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Abdominal Aortic Aneurysm: Has the Bubble Burst?
Rick C Jiang, MBBS, BMedSc, PostGradDipSurgAnat, FRACS; Mark P Brady, PA-C | May 10, 2017
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Image courtesy of Medscape by Sam Shlomo Spaeth.
Abdominal Aortic Aneurysm: Has the Bubble Burst?
Rick C Jiang, MBBS, BMedSc, PostGradDipSurgAnat, FRACS; Mark P Brady, PA-C | May 10, 2017 | Contributor Information
An aneurysm is defined as an increase of greater than 50% from the vessel's original size. For an abdominal aortic aneurysm (AAA), this equates to a diameter of approximately 3 cm. The larger the aneurysm, the greater the risk of rupture. AAAs are commonly diagnosed either incidentally or when they become symptomatic or rupture. Whereas morbidity and mortality are low for elective treatment of an AAA, outcome for a ruptured AAA (rAAA) remains poor even when prompt treatment is provided.
Image courtesy of Medscape | Sam Shlomo Spaeth.
Abdominal Aortic Aneurysm: Has the Bubble Burst?
Rick C Jiang, MBBS, BMedSc, PostGradDipSurgAnat, FRACS; Mark P Brady, PA-C | May 10, 2017 | Contributor Information
A 67-year-old man who is a long-term smoker arrives in the emergency department (ED) via ambulance with complaints of severe back and abdominal pain. He reports that the pain is tearing in nature and is constant. Upon arrival in the ED, the patient's heart rate (HR) is 130 beats/min, his blood pressure (BP) is 70/40 mm Hg, and his respiratory rate (RR) is 20 breaths/min. His Glasgow Coma Scale (GCS) score is 15, and he is able to hold a conversation. Electrocardiography (ECG) shows sinus tachycardia with no ST-segment changes. Examination of the abdomen reveals a tender pulsatile mass. There is a high index of suspicion for a symptomatic or ruptured AAA.
In view of these findings, what is the most appropriate imaging approach at this point?
Ultrasonography (US)
Computed tomography (CT) angiography (CTA)
Magnetic resonance imaging (MRI)/magnetic resonance angiography (MRA)
Percutaneous angiography
Image courtesy of Medscape.
Abdominal Aortic Aneurysm: Has the Bubble Burst?
Rick C Jiang, MBBS, BMedSc, PostGradDipSurgAnat, FRACS; Mark P Brady, PA-C | May 10, 2017 | Contributor Information
Answer: A. Ultrasonography (US).
US (shown) is an easy imaging study that most emergency physicians can perform effectively. In an emergency, aortic evaluation is often done as an extension of FAST (focused assessment with sonography in trauma), whereby the diameter of the abdominal aorta can be assessed for the presence of an aneurysm. The presence of free fluid, the visualization of an AAA, and the clinical correlation usually are strongly indicative of a symptomatic or ruptured AAA. In an elective or clinic situation, US provides an inexpensive and effective method of screening for an AAA that may require treatment or ongoing surveillance. Both the Gloucestershire Aneurysm Screening Program[1] and the Huntington Trial[2] showed that aneurysm-related mortality can be reduced by employing ultrasound-based screening of at-risk population groups, capturing patients with previously undetected AAAs, and proceeding to appropriate treatment on the basis of the rupture risk. However, screening programs in the United Kingdom have not been extended to women, because of their lower incidence of aneurysms.
Image courtesy of Medscape.
Abdominal Aortic Aneurysm: Has the Bubble Burst?
Rick C Jiang, MBBS, BMedSc, PostGradDipSurgAnat, FRACS; Mark P Brady, PA-C | May 10, 2017 | Contributor Information
In the scenario described in slide 2, CTA is not appropriate, because of the patient's hemodynamic instability (BP 70/40 mm Hg), especially if abdominal US visualizes an AAA. Attempts to perform CTA will only delay the necessary surgical treatment. Nevertheless, CTA remains the gold standard for diagnosing rAAAs and may still be indicated if the patient is hemodynamically stable enough and if endovascular aneurysm repair (EVAR) for an rAAA (rEVAR) is being considered as an option. It may also reveal alternative pathologic conditions, such as ruptured viscera or aneurysms of arteries other than the abdominal aorta. The image in the slide reflects enhanced spiral CT with multiplanar reconstruction and CTA.
If the patient in this scenario is found to have an AAA that is at least 3 cm in its maximal dimension (anteroposterior or transverse), what does that imply? What is the risk that an AAA will rupture at any given size?
Data in table from Law MR et al.[3]
Abdominal Aortic Aneurysm: Has the Bubble Burst?
Rick C Jiang, MBBS, BMedSc, PostGradDipSurgAnat, FRACS; Mark P Brady, PA-C | May 10, 2017 | Contributor Information
Answer: The presence of an aneurysm that is at least 3 cm in its largest dimension implies some degree of rupture risk. As might be expected, a larger aneurysm carries a higher risk of rupture and ensuing morbidity and mortality even when treated promptly.[3] A smaller aneurysm still carries a risk of rupture, but the risk is so small that elective repair is not indicated, despite the low incidence of complications from such treatment.
The UK Small Aneurysm Trial[4] showed that aneurysms smaller than 5.5 cm do not benefit from early intervention as compared with those larger than 5.5 cm. This finding was confirmed by the Aneurysm Detection and Management (ADAM) study.[5,6] It has been suggested, however, that this threshold should be lowered to 5 cm for female patients, who are at greater risk for rupture with AAAs larger than 5 cm.
Image courtesy of Medscape | Sam Shlomo Spaeth.
Abdominal Aortic Aneurysm: Has the Bubble Burst?
Rick C Jiang, MBBS, BMedSc, PostGradDipSurgAnat, FRACS; Mark P Brady, PA-C | May 10, 2017 | Contributor Information
Therefore, ongoing surveillance is recommended for patients with aneurysms smaller than 5.5 cm; as a rule, surveillance should be more frequent in those with aneurysms larger than 4 cm. These patients should be on best medical therapy for optimization of cardiovascular risk status. Antiplatelet agents,[7] statins,[8] and smoking cessation[9] have all been shown to decrease cardiovascular risks.
In conjunction with the diagnosis of rAAA, how would you manage this patient's fluid status and BP? What type of fluid would you use, and what would be the ideal BP range?
Image courtesy of Radiopaedia.org.
Abdominal Aortic Aneurysm: Has the Bubble Burst?
Rick C Jiang, MBBS, BMedSc, PostGradDipSurgAnat, FRACS; Mark P Brady, PA-C | May 10, 2017 | Contributor Information
Answer: No fluid resuscitation is necessary.
Although large-bore access in the cubital fossae is mandated, fluid resuscitation is not required in this instance, because BP is sufficient to maintain cerebral and cardiac perfusion. Permissive hypotension prevents further blood loss from the rupture and improves the outcome of an rAAA.[10-13] Attempting to elevate BP to the normal range might precipitate further intra-abdominal blood loss. The image in the slide shows a hematoma developing from an rAAA.
Obviously, rAAA patients may present with a wide spectrum of shock, from the patient with a stable contained rupture to the patient who is essentially moribund. Which of these patients should be operated on to obtain the best possible outcome?
Image courtesy of Medscape | Sam Shlomo Spaeth.
Abdominal Aortic Aneurysm: Has the Bubble Burst?
Rick C Jiang, MBBS, BMedSc, PostGradDipSurgAnat, FRACS; Mark P Brady, PA-C | May 10, 2017 | Contributor Information
Answer: Models predicting outcomes in rAAA patients are derived from retrospective analysis of characteristics predictive of poor outcome. A Glasgow Aneurysm Score (GAS) higher than 85 is predictive of mortality.[14] Similarly, a Hardman index score of 2 predicts a mortality of 80%. Nevertheless, such scores should not be used as the sole basis of the clinician's decision whether to opt for operative management. Moreover, the advent of EVAR and its growing use for rAAA have led some to argue that the GAS and other similar systems may be increasingly irrelevant because they were developed in the setting of open aneurysm repair.
Apart from rAAA and an aneurysm size in excess of 5.5 cm, what other indications exist for repair of noninfective aneurysms?
Image courtesy of Medscape.
Abdominal Aortic Aneurysm: Has the Bubble Burst?
Rick C Jiang, MBBS, BMedSc, PostGradDipSurgAnat, FRACS; Mark P Brady, PA-C | May 10, 2017 | Contributor Information
Answer: A tender or symptomatic aneurysm or an aneurysm that is growing rapidly (>10% annually). A tender aneurysm is an indicator of impending rupture; the rapid growth in size stretches the retroperitoneal tissue and causes pain. Because larger aneurysms can cause discomfort during examination, the examiner may be uncertain whether the pain a patient feels is due to the large size of the aneurysm or to true tenderness signaling impending rupture. In some cases, stranding in the periaortic tissue may be observed on CTA in a tender but nonruptured aneurysm. Similarly, rapidly growing aneurysms are thought to be associated with a higher risk of rupture because of their potential to grow substantially between surveillance scans. In these scenarios, it may be safer for the patient to undergo elective repair even if the aneurysm is smaller than 5.5 cm. The image in the slide shows an AAA with retroperitoneal fibrosis and adhesion of duodenum.
In a situation where the AAA has not ruptured, once the decision has been made to intervene, what are the options?
Image courtesy of National Institutes of Health (NIH) Department of Health and Human Services (DHHS).
Abdominal Aortic Aneurysm: Has the Bubble Burst?
Rick C Jiang, MBBS, BMedSc, PostGradDipSurgAnat, FRACS; Mark P Brady, PA-C | May 10, 2017 | Contributor Information
Answer: Open AAA repair and EVAR (shown). Currently, with the advent of EVAR, elective open AAA repair is being performed less frequently; it is more commonly used in younger patients or in patients whose anatomy is not suitable for EVAR. As a general rule, the patient must have adequate cardiovascular and respiratory fitness and a life expectancy of at least 2 years.
Open AAA repair can be carried out via either a transperitoneal or a left retroperitoneal approach, each of which has advantages and disadvantages. The transperitoneal approach affords good access to all vessels, including the common and external iliac vessels on both sides, and allows inspection of abdominal organs; however, it can be cumbersome and increases the risk of bowel injury in the setting of a previous laparotomy. The left retroperitoneal approach avoids bowel adhesions while accessing the aorta, especially the juxtarenal and suprarenal aorta; however, it affords only limited access to the right iliac vessels, making bifurcated repair difficult. Systemic heparin is frequently given in the elective setting but is generally avoided in cases of rAAA.
Image courtesy of Medscape.
Abdominal Aortic Aneurysm: Has the Bubble Burst?
Rick C Jiang, MBBS, BMedSc, PostGradDipSurgAnat, FRACS; Mark P Brady, PA-C | May 10, 2017 | Contributor Information
An aortic crossclamp is usually placed in the infrarenal position, but suprarenal clamps may sometimes be required until the sac is opened and depressurized and an infrarenal clamp can be placed. In some rAAA cases, supraceliac clamps may be required to gain control. A bifurcated graft may be required if the aneurysm involves the iliac vessels. Usually, the graft is sewn in as an inlay, but occasionally, the aorta may be transected and the graft sewn on in an end-to-end fashion. The inferior mesenteric artery typically is not replanted unless it is of a large caliber. The aneurysm sac is usually closed over the graft (shown), with special attention to covering the upper anastomosis. It has been suggested that this may decrease the incidence of aortoduodenal fistulas.
Image courtesy of Radiopaedia.org.
Abdominal Aortic Aneurysm: Has the Bubble Burst?
Rick C Jiang, MBBS, BMedSc, PostGradDipSurgAnat, FRACS; Mark P Brady, PA-C | May 10, 2017 | Contributor Information
For EVAR, various off-the-shelf devices are commonly available (shown). However, there are some conditions that must be met to ensure success. The anatomy of the aneurysm is by far the most important factor dictating whether an endograft is a suitable choice for a given patient.
First, to ensure good proximal sealing of the endograft, an adequate "neck" is required; this is usually defined as 15 mm between the lowest renal artery to be preserved and the start of the aneurysm, though some devices only require 10 mm. This boundary is being challenged by the ongoing development of newer devices and adjuncts such as Medtronic EndoAnchors. The Endologix Nellix graft offers an endovascular sealing approach to secure the aneurysm; early to midterm results from New Zealand and the United Kingdom are promising. For juxtarenal or pararenal aneurysms without an adequate neck, an alternative endovascular technique would be required, such as the use of an endograft plus chimney stents or the use of a custom-made fenestrated or branched device.
Image courtesy of Medscape.
Abdominal Aortic Aneurysm: Has the Bubble Burst?
Rick C Jiang, MBBS, BMedSc, PostGradDipSurgAnat, FRACS; Mark P Brady, PA-C | May 10, 2017 | Contributor Information
Second, because access to the aorta is commonly obtained via a transfemoral approach, adequate-sized access vessels must be available. Severely diseased, calcified, or tortuous iliac vessels or a stenosed aortic bifurcation may prevent passage of the endograft to the desired destination. Different companies suggest different optimal access-vessel dimensions for their products; the clinician should therefore refer to the instructions for the particular device being employed. Adjunctive procedures (eg, angioplasty, stenting, or placement of surgical conduits) may be performed to facilitate delivery of the endograft. Other anatomic factors (eg, neck angulation, thrombus in the neck, or tortuous anatomy) may persuade the clinician to use one device in preference to others. Patient factors (eg, renal function) may also dictate whether EVAR is the best option.
Image courtesy of Medscape.
Abdominal Aortic Aneurysm: Has the Bubble Burst?
Rick C Jiang, MBBS, BMedSc, PostGradDipSurgAnat, FRACS; Mark P Brady, PA-C | May 10, 2017 | Contributor Information
The perioperative mortality associated with elective EVAR is approximately 1.5% in most major studies, which is significantly better than that associated with open aneurysm repair (~4.5%) in the EVAR-1[15] and DREAM[16] trials. Long-term outcomes of EVAR have been studied through large registries such as EUROSTAR; the annual rate of reintervention for stent-graft–related problems is approximately 5%, and the annual risk of rupture after implantation is approximately 1%.[17,18]
Image courtesy of Radiopaedia.org.
Abdominal Aortic Aneurysm: Has the Bubble Burst?
Rick C Jiang, MBBS, BMedSc, PostGradDipSurgAnat, FRACS; Mark P Brady, PA-C | May 10, 2017 | Contributor Information
Aneurysm- and graft-related complications include the following:
Endoleak
Graft occlusion
Renal artery occlusion
Infection
Endoleaks may be divided into the following four types:
Type I - Lack of seal at proximal or distal sealing zones, resulting in arterial pressurization of the aneurysm sac
Type II - Backbleeding from patent lumbar vessels or the inferior mesenteric artery (shown)
Type III - Graft dissociation or tear through the graft material
Type IV - Graft porosity
Type I and III endoleaks require urgent treatment because the aneurysm sac remains pressurized and continues to be at risk for rupture. Type II endoleaks generally do not require treatment unless there is ongoing sac expansion.
Image courtesy of Medscape.
Abdominal Aortic Aneurysm: Has the Bubble Burst?
Rick C Jiang, MBBS, BMedSc, PostGradDipSurgAnat, FRACS; Mark P Brady, PA-C | May 10, 2017 | Contributor Information
Large randomized trials have been carried out evaluating the outcomes of EVAR against those of open aneurysm repair. The major trials include EVAR-1,[15] DREAM,[16] and OVER,[19] and their overall perioperative outcomes may be summarized as follows:
Perioperative mortality for EVAR ranged from 0.5% (OVER) to 1.7% (EVAR-1), whereas that for open repair was in the range of 3-5%
The combined rate of operative mortality and severe complications (shown) was 4.7% for EVAR and 9.8% for open repair (DREAM)
EVAR is undoubtedly associated with lower perioperative morbidity and mortality, but the survival benefit seems to be lost over the longer term. Long-term outcomes from the EVAR-1 trial and the DREAM trial are summarized in slide 17.
Image courtesy of Medscape.
Abdominal Aortic Aneurysm: Has the Bubble Burst?
Rick C Jiang, MBBS, BMedSc, PostGradDipSurgAnat, FRACS; Mark P Brady, PA-C | May 10, 2017 | Contributor Information
At 2 years after intervention, the overall survival benefit of EVAR is lost. In both EVAR-1[15] and DREAM,[16] there was no significant difference in all-cause mortality between EVAR and the open repair at 2-year follow-up; however, there was a difference in aneurysm-related mortality favoring EVAR in the DREAM trial. The similarity in overall mortality was due to an increased proportion of cardiovascular-related deaths in EVAR patients. At 6-year follow-up, EVAR again conferred no survival advantage in either trial, and the rates of aneurysm-related death were similar in the two studies; this finding was repeated at 15-year follow-up.[20]
Moreover, studies have suggested that more repeat interventions are required for patients treated with EVAR:
In the DREAM trial, the 2-year reintervention rate was 30% for EVAR and 19.1% for open repair (a statistically significant difference)
In the EUROSTAR Registry,[17,18] the annual risk of reintervention in EVAR patients was 5%
To return to the clinical scenario outlined earlier, the male patient described has an rAAA that is anatomically suitable for either EVAR or open repair. The decision has been made to intervene. Which of the two options is the more appropriate choice here?
Image courtesy of Medscape.
Abdominal Aortic Aneurysm: Has the Bubble Burst?
Rick C Jiang, MBBS, BMedSc, PostGradDipSurgAnat, FRACS; Mark P Brady, PA-C | May 10, 2017 | Contributor Information
Answer: At present, more vascular surgeons would probably be comfortable with open repair in this scenario. Given the long history of open AAA repair, most vascular surgeons and the institutions where they work should be comfortable dealing with AAAs both in the elective setting and in the context of rupture. Generally, surgeons, anesthesia personnel, and nursing staff members will all be well aware of the steps and equipment required for open rAAA repair.
In contrast, treatment of an anatomically suitable rAAA by means of EVAR (ie, rEVAR) is a relatively new concept that often cannot be implemented, whether because the surgeons lack the necessary experience, because the available infrastructure is inadequate, or both. To perform rEVAR, the surgeon must have rapid access to the angiography suite or an angiography-capable hybrid operating theatre, must have a wide range of stent grafts readily available, and must have the assistance of nurses skilled in the smooth handling of angiography wires and devices. To date, only specialized centers have been set up to perform rEVAR, and outcomes often depend on the experience of the local centers.
Image courtesy of Medscape.
Abdominal Aortic Aneurysm: Has the Bubble Burst?
Rick C Jiang, MBBS, BMedSc, PostGradDipSurgAnat, FRACS; Mark P Brady, PA-C | May 10, 2017 | Contributor Information
The IMPROVE study compared the outcomes of rEVAR with those of open rAAA repair by randomizing potential patients to one of the two study arms.[21] IMPROVE was a multicenter trial, primarily based in the United Kingdom, that included centers capable of performing either type of treatment expeditiously. Its 30-day outcomes may be summarized as follows:
There was no difference in 30-day mortality between patients initially randomized to open repair and those assigned to EVAR (37.4% vs 35.4%; P=0.62)
There was significant patient crossover from the initial randomized groups; 112 of 275 patients initially randomized to EVAR eventually underwent open repair for varying reasons, and 36 of 261 initially randomized to open repair crossed over and underwent EVAR
Mortality was approximately 25% in patients who eventually received EVAR, compared with approximately 38% in those who underwent open repair; it was not stated whether this difference was significant
There were no significant differences between the two study groups with respect to length of hospital stay or average cost
A subsequent report of 1-year outcomes from the same trial found that an EVAR-first approach to rAAA management offered no significant survival benefit at 1 year but was associated with shorter hospital stays, afforded patients better quality of life, and was cost-effective.[22] These findings still held true at the study's 3-year follow-up, which was presented in April 2017 at the Charing Cross Symposium in London.
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Authors
Rick C Jiang, MBBS, BMedSc, PostGradDipSurgAnat, FRACS
Senior Vascular Registrar
Department of Vascular Surgery, Monash Health
University of Melbourne
Melbourne, Victoria, Australia
Disclosure: Rick C Jiang, MBBS, BMedSc, PostGradDipSurgAnat, FRACS, has disclosed no relevant financial relationships.
Mark P Brady, PA-C
Department of Emergency Medicine
Cambridge Health Alliance
Cambridge, MA
Disclosure: Mark P Brady, PA-C, has disclosed no relevant financial relationships.
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