Ann Thorac Surg 2009;87:1377-1378. doi:10.1016/j.athoracsur.2009.03.025
© 2009 The Society of Thoracic Surgeons
Original Articles: Adult Cardiac
Invited Commentary
George J. Koullias, MD
Illinois Cardiac Surgery Associates, 515 NE Glen Oak Dr, Suite 202, Peoria, IL 60613
(Email: georgekoullias{at}hotmail.com).
I read with great interest the article of Shingu and colleagues [1], demonstrating an elevated augmentation index (AI) in thoracic aortic aneurysms and thoracic aortic dissections.
The concept of AI is not very well known to many cardiac surgeons, but it has received intense study and attention in the last decade of the cardiac physiology literature.
As the incident systolic pressure wave generated by cardiac ejection encounters zones in impedance, such as arterial bifurcations and obstructive lesions, part of the wave is reflected backward, summing with the systolic wave, something that is noticed as a notch to the ascending part of the blood pressure waveform (Fig 1). In young patients who do not have significant atherosclerotic disease and preserved ejection fraction, this notch is almost at the top of the systolic part of the waveform, because this backward-moving wave reaches the pressure sensor much later. After a coronary artery bypass procedure in a young patient, it is common, and very familiar to cardiac surgeons, during the first hours in the intensive care unit, to observe a dicrotic blood pressure waveform, which is something commonly referred as "hyperdynamic circulation" (Fig 1; Left). This is in contrast to patients of advanced age, hypertension, and left ventricular heart failure; in these cases, the increased wave velocity causes the reflected wave to reach back to the heart earlier, in mid-systole, considerably increasing the late-systolic load, impairing cardiac ejection, and diastolic relaxation (Fig 1; Right). Normal elastic arterial tissue absorbs more energy and reflects and propagates a pressure wave much slower than a stiff atherosclerotic vessel.
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Fig 1. Aortic pressure (mm Hg). (Left) Dicrotic blood pressure waveform, commonly referred to as "hyperdynamic circulation." (Right) Increased wave velocity causes the reflected wave to reach back to the heart earlier, in mid-systole, considerably increasing late-systolic load, impairing cardiac ejection, and diastolic relaxation. (AI = augmentation index; IP = inflection pressure; PP = pulse pressure.)
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The magnitude of this reflected pressure wave can be quantified by the AI (Fig 1). The AI is essentially proportional to peripheral afterload. High AI means high arterial stiffness and afterload. Consequently, high AI is associated with increased myocardial mass, increased myocardial oxygen consumption, and increased left ventricular diastolic dysfunction. It is intuitive for surgeons that a dilated thoracic atherosclerotic aorta and a chronic thoracic aortic dissection with a thrombosed false lumen and a true lumen with a decreased diameter represent a state of increased afterload (ie, increased AI); the study of Shingu and colleagues [1] demonstrates this in a very clear, concise, and easily reproducible fashion.
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References
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- Shingu Y, Shiiya N, Ooka T, et al. Augmentation index is elevated in aortic aneurysm and dissection Ann Thorac Surg 2009;87:1373-1378.[Abstract/Free Full Text]
Related Article
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Augmentation Index Is Elevated in Aortic Aneurysm and Dissection
- Yasushige Shingu, Norihiko Shiiya, Tomonori Ooka, Tsuyoshi Tachibana, Suguru Kubota, Satoshi Morita, and Yoshiro Matsui
Ann. Thorac. Surg. 2009 87: 1373-1377.
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