Acute aortic dissection: a missed diagnosis

Abstract

A 60-year-old man with a history of indigestion and untreated hypertension presented with sudden-onset central chest pain which radiated to his back. Acute coronary syndrome was initially suspected but excluded in the emergency department before the patient was discharged. The pain subsequently abated to mild intermittent episodes and was misdiagnosed as indigestion. A week later the patient developed new shortness of breath and ‘flu-like’ symptoms with a positive d-dimer test. CT angiography revealed a Stanford type B aortic dissection which was causing hypoperfusion of the right kidney, resulting in an acute kidney injury. Due to uncontrolled hypertension despite rigorous antihypertensive medication and his failing renal function, the patient underwent endovascular repair and made a good recovery postoperatively.

Background

Acute aortic dissection (AAD) is a potentially fatal condition where an intimal tear in the medial layer of the aortic wall permits blood to create and flow into a ‘false lumen’ and force the layers of the aorta apart. AAD can be categorised by the Stanford classification as type A (involving the ascending aorta and/or the aortic arch, and possibly the descending aorta) or type B (involving the distal arch or descending aorta only). Due to the weakened aortic wall, the aorta may develop into an aneurysm, and is at risk of rupture. Retrograde dissection into the pericardium may cause subsequent cardiac tamponade or coronary ischaemia. If the dissecting flap occludes the visceral branches in the abdominal aorta, this may cause hypoperfusion and end-organ ischaemia including paraplegia of the lower limbs. Risk factors for AAD include hypertension, atherosclerosis, male gender, smoking and connective tissue disorders such as Marfan’s syndrome.¹

Classically, AAD presents with abrupt-onset chest pain radiating to the back which is described as a tearing or ripping sensation. However, diagnosis is often difficult as clinical presentation for AAD is diverse and the medical history usually insignificant, resulting in less than half of AAD cases being misdiagnosed² and treatment is often delayed despite the availability of imaging modalities that are accurate and quick to perform.³ Although uncommon, AAD is associated with high rates of morbidity and mortality: Approximately one-third of AAD patients die before reaching the hospital; and those who make it to hospital care have a 1% per hour mortality due to rupture or tamponade.⁴ Hence, AAD patients need to be clinically recognised and rapidly assessed through correct imaging studies to minimise the delay to receiving appropriate treatment.⁵

Case presentation

A 60-year-old man with a history of indigestion and untreated hypertension (blood pressure (BP) 192/105 mm Hg on arrival) presented to the emergency department (ED) with sudden-onset central chest pain radiating to his back and the tip of his left scapula. The pain was ‘searing’ in character, non-pleuritic, 8/10 severity and non-relenting at rest or on exertion. He felt clammy and pale during the episode; and the pain subsided while he was in ED. He had no palpitations, shortness of breath (SOB), haemoptysis, leg pain or swelling. He was queried for acute coronary syndrome (ACS) but was discharged home after investigations showed a normal ECG trace and troponin (9 ng/L), as well as a clear chest X-ray (CXR). He was noted to have chronic kidney disease (CKD) stage III with a baseline estimated glomerular filtration rate (eGFR) of 57 mL/min.

The patient visited his general practitioner 5 days later due to persistent pain symptoms which have now abated to intermittent episodes 1–2 times a day regardless of rest or exertion, lasting 5 min each, with 2/10 severity and no other symptoms. This was misdiagnosed as a progression of indigestion and the patient was offered a higher dose of omeprazole (40 mg once daily).

Three days afterwards, the patient developed a new-onset SOB in the morning without a cough, along with ‘flu-like’ symptoms including tiredness, shivers and nausea. He was apyrexial and examination of his cardiovascular and respiratory systems were normal. His blood tests showed normal troponin (6 ng/L) and a raised C reactive protein (CRP, 20 mg/L), as well as a positive d-dimer test with a Wells score of 0. He was referred back to ED on suspicion of a pulmonary embolism (PE) or AAD; the latter was confirmed via CT angiography (CTA) which showed an acute type B aortic dissection (TBAD) originating from distal to the left subclavian artery extending through the descending aorta to both common iliac arteries (figure 1). There was no organ ischaemia at the time although the right kidney appeared to be less perfused than the left (figure 2). The patient was admitted for vascular referral and put on intravenous labetalol and 4 mg oral doxazosin daily for BP control for conservative treatment—however this was unsuccessful and his BP remained high at 166/80. The patient’s renal function also continued to decline over the next few days with an eGFR of 33 mL/min which was indicative of an acute kidney injury (AKI) as a result of his AAD.

Figure 1.

Axial CT angiography of aortic arch showing dissection flap.

Figure 2.

Axial CT angiography at the level of the visceral abdominal aorta showing dissection and right renal hypoperfusion.

Due to concerns of kidney infarction and need for dialysis from renal failure, the patient underwent thoracic endovascular aortic repair (TEVAR) (figure 3). Postoperative management was complicated by a fever of unknown source, but the patient made a good recovery and his eGFR was 51 mL/min on discharge. A follow-up CTA surveillance scan was organised in 6 weeks and the patient was put on new daily oral medications for BP control including 5 mg bisoprolol, 10 mg amlodipine, 2.5 mg ramipril and 4 mg doxazosin.

Figure 3.

TEVAR stent placement. LAO, left anterior oblique; TEVAR, thoracic endovascular aortic repair.

Differential diagnosis

AAD poses a certain diagnostic challenge as it frequently presents with non-specific symptoms which may vary significantly, and as a result is missed or misdiagnosed on initial evaluation.⁵ Acute-onset severe chest pain is the most common and often the only symptom—hence this should always prompt investigations for AAD. It is classically described as tearing or sharp and may radiate to the back, shoulders and abdomen; it may also migrate as the dissection progresses. Other common signs and symptoms include hypertension, pulse deficit and syncope.¹ Some patients may present less commonly with heart failure, neurological deficits such as limb paraplegia, and signs of organ failure from malperfusion such as anuria in renal compromise.^{3 6} Around 4%–5% of patients present painlessly with other symptoms such as syncope.⁷

The main differential for AAD is myocardial infarction (MI) or ACS, which can present similarly but the onset of pain is typically less abrupt and gains intensity with time, which is usually more dull and oppressive in nature. An MI may also coexist with AAD if the coronary vessels are affected. It is important to distinguish the two as thrombolytic treatment for ACS can prove fatal if AAD is present. Other principle differentials for AAD include aortic regurgitation, aortic aneurysms, pericarditis, PE, cholecystitis and musculoskeletal pain among others depending on the presenting complaint.⁸

Investigations

An ECG is one of the most important bedside tests to distinguish AAD from ACS. Patients with symptoms suggestive of an MI but with a normal ECG should be considered to have AAD. However, ECGs in AAD patients are frequently abnormal and not specific for ACS.⁹ Biochemical markers including d-dimer, creatine kinase, CRP may be deranged, however, they remain largely investigational rather than diagnostic; although d-dimer may be used to rule out AAD as it is a sensitive test with good negative predictive value.

The principle approach to diagnosing AAD is through radiographic imaging, which aims to establish the diagnosis, localise the intimal tear, assess the extent of dissection and identify any complications such as organ malperfusion and arterial occlusion.⁶ Often times more than one imaging study is required to determine a diagnosis of AAD. A routine CXR is abnormal in 60%–90% of cases, however may be normal in the acute setting.⁵ Transthoracic echocardiography (TTE) and transoesophageal echocardiography (TEE) provide a rapid assessment for any cardiac complications and can visualise the distal ascending, transverse and descending aorta to identify an AAD and any penetrating atherosclerotic ulcers. They are often used in conjunction as TTE alone provides only minimal imaging of the aorta. Together, they have a sensitivity of 99% and specificity of 89% for AAD.¹⁰ TEE is limited by its invasive nature and any significant oesophageal disease.

CTA is most commonly used in AAD cases as it can be quickly performed in the emergency department and has a high sensitivity and specificity for AAD (95% and 85%–100%, respectively).⁶ However, contrast load may be contraindicated in patients who have or may develop an AKI as a result of AAD. CT scans also have limited ability to identify the site of the entry tear in comparison to MRI, which has the highest sensitivity and specificity for AAD (approaching 100%)¹⁰ with the added advantages of not requiring contrast dyes and no exposure to ionising radiation. However, it is not as readily available or time efficient as TTE or CT and is contraindicated in patients with metal implants.

Treatment

The three goals of initial management are to decrease shear and total aortic wall stress by limiting ventricular contraction force and lowering BP; in addition to maintaining adequate end-organ perfusion.¹¹ This is achieved by administering beta-blockers such as metoprolol, esmolol, propanolol and labetalol with a goal heart rate of <60 bpm and systolic BP of 100–120 mm Hg. If patients are intolerant of beta-blockers or BP control is inadequate, calcium-channel blockers and vasodilators may be used. Pain control with morphine is also an important aspect of managing heart rate and BP.⁶

Type A dissections always require surgical intervention to replace the aortic root as it carries risks of coronary involvement or cardiac tamponade. Uncomplicated acute TBAD (ie, without organ ischaemia) should be managed with best medical therapy (BMT) by rigorous BP control, along with close monitoring for development of any complications. In complicated TBAD where there is visceral or peripheral compromise, endovascular or surgical intervention should be considered.¹ There is some debate over whether both complicated and uncomplicated TBAD should be managed surgically: the Investigation of Stent Grafts in Aortic Dissection trial compared patients with acute TBAD who are managed with BMT alone against TEVAR plus BMT. Long-term results showed that TEVAR is associated with improved 5-year aortic-specific survival and delayed disease progression. Aortic remodelling was also observed in 91% of TEVAR patients and only 19% in the BMT group.¹²

Outcome and follow-up

The postoperative CTA showed satisfactory TEVAR and stent placement. There is reconstitution of true lumen flow with partial thrombosis of the false lumen. There was no extension of dissection or early dilatation of the aorta, and the right kidney is now perfused well along with all visceral vessels. The patient’s eGFR has now improved to 67 mL/min.

Follow-up imaging is recommended at 7 days after dissection, at discharge, 6 weeks, 3 months, 6 months, 12 months and annually thereafter. Surveillance should aim to assess for aortic expansion, aneurysm formation and any postoperative complications such as endoleaks.⁶

Discussion

It is important to recognise AAD as it can be a fatal condition: The International Registry of Acute Aortic Dissection demonstrated an overall mortality of around 23% for AAD; and 12% among those with acute TBAD.⁷ However, due to the heterogeneity of clinical features of AAD, misdiagnosis is common and occurred in 38% of cases in a study by Hagan et al,⁵ where AAD is most often confused with ACS. This does not only delay diagnosis and treatment but may also cause harm due to initiation of antithrombotic agents in the treatment of MI. In addition, patients who presented with painless AAD tend to have a worse prognosis perhaps due to delay in diagnosis.²

The patient described in this case presented with some classic features of an AAD, although clinical features could also be confused with ACS. However, after this has been ruled out with a normal ECG, troponin and CXR, given his initial presentation, further investigations should have been warranted. A TTE and TEE would have been an appropriate investigation which would have revealed his AAD. Although the patient is known to have CKD, his eGFR of 57 mL/min would still have warranted normal administration of intravenous contrast for CTA imaging according to the National Health Service protocol.¹³ This brings to attention that exclusion of ACS and a normal initial CXR should not distract physicians from pursuing further imaging with higher sensitivity and specificity.

Learning points.

• Acute aortic dissection (AAD) has a diverse clinical presentation as it can involve any part of the aorta. The principal symptom is acute-onset sharp pain, which should always require assessment for AAD.

• Special attention should be given to differentiate acute coronary syndrome and AAD.

• A normal chest X-ray does not rule out AAD. Transthoracic echocardiography, transoesophageal echocardiography and CT angiography are sensitive and specific first diagnostic tests.