Since the first reported ascending aortic replacement by Cooley and DeBakey in 1956, operative technique refinement and critical care advancement have led to a significant improvement in survival for patients with ascending aortic aneurysmal disease. An improved understanding of distinct aortic pathologies and predisposing factors for aortic rupture and dissection has inspired a commitment to risk stratification and guidelines for elective surgical intervention. Improvements in diagnostic imaging and an increase in the incidental identification of aortic pathology on unrelated imaging have supported a significant increase in the incidence of thoracic aortic aneurysms to a projected rate of 10.4 cases per 100,000 person-years.

Isolated aneurysms of the ascending tubular aorta that taper to a normal diameter in the distal ascending aorta with a normal diameter at the sinuses of Valsalva are relatively uncommon and are estimated to occur in 13.5% of cases, with the majority of cases involving either the aortic annulus and the sinotubular junction or the aortic arch and branch vessels. Therefore, techniques for aortic valve conservation or replacement and branch vessel reconstruction are often needed in the operative reconstruction of the ascending aorta. The two surgical approaches to ascending aortic aneurysms involving the aortic root include aortic valve-sparing operations and composite replacement of the aortic valve and ascending aorta with a heart valve conduit. Aneurysms isolated to the ascending aorta without aortic root involvement are selectively approached by replacement of the aneurysmal segment with a composite ascending aortic graft.

In addition to anatomic principles for reconstruction, an understanding of distinct aortic pathologies and concomitant aortic valve disease is needed in the operative repair of ascending aortic aneurysms. Annuloaortic ectasia comprises a spectrum of aortic pathologies that involve dilation of the aortic annulus. This condition is predominately associated with an aneurysm of the aortic root; however, may occur independent of aneurysm formation and manifest as bicuspid or tricuspid aortic valve insufficiency or occur in patients with a subaortic ventricular septal defect. Importantly, ascending aortic aneurysms may also occur in the absence of annuloaortic ectasia. Dilation of the aortic sinuses results in aortic insufficiency when the aortic annulus and sinotubular junction dilate, resulting in poor leaflet apposition and central insufficiency. As the aortic root dilates, the aortic cusps become thinner, overstretched, and may develop stress fenestration in the commissural areas. This is an important consideration for the aortic valve repair at the time of ascending aortic aneurysm reconstruction.

The focus of this chapter is to review diagnostic standards and surgical principles for reconstruction in the treatment of aortic root and ascending aortic aneurysm with or without annuloaortic ectasia.

Aortic dimensions remain a principle consideration for intervention and reconstruction of the aortic valve, root, and proximal ascending aorta. Chest radiography may impart the initial diagnosis of ascending aortic aneurysm, with the findings of a convex contour to the right superior mediastinum or a loss of the retrosternal air space on lateral examination. Computed tomography (CT) and magnetic resonance imaging (MRI) provide detailed aortic wall assessment in addition to the capability for three-dimensional reconstruction, branch vessel evaluation, and aortic valve characterization. The reliability and reproducibility provided by these novel imaging techniques in coordination with transesophageal echocardiography (TEE) have largely replaced traditional aortography for the evaluation of the proximal ascending aorta, aortic valve, and aortic branch vessels, as aortography is limited in the determination of the presence of intraluminal hematoma. Aortography may be used selectively to localize the coronary ostia and to detect concomitant aortic regurgitation or coronary atherosclerotic disease. Measurements obtained with CT or MRI should be obtained perpendicular to the axis of blood flow and represent the external diameter of the aorta. Echocardiographic measurements are obtained in a similar plane; however, should be calculated for the internal aortic diameter. The dimension of the aortic root should be obtained at the segment of widest diameter, typically the mid-sinus level. In addition to dedicated aortic imaging, duplex carotid ultrasonography is indicated in patients older than 65 years of age or in younger patients with symptomatic presentation, physical exam findings, or additional atherosclerotic vascular disease consistent with an increased risk for cerebrovascular disease, as undetected carotid disease is a significant risk factor for stroke following ascending aortic replacement.

CT provides an estimated diagnostic accuracy of 92% for abnormalities of the thoracic aorta, with correct prediction of a requirement for circulatory arrest in 94% of patients. Electrocardiogram gating is required for ascending aortic disease to eliminate motion artifact that can resemble aortic dissection. In addition, CT provides a reliable method for the localization of calcification and evaluation of aortic valve morphology, function, and coronary artery anatomy. Axial CT introduces the potential for misinterpretation of the proximal aortic diameter, as ascending aortic elongation results in a C-shape of the aorta and resultant vertical plane orientation of the aortic valve.

MRI provides a comparable sensitivity and specificity for thoracic aortic pathology
that may exceed that afforded by CT. The principle advantages to MRI include the identification of anatomic dissection variants and the enhanced diagnosis of branch vessel disease, aortic valve pathology, and left ventricular dysfunction in the absence of radiation or iodinated contrast. Clinical adoption has been limited by the time required for image acquisition, an inability to utilize gadolinium in patients with renal insufficiency, and a contraindication for use in patients with metallic implants including pacemakers.

Transthoracic echocardiography (TTE) provides an understanding of biventricular function while enabling visualization of the aortic valve and the proximal several centimeters of the ascending aorta to above the sinotubular junction. This capability supports the application of TTE in the evaluation of patients with proximal aortic aneurysms to determine the potential presence of concomitant valvular pathology or ventricular dysfunction. Importantly, TTE lacks reliability in mid-ascending aortic assessment. Thus, TTE is not recommended as the primary imaging modality for ascending aortic aneurysm surveillance. TTE may, however, be used to follow patients with aortic disease limited to the aortic root. TEE allows the assessment of biventricular function, segmental wall motion, and the potential for coronary artery ostia involvement in the setting of concomitant proximal aortic dissection. Intraoperative TEE provides a principle technique for the confirmation of preoperative diagnoses and the detection of pericardial or pleural effusions and aortic regurgitation. In addition, TEE enables the determination of the extent of aortic dissection and the identification of the intimal tear location, while providing characterization of aortic aneurysms and the confirmation of appropriate true lumen flow upon commencement of cardiopulmonary bypass.

Aortic aneurysm formation is most commonly the result of medial degeneration, which is characterized by noninflammatory smooth cell loss, fragmentation of elastic fibers, and basophilic ground substance accumulation in the medial layer of the vessel wall. Debate persists regarding the pathogenesis of aortic medial degeneration and the resultant ascending aortic aneurysmal dilation; specifically, whether medial lesions are the result of primary connective tissue defects or arise secondary to hemodynamic forces, or both. Functional and structural asymmetry and decreased elastic performance of the aorta are proposed mechanisms for aneurysm formation, implicating advanced age, coronary artery disease, chronic smoking, and 17β-estradiol deficiency as primary predisposing factors to aneurysm formation. An increased incidence of ascending aortic aneurysm is also demonstrated in the setting of congenital or acquired aortic valve malfunction, an aortic bicuspid or unicuspid valve, and in hereditary connective tissue disorders including Marfan syndrome (fibrillin-1 gene mutation), Ehlers-Danlos syndrome type IV (deficiency in type III collagen), Loeys-Dietz syndrome, and familial thoracic aortic aneurysm and dissection. Medial degeneration may, therefore, be the result of damage and repair events in the aging aorta, abnormal postvalvular hemodynamics (excessive injury), and connective tissue disorders (impaired repair).

In addition to medial degeneration, established etiologies for thoracic aortic aneurysm formation include atherosclerosis, infection, inflammation, trauma, cardiopulmonary resuscitation, and chronic dissection. While atherosclerosis is considered a principal factor in the development of descending aortic aneurysms, dedicated study has demonstrated only a minor role for atherosclerosis in the pathogenesis of aneurysms of the ascending aorta. Inflammatory conditions include bacterial or fungal aortitis, Takayasu arteritis, and giant cell arteritis. Prior to improved diagnosis and the development of effective antibiotic therapies, syphilitic aortitis was the most common cause of ascending aortic aneurysmal enlargement, characterized by an obliterative end arteritis of the vasa vasorum. Risk factors associated with the development of thoracic aortic aneurysms include hypertension, smoking, and chronic obstructive pulmonary disease. Dedicated preoperative risk stratification and determination of underlying cardiopulmonary function, potential bleeding diatheses, and underlying connective tissue defects are critical in the operative planning for reconstruction of the ascending aorta.

Bicuspid aortic valves (BAVs) represent the most common congenital heart anomaly, occurring in 0.9% to 2% of the population. Patients with a BAV demonstrate significantly increased wall stress, accounting for the increased propensity for aortic dilation, rupture, and dissection in this patient population. In addition to increased wall stress, patients with BAV disease have larger dimensions at the aortic annulus, sinus of Valsalva, the sinotubular junction, and the ascending aorta irrespective of the valve hemodynamic function. Microscopic studies and gene expression profiles for patients with BAV and concomitant ascending aortic aneurysm have demonstrated that the media of the aorta above the BAV is consistently abnormal and independent of both inflammatory response and the hemodynamic function of the valve. These data demonstrate that aortic root dilation is a morphological correlate of intrinsic structural aortic abnormalities in patients with BAV disease.

In retrospective study of patients with BAV disease, the aortic valve morphology was found not to be predictive of the pathologic anatomy of the thoracic aorta; however, patients with predominant aortic insufficiency demonstrated the highest incidence of aortic root dilation. In patients with a BAV and an absence of baseline aortic aneurysm, a 16-year mean follow-up (6,530 patient-years) has demonstrated an estimated age-adjusted relative risk of 86.2 for aneurysm formation in comparison to the general population. In patients with BAVs, aortic dissection incidences for patients 50 years and older at baseline was 17.4 per 10,000 patient-years and increased to 44.9 per 10,000 patient-years in individuals with concomitant aortic aneurysm. These epidemiologic data support a research commitment to risk-stratification modeling and selective preventative reconstruction in patients with BAV disease.

The aortic valve is described as the aortic root, given the anatomic and functional relationships of the aortic cusps and surrounding structures. The aortic root is defined by four distinct anatomic components: the aortic annulus, the aortic cusps, the aortic sinuses or sinuses of Valsalva, and the sinotubular junction. The aortic annulus is the attachment between the aortic root and the left ventricle. The aortic root is attached to the ventricular myocardium throughout 45% of its circumference and to the anterior leaflet of the mitral valve and the membranous septum in the remaining 55%. The aortic annulus forms a superior border to the three triangular structures of the left ventricular outflow
tract. The triangle below the right and left cusps consists of ventricular muscle and is rarely affected by connective tissue disorders of the aortic root. The additional two triangles are fibrous and flatten to acquire a broader base in patients with a dilated aortic annulus. The semilunar aortic cusps have a base and free margin extending from commissure to commissure. The sinotubular junction refers to the ridge above the commissures and is functionally important for the aortic root as it suspends the aortic cusps. Dilation at the sinotubular junction moves the free margins of the aortic cusps away from one another to result in central aortic insufficiency with ineffective coaptation. The aortic sinuses are anatomically described as the arterial walls contained within the aortic annulus and sinotubular junction (Fig. 60.1). Isolated dilation of the sinuses has no effect on valvular competence. The aortic sinuses maintain coronary artery blood flow during the cardiac cycle while maintaining eddies and currents to facilitate closure of the aortic cusps during diastole.

The aortic root contains a proportionally high content of elastin with a resultant compliance that diminishes with anatomic progression into the aortic arch and descending aorta. Systolic expansion of the ascending aorta represents the transfer of a portion of left ventricular kinetic energy into potential energy within the aortic wall. Diastolic recoil transfers this potential energy into kinetic energy for resultant forward flow. The transverse diameter of the aortic annulus is approximately 15% to 20% larger than the sinotubular junction diameter in young patients. The aging process results in a loss of elastic fibers within the arterial wall and the aortic root becomes less compliant, an effect that is associated with the presence of diastolic left ventricular dysfunction. An understanding of these dynamic physiologic and disease-specific changes in the ascending aorta will guide the approach to reconstruction.

Acute rupture of the aneurysmal ascending aorta is manifested as severe anterior chest pain with sudden-onset of congestive symptoms resulting from associated cardiac tamponade. Patients with acute rupture or dissection necessitate emergent resuscitation and operative intervention. In the absence of rupture or dissection, ascending aortic aneurysms are primarily identified on unrelated imaging or during surveillance of associated anomalies. The predominant symptoms of aneurysmal enlargement result from distal arch involvement and impingement on nearby structures and may manifest as chest pain, back pain, dyspnea, hoarseness, or transient neurologic deficit. Ascending aortic enlargement may result in airway compression or superior vena cava obstruction. Heart failure symptoms may arise in the setting of aortic valve regurgitation secondary to aortic root or ascending aortic dilation. On physical examination, a widened pulse pressure or diastolic murmur signifying aortic insufficiency may be present in the setting of sinotubular ridge or aortic root enlargement. BAV disease may manifest as asymptomatic stenosis or regurgitation of the valve on physical examination.

Central venous access is obtained through the internal jugular vein and hemodynamic pressure monitoring is placed into the radial artery. Pulmonary artery catheter monitoring is recommended to follow intraoperative filling pressures and cardiac output. Large-bore peripheral intravenous access is achieved for intraoperative resuscitation. In preparation for potential circulatory arrest, continuous pressure monitoring through the femoral artery is recommended as the radial artery waveform may be dampened. General endotracheal anesthesia is initiated and maintained through a single-lumen endotracheal tube. A nasopharyngeal temperature probe is recommended to monitor cooling and rewarming.