Overview
Definition:
The chimney (or periscope) and snorkel techniques are adjunctive endovascular strategies used in EVAR for juxtarenal, suprarenal, or thoracoabdominal aortic aneurysms (TAAAs) when standard fenestrated or branched EVAR (F/BEVAR) is not feasible or anatomically challenging
These techniques involve deploying a bridging stent-graft from the main aortic stent-graft into a target visceral or renal artery, thereby maintaining flow to these vital branches
The snorkel technique involves a single bridging stent, whereas the chimney technique uses multiple bridging stents to revascularize several branch vessels
They are often employed to treat complex aortic pathologies involving the visceral and renal arteries, which are compromised by the aneurysm sac
These techniques aim to extend the sealing zone of the EVAR device proximally or distally, or to preserve visceral/renal artery patency when direct cannulation for F/BEVAR is not possible due to tortuosity, short landing zones, or unfavorable anatomy.
Epidemiology:
Complex aortic aneurysms requiring chimney or snorkel techniques are less common than infrarenal AAA
However, the prevalence of TAAAs and juxtarenal aneurysms is significant, and these techniques are increasingly utilized as the understanding and application of endovascular repair evolve
Patient demographics typically include older individuals with comorbidities, making open surgical repair a higher-risk option
Incidence data specific to chimney/snorkel use is still evolving, but they represent a growing proportion of complex EVAR cases
Indications are driven by anatomical limitations for standard F/BEVAR, with studies suggesting their use in 10-20% of complex EVAR cases, depending on institutional expertise and patient selection criteria.
Clinical Significance:
These techniques are critically important for expanding the applicability of minimally invasive EVAR to complex aortic pathologies that were previously managed with open surgery
They offer a less morbid alternative for high-risk patients who may not tolerate extensive abdominal or thoracoabdominal repairs
Successful application can significantly reduce operative morbidity and mortality compared to open surgery, improving patient outcomes and quality of life
Mastery of these techniques is essential for vascular surgeons and interventional radiologists involved in complex aortic endovascular interventions, directly impacting patient management and outcomes in challenging anatomical scenarios
Their appropriate selection and execution are vital for preventing complications such as endoleaks and branch vessel occlusion.
Indications
Indications For Use:
Primary indications include juxtarenal, suprarenal, or thoracoabdominal aortic aneurysms (TAAA) where a sufficient proximal or distal sealing zone for standard EVAR is absent
They are also indicated when the visceral or renal arteries originate from the aneurysm sac itself, precluding standard F/BEVAR due to anatomical constraints like severe tortuosity, short neck length, or unfavorable angles
Patients who are poor candidates for open surgical repair due to advanced age or significant comorbidities are prime candidates for these advanced endovascular techniques
Complex aortic arch pathologies may also benefit when visceral branch involvement is present.
Contraindications:
Absolute contraindications are similar to standard EVAR, including active infection, uncorrectable coagulopathy, and limited life expectancy
Relative contraindications include severely tortuous or calcified access vessels, severe iliac or femoral artery disease precluding device delivery, and extensive mural thrombus in the target branch arteries that could embolize
A lack of a suitable landing zone for the main body of the EVAR device, even with chimney/snorkel grafts, can be a contraindication
Inadequate infrarenal neck length for an infrarenal device if the aneurysm extends below the renal arteries, or if proximal sealing is not achievable
Significant hemodynamic instability can also be a contraindication for elective complex procedures.
Anatomical Considerations:
Key anatomical considerations include the length and morphology of the infrarenal, suprarenal, and visceral neck segments
The angle of origin of the target visceral and renal arteries from the aorta is crucial
sharp angles can make cannulation and stenting more challenging
The diameter and patency of the target branch arteries (renal arteries, SMA, celiac artery) are important for successful stent deployment and long-term patency
The overall diameter and tortuosity of the aorta and iliofemoral access vessels also play a significant role in device selection and deliverability.
Procedure Technique
Snorkel Technique:
In the snorkel technique, a single bridging stent-graft is deployed through a fenestration or scallop in the main EVAR device, extending from the aortic lumen into a target visceral or renal artery
This typically involves pre-cannulating the target vessel, deploying a guidewire, and then advancing a self-expanding stent-graft through the main EVAR device into the desired branch
The proximal end of the bridging stent-graft sits within the main EVAR stent-graft, and the distal end is deployed within the target artery, effectively "snorkeling" the vessel
This is commonly used for single-target revascularization or when only one visceral/renal artery requires direct connection.
Chimney Technique:
The chimney technique involves deploying one or more bridging stent-grafts alongside the main EVAR device, originating from a hole or scallop in the EVAR stent-graft and extending into the target visceral or renal artery
Multiple bridging stents (chبات) are deployed in parallel fashion to revascularize multiple branch vessels simultaneously
This is often performed by percutaneous access to the target branch vessels via contralateral femoral access or direct brachial/axillary access
A common approach involves cannulating the target arteries, deploying guidewires, and then deploying balloon-expandable stent-grafts (e.g., Viabahn, Advanta V12) through the main EVAR stent-graft into the visceral/renal arteries
The main EVAR device is then deployed, trapping the proximal ends of the bridging stents and creating a seal
Careful positioning of the main EVAR device and bridging stents is critical to prevent gutters and leaks.
Device Selection:
Device selection is paramount and depends on the specific anatomy and the number of target vessels
Standard EVAR devices may be used with bifurcated or straight extensions
Bridging stent-grafts for the chimney/snorkel technique are typically balloon-expandable and chosen for their flexibility and ability to conform to tortuous anatomy
Common examples include Gore Viabahn, Cook Zilver PTX, and Boston Scientific Palmaz stent in combination with other balloon-expandable grafts
Graft length and diameter must be carefully chosen to ensure adequate seal within the main EVAR device and the target branch artery
Balloon-expandable stents are often favored for their ability to be precisely deployed and expanded to seal against the aortic wall and the main stent-graft.
Access And Cannulation:
Access is typically gained via standard bilateral femoral artery cutdowns or percutaneous access
For chimney/snorkel techniques, particularly when multiple vessels are involved, access to the visceral and renal arteries is achieved through pre-cannulation using microcatheters and guidewires
This may involve standard angiography catheters or specialized steerable catheters
Sometimes, brachial or axillary access might be necessary for proximal vessel cannulation or difficult anatomy
Careful angiography is performed throughout the procedure to guide wire placement, stent deployment, and assess for endoleaks or malapposition.
Postoperative Care
Immediate Postoperative Management:
Close monitoring of vital signs, urine output, and hemodynamic status is essential
Patients are typically monitored in an intensive care unit (ICU) or a high-dependency unit
Pain management and fluid balance are crucial
Anticoagulation is managed based on institutional protocols and specific device used
Early ambulation is encouraged as tolerated
Serial imaging (e.g., CT angiography) is often performed within 24-48 hours to assess device integrity, seal, and exclude major endoleaks.
Pharmacological Management:
Dual antiplatelet therapy (DAPT) with aspirin and clopidogrel is generally recommended for at least one month post-EVAR, and often longer, especially with bridging stents, to maintain patency and prevent thrombosis
Anticoagulation with heparin or low molecular weight heparin may be used perioperatively
Long-term antiplatelet therapy is usually continued indefinitely, particularly for bridging stents
Statins are routinely prescribed for their pleiotropic effects and to reduce cardiovascular risk
Blood pressure control is vital to minimize stress on the repair.
Monitoring And Follow Up:
Regular clinical follow-up is essential, typically at 1, 6, and 12 months, and annually thereafter
This includes clinical assessment, blood pressure monitoring, and imaging studies
Imaging modalities commonly include duplex ultrasound, CT angiography (CTA), or MRA
The primary goals of follow-up are to monitor for endoleaks, assess the patency of the main stent-graft and bridging stents, detect aneurysm sac shrinkage, and identify any complications such as graft migration or limb occlusion
Specific attention is paid to the patency of the revascularized visceral and renal arteries.
Complications
Early Complications:
Early complications include endoleaks (Type I, II, III, IV, V), graft migration, limb occlusion, stent thrombosis, access site complications (hematoma, pseudoaneurysm), renal artery or visceral artery occlusion, myocardial infarction, stroke, and acute kidney injury
Type II endoleaks from lumbar or IMA collateral flow are common but may resolve spontaneously
Type I and III endoleaks typically require reintervention
Acute occlusion of bridging stents can lead to visceral ischemia or renal infarction.
Late Complications:
Late complications include graft infection, graft thrombosis, late endoleaks, aneurysm rupture despite repair, development of new aneurysms in other segments of the aorta, re-stenosis of bridging stents, and late occlusion of revascularized visceral or renal arteries
Late graft failure can occur due to material fatigue or chronic inflammatory processes
Progressive dilatation of the aneurysm sac can occur if endoleaks are not adequately sealed or if the endograft fails over time.
Prevention And Management Of Complications:
Prevention involves meticulous patient selection, precise anatomical assessment, careful procedural planning, and meticulous execution of the endovascular technique
Intraoperative imaging and post-deployment assessment are crucial for identifying and correcting endoleaks
Careful selection of appropriate stent-graft sizes and lengths is vital
For bridging stents, ensuring adequate length within the native artery and sufficient overlap with the main EVAR graft is important
Management of complications often requires reintervention, which may involve further endovascular procedures (e.g., embolization of collateral feeders for Type II endoleaks, deployment of additional stents, balloon angioplasty) or, in severe cases, open surgical conversion
Early detection through diligent follow-up is key to successful management.
Key Points
Exam Focus:
Understand the indications for chimney/snorkel techniques in complex aortic aneurysms (juxtarenal, suprarenal, TAAA)
Differentiate between snorkel (single vessel) and chimney (multiple vessels) techniques
Recognize common bridging stent-graft devices used
Be aware of the high risk of endoleaks and branch occlusion
Key complications include Type I/III endoleaks and visceral/renal ischemia
Postoperative management includes DAPT and close imaging surveillance.
Clinical Pearls:
Pre-operative planning with detailed CTA is non-negotiable
Consider using a bifurcated EVAR device with a single limb and a separate fenestration for the contralateral iliac artery if possible, to facilitate easier cannulation of visceral vessels
Always aim for a robust seal between the main EVAR device and the bridging stents
Overlapping the bridging stent sufficiently within the main EVAR device is critical
Aggressive management of endoleaks, especially Type I and III, is paramount
Careful selection of balloon-expandable stents for the chimney/snorkel component is often preferred for flexibility and conformability.
Common Mistakes:
Inadequate sealing of the main EVAR device leading to Type I endoleaks
Insufficient overlap of the bridging stent with the main EVAR graft
Failure to adequately cannulate or secure the target visceral/renal artery
Misjudgment of anatomical angles, leading to difficult stent deployment
Overreliance on a single imaging modality for assessment
Delay in reintervention for significant endoleaks or branch occlusions
Inadequate antiplatelet therapy post-procedure, leading to stent thrombosis.