Acute Aortic Dissection

Acute aortic dissection is a tear in the inner lining of the aorta that lets blood force its way into the wall and split it, creating a second, false channel. Untreated, a type A dissection kills about half of patients within 48 hours. Survival depends on suspecting it early, confirming it with CT angiography (a contrast-enhanced CT scan of the aorta) and sending the patient straight to a surgical team.

That is the case Dr. Dinesh Kumar Mittal, Senior Director & HOD Cardiothoracic and Vascular Surgery, Fortis Hospital, Shalimar Bagh, New Delhi, India, made to general practitioners, physicians and cardiologists in August 2024. He chose the topic deliberately: aortic dissection is among the most lethal emergencies in cardiac medicine, and one of the easiest to miss. This guide sets out the disease, how it is classified, what the treatment paths are and what it takes for a health system to get patients to theatre alive. Two companion articles go deeper: aortic dissection symptoms and diagnosis, and treatment of type A and type B aortic dissection.

What is acute aortic dissection?

Aortic dissection begins with a tear in the intima, the innermost layer of the aortic wall. Blood under arterial pressure enters the tear and tracks into the media, the middle layer, separating it and creating a false lumen alongside the true lumen through which blood normally flows.

The aortic wall has three layers. The intima lines the vessel. The media carries most of the smooth muscle and collagen that give the wall its elasticity and strength. The adventitia, the outer layer, is the toughest of the three. When the connective tissue of the media is defective, an intimal tear can propagate easily into it. Dr. Mittal described this as the common thread in patients with connective tissue disorders, citing Marfan syndrome and Loeys-Dietz syndrome as examples of inherited conditions that weaken the aortic wall.

Once the false lumen forms, it tends to enlarge. As it fills, it compresses the true lumen, and branches of the aorta supplied by the true lumen lose flow. That is the mechanism behind malperfusion: an organ or limb starved of blood because its artery now arises from, or is squeezed by, the false lumen. Over time, a dissected aorta often becomes aneurysmal. Dr. Mittal has seen chronically dissected aortas reach 8 to 10 cm in diameter, and in one case 12 cm.

Aortic dissection mortality: why it is so dangerous

Aortic dissection carries an early mortality of 1 to 2% for every hour it goes untreated. Dr. Mittal called it the most lethal of the aortic emergencies, and in his closing remarks the most catastrophic cardiac event of all.

The figures he presented make the point:

• Incidence: about 3 cases per 100,000 people each year.
• Untreated type A dissection: about 50% of patients die within 48 hours, and very few survive the first year without surgery.
• Missed diagnosis: as many as 65% of dissections were missed at the initial examination, and diagnosis was delayed by more than 24 hours in 39% of patients. Published series vary widely; a 2022 systematic review of 12 studies put the overall rate of initial misdiagnosis at about one in three.

Death comes in two ways. The dissection can rupture into the pericardium (the sac around the heart), the mediastinum (the central compartment of the chest), the pleural space or the abdomen. Or it can extend into a branch vessel: into the coronary arteries, causing a heart attack; into the vessels of the brain, causing a stroke; or into the visceral and limb arteries, causing end-organ malperfusion. In Dr. Mittal's account, much of the morbidity comes from that malperfusion rather than from the tear itself.

Risk factors are not always present. Many patients have hypertension, often poorly controlled or episodic, but some have no apparent risk factor at all. Correct diagnosis, he stressed, is what improves survival; misdiagnosis often leads to death.

Type A and type B aortic dissection: the classification that decides treatment

Aortic dissection is classified by whether it involves the ascending aorta, because that single fact determines the treatment.

• Type A dissection involves the ascending aorta. The mainstay of treatment is emergency surgery.
• Type B dissection spares the ascending aorta, usually with the entry tear in the descending aorta beyond the left subclavian artery. The mainstay of treatment is medical, with endovascular or surgical intervention reserved for complicated cases.

This is the Stanford classification. The older DeBakey system describes the same disease by extent: DeBakey types I and II involve the ascending aorta and correspond to Stanford type A, and DeBakey type III is confined to the descending aorta and corresponds to Stanford type B. The defining feature of type A is involvement of the ascending aorta, wherever the tear began: a dissection that starts in the descending aorta but extends backwards into the ascending aorta behaves like type A, with the same presentation and prognosis, and Dr. Mittal treats it as such.

In the data he presented, type A accounted for 62% of dissections and type B for 38%. The prognosis of the two differs sharply. Proximal (type A) dissection carries the frightening mortality figures above; distal (type B) dissection, managed well, carries far lower early mortality.

How aortic dissection presents

The classic presentation is severe chest pain, often radiating to the back. But the symptoms follow the path of the dissection, so they vary: back pain as the tear travels down the descending aorta, abdominal pain when it reaches the abdominal aorta, stroke or paraplegia when it involves the vessels to the brain or spinal cord, syncope, acute heart failure from sudden aortic regurgitation, a cold, ischaemic leg, or acute renal failure when both renal arteries arise from the false lumen.

That variety is why the disease is so often misread in the emergency department as gastritis, a heart attack or simple back pain. A blood pressure or pulse difference between the arms, or between arms and legs, is one of the most useful bedside clues. The full set of warning signs, and the ECG and chest X-ray findings that should prompt a CT scan, are covered in aortic dissection symptoms and diagnosis.

How aortic dissection is diagnosed

CT aortography (CT angiography of the aorta) is the investigation of choice. Dr. Mittal described it as the most specific and most reliable test: it confirms the dissection, shows where it starts and how far it extends, and maps which branch vessels arise from the true lumen and which from the false lumen. It takes minutes and is available around the clock.

Echocardiography complements it, showing the state of the aortic valve, the degree of aortic regurgitation, left ventricular function and any pericardial effusion. MRI is accurate but slower and less widely available, and catheter angiography now has a role mainly in assessing malperfusion.

Treatment at a glance

• Type A: surgery is the only treatment. The surgeon replaces the torn ascending aorta, and often the aortic arch, with a fabric graft, frequently a composite graft with a built-in aortic valve (the Bentall operation), and reimplants the coronary arteries. The brain is protected with deep hypothermia (cooling the body to slow the brain's demand for oxygen) and antegrade cerebral perfusion (blood pumped directly into the arteries to the brain). Endovascular stent grafts have no established role in type A dissection.
• Uncomplicated type B: medical treatment to control heart rate and blood pressure, beginning with an intravenous beta blocker.
• Complicated type B: malperfusion, rupture or impending rupture, refractory pain or hypertension, or rapid enlargement call for intervention, usually thoracic endovascular aortic repair (TEVAR), which covers the entry tear with a stent graft.

The operative steps, blood pressure targets and indications for TEVAR are set out in aortic dissection treatment: type A surgery and type B TEVAR.

Aortic dissection survival: outcomes since the early registry data

The International Registry of Acute Aortic Dissection (IRAD) pools data from more than 50 centres worldwide. Dr. Mittal was part of the team at Medanta, The Medicity, Gurugram, that contributed to it. The early IRAD results, published in 2000, showed:

The table captures the logic of treatment: surgery cuts the death rate in type A by more than half, while in type B, medical treatment outperforms surgery for most patients.

Results have improved substantially since then. In Dr. Mittal's practice today, aortic root surgery carries a mortality below 2% and a risk of neurological injury below 2%. Emergency surgery for acute type A dissection carries a mortality of around 10%, with neurological injury below 5%; extending the repair to the aortic arch adds about 5% to the mortality, and thoracoabdominal repair carries a mortality below 8%. Acute type A cases are harder because they arrive as emergencies, often at night and often in poor condition.

Across his last 100 patients, he reported losing about two, both of whom arrived with a ruptured aorta. Once patients leave hospital, he said, they do well for the rest of their lives.

Why aortic dissection surgery is demanding

Surgery for aortic dissection is intricate. Reimplanting the coronary buttons (the openings of the coronary arteries, cut out with a rim of aortic wall) is exacting work, these patients bleed heavily, and a repair that looks simple in a diagram can take 8 to 10 hours, against 2 to 3 hours for a routine coronary bypass. The cerebral circulation may have to be stopped for 40 to 45 minutes, which carries a risk of neurological injury. Bleeding often continues after the patient reaches intensive care. Dr. Mittal described the work as scary and challenging but tremendously rewarding, and said his team has learned from its mistakes to reach the results above.

Improving outcomes where aortic programmes are still developing

The second half of Dr. Mittal's session addressed doctors in countries where cardiac surgery and aortic programmes are still being built. His prescription had five parts.

1. Awareness. Clinicians first, then patients, need to know the disease exists. A doctor who has never considered aortic dissection will not suspect it.
2. Effective transfer. A patient with suspected dissection must reach a capable centre within the time window that keeps surgery possible.
3. Designated centres with echocardiography. Centres that can perform proper echocardiography can see a dissection flap, aortic regurgitation or a dilated aorta, and raise a strong suspicion while CT is arranged.
4. Timely intervention. This is a disease that cannot wait. In 25 years of practice, Dr. Mittal has seen about 10 patients die after reaching hospital, some because consent was delayed, some because of other delays, and some who deteriorated in front of the team.
5. Readiness for new technology. Hybrid repair, which combines open surgery with endovascular stent grafting, is in his view among the best options for ruptured type B dissection, and is a technique teams can learn.

He was candid that even in India, not many surgeons take on this work, because it is intimidating: the timing is difficult, rupture is always a threat, and the operation is long.

Related reading

Questions from doctors in the session, on false-lumen thrombus, coarctation of the aorta in children and protecting the brain and kidneys during surgery, are answered in the Live Discussion. For the wider surgical context, see the guides to when to refer to a vascular surgeon and advances in heart valve surgery, and the cardiac surgery and cardiology specialty hubs.