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The diagnosis and management of disorders of the ascending aorta and aortic arch remain as formidable challenges in cardiovascular medicine and surgery. Until the advent of the modern era of cardiac surgery with cardiopulmonary bypass, this region of the aorta was all but inaccessible to any surgical intervention and even now definitive medical therapies remain elusive. Accurate diagnosis requires the sophisticated, yet now readily available, imaging techniques developed over the past few decades and rarely can be made on clinical grounds alone. While not as prevalent as atherosclerotic peripheral and coronary arterial occlusive disease, diseases of the proximal aorta are common enough that cardiovascular specialists are inevitably confronted with them in many different clinical settings. The sometimes enigmatic but dramatic and lethal presentation of ascending aortic dissection (AD) has attracted considerable public attention in recent years (See, for example, the 2004 Pulitzer Prize winning series by Kevin Helliker and Thomas Burton of The Wall Street Journal). Dissection and rupture, often occurring in otherwise vigorous individuals, are catastrophic biomechanical failures, and the end result of many different aortic pathologies. Aneurysmal degeneration is a common manifestation of proximal aortic disease and precedes many, but not all, instances of dissection. Congenital disease often involves obstructive lesions while atherosclerosis in this region does not. Yet even in the absence of luminal narrowing or aneurysm, the changes in aortic compliance or stiffness that accompany disease and aging have important pathophysiologic effects not only downstream in other organ systems but upstream in the heart.
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In this chapter the focus is on the anatomy, microstructure, functional mechanics, and pathophysiology of the proximal aorta. This field encompasses a broad range of disciplines from multiple areas of clinical medicine, genetics, cell biology, and biomedical engineering and an attempt has been made to integrate information derived from all these areas to provide a basic level of understanding of the function, structure, and pathologies and their systemic ramifications of this unique segment of the arterial system. The preceding chapter is designed to provide a more immediately clinical discussion.
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PROXIMAL AORTIC STRUCTURE AND MECHANICS
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The ascending aorta includes the aorta from the level of the aortic valve to the origin of the brachiocephalic artery. It is further divided into the sinus portion containing the three sinuses of valsalva and the tubular portion. The aortic valve, aortic sinuses, and coronary ostia are integral elements of the sinus portion of the aorta. The proximal aorta from the ventricular outlet to the tubular part of the ascending aorta including the sinotubular junction (STJ) is called the aortic root. The precise anatomy of the aortic root1 is of considerable clinical importance in the surgical treatment of both aneurysmal disease and aortic valvular disease. The aortic arch, which gives rise to the brachiocephalic, left common carotid, and left subclavian arteries, extends transversely from the ascending aorta to the descending ...