Aortic dissection with concomitant acute myocardial infarction: From diagnosis to management.

Acute aortic dissection an extremely severe condition having a high risk of mortality. The classic symptom may mimic other conditions such as myocardial ischemia, leading to misdiagnosis. Coronary malperfusion associated with aortic dissection is relatively rare, but when it occurs, it may have a fatal result for the patient. The diagnosis of acute coronary syndrome may lead to the inappropriate administration of thrombolytic or anticoagulant treatment resulting in catastrophic consequences. Emergency imaging techniques help to guide the correct diagnosis. Transthoracic echocardiography is useful as a first imaging test, and may be followed by transesophageal echocardiography, or other imaging techniques. Surgery represents the treatment for these patients. However, with the aim to stabilize the patient and to reduce myocardial damage, initial preoperative endovascular coronary intervention has been reported.

INTRODUCTION

Acute aortic dissection (AD) is an extremely severe condition with an incidence of 5–30 cases per million inhabitants per year, having a high risk of mortality.[1]

The classic symptom of a sudden tearing chest or interscapular migrating pain, as well as other clinical signs of AD, may mimic other conditions such as myocardial ischemia, or in some cases may coexist with other conditions. In these cases, the diagnosis of aortic dissection may be delayed or even missed and is sometimes made only at postmortem examination.[2]

Coronary malperfusion associated with aortic dissection is relatively rare, but when it occurs, it may have a fatal result for the patient. Up to 30% of patients suffering from AD are initially suspected of having other conditions.[2] Nevertheless, there are several reported cases of acute AD associated with electrocadiographic (ECG) signs of myocardial ischemia.[1-3]

The diagnosis of acute coronary syndrome (ACS) may lead to the inappropriate administration of thrombolytic or anticoagulant agents or platelet glycoprotein IIb/IIIa receptor antagonists, resulting in catastrophic outcomes.[45] Antithrombotic and thrombolytic treatments double hemorrhagic complications and mortality. Cannesson et al. found 25 patients with acute myocardial infarction (MI) induced by AD who were erroneously treated by fibrinolysis. In such cases, the mortality ranges from 69% to 100%, and probably this is an underreported problem.[6]

Therefore, it is critical for these patients to obtain, as soon as possible, a correct diagnosis in order to rule out or confirm the presence of dissection, and to proceed with the correct treatment.

In order to save such compromised patients, aggressive coronary revascularization and aortic repair is essential.

CLASSIFICATION OF AORTIC DISSECTION

The two common classification criteria for aortic dissection are the DeBakey and Stanford classifications.

The Stanford classification divides aortic dissection into type A and type B. Type A dissection involves the ascending aorta, and eventually progresses to the distal aorta. Type B dissection starts at the level of the descending aorta.[7]

The DeBakey classification distinguishes types I, II, and III. Type I involves both the ascending and descending aorta, type II involves only the ascending aorta, including the arch, and the type III aortic dissection spares the ascending aorta and the arch of the aorta.

A further subdivision distinguishes between five classes of aortic dissection as follows:[8]

Class 1: classic aortic dissection with an intimal flap between the true and false lumens;

Class 2: medial disruption leading to intramural hemorrhage or hematoma;

Class 3: subtle or discrete aortic dissection with bulging of the aortic wall;

Class 4: aortic plaque ulceration following plaque rupture;

Class 5: iatrogenic or traumatic aortic dissection.

ETIOLOGY

In AD, there is a separation of the different aortic layers and formation of an intimal flap separating the true and false lumen. Different mechanisms weakening the aorta's media layers may lead to higher wall stress, inducing aortic dilatation and aneurysm formation. Eventually intramural hemorrhage, aortic dissection, and rupture may occur.[9]

Many conditions have been described as predisposing factors:

Long-standing hypertension can be a risk factor for aortic dissection. A retrospective study of 161 necropsy cases of aortic dissection found that hypertension had been present in 52% of type I or II dissections and in 75% of patients with type III dissections.[10]

Connective tissue disorders leading to aortic dissection can be subdivided into hereditary fibrillinopathies (including Marfan's syndrome and Ehlers–Danlos syndrome), hereditary vascular diseases (such as bicuspid aortic valve), or vascular inflammation (as in giant cell arteritis, Takayasu arteritis, Behçet disease, and syphilis).

Trauma may be a cause of aortic dissection, such as deceleration trauma occurring in car accidents or falls from heights.[9]

Iatrogenic factors may be represented by complications of catheterization or cardiothoracic surgeries.

The transient rise in blood pressure occurring with cocaine use has been reported as a cause of aortic dissection as well.[11]

Aortic dissection can follow a circadian rhythm. It happens most frequently in the early morning hours between 6 and 10 o’clock and in the early afternoon. It is also more common in the cold seasons of winter and spring compared to summer.[12]

CLASSIFICATION OF ACS

The basic pathophysiological mechanism in most ACS is represented by myocardial underperfusion. The classic symptom is chest pain.

Patients with ACS can be classified into two groups, based on the electrocardiogram (ECG) study:[13]

Patients with typical chest pain and persistent ST-segment elevation (>20 min). This ACS is usually due to acute total coronary occlusion. Many of these patients will progress to an ST-elevation MI (STEMI).

Patients with chest pain but without persistent ST-segment elevation. They present with transient ST-segment depression or T-wave inversion. They may progress into non-ST elevation MI (NSTEMI) or unstable angina.

DEFINITION OF MI AND CONCOMITANT AD

In the document ‘Universal definition of MI’ by the Joint ESC/ACCF/AHA/WHF Task Force, it is reported “myocardial cell necrosis might occur in the absence of clinical signs of ischemia (among others) in AD”.[14]

The ESC Guidelines for NSTE-ACS, mention AD as a “non-coronary condition with troponin elevation”.[13]

On the other hand, there have been many reports of AD with coronary artery involvement producing myocardial ischemia/infarction with different mechanisms. For this reason, it has been suggested that AD should be listed as a possible cause of type 2 AMI.[15]

MECHANISM OF CORONARY MALPERFUSION IN PATIENTS WITH AORTIC DISSECTION

The intimal flap in the ascending aorta can tear the remaining intimal layer of the aorta producing a circumferential flap. The fluctuating flow of blood produces a back-and-forth movement of the circumferential flap with a consequent dislodgement.[16-22] The consequent invagination of the flap can occur both distally, as described for the first time by Hufnagel and Conrad in 1962, and proximally. They named this particular presentation of acute aortic dissection as “intimointimal intussusception”.[23] During diastole, the circumferentially dissected flap prolapses into the left ventricle outflow tract resulting in intermittent diastolic occlusion of the coronary ostia and aortic valve insufficiency:[2425] The length of the prolapsing intimal flap can influence the severity of coronary occlusion. Long prolapsing flaps reaching the middle of the left ventricle cavity can probably cause ischemia by completely blocking the coronary ostia during the diastole, while shorter ones can produce only their partial occlusion.[162026] In the first case, myocardial infarction usually occurs due to the complete and persistent occlusion of the coronary ostia. In the second case, partial occlusion may be intermittent and myocardial ischemia may be present as an intermittent pattern.

Spittell studied 236 cases of aortic dissection and found that dissection affects the right coronary artery more often than the left coronary artery.[2] Therefore, aortic dissection complicated by MI is considered to involve more often the inferior wall rather than the anteroseptal wall.

During dissection of the ascending aorta, the false lumen can extend proximally toward the coronary ostia producing several mechanisms of coronary occlusion.[27-34]

Neri et al.[27] classified into three main types of lesions:

Type A ostial dissection, with a disruption of the inner layer limited to the area of the coronary ostium. He reported that this type of lesion might create a local flap and cause coronary malperfusion by a trapdoor mechanism.

The type B dissection, with a coronary false channel, is a retrograde extension of the aortic dissection extending into the coronary artery wall. The false lumen can extend for several centimeters along the length of the artery and, in diastole, its blood flow compresses the true lumen.

The type C lesion is a circumferential detachment with an inner cylinder intussusception. The coronary artery is completely detached from the aortic root and the dissection encircles the coronary artery. In this case, there is a direct coronary obstruction resulting in ischemia.

With these lesions, the coronary artery can be compressed by a hematoma formed in the false lumen.[35]

CLINICAL SIGNS AND DIAGNOSES

In AD, the classic sign is represented by an abrupt onset of tearing interscapular or chest pain.

Pain localization typically shifts from one area to another, in relation to disease progression. Signs of malperfusion of different body areas may be present, including absent or reduced pulses and a different blood pressure between the limbs, neurologic signs, or visceral abdominal malperfusion may be present as well. However, sometimes classic clinical signs may be absent, and other conditions might mimic AD. The risk is to delay the diagnosis and the appropriate surgical treatment. Nevertheless, in AD patients with concomitant ECG signs of myocardial ischemia,[1236] the prompt and correct diagnosis of AD is very important in preventing misdiagnosis with inappropriate treatment. Thrombolytic or anticoagulant therapy would have catastrophic consequences. Emergency transthoracic echocardiography (TTE), performed at the bedside or in the emergency room, is useful in finding images of AD. TTE represents a valuable diagnostic imaging technique for the initial evaluation of patients with suspected AD, and is often sufficient for diagnosis. Transesophageal echocardiography (TEE) may also be performed at bedside, and would represent the subsequent imaging technique for unclear cases, or to complete the diagnosis.[3738] Computed tomography and magnetic resonance imaging are excellent for the diagnosis of AD, but the results are more time consuming and not always easily available.[39-41]

The question is whether to delay thrombolytic or anticoagulant therapy in patients presenting with acute MI, considering the low incidence of concomitant AD. However, the benefits of this strategy that allows an exact imaging diagnosis, probably outweigh the risks of potentially dangerous treatment in patients with AD.

INITIAL MANAGEMENT

The initial management of patients with suspected aortic dissection should consist of the following steps:[8]

Detailed medical history, complete physical examination, and transfer to the intensive care unit

Intravenous line and blood sample. Laboratory test should include: CK, TnT(I), myoglobin, WBC, D-dimer, hematocrit, lactate dehydrogenase (LDH)

ECG for documentation of ischemia

Heart rate and blood pressure monitoring

Pain relief (using, i.e., morphine sulphate)

Reduction of systolic blood pressure. This may be attained with beta-blockers (i.v. propranolol, metoprolol, esmolol, or labetalol), or with i.v. sodium nitroprusside in patients with severe hypertension. Calcium channel blockers may be used to lower blood pressure in patients with obstructive pulmonary disease.

Imaging tests (TOE, CT, and MRI) to confirm or exclude AD (especially in patients with signs of ischemia on ECG) before starting thrombolysis, anticoagulation, or antiaggregation therapy.

INVASIVE MANAGEMENT

Sometimes, in patients with AD and concomitant MI, under critical hemodynamic conditions and with clinical symptoms suggestive of MI alone, the correct diagnosis may be missed.

In this clinical scenario, the patient may arrive directly in the catheterization laboratory for primary percutaneous intervention. The diagnosis in this case is done during angiography.[42] Nevertheless, both in cases of missed or correct diagnosis, it is possible to start the first step of invasive management with the aim to stabilize the patient's clinical condition.

Several authors reported on the treatment of dissected coronary arteries with stent implantation, both into the right coronary artery and left main coronary trunk.[333443-48] This procedure, allowing a prompt and adequate myocardial blood flow, can prevent extensive myocardial damage. These authors reported an immediate clinical improvement with resolution of chest pain and normalization of blood pressure in many of the treated cases.

Other authors also report on the use of a coronary perfusion catheter positioned into the dissected coronary artery.[314950] Passive perfusion balloon catheters were first designed for the prevention of ischemia during standard percoutaneus coronary angioplasty (PTCA), and to treat periprocedural coronary artery perforation.[51] There are several types of passive perfusion balloon catheters available in the market. All of them have the same principle design: side-holes in the shaft of the catheter proximally and distally to the balloon, allowing passive perfusion during balloon inflation. Coronary flow will be re-established and will depend on the aortic perfusion pressure. These perfusion catheters are tracked over standard PTCA guidewires and inserted into the coronary vessel. Thus, they are not intended to treat the cause of abrupt vessel closure, i.e., to attach the dissection membrane to the vessel wall, but to provide blood flow into the region at risk of ischemia, until surgery can be performed. In patients with symptomatic coronary artery dissection, the effectiveness of this approach has been documented by studies comparing the surgical outcome of patients with acute coronary artery dissections. Q-wave infarctions were reduced, and the use of the internal mammary artery was possible in a large number of cases in comparison to emergency bypass grafting performed in patients without perfusion catheter insertion. Moreover, patients with a perfusion catheter in place had a more favorable outcome after surgery in comparison to patients brought to the operating theatre with aortic counterpulsation or medical treatment.[5253]

Intracoronary stenting or positioning of a coronary perfusion catheter, by maintaining an adequate coronary perfusion, reduce myocardial damage and improve the hemodynamic status. In the specific concomitant condition of AD and MI, some authors have reported their experience on this subject.[46-48] These lifesaving procedures can serve as bridge approach to gain time for critical unstable patients before definitive surgery. The aim of this invasive management is to reduce the extent of myocardial cell necrosis.

The subsequent immediate surgical repair then promises better short- and long-term outcomes for these patients.

However, it should be mentioned that cardiac catheterization is not always a straightforward procedure in patients with AD, due to the presence of intimal flaps. In these conditions, the true lumen may be missed and iatrogenic complications may occur.

SURGICAL MANAGEMENT

The surgical management of dissected coronary arteries during AD is controversial.

Neri et al. treated 24 dissected coronary patients from a total of 211 patients with acute type A dissections. They preferred to repair the dissected coronary arteries instead of performing coronary artery bypass graft (CABG) and described various local repair techniques. These different techniques were dependent on the type and extent of the lesion, and on which coronary artery was involved.[27] In type A coronary dissection (Neri classification), where the dissection involves the ostium without disrupting the coronary vessel, the coronary artery can be repaired with a continuous suture conjoining the dissected artery layers, leaving the ostium in continuity with the aortic wall. If the ostium is completely surrounded by the dissection or in the presence of a fragile tissue, the author prefers to excide the ostium, conjoin the dissected aortic layers with gelatin–resorcinformalin glue and a running suture, and anastomise the ostial button to the tubular graft.[27] If the dissection progresses beyond the ostium, the repair depends on the extent of the dissection and the presence of intussusception. In the event of type B coronary dissection, the coronary artery is incised longitudinally and a patch repair is performed with a running suture conjoining the dissected arterial layers and the patch. Either a saphenous vein or an autologous pericardium can be used as a patch.[27] In the presence of a type C coronary dissection, with coronary intussusception, the segment of coronary artery is transected and a saphenous vein reconstruction of the vessel is performed.

The advantages of this local repair are: anatomic reconstruction of the coronary artery ostia, avoidance of complete graft-dependent perfusion of large areas of the myocardium, and preservation of antegrade flow in the coronary trees, thus avoiding the risk of competitive flow and coronary redissection.[2754] However, mobilization and repair of acutely dissected coronary arteries is potentially dangerous and problematic.

In contrast, in other reports, most patients received CABG and ascending aorta replacement.[28] In fact, other authors consider the CABG technique preferable to local repair because the procedure is simple and less invasive, while local repair requires proven surgical skills. Kawahito et al. suggested performing CABG in all types of coronary artery dissections.[28] However, along with the above mentioned potential disadvantages there is also the risk of closure of the vein graft anastomosed to a woven Dacron graft.[54] However, in type A, where the dissection is localized to the ostium, the local repair may be easier to perform.

Kazui emphasizes the importance of protecting the myocardium during this type of surgery. He suggests the use of blood cardioplegia delivered both retrograde via the coronary sinus, and antegrade through the non-dissected coronary ostium.[54]

If the valve can be preserved, the dissected aortic valve commissures are resuspended.[27284445] If damaged, the valve can be changed with a tubular graft or a separate aortic valve replacement and ascending aorta replacement with a tubular graft in supravalvular position can be performed.

However, despite all the efforts to save these patients, even with earlier referral to surgery, good myocardial protection and improved surgical techniques, the mortality rate for patients with AD complicated by extensive myocardial damage remain high. For this reason, in his authoritative commentary on the treatment of these patients, Kazui concludes: “it is advisable to establish exclusion criteria for emergency operation in these patients”.[54]

CONCLUSIONS

AD complicated by MI is an extremely serious condition. The correct diagnosis is very important in these patients before starting any other therapy. Misdiagnosis with early thrombolytic or anticoagulant treatment may result in catastrophic consequences. Emergency imaging techniques help to guide the correct diagnosis. Transthoracic echocardiography is useful as a first imaging test, and may be followed by other tests. Treatment is by surgery. However, with the aim to stabilize the patient and to reduce myocardial damage, initial endovascular coronary intervention has been reported. Unfortunately, even with prompt and correct treatment, the mortality rate remains high.