Aortic Dissection Symptoms and Diagnosis: CT, Echo and ECG

Aortic dissection symptoms are severe chest pain, often tearing through to the back, together with signs that the blood supply to an organ or limb is failing: a stroke, a cold leg, abdominal pain or a pulse or blood pressure difference between the limbs. Diagnosis rests on a high index of suspicion and is confirmed by CT angiography of the aorta, supported by echocardiography (ultrasound of the heart).

For Dr. Dinesh Kumar Mittal, Senior Director & HOD Cardiothoracic and Vascular Surgery, Fortis Hospital, Shalimar Bagh, New Delhi, India, diagnosis is the weakest link in the care of these patients. In the figures he presented, as many as 65% of dissections were missed at the first examination, and the 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. With an untreated mortality of 1 to 2% an hour, that delay is often fatal. This article sets out the warning signs, the traps in the ECG and chest X-ray, and exactly what the CT scan must answer before treatment is planned. For the disease as a whole, see the complete guide to acute aortic dissection.

Aortic dissection misdiagnosis: why it is so often missed

Aortic dissection is missed because its symptoms imitate commoner conditions. Patients arriving in the emergency department are suspected of gastritis, a heart attack or musculoskeletal back pain, and the possibility of dissection is never raised. Dr. Mittal called it one of the biggest diagnostic dilemmas in emergency medicine.

The second reason is that the classic risk factor is not always there. Many patients have hypertension, but some do not, and some have no apparent risk factor at all. A doctor waiting for a textbook patient will miss a large share of cases.

Symptoms of aortic dissection: what the patient describes

The symptoms follow the dissection as it travels along the aorta and into its branches.

• Chest pain: severe and sudden, typically when the dissection involves the ascending aorta or arch, and compounded by myocardial ischaemia when it reaches the coronary arteries.
• Back pain: as the dissection extends down the descending aorta.
• Abdominal pain: when it reaches the abdominal aorta and the gut loses its blood supply (mesenteric or splanchnic ischaemia).
• Stroke or paraplegia: when the vessels to the brain or spinal cord are involved.
• Syncope: a sudden faint.
• Acute heart failure: when the dissection disrupts the aortic valve and causes sudden, severe aortic regurgitation.
• Acute limb ischaemia: when the dissection flap or false lumen cuts off the artery to a leg.
• Acute renal failure: when both renal arteries arise from the false lumen.

Dr. Mittal's rule for the clinic and the emergency department is practical: unexplained, excruciating chest, back or abdominal pain that nothing else explains should make a doctor think of dissection, particularly in a patient with a history of uncontrolled hypertension. So should a stroke, acute heart failure, a difference between the radial and leg pulses, or severe abdominal pain with signs of bowel ischaemia.

Signs of aortic dissection on examination

Examination adds three groups of clues to aortic dissection.

1. History of hypertension. Often episodic or untreated rather than steady and controlled.
2. Pulse and blood pressure differences. A difference between the arms, or between the radial pulses and the pulses in the legs, results from the false lumen compromising flow into one branch. It is among the most useful bedside signs.
3. Signs of rupture or leak. Hypotension, pallor and anaemia suggest the aorta is bleeding. Bruits may be heard over the carotid, subclavian or femoral arteries.

A pulse or blood pressure difference, or signs of bleeding, in a patient with severe pain raises the probability of dissection enough to justify urgent imaging.

Aortic dissection on the ECG: ST elevation and the thrombolysis trap

The ECG in aortic dissection matters mostly because it can mislead. Some patients present with ST elevation and Q waves, and the emergency team diagnoses a myocardial infarction (heart attack). In the data Dr. Mittal presented, about 4.6% of patients with type A dissection had ST elevation and Q waves.

The consequence can be catastrophic. Dr. Mittal has seen, at many centres, patients with dissection thrombolysed because of their ST changes. Thrombolytic (clot-dissolving) and anticoagulant drugs are contraindicated in aortic dissection, because they can turn a contained dissection into a fatal haemorrhage.

ST elevation appears when the dissection involves a coronary ostium, most often the right coronary artery, and the changes are then confined to that coronary territory. Most patients with dissection do not show ischaemic changes at all; the ECG is often normal or shows non-specific changes or left ventricular hypertrophy from long-standing hypertension. A patient with chest pain, an ECG showing only left ventricular hypertrophy and a pulse difference between the arms is a patient who needs a CT scan, not thrombolysis.

Chest X-ray signs of aortic dissection

A chest X-ray cannot confirm or exclude dissection, but Dr. Mittal wanted physicians to know the signs, because they may be the first investigation a clinic can perform. If one or two of these are present, the patient needs further investigation:

• widening of the mediastinum (the central compartment of the chest), more than 8 cm;
• enlargement of the aortic knob (the shadow of the aortic arch);
• inward displacement of calcification in the aortic wall;
• displacement of a bronchus;
• pleural effusion.

He showed a case in which the right border of the ascending aorta was visibly enlarged on the plain film, and the CT of the same patient showed the dilated aorta and the entry tear.

Blood tests for aortic dissection

Blood tests support the diagnosis and assess the damage rather than make the diagnosis. Dr. Mittal's panel covers:

• Full blood count and haemoglobin, which falls with bleeding.
• Renal function, because malperfusion can affect the kidneys.
• CPK (creatine phosphokinase), as a marker of myocardial ischaemia when a coronary artery is involved.

Serum smooth muscle myosin heavy chain is reported to have good diagnostic accuracy, but it is not widely available and his team does not use it.

CT angiography: the test that confirms aortic dissection

CT angiography of the aorta (CT aortography), a contrast-enhanced CT scan of the whole aorta and its branches, is the diagnostic test of choice. Dr. Mittal listed the reasons:

• high specificity, so a positive scan is reliable;
• available 24 hours a day;
• rapid, with a diagnosis in 5 to 10 minutes;
• minimally invasive;
• less operator-dependent than the alternatives;
• able to show the true and false lumens, the extent of the dissection and every branch artery;
• useful for follow-up after treatment.

The checklist a CT must answer

Confirming a dissection is only the first question. Before treatment is planned, Dr. Mittal works through a full checklist using CT angiography together with a detailed echocardiogram.

1. Is it a dissection? Confirm the diagnosis.
2. Proximal or distal? Does it involve the ascending aorta? The treatment of the two is entirely different.
3. Site of the entry tear. In the ascending aorta or not.
4. Extent. How far the dissection runs, and which vessels arise from the true lumen and which from the false lumen.
5. Cerebral vessels. How far the arteries to the brain are involved.
6. Limb vessels. Whether a limb is at risk of ischaemia.
7. Aortic diameter. Recorded, though less decisive in the acute setting.
8. The aortic valve. How far the valve is involved. In his last two patients, the valve itself was normal despite moderate aortic regurgitation, and it could be preserved.
9. Coronary arteries, arch branches and visceral arteries.
10. Pericardial effusion. A sign that the aorta may be leaking or about to rupture. A ruptured or impending rupture changes the treatment strategy and the prognosis entirely.
11. False-lumen patency. Whether the false lumen is open or contains thrombus.
12. Landing zones. If endovascular repair is planned, whether there is healthy aorta in which a stent graft can seal.

The treatment decisions that follow from these answers are set out in aortic dissection treatment: type A surgery and type B TEVAR.

Echocardiography, MRI and angiography in aortic dissection

Echocardiography is the essential partner to CT. It shows the status of the aortic valve, quantifies aortic regurgitation (a leak back through the aortic valve, present in many of these patients), assesses left ventricular function and detects pericardial effusion. Dr. Mittal wants centres without a surgical programme to be capable of good echocardiography, because an echo showing a dissection flap, aortic regurgitation or a dilated aorta is enough to raise a strong suspicion and set transfer in motion. Transthoracic echocardiography is the usual first look; transoesophageal echocardiography gives a closer view of the aortic root and valve and is routine in the operating theatre.

MRI is accurate but, in his assessment, less suitable in the acute setting: it takes longer and is not available everywhere.

Digital subtraction angiography is no longer useful for diagnosis. It retains a role when malperfusion needs to be confirmed or excluded.

When to suspect aortic dissection and refer

Dr. Mittal's message to physicians outside surgical centres was that the first step is entirely in their hands: think of the diagnosis. Educate clinicians first and patients later, so that dissection is on the list for any unexplained severe pain. Arrange CT angiography where it exists, use echocardiography where it does not, and transfer suspected cases to a cardiac surgery centre without delay. In 25 years of practice, he has seen about 10 patients die after reaching hospital, some because consent was delayed.

How a team decides between surgery, medical treatment and endovascular repair, and the questions doctors put to him in the session, are covered in the aortic dissection treatment guide and the Live Discussion.