Dissection of the as- cending aorta almost invariably requires emergency surgical replacement

(1)

Contents

24.1 Introduction . . . . 247

24.2 Malperfusion Symptomatology . . . . 247

24.3 Mechanisms . . . . 248

24.4 Para-clinical Examinations . . . . 249

24.5 Endovascular Treatments . . . . 249

24.6 Conclusion ± Therapeutic Guidelines . . . . 251

24.1 Introduction

Acute aortic dissection is a medical, radiological and surgical emergency that rapidly compromises the patient's chances of survival [1, 2]. Dissection of the ascending aorta almost invariably requires emergency surgical replacement; when the ascending aorta is not involved, dissection is primarily treated medically, ex- cept in the event of complications [3]. The traditional management, based on Stanford classification, is dis- cussed because of emergent endovascular treatment for aorta and malperfusion syndrome.

Malperfusion is defined in this context by the ischemia of an organ during aortic dissection. Malperfu- sions can concern the heart, brain and spinal cord, and in the case of extension of the dissection to the abdominal aorta and the iliac axes, the digestive tract, kidneys and lower limbs. This type of complication aggravates the already high morbidity and mortality linked to the thoracic complications of dissection [4, 5]. Several mechanisms may be responsible for this malperfusion, and the necessity for endovascular treatment is depen- dent on these mechanisms.

The purpose of this chapter is to describe the mechanisms behind the malperfusions and to propose the in-

dications and endovascular treatment techniques. In this publication, we only cover renal, digestive and lower-limb malperfusions.

24.2 Malperfusion Symptomatology

In accordance with the Stanford classification, type A dissection concerns the ascending aorta, regardless of the entry site; type B dissection concerns the descending aorta, the entry site being generally situated on the descending aorta, sometimes on the aortic branch. Mal- perfusion of the visceral branches of the abdominal aorta or the iliac axes can occur in cases of extension of the dissection to the abdominal aorta, whether or not the ascending aorta is concerned with the dissection.

In the case of an aortic dissection with acute symptoms of malperfusion (Table 24.1), diagnosis must be done quickly in order for emergency treatment to be administered.

An aneurysmand/or renal insufficiency should make the practitioner suspect renal ischemia. It is particularly important to check the condition of the renal vascular systemrapidly, as soon as dissection is diagnosed. In-

Endovascular Treatment of the Complications of Aortic Dissection:

Fenestration and Stenting

Jean-Paul Beregi, Philippe Asseman, Alain Prat, Frdric Thony, Virginia Gaxotte,

Christophe Lions, Ziad Negaiwi, Serge Willoteaux

24

Table 24.1.Symptoms due to malperfusion syndrome in the case of aortic dissection with involvement of the abdominal aorta

Organs Acute symptoms Chronic symptoms Kidneys Renal failure,

anuria Refractory

hypertension Digestive Abdominal pain,

biological signs (hepatic enzymes)

Digestive angina Lower limb Acute ischemia with

white and painful leg Claudication

(2)

deed, secondarily, the onset of renal insufficiency in the recovery period or postoperatively (replacement of the ascending aorta) can depend on multiple factors. Early diagnosis of renal malperfusion allows the appropriate endovascular treatment to be initiated without delay.

In the context of aortic dissection extending to the abdominal aorta, spontaneous pain or palpation-in- duced pain must lead to the rapid diagnosis of intestinal ischemia. This ischemia is difficult to confirm with para-clinical examinations but, if untreated in the hours following the onset of the symptoms, will prove fatal.

Lastly, ischemia of the lower limbs is easily detected using the usual symptomatology (coldness and pain in the limbs and lack of pulse).

The symptoms observed in the acute phase of an aortic dissection must lead to the rapid administration of treatment. Such treatment must sometimes be carried out before the ascending thoracic aorta can be re- paired, as in the case of a type A aortic dissection [6, 7].

At the chronic stage, whether a medically treated type B dissection or a type A surgical dissection is involved, the symptoms of malperfusion can appear during follow-up. This can consist of refractory arterial hypertension, digestive angina or intermittent claudication of a lower limb. A morphological analysis of the dissection must be conducted in order to plan the appropriate treatment according to the mechanism of the malperfusion.

24.3 Mechanisms

Malperfusions can currently be treated by endovascular means: implantation of arterial stents in the visceral branches of the abdominal aorta, in the iliac axes, in the abdominal aorta, fenestration of the intimal flap, implantation of a thoracic aortic stent-graft and a com- bination of these different techniques. These forms of treatment seem to yield better results than surgery in cases of malperfusion-related complications. In order to choose the appropriate treatment, it is essential to know the morphology of the aortic dissection and the extension into vascular branches to understand the mechanisms responsible for the malperfusion(s).

These mechanisms of visceral malperfusion were studied in 1997 by Williams et al. [8]. These authors proposed a systemof classification that separates the so-called static mechanisms from those considered dynamic. The static character is described by analogy to classic athermatous lesions that narrow the diameter of the artery like ostial or proximal stenosis. Dynamic lesions are described as resulting fromcompression of the true arterial lumen by a false lumen secondary to extremely high pressure in the latter. However, this classification systemdoes not describe all possible cases

and it is often difficult to link the symptoms with the mechanisms, thus resulting in treatment problems. In fact, all lesions are dynamic. The lesion defined as static is an extension of the dissection into a dead-end visceral artery. This extension leads to a reduction in the true channel by compression of the false channel where the blood enters but cannot exit. Given the blind aspect of the lesion, it tends to thrombose, giving rise to the erroneous diagnosis of a static lesion.

We propose an analysis of lesions in relation to the position of the dissection flap in the aorta followed by examination of the visceral arteries to investigate a possible dissection or an ostial tear (Fig. 24.1). This approach, in a study of 61 patients [9], demonstrated that type 1c and 1d lesions with malperfusion lead to fenestration (Fig. 24.2), whereas type 2a, 2b, 2c and 3c lesions lead to the implantation of a stent in the artery affected by the dissection with downstreamischemia (Fig. 24.3).

Fig. 24.1. Type 1A, 1B, 1C and 1D lesions. FL false lumen, TL true lumen

Fig. 24.2. Type 2A, 2B, 2C and 2D lesions. FL false lumen, TL true lumen

(3)

24.4 Para-clinical Examinations

The objectives of imaging techniques in cases where aortic dissection is clinically suspected are given in Ta- ble 24.2. The diagnostic imaging techniques at our dis- posal are transthoracic echocardiography, transoesopha- geal echocardiography (TOE), computed tomography (CT) angiography, MRI and arteriography. TOE, CT angiography and MRI display high, identical levels of sensitivity (greater than 90%) in the diagnosis of aortic dissection [2, 10±12]. TEE responds partially to the objectives mentioned; it does not facilitate complete diagnosis of the dissection, as it is limited to the study of the thoracic aorta. However, this technique can be used in the intensive care unit with no displacement of the patient.

There is less access to MRI in France and we have few machines dedicated to emergencies and to the treatment of haemodynamically unstable patients.

A CT angiogramacquires a large volume of data (thoracic±abdominal±pelvic), allowing thorough investi- gation of the dissected aorta. Its performance in the exploration of the aorta has been well established [13±15].

The technological contribution of helicoidal data acquisition in the diagnosis of aortic dissection has improved its sensitivity, which now varies between 88 and 100%.

The essential objectives mentioned can be achieved using this technique. Exploration is conducted without and then with the injection of a contrast medium. The data acquisition techniques for axial sections are vari- able and depend on the performance of the equipment used. This technology has allowed more extensive inves- tigation and thorough comprehension of malperfusions.

It is also the preferred technique for detecting and ana- lysing malperfusions on a practical level.

Although the technique has been in use for a long time, arteriography is no longer used to diagnose dis-

section but is employed only as a complementary technique (e.g. before implantation of a thoracic stent-graft) or for an endovascular procedure.

24.5 Endovascular Treatments

Besides surgical treatments such as bypasses, surgical fenestration [16] or closure of the entry points, endovascular techniques have developed as they are better tolerated in the context of aortic dissection with malperfusion [11].

Endovascular fenestration is specific to the treatment of aortic dissections. This technique is carried out when- ever malperfusion is suspected in association with a dynamic mechanism or with types 1c and 1d. The principle consists in creating a wide orifice of communication between the true and false channels or in increasing the passage of blood between these two channels [17]. The former technique involves creating an exit site by perfor- ating the intimal flap, from the true channel towards the false channel, using a trans-septal needle. This technique is currently made safer by the use of an endovascular ul- trasound probe; this enables surgeons to better locate the position of the intimal flap and to guide movements on perforation [18]. Once the aperture has been made in the flap, it is enlarged by angioplasty with a balloon mea- suring over 12 mm in diameter. The second possibility for carrying out fenestration, termed the scissor technique [19], involves the introduction of a rigid guide wire into the true channel and another into the false channel, both using the same sheathed introducers (8-F minimum, 45 cmlong) installed by the femoral route. A fixed point on the guide wires and graduated, clear-cut advance of the introducer allow a tear to be made in the flap. A tear is observed either in the centre of the flap or at the ex- Fig. 24.3.Type 3A, 3B and 3C lesions. FL false lumen, TL true

lumen

Table 24.2. Objectives of imaging techniques when aortic dissection is suspected

To perform the diagnosis of aortic dissection or hematoma To determine the level of the extension into the aorta (ascending, cross, descending)

To analyse the trajectory of the true and false lumens throughout the total aorta and to evaluate the position of the intimal flap (compression or not of the true lumen) To detect entry tears: numbers and location

To diagnose thoracic complications of the aortic dissection To analyse possible extension into branches of the aorta and disconnection of the origin; to look for ischemic signs in the organs:

Supra-aortic vessels (brain ischemia) Visceral arteries (kidneys and bowel ischemia) Iliac arteries (lower limb ischemia)

To evaluate tortuosity, calcification and the diameter of the iliac and common femoral arteries for a possible endovascular treatment such as a thoracic stent-graft

(4)

tremities of the flap, or else the dissection is continued around the remainder of the circumference, extending the height of the fenestrated aorta. This latter mechanism is the most frequent. It can then be useful to unfold the flap by inflating a large-diameter balloon (over 12 mm) inside the thoracic aorta and retracting it as far as the iliac junction, with the balloon inflated. The risk of a torn flap folding back on itself must be taken into account as this can turn and trigger ischemia in the lower limbs [20].

The insertion of a complementary stent will then become necessary. It is also important to carry out stenting of the flap beneath the fenestration site if the false channel is perfused without an exit; there is a risk of aortic rupture linked to the very high pressure in the false channel.

Lastly, the scissor fenestration technique does not need to be extensively long; fenestration of 3±5 cmseems sufficient. This generally lowers the pressure in the false channel, relieves compression of the true channel, relieves the ischemia linked to the dynamic mechanism, in- hibits complications and gives the surgeon the option of returning at the end of the acute episode with a view to closing all the entry sites. However, in certain cases, fenestration of the intimal flap at the subrenal level is not sufficient to relieve dynamic compression on the renal and digestive arteries; this can be explained by blood flowing predominantly in the true channel, to the low-re- sistance organs, provoking an attraction of the intimal flap, which remains pressed against the ostium. It then becomes necessary also to install an aortic stent in the true lumen, above the visceral branches. The technique of fenestration is reserved for emergency cases with se- vere intestinal ischemia (Fig. 24.2). This technique, which is carried out in less than 1 h in the angiography room,

provides immediate relief from the symptoms. In the event of renal lesion and delayed treatment, an acute tu- bular necrosis can also arise with recovery of renal func- tions in 3 weeks. In patients presenting with chronic symptoms, it is rare to have to carry out a fenestration.

Implantation of bare stents in the abdominal aorta or in the arteries of the organs affected by the malperfusion is carried out using classic endoprostheses. The use of a strong radial action stent is preferable in cases where the true channel is compressed by the false channel. This is why we currently prefer to use balloon- mounted stents. The positioning of a stent at the root of a visceral branch can sometimes prove tricky; this stent must, in effect, push back the false channel that is com- pressing the true channel in the artery but also at the root. The stent must therefore overlap into the aorta and apply pressure on the false channel (Fig. 24.3), but the latter does not provide stable support; a sufficiently long stent is required in the artery to maintain the whole system. Negotiation of the bend between the aorta and the malperfused artery can be difficult if the balloon-mounted stent, with strong radial action, exceeds 3 cmin length. Account should also be taken of the lack of atheroma, which normally maintains the stent after expansion, and therefore of the risk, after retraction of the balloon, of the stent falling into the aorta, carried away by the balloon. The implantation diameter of the stent must be equal to or greater than that of the treated artery to prevent any secondary movement. The ostial tears, with malperfusion (type 3c) (Fig. 24.1), also necessitate implantation of a stent (Fig. 24.3).

The mechanisms of malperfusion of the visceral branches of the abdominal aorta and the iliac axes can

Fig. 24.4.Schematic proposition for new clinical practices in aortic dissection

(5)

be related. When fenestration is necessary, it is this treatment that is carried out first; it is often necessary to complement fenestration with the implantation of a stent on one or several branches. However, the full ex- tent of the remaining lesions is not always easy to as- certain by postfenestration angiography. This highlights the importance of preoperative contrast angiography for a better understanding of the mechanisms of malperfusion, before carrying out arteriography. It is sometimes useful to carry out the procedure in two phases with a new clinical evaluation and diagnostic imaging (echo-Doppler or contrast angiography).

In cases of type B dissection, the implantation of a stent-graft to close the entry site at thoracic level is a therapeutic possibility [21]; it is rarely carried out in the emergency treatment of malperfusion. The availabil- ity of stent-grafts, the necessity for a full examination beforehand and the slow regression of the symptoms after implantation are the principal reasons. Emergency implantation of a thoracic stent-graft is indicated in cases of rupture of the false channel. In cases of sub- acute or chronic symptoms, treatment with a stent-graft can be proposed after anatomical evaluation. The symptoms can take several weeks to disappear owing to thrombosis in the false channel and the slow regression of the latter.

We systematically combine endovascular treatment with medical treatment and observation in recovery or in the cardiac intensive care unit [2]. Blood pressure must be controlled, even if this requires the intravenous administration of several antihypertensive drugs. We start an anticoagulant treatment with intravenous heparin in cases of malperfusion in order to combat organ ischemia. Aortic dissection is no longer a contraindica- tion to the use of heparin in cases of associated malperfusion. The dose administered must ensure efficient anti- coagulation. After fenestration, regardless of whether a stent was installed in the visceral branches or a stent graft was used, anticoagulant treatment is continued until malperfusion is relieved and the symptoms disappear. No antiaggregation treatment is used.

24.6 Conclusion ± Therapeutic Guidelines

To conclude, visceral malperfusions must be systematically investigated (preferably by thoracic, abdominal and pelvic CT angiography) during the course of aortic dissections as their presence leads to high mortality. Yet visceral malperfusions can be treated using effective endovascular therapies. Their presence leads to a change in the treatment guidelines and lends too much cre- dence to the overly classic dogma: a type A dissection must be surgically corrected and a type B dissection must be treated medically. Modern treatment guidelines are based on the presence or absence of complications.

The dissection complications must be treated immedi- ately before considering prophylactic treatment. Type B dissections, just like type A ones, can become compli- cated owing to malperfusion. It is therefore important to hospitalise the patients, in order to carry out essential diagnostics and design an appropriate course of treatment. Relying on a multidisciplinary treatment protocol, we propose that the organisation chart in Fig. 24.4 should reduce the mortality and morbidity of patients with this condition.

References

1. Wolf JE, Eicher JC, Rezaizadeh-Bourdariat K. Dissection aortique. Rev Prat 2002; 52:1084±1088.

2. Erbel R, Alfonso F, Boileau C, Dirsch O, Eber B, Haverich A, Rakowski H, Struyven J, Radegran K, SechtemU. Diag- nosis and management of aortic dissection: Task Force on Aortic Dissection, European Society of Cardiology. Eur Heart J 2001; 22:1642±1681.

3. Kouchoukos NT, Dougenis D. Surgery of the thoracic aorta. N Engl J Med 1997; 336:1876±1888.

4. Cambria RP, Brewster DC, Gertler J, Moncure AC, Gus- berg R, Tilson MD, Darling RC, Hammond G, Mergerman J, Abbott WM. Vascular complications associated with spontaneous aortic dissection. J Vasc Surg 1988; 7:199±

5. Mehta RH, Suzuki T, Hagan PG, Bossone E, Gilon D, Llo-209.

vet A, Maroto LC, Cooper JV, Smith DE, Armstrong WF, Nienaber CA, Eagle KA. Predicting death in patients with acute type A aortic dissection. Circulation 2002; 105:200±

6. Fabre O, Vincentelli A, Willoteaux S, Beregi JP, Prat A.206.

Preoperative fenestration for type A acute aortic dissection with mesenteric malperfusion. Ann Thorac Surg 2002; 73:950±951.

7. Deeb GM, Williams DM, Bolling SF, Quint LE, Monaghan H, Sievers J, Karavite D, Shea M. Surgical delay for acute type A dissection with malperfusion. Ann Thorac Surg 1997; 64:1669±1675.

8. Williams DM, Lee DY, Hamilton BH, Marx MV, Narasim- hamDL, Kazanjian SN, Prince MR, Andrews JC, Cho KJ, Deeb GM. The dissected aorta: part III. Anatomy and radiologic diagnosis of branch-vessel compromise. Radiol- ogy 1997; 203:37±44.

9. Gaxotte V; Cocheteux B, Haulon S, et al. Relationship of intimal flap position to endovascular treatment of malperfusion syndromes in aortic dissection. J Endovasc Ther 2003; 10:719±727.

10. Chemla P, Rousseau H, Otal P, Chabbert V, Joffre F. Ima- gerie de l'aorte. Rev Prat 2002; 52:1066±1072.

11. Rousseau H, Otal P, Soula P, Colombier D, Joffre F. Diag- nostic et traitement endovasculaire de la pathologie aortique thoracique. J Radiol 1999; 80:1064±1079.

12. Sommer T, Fehske W, Holzknecht N, Smekal AV, Keller E, Lutterbey G, Kreft B, Kuhl C, Gieseke J, Abu-Ramadan D, Schild H. Aortic dissection: a comparative study of diagnosis with spiral CT, multiplanar transesophageal echocardiography, and MR imaging. Radiology 1996; 199:347±

13. Ledbetter S, Stuk JL, Kaufman JA. Helical (spiral) CT in352.

the evaluation of emergent thoracic aortic syndromes.

Traumatic aortic rupture, aortic aneurysm, aortic dissection, intramural hematoma, and penetrating atherosclerot- ic ulcer. Radiol Clin North Am1999; 37:575±589.

(6)

14. Sebastia C, Pallisa E, Quiroga S, Alvarez-Castells A, Dom- inguez R, Evangelista A. Aortic dissection: diagnosis and follow-up with helical CT. Radiographics 1999; 19:45±60.

15. Rubin GD, Shiau MC, Schmidt AJ, Fleischmann D, Logan L, Leung AN, Jeffrey RB, Napel S. Computed tomographic angiography: historical perspective and new state-of-the- art using multi detector-row helical computed tomography. J Comput Assist Tomogr 1999; 23(Suppl 1):S83±90.

16. Elefteriades JA, Hammond GL, Gusberg RJ, Kopf GS, Baldwin JC. Fenestration revisited. A safe and effective procedure for descending aortic dissection. Arch Surg 1990; 125:786±790.

17. SlonimSM, Miller DC, Mitchell RS, Semba CP, Razavi MK, Dake MD. Percutaneous balloon fenestration and stenting for life-threatening ischemic complications in patients with acute aortic dissection. J Thorac Cardiovasc Surg 1999; 117:1118±1126.

18. Chavan A, Hausmann D, Dresler C, Rosenthal H, Jaeger K, Haverich A, Borst HG, Galanski M. Intravascular ultra- sound-guided percutaneous fenestration of the intimal flap in the dissected aorta. Circulation 1997; 96:2124±

2127.

19. Beregi JP, Prat A, Gaxotte V, Delomez M, McFadden EP.

Endovascular treatment for dissection of the descending aorta. Lancet 2000; 356:482±483.

20. Lookstein RA, Mitty H, Falk A, Guller J, Nowakowski FS.

Aortic intimal dehiscence: a complication of percutaneous balloon fenestration for aortic dissection. J Vasc Interv Radiol 2001; 12:1347±1350.

21. Dake MD, Kato N, Mitchell RS, Semba CP, Razavi MK, Shimono T, Hirano T, Takeda K, Yada I, Miller DC. Endo- vascular stent-graft placement for the treatment of acute aortic dissection. N Engl J Med 1999; 340:1546±1552.