Diseases of Aorta - Aortic dissection

AORTIC​ ​DISSECTION

Aortic dissection ​is a condition which involves a tear in the inner layer of aorta.

Aortic wall has three layers. When the tear occurs in the intima, blood flowing inside the aorta under pressure creeps into the layers of aortic wall and dissects it.

One​ ​of​ ​the​ ​major​ ​contributing​ ​factors​ ​is​ ​uncontrolled​ ​hypertension.

The extent of the split can vary and this decides the severity and symptoms of Aortic​ ​dissection.

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Aortic​ ​dissection​ ​can​ ​be​ ​classified​ ​based​ ​on ● Location​ ​and​ ​extent​ ​of​ ​dissection ● Duration​ ​of​ ​symptoms

Types​ ​according​ ​to​ ​location​ ​of​ ​Aortic​ ​Dissection: Different​ ​segments​ ​of​ ​aorta​ ​can​ ​be​ ​affected​ ​by​ ​the​ ​dissection.

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Type​ ​A​ ​Dissection: When​ ​the​ ​ascending​ ​aorta​ ​is​ ​affected​ ​irrespective​ ​of​ ​the​ ​extent Type​ ​B​ ​Dissection: When Ascending Aorta is not affected. Here usually dissection is limited to the Descending​ ​aorta.

Types​ ​according​ ​to​ ​onset​ ​and​ ​duration: Acute​ ​Aortic​ ​dissection: Sudden and recent onset is described as acute. Usually less than 4 weeks in duration Chronic​ ​Aortic​ ​Dissection: Duration​ ​more​ ​than​ ​4​ ​weeks

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Symptoms: Pain: Aortic dissection is usually associated with severe pain. Site of pain may vary depending on the location of dissection. For example, ascending and arch dissection will have severe chest pain. Descending thoracic aortic dissection may have chest and upper back pain. Abdominal aortic dissection presents with severe lower​ ​back​ ​pain​ ​and​ ​abdominal​ ​pain.

Other​ ​Symptoms: Depending on the aortic branches affected by the dissection some symptoms may appear. When the abdominal branches are involved pain may be predominant.

Dissection can affect the lower limb vessels and that can cause severe leg pain. If coronary arteries are involved, the symptoms may be severe and patient may have angina or even heart attack (MI). Involvement of Carotid arteries can rarely cause strokes.

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Diagnosis: Clinical suspicion is very crucial in clinching the diagnosis, as the situation can mimic many conditions. The definite diagnosis is made by an ECHO and CT aortogram.

Echo can detect the dissection flap and the extent can be seen. Aortic valve can be assessed. CT aortogram can give precise location, extent, branch involvement and any rupture of pseudo lumen. Due to the accuracy and detail, CT aortogram is the GOLD​ ​STANDARD​ ​in​ ​aortic​ ​dissection.

Treatment: Treatment broadly depends on the type of dissection. As a rule of thumb, Acute type A dissection warrants an emergency surgery. This is because it can potentially affect the coronaries and can be fatal. The mortality approaches 60% with out surgical​ ​intervention.

On the contrary, type B dissections are largely managed conservatively. Surgery is generally reserved for complications like visceral, renal or limb artery ischemia or aneurysm​ ​of​ ​pseudolumen.

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Type​ ​A​ ​Aortic​ ​Dissection: As soon as the diagnosis is made, planning of treatment should be started. The extent of dissection, aneurysm formation, presence of rupture and the branch involvement​ ​usually​ ​dictates​ ​the​ ​type​ ​of​ ​surgery.

The commonest scenario is a dissection starting at the ascending aorta just above the level of Right Coronary Artery and extending to variable distance of aorta. The tear usually involves the arch partly or completely. It may even involve one or more of the major arch vessels. But as long as the perfusion to these vessels are intact and there is no aneurysm formation of the pseudolumen, surgical intervention of arch is not indicated. The treatment then would be an Aortic root replacement. The valve may be replaced or preserved depending on the presence or absence​ ​of​ ​valve​ ​or​ ​annulus​ ​involvement.

When the arch of aorta is badly damaged or the psuedolumen is aneurysmal in this area, the arch should be addressed during surgery. Depending on the extent of involvement,​ ​part​ ​(Hemiarch)​ ​or​ ​entire​ ​(Total​ ​Arch)​ ​arch​ ​may​ ​be​ ​replaced.

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Type​ ​B​ ​Aortic​ ​Dissection: Traditionally, type B dissections (Dissections beyond the left subclavian artery) are treated​ ​conservatively​ ​unless​ ​one​ ​of​ ​the​ ​following​ ​situations​ ​is​ ​present. ● Aneurysm​ ​of​ ​pseudolumen. ● Tear​ ​or​ ​leak​ ​of​ ​the​ ​psudolumen ● Viscral branch or limb branch involvement causing decrease in perfusion of an​ ​organ.

However, persisting pain not responding to conservative treatment is a relative indication for intervention now a days. Various methods of interventional procedures​ ​are​ ​attempted​ ​to​ ​control​ ​the​ ​primary​ ​tear​ ​in​ ​the​ ​intima.

One​ ​common​ ​interventional​ ​method​ ​is​ ​to​ ​stent​ ​across​ ​the​ ​proximal​ ​intimal​ ​tear.

This prevents the blood from entering the pseudo-lumen and eventually blood in the​ ​pseudo-lumen​ ​gets​ ​thrombosed.

Whenever decision is made to treat the type B Dissection conservatively, a close follow up is mandatory. CT Aortogram/MR Aortogram should be performed at 3 months​ ​and​ ​one​ ​year.

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