Recent Advances in Acute Type A Aortic Dissection

Acute type A aortic dissection (TAAAD) is a critical condition in patients presenting with chest pain, but it seems relatively rarer than acute coronary syndrome. The incidence of TAAAD is estimated at 2.0-4.04 per 100,000/year; about 22% of patients with TAAAD die before being sent to a hospital. The mortality is high but is different based on the location of the dissection. Many classifications systems, e.g., the DeBakey, Stanford, Lansman, and European Working Group, have been developed to classify the types of TAAAD. First, we define TAAAD and its two variants, intramural hemorrhage (IMH) and penetrating atherosclerotic ulcer (PAU). Second, we introduce the classification systems of TAAAD. Third, we show the incidence, prevalence, and mortality of TAAAD and its variants. Fourth, we discuss the gender, age, and ethnic differences in the presentations of TAAAD. In the last part of the chapter, we talk about the incidence and mortality of TAAAD comorbid with some specific conditions, diseases, and disorders, viz., aortic aneurysm, atherosclerosis, hypertension, diabetes, pregnancy, trauma, substance abuse, Marfan, Loeys-Dietz syndrome, vascular type Ehlers-Danlos syndrome, bicuspid aortic valve, and coarctation of the aorta.

Acute aortic dissection is life-threatening. The pathophysiology of aortic dissection usually starts from an intimal tear with subsequent penetration of blood through the aortic media layer. Sometimes, a spontaneous hemorrhage of the vasa vasorum within the aortic wall will cause an aortic intramural hematoma to form, which will initiate aortic dissection. Blood in the aortic wall results in a dissection plane within the media and creates a false lumen, which may propagate antegradely or retrogradely along the aorta. Aortic media degeneration and cystic medial necrosis are common findings in aortic dissection. In addition to aortic medial abnormalities, there are several risk factors that are associated with acute aortic dissection. Hypertension is the most common prevalent risk factor. Recent studies have found that several mutations involving genes encoding for components of extracellular matrix and smooth muscle cell proteins are responsible for aortic dissection in Marfan syndrome, Loeys-Dietz syndrome, vascular Ehlers-Danlos syndrome, and familial thoracic aortic aneurysm and dissection. Congenital aortic diseases, such as coarctation of the aorta or bicuspid aortic valve are important risk factors for aortic dissection. Other acquired conditions, such as aortitis, pregnancy, drug abuse, trauma, and some medical and surgical procedures are also related to aortic dissection. This chapter makes an extensive review of the current knowledge about the pathophysiology of acute aortic dissection. The known risk factors that contribute to the occurrence of aortic dissection will be discussed.

Aortic aneurysms are challenging surgical entities of the utmost importance to cardiovascular surgeons; when coupled with a connective tissue disorder, the complexities are multifold. The prevalence of these diseases is low, but Marfan, Ehlers- Danlos, and Loeys-Dietz syndromes are ubiquitous, affect both genders, and occur in all ethnic groups and geographical locations. Because of this, knowledge of the genetic and clinical manifestations of each syndrome is indispensible to the physician. A comprehensive overview incorporating the biomolecular and physical anomalies described in the literature is essential to providing optimal care for patients with these diseases.

Acute (type A) aortic dissection is a life-threatening condition that requires prompt diagnosis and management. Risk factors include hypertension, pregnancy, coarctation of the aorta, bicuspid aortic valve, inflammatory and connective tissue disorders, and prior aortic or cardiac surgery. The typical clinical presentation includes sudden-onset severe chest pain that may radiate to the neck or back. Although routine tests, such as an electrocardiogram (ECG), a chest X-ray (CXR), and a D-dimer may raise the suspicion of aortic dissection, none is sufficient as the sole diagnostic test. A triple rule-out computed tomography (CT) scan has a high negative predictive value for excluding acute coronary syndrome, pulmonary embolism, and aortic dissection in patients who present with an undifferentiated chest pain syndrome, negative cardiac biomarkers, and a non-diagnostic ECG. Patients presenting with conditions that predispose them to aortic dissection or high-risk features in a history or on a physical examination should undergo definitive diagnostic imaging of the aorta. CT is the most frequently used imaging modality because of its availability, speed, and high sensitivity and specificity. Transesophageal echocardiography, which offers sensitivity and specificity similar to that of CT, can be used with unstable patients. Currently, magnetic resonance imaging (MRI) is infrequently used in acute settings because image acquisition times are longer and the modality is less widely available. However, newer imaging sequences that can be done rapidly without breath-holding and without an intravenous contrast medium may increase the utility of MRI in the future.

Malperfusion in type A aortic dissection (TAAAD) describes symptoms and signs of end-organ dysfunction attributable to low blood flow. It is associated with a high mortality rate. Differentiating between static and dynamic malperfusion provides some explanation of its pathophysiology. However, the surgical outcomes of patients with malperfusion are yet to be improved despite progress in perioperative care. This chapter addresses the issues associated with managing patients with TAAAD complicated with malperfusion. We reviewed the major contemporary series to collect the best clinical evidence. Although new techniques, such as percutaneous fenestration and stenting, are emerging as alternative treatments, the best strategy for managing patients with malperfusion is controversial. Some groups have proposed a nonsurgical approach followed by delayed surgery for primary aortopathy. The pros and cons of this strategy are discussed. Patient selection is critical. The delayed-surgery strategy provides patients with mesenteric malperfusion or multiorgan malperfusion an option when the surgical risk is prohibitively high. In contrast, immediate proximal aortic repair is still indicated for coronary malperfusion.

Acute type A aortic dissection (TAAAD) is potentially fatal. Emergency or urgent surgery is generally believed to be able to save and extend the patient’s life, and delayed surgery or overtly conservative medical treatment can result in a high probability of sudden death. Approximately one-third of all patients with TAAAD have preoperative end-organ malperfusion syndromes that might cause myocardial, cerebral, spinal, mesenteric, renal, and limb ischemia. Acute coronary involvement (ACI) has an approximate incidence of 6-19% in patients with TAAAD. TAAAD with sinus of Valsalva involvement and coronary malperfusion generally requires aortic root replacement and coronary artery bypass grafting; it is also associated with significant surgical mortality. The therapeutic goal for patients with ACI is the rapid restoration of myocardial perfusion and correction of the damaged aortic root structure in order to alleviate the malperfusion syndrome. Techniques selected for treating these patients should be considered based on the causal mechanism. Endovascular strategies are emerging that may lead to less-invasive treatment options for patients who are considered poor candidates for direct surgical repair because they have TAAAD, which involves the ascending aorta. Nevertheless, it is questionable whether these treatment options can be used on patients with ACI. TAAAD patients with ACI have an increased risk of postoperative in-hospital mortality and less-favorable long-term survival. Regular medical follow-up, careful periodic imaging surveillance of the aorta, and lifestyle modification are mandatory for patients after repairs for ACI.

In operations requiring a cardiopulmonary bypass (CPB), surgery for acute ascending aortic dissection still has high morbidity and mortality. Known major complications are impairment of consciousness and neurologic disability. To improve outcomes, many methods have recently been introduced: varying degrees of systemic hypothermia to increase the hypoxemic tolerance of the brain, and different arterial cannulated sites for brain perfusion. Previously, the CPB was set up using femoral artery cannulation with deep hypothermic circulatory arrest (DHCA) (16-18 °C). Because more neurologic complications were found, other extra-perfusion methods with retrograde cerebral perfusion from the superior vena cava have been used for years. Recently, peripheral right subclavian and axillary artery cannulation have been used, and reported outcomes seem better. Selective cerebral perfusion is another choice for peripheral cannulation. Innominate artery cannulation has also recently become popular. Some surgeons prefer central arterial cannulation, in which the approach is directly from the dissected ascending aorta, to peripheral cannulation, in which the approach is through the cardiac apex. Transapical cannulation consists of inserting the arterial cannula through the apex and the aortic valve so that it lies in the sinus of Valsalva. In summary, cannulation sites for CPB can be peripheral arteries or central arteries. Although we recommend using axillary arterial cannulation, we discuss and summarize the advantages and disadvantages of multiple methods of CPB, and compare clinical outcomes between the two cannulated sites.

Brain protection is a critical issue in distal reconstruction of acute type A aortic dissection, during which the open anastomosis within the aortic arch inevitably requires temporary exclusion of the cerebral blood flow. Several brain protection strategies, either by decreasing brain metabolism or by supplying the brain with oxygenated blood, have been developed and widely investigated. This chapter reviews the history, rationale, experimental studies, and clinical results of different brain protection strategies. Their individual pros and cons, clinical comparative results, and evolving trends are discussed.

Acute aortic dissection is the most lethal cardiovascular disease. Despite improvements in diagnosis, surgical techniques, anesthetic techniques, organ protection, and perioperative management, surgery for acute type A aortic dissection still has high morbidity and mortality rates, particularly in cases in which the aortic root is involved. The surgical management strategy of choice for aortic root repair remains controversial. The important characteristic of this strategy is to judge which root reconstruction procedure should be done and whether the aortic valve should be preserved or replaced. The choice is based on saving the patient’s life and reducing the likelihood of reoperation. Other critical factors include the extent of aortic sinus involvement, the magnitude of regurgitation, and the surgeon’s experience and skill.

Acute type A aortic dissection (TAAD) is an emergency condition that requires immediate surgical intervention. Marfan syndrome (MFS) is an inherited autosomal dominant disease with an incidence of approximately 1 per 5000 live births. The mean age at death for untreated patients with MFS is 32 years with aortic dissection, aortic rupture, or cardiac failure caused by mitral and aortic valve insufficiency (also called “regurgitation”) as the predominant cause of death in more than 90% of cases. There is an overall annual risk of 0.17% of aortic events and death occurring in patients with MFS; the risk is 4 times higher with an aortic diameter greater than 50 mm. The best surgical options for treating patients presenting with MFS, TAAD, and a normal aortic valve remain controversial. The modified Bentall procedure with a composite graft replacement of the aortic root has been used for decades with acceptable results. Alternatively, emerging techniques of aortic valve-sparing root replacement are increasingly being evaluated as a potential option. The focus of this chapter will be the techniques of aortic valve-sparing root replacement in patients with MFS presenting with TAAD and normal aortic valve morphology, as well as the early and long-term results of this operation based on the current literature.

Acute type A aortic dissection (TAAAD) is the most lethal disease of the aorta and requires emergency surgery to prevent sudden death caused by an aortic rupture and secondary end-organ ischemia due to compromised aortic branch vessels. Despite technical advances in surgery, anesthesia, organ-protection, and critical care, surgical morbidity and mortality remains high because of hemodynamic instability, of repairing the acutely dissected aorta, and of manipulating the secondary compromised multiple organs. To save the life of the patient, a complete resection of the intimal tear and reapproximation of the proximal and distal edges of the dissected aorta are widely accepted as the primary objectives of surgery. However, late reoperation after surgery for acute TAAAD has been frequently reported. Extended aortic arch replacement and concomitant intervening of the distal aorta can be undertaken to reduce the incidence of late complications of the distal aorta. Total arch replacement combined with implanting a stented elephant trunk-graft is recommended to treat TAAAD when the aortic arch requires repair. This technique offers the superiority of combined surgical and interventional approaches while simultaneously avoiding the shortcomings of either of these approaches alone. The sooner a patient with TAAAD is treated, the better will be the remodeling of the two layers of the dissected aortic wall after a stented elephant trunk-graft has been implanted, and the less end-organ ischemia secondary to aortic branch vessel compromise there will be.

The early and late results of surgery for acute type A aortic dissection (TAAAD) has improved significantly since the 1960s. The common causes of death are perioperative bleeding and organ dysfunction because of the dissected aorta. The commonly reported variables that predict surgical mortality are preoperative shock, advanced age (> 70 years old), and malperfusion of distal organs. The late (postdischarge) survival rate for patients with TAAAD is consistently lower than that of the general population. Surveillance of these patients of aortic expansion, cardiac disease, and medical adherence to anti-impulse therapies is important. Late reoperation rates among these patients are decreasing and the mortality rates of reoperation have become acceptable. Distal aortic reoperation is more common than proximal aortic reoperation, and preventing open repair might be promising with endovascular techniques.

Acute type A aortic dissection (TAAAD) in the octogenarian is clinically complex because the risk-benefit ratio for surgical intervention is debatable. This is reflected by the equal incidence of medical and surgical management between the 8^th and 9^th decades of life. The goals of therapy must be individualized, and they often lean towards the maintenance quality of life. Poor postoperative outcomes may be mitigated by improving patient selection and recognizing the predictors of poor outcome. These include shock, previous aortic valve replacement, migrating chest pain, pulse deficits, and evidence of myocardial ischemia. In addition, small series have explored less invasive surgical techniques successfully used for TAAAD in the elderly. These techniques can be considered in high-risk elderly patients scheduled for surgery.

Patients who survive the initial operation of acute type A aortic dissection (TAAAD) still face the risk of aneurysm formation and rupture of the residual dissected aorta. Although surveillance of the postoperative distal aortic size is the current standard of follow-up and indication of reoperation, several parameters of false lumens have been analyzed in order to earlier identify the subgroup at risk for adverse aortic events. The associations between postoperative false lumen patency and late aortic growth, aneurysm formation, and the reoperation rate have been extensively investigated and generally accepted. Controversies do exist, however, and more detailed studies of false lumen status, including the role of partial thrombosis and the character of tear entries, have challenged the effectiveness of prognosis prediction based on false lumen patency alone. These parameters of false lumens will change our concept of postoperative follow-up and may potentially improve the long-term outcome of TAAAD by earlier selection of patients who will benefit from secondary interventions.

Acute type A aortic dissection (TAAAD) is a rare, life threatening emergency. Improvements in surgical management and postoperative blood pressure control have made it clear that the TAAAD is a brief phase in a chronic disease process. Dissection that extends to the distal arch and aorta may cause late complications such as aneurysmal degeneration. The surgeon, therefore, must manage TAAAD with this in mind, and allow extra graft length or debranch the supra-aortic vessels to facilitate late reintervention. This is particularly important in younger patients with distal aortic involvement. Options for late distal reintervention include open surgical replacement of the aorta, aneurysm exclusion with endovascular stent grafts, including the rapidly maturing branched graft technologies, or a combination of the two in a hybrid procedure.

Over the past few decades, various kinds of aortic pathologies mimicking classic aortic dissection have been demonstrated on different imaging modalities. “Acute aortic syndrome”, a new term, includes all these diseases. The most prevalent is aortic intramural hematoma (IMH). In this uncommon and potentially fatal disease, there is no intimal tear. Instead, hemorrhage within the media layer may lead to subsequent communication with the true lumen. Although the prognosis for IMH seems better than that for aortic dissection, survivors are still at risk for late adverse aortic complications such as aneurysm formation, dissection, rupture, and ulceration. The exact definition, prevalence, and outcomes for acute IMH continue to be debated. Furthermore, its management, which varies from immediate surgery to medical management only, remains controversial. The purpose of this review is therefore to present and analyze the natural history and clinical presentation of acute type A IMH. The various diagnostic modalities used and the management of type A IMH are also reviewed, with an emphasis on the current controversies.