgical interventions of the aortiac arch and proximal descending aorta and facilitates (as the classical ET) a second stage procedure, either as a endovascular or open procedure. A FET may be a superior landing zone for secondary endovascular procedures.
Although endovascular expansion after classical ET is possible, locating the ET endovascularly is technically more challenging than inserting a wire into a FET. Our group has shown that a FET can facilitate distal second stage repair.
A branched hybrid graft allows for selective anastomosis of the supra-aortic vessels, which might result in improved hemostasis. Selective anastomosis of the supraaortic vessels allows improved localization of bleeding than the island technique, where bleeding from the distal portion can be surgically hard to stop.
Over the years, our results have proven that total aortic arch replacements with 4 branched FET can be performed with excellent results in patients with AADA DeBakey I.
Patients that gain sustainable benefits from FET implantation in AADA DeBakey I should be carefully selected. Meticulous improvement of the surgical management, such as cannulation strategy, zone 2 anastomosis and organ protection methods (eg, flush RCP and cardiac perfusion) have significantly reduced morbidity and mortality of this complex procedure. This increases availability in more desperate situations such as distal malperfusion syndrome (Figs. 2-11).
The frozen elephant trunk technique: A new treatment for thoracic aortic aneurysms.
In acute type A aortic dissection (aTAAD), total arch replacement (TAR) with frozen elephant trunk (FET) is controversial outside of the indications of tear involvement or significant aneurysm of the arch. While some single-center studies have suggested that TAR imposes no additional mortality to aTAAD repair,1-2 data from clinical registries,3 meta-analyses4,5, and the Society of Thoracic Surgeons (STS) database6 have shown significantly higher mortality rates with TAR than with hemiarch repair.