Atherosclerosis: Practical Implications for Pathologists
Section 9 -
Large Vessel Disease, Aortic Aneurysms and Stent Therapy
This 19-year-old woman was a passenger in an automobile involved in a head on
collision. She suffered extensive trauma including "laceration" of the thoracic aorta resulting in a
leaking aortic aneurysm (TAA). The latter was noted after attempts at stabilizing her other injuries.
After special permission was obtained from the hospital authorities and ethics board, permission was
obtained from the FDA for use of an endovascular aortic stent to treat the leaking TAA. The endovascular
stent was deployed and the aortic injury stabilized. However, she remained in a coma and ultimately
died, nearly 12 months after the injury. The aorta was made available for
Most aortic disease results in aneurysm formation. Aneurysms are commonest in the abdominal aorta,
followed by the ascending arch and thoracic aortas in that sequence.
The aortic aneurysms are honest comment than many of the cut or ask the conditions. However they can
be life-threatening and it is an unfortunate fact that even a large aneurysms may be totally asymptomatic
Abdominal aortic aneurysms (AAA) are amongst the
commonest of vascular conditions with life-threatening complications. When diagnosed early (diameter up
to 5.0 cm and without evidence of leakage) they are easily treated surgically with the use of
interposition grafts. However, aneurysms frequently occur in elderly individuals and individuals with
many other co-morbid conditions, making surgical management difficult. These patients were often refused
surgery, in the past and today.
At the same time, thoracic aortic aneurysms (TAA) are an uncommon but equally life-threatening
condition. Three percent of all aortic aneurysms are believed to be TAA and are commonly due to
atherosclerosis and chronic aortic dissection. (I personally believe that aortopathies also play a role
in the incidence of TAA. However these aneurysms are more likely to be large, fusiform or spindle shaped
rather than the localized saccular type that are seen with atherosclerosis.)The actual prevalence and
mortality rate of TAA (and of AAA) in any particular population is not well established.
The purpose of treating aortic aneurysms is two-fold:
Open surgical repair with prosthetic vascular graft interposition is the traditional and accepted
method of treating TAA as well as AAA .
- To prevent rupture
- To eliminate compression symptoms related to the mass effect of the aneurysm,
damage to the spinal cord and dysphagia.
Perioperative morbidity and mortality rates however remain high and these are due to many reasons, the
chief of which is the patient population and their age, and high incidence of co-morbidities. Other
factors include the morbidity associated with a major thoracotomy, the use of cardiopulmonary bypass,
post operative complications including bleeding, paraplegia, stroke, renal insufficiency and a necessity
for ventilatory support (often prolonged). In thoracoabdominal aortic aneurysms, the mortality rate was
reported at 4.8% and the incidence of paraplegia at 4.6% by Cosellie JS et al.  In view of
the persistent morbidity and mortality associated with open surgical repair of descending TAA,
thoracoabdominal aortic aneurysms (TAAA) and leaking abdominal aortic aneurysms, a less invasive and
potentially safer technique for aneurysm repair was clearly necessary.
Parodi et al were the first to describe the treatment of AAA with an endovascular stent graft in
These grafts were initially devised for the purpose of treating aortic aneurysms
in individuals with likely high morbidity and mortality. Progress has been made and several reports
substantiate the safety and effectiveness of stent grafts in the repair of AAA and TAAA .
With increasing experience in the use of stent grafts for TAA and AAA, many other aortic diseases,
such as traumatic aortic injury, aortic dissection, penetrating atherosclerotic ulcers, aortopulmonary
fistulae and acute aortic rupture related to blunt chest trauma or mycotic aneurysms have been treated as
indications for endovascular treatment.
The endovascular treatment of aortic aneurysms entails the use of a fairly large balloon catheter,
with a collapsed stent graft mounted on it. The grafts may be open, covered or a combination. The
length of most of these stent grafts can be increased by attaching additional segments to their end. The
device is inserted following a femoral artery cutdown. No thoracotomy or clamping of the aorta is
necessary. The length of the aorta that is likely to be "covered" by the graft is generally short and
limited to the diseased segment so that the risk of spinal cord ischemia is reduced. There is no need
for full heparinisation and major bleeding complications or bleeding from cerebral vascular lesions, is
Stent graft systems:
The initial endovascular devices used were homemade devices. Technological innovations, continued at
a brisk pace, and an increasing number of commercially available aortic stents have been developed and
refined endovascular prosthetic devices. Today, custom designed, homemade and commercially available
stent grafts are used in the treatment of thoracic aortic disease as well as abdominal aortic disease.
The homemade stent grafts used at Stanford University are comprised of a series of self-expanding
Z-shaped stainless steel stents, boxcar together and interconnected by two zero polypropylene sutures.
This skeleton is covered with a woven-Dacron polyester tube graft attached to the stent with five zero
polypropylene sutures. These are loaded onto a delivery capsule, advanced through a delivery sheath on a
28 French catheter.
Commercially available stent grafts: Several
different manufacturers have introduced grafts. Some of these unfortunately have suffered significant
problems at intermediate term and are now no longer available. The Talent endoluminal stent graft
device, the AneurX stent graft and the Excluder endoprosthesis are some of the devices that have been
available for current use and are available in the market.(See Butany et al, J Clin Pathol in press)
These devices are still in the early stages of clinical use and long term results are not available,
especially results based on pathologically examined explants (whether at autopsy or at surgical
re-exploration. While they have been studied to a good extent in experimental animals, human experience
is still relatively small, and reports are awaited. It is therefore critical for
pathologists who get these cases at autopsy to examine them in detail or to send them to someone who will
examine them in detail. The detailed examination is a fairly intense and expensive, time
consuming process but the results should be very relevant. Additionally, since many of these devices are
still in the clinical trial stages, the results often need to be conveyed to the Food and Drug
Administration or the Device Control Agencies in the country in which they are being use for explanting.
Major considerations to keep in mind when examining these devices include getting ALL the relevant
clinical and imaging information, and at the time of examination :
We will present some examples of cases of use of this device and associated changes.
- Radiologic examination to see if the metal components are intact -rule out poor strut expansion
and strut fractures.
- Detailed examination of the covering fabric to see if there is fraying or
damage due to fractured device components, tearing / ripping the fabric
- Excessive movement of the device, beyond the point of implantation—migration of the device
- Rupture of the aorta - Leakage of blood
- Damage to the aorta (generally away from the diseased or torn segment)
- Endoluminal leak(hemorrhage of any kind)
- Intimal hyperplasia at the ends of the device
Abdominal aortic aneurysms (AAA) repaired by endovascular grafting offer a tremendous promise of
effective and durable repair by improving morbidity and mortality as compared to the open or surgical
correction. This, in time, will also likely lead to significantly reduced hospital costs .
To summarize, endovascular stent grafts are comprised of a metal stent (stainless steel or nitinol -
an alloy of nickel and titanium) covered with a fabric graft, which resembles a usual vascular graft
except that it has a metal stent or frame inside it. The device is therefore known commonly as a
stent-graft. These grafts may be straight or tubular grafts, in which case the two ends are meant to be
anchored to the infrarenal aorta (they have little hooklets which help them to get so attached) or, the
grafts may be bifurcated with the proximal end attached to the infrarenal aorta or another part of the
aorta if necessary, while the distal end is bifurcation (like a pair of pantaloons) and the two limbs are
fastened to the iliac arteries. The stents used are self expanding stents and some of the devices have
little hooks on their outer aspect which allow them to get embedded in the surrounding wall. For obvious
reasons, it is imperative for the operator to be able to anchor the device against the vessel wall.
Complications associated with the device include: thrombosis, dislodgement of the device
(inadequate attachment to the walls) with movement (migration) of the device, often away from the site at
which it should be attached, infection and twisting or kinks in the device leading to vascular
obstruction. Structural failure, related to the metal component and / or the fabric covering it
with the associated possibility of hemorrhage (generally slow and ongoing). A complication not
associated with other devices, is the occurrence of an "ENDOLEAK".
An endoleak means that either because of inappropriate placement', damage to the fabric, or
retrograde blood flow , blood leaks into the perigraft space, that is into the aneurysm or into the
lumen of the endoluminal graft and into the native vessel This blood is contained by the aneurysm wall.
However, it can lead to ongoing aneurysm expansion and potentially likely to rupture .
Examination of these specimens when obtained at autopsy or even at surgical "redo" procedures is often
difficult. The specimen is large as the device used is implanted inside the aneurysmal segment and
anchored above it with the two limbs extending into the iliac vessels beyond it. The device should be
examined radiologically to look for evidence of changes in the metal components.
Perhaps the single most significant problem associated with these devices, certainly unusual and
associated largely with this type of device alone, is the endoleak. An endoleak is due to the
incomplete "plastering" or sealing of the device to the wall of the vessel. It may happen at the time of
implantation when the proximal end does not attach fully or leaves a small space between the graft and
the wall of the native vessel.or when the fabric tears for some reason. It is entirely possible that the
fabric was defective or that retrograde blood flow has occurred through small aortic branches. In some
instances reoperation has been necessary and the incidence of this complication is reportedly
approximately 6%  In a small number of cases, AAA have been reported to continue to increase
in size. The explanation for this is not known and has been reported to occur even without an endoleak.
A few possible explanations have been offered for this. These can be suspected at CT scan,
With improved devices, better delivery systems and the good results that are being reported, the
device is now being used more extensively and in some instances as a first line procedure, in essence the
device has gone "mainstream"-and has made it to "prime time"! That is, though it was meant initially for
use in individuals who were "inoperable" for many reasons they are now being used in individuals who do
not wish to have the usual surgery.
29 year old male, History of Dilated cardiomyopathy .New onset Severe Congestive Heart
Failure.Ventricular Assist Device (Heartmate) inserted: Bridge to transplant
Readmitted 17 months later---"device malfunction"
Device adjusted and placed again on urgent transplant waiting list:
Heart transplant : end Feb '05.Device removed and examined.
A 62 year old patient with long standing ischemic heart disease (refused
heart transplant) underwent VAD placement as Destination Therapy. On day 9 he started developing
refractory ventricular arrhythmias, and died on day 11, despite all efforts. (the pathology will be
At this time, the best form of treatment for intractable congestive heart failure or end stage heart
disease is heart transplantation. However, the number of hearts available for transplantation is limited
and this precludes the use of this approach for all patients. In addition, hearts are not available
exactly when needed. Hence, the availability of a device, which takes the place of a graft heart, even
if temporarily, provides a valuable adjunct to treatment. Ventricular assist devices are one such group
of mechanical devices, which serve this purpose - that is they are a bridge to transplantation. Some of
these devices are meant only for short-term use (that is a week to two weeks), white others can be used
for several months and even long to. These devices are expensive and do have complications. There are
peri and postoperative considerations when managing a critically ill patients whose life depends on the
mechanical circulatory support or ventricular assist device. Careful patient selection and care of a
patient with such a device is obviously essential.
Mechanical circulatory support is today "a standard of care" for some patients having acute or even
chronic heart failure. One of the major criteria for the use off a VAD is, inadequate cardiac output,
for preservation of end organ perfusion.
Table : Currently available Ventricular Assist Devices
|Device Name ||Type-Chamber to which attached ||Mechanism of Blood propulsion ||Duration of Implantation ||Position/Location of Device|
|Abiomed BVS5000 ||BiVAD ||Pneumatic ||Days-Weeks ||Paracorporeal|
|Thoratec ||BiVAD ||Pneumatic ||Months ||Paracorporeal|
|HeartMate ||LVAD ||Electrical ||Months ||Implantable|
|Novacor ||LVAD ||Electrical ||Months ||Implantable|
|Cardiowest TAH ||BiVAD ||Pneumatic ||Months ||Paracorporeal|
|Debakey ||LVAD ||Axial Flow ||Months ||Implantable|
|Jarvik 2000 ||LVAD ||Axial Flow ||Months ||Implantable|
|HeartMate II ||LVAD ||Axial Flow ||Months ||Implantable|
|Abiomed BiVAD ||BiVAD ||Pneumatic ||Months ||Paracorporeal|
LVAD--Left ventricular assist device. BiVAD-Biventricular assist device.
(Modified from Ventricular Assist Devices, in 'A practical approach to perioperative care in cardiac
anesthesia and surgery".
Complications associated with VAD:
Late complications associated with VAD usage, are likely to be device specific. However there are few
morphological reports documenting these in devices that have been explanted and analyzed and hence no
reference is available for. Complications that have been seen and recorded by us include:
- The mortality associated with VAD insertion is about 25%.
Most patients today are stabilized on the VAD are sent home while awaiting heart . transplantation.
- General complications include :
- Drive line infections
- other infections
- prostheses thrombosis and thromboembolic events
- HLA sensitization
Ventricular assist devices are now accepted as standard of care devices. The new
generation of devices is smaller and has a lower morbidity, mortality and likely lower complication
rate. However, in the absence of detailed pathological analyses of the devices, and reporting of these,
further progress would appear to be hindered. I would therefore urge you to to examine these devices or
send them to a colleague interested in these devices and help accumulate a body of knowledge about their
complications and changes post implantation.
- the development of thrombus around the device cannulae
- the development of host tissue reaction or pannus around the cannulae at each site
- infection around the cannulae
- fibrous adhesions around the device cannulae
- changes in the prosthetic valves in the device, including:
- bio prostheses tissue degeneration
- cusp tear
Table.1 Endothelial Cell Functions
|Function ||Size of Molecules ||Mechanisms|
|Permeability ||Large Molecules ||Vesicular transport through intercellular junctions|
|"Filter" ||Small Molecules ||Vesicles, Junctions, through cytoplasm|
|Vascular Tone ||S.M.C. Relaxation ||Nitric Oxide, etc.|
| ||S.M.C. Contraction ||Endothelin-1, Angiotensin 2|
|Hemostasis / Inflammation ||Activate - Platelet Adhesion ||Von Willebrand Factor|
U-PA, PAI -1
|[S.M.C Stimulation] ||Growth Factors|
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