This Article Full Text (PDF) Data Supplement Alert me when this article is cited Alert me if a correction is posted Services Email this article to a colleague Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (2) Citing Articles via Google Scholar Google Scholar Articles by Pybus, D. A. Search for Related Content PubMed PubMed Citation Articles by Pybus, D. A. Related Collections Cardiovascular Equipment Complications Monitoring (Cardiac)

---

CARDIOVASCULAR ANESTHESIA

Aortic Atheromatous Plaque Instability Associated with Rotational Aortic Flow During Cardiopulmonary Bypass

From the Department of Anaesthesia, St. George Hospital, Kogarah, Australia.

Address correspondence to David A. Pybus, FANZCA, Department of Anaesthesia, St. George Hospital, Belgrave Street, Kogarah, NSW 2217, Australia. Address e-mail to dpybus{at}bigpond.net.au.

	Introduction

Top Introduction Video 1. REFERENCES

 
Rotational blood flow ("chiral asymmetry") is a common feature of blood flow in the distal aortic arch and descending thoracic aorta during the cardiac cycle (1). Although this pattern of flow has been disputed (2), Koh et al. (3) have demonstrated that chiral asymmetry is often exaggerated during cardiopulmonary bypass (CPB). These authors suggest that this exaggeration of rotational flow might be a mechanism of atheroembolism during CPB. In this report, the development of exaggerated rotational flow in the distal aortic arch and descending thoracic aorta is demonstrated in a patient undergoing CPB and the impact of this flow on the stability of an atheromatous plaque in the descending thoracic aorta is illustrated.

The patient was a 70-yr-old male undergoing semi-elective coronary artery bypass grafting. A composite image obtained after initiation of CPB but before aortic cross-clamping is shown in Figure 1. The color Doppler image in the upper left quadrant is a short-axis view of the distal aortic arch. At a Nyquist limit of 151 cm/s, note the red:blue separation across the aortic lumen with the axis of separation being between 6 and 12 o’clock. This is consistent with clockwise rotational flow in this region. The pulsed wave Doppler image in the lower right quadrant confirms the presence of rotational flow when the sample volume is moved steadily from the 3 o’clock to the 9 o’clock position across the aortic lumen. As the sample volume crosses the center of the lumen, the direction of flow changes from "away from the transducer" (below zero) to "towards the transducer" (above zero). The average mean transverse (tangential) velocity at the luminal periphery in regions "1" and "2" is 70 cm/s, corresponding to a rotational frequency of 8–9 Hz given an aortic diameter of 2.60 cm as per the following equation:

View larger version (45K): [in this window] [in a new window]   Figure 1. A composite image obtained after initiation of cardiopulmonary bypass (CPB) but before aortic cross-clamping. The color Doppler image in the upper left quadrant is a short axis view of the distal aortic arch. The red:blue color separation which is evident should not be confused with that which is observed in aortic dissection. In particular, in the case of dissection: 1. Separation is typically not red:blue (which indicates flow of similar velocity but in an opposite direction); rather, one lumen usually has a much higher velocity than the other and so one lumen appears colored while the other appears largely "black." 2. The plane of color separation can be at any angle across the lumen. 3. An intimal flap separating the color planes is usually apparent. 4. Luminal flow is typically more chaotic than in the normal aorta and thus the color mapping is characteristically "mosaic." A pleural effusion is also usually found in the patient with dissection (4). The lower left quadrant is a pulsed wave Doppler traverse of the same region. The traverse was made from the 3 o’clock position ("1") to the 9 o’clock position ("2"). The typical features of dissection can be seen in a supplementary video clip located at www.manbit.com/ERS/ERS.asp?R=36&S=0.

f = v/( * d)

where f = rotational frequency (Hz); v = transverse velocity (cm/s) and d = aortic diameter (cm).

For comparison, the average mean transverse velocity (over 2 cardiac cycles) after CPB was 6 cm/s—corresponding to a rotational frequency of <1 Hz. A composite short-axis and long-axis view of the descending thoracic aorta at the level of the aortic valve is shown in Figure 2. The presence of a cystic, ulcerated plaque measuring over 10 mm at its thickest point is demonstrated. A composite two-dimensional image of the same plaque is provided in a video loop available at www.anesthesia-analgesia.org. Before initiation of bypass, the plaque can be seen to be relatively stable (upper left quadrant). However, after initiation of CPB, extreme instability of the plaque develops as it is exposed to the prevailing, clockwise flow (lower right quadrant).

View larger version (78K): [in this window] [in a new window]   Figure 2. A composite two-dimensional short-axis and long-axis view of the atheromatous plaque in the descending aorta at the level of the aortic valve. Note the presence of cystic change and fragmentation in the plaque.

This case illustrates the fact that, during CPB, unstable aortic plaques can be exposed to new shear forces that arise because of the changes in pattern and velocity of blood flow in the aorta that accompany bypass. It confirms the view expressed by Koh et al. (3) that changes in the rotational component of aortic blood flow during CPB may have important implications for patients. Although this plaque was unchanged after weaning from CPB, it is easy to imagine such plaques disintegrating and embolizing under the forces imposed during the bypass process.

	Video 1.

Top Introduction Video 1. REFERENCES

 
A composite two-dimensional short axis view of an atheromatous plaque in the descending aorta at the level of the aortic valve before and during cardiopulmonary bypass (CPB). Plaque stability decreases dramatically during CPB.

	Footnotes

 
This article has supplementary material on the Web site: www.anesthesia-analgesia.org.

Accepted for publication April 4, 2006.

	REFERENCES

Top Introduction Video 1. REFERENCES

 

1. Frazin LJ, Lanza G, Vonesh M, et al. Functional chiral asymmetry in descending thoracic aorta. Circulation 1990;82:1985–94.[Abstract/Free Full Text]
2. Thomas JD. Flow in the descending aorta. A turn of the screw or a sideways glance? Circulation 1990;82:2263–5.[Free Full Text]
3. Koh TW, Parker KH, Kon M, Pepper JR. Changes in aortic rotational flow during cardiopulmonary bypass studied by transesophageal echocardiography and magnetic resonance velocity imaging: a potential mechanism for atheroembolism during cardiopulmonary bypass. Heart Vessels 2001;16:1–8.[Web of Science][Medline]
4. Hata N, Tanaka K, Imaizumi T, et al. Clinical significance of pleural effusion in acute aortic dissection. Chest 2002;121:825–30.[Abstract/Free Full Text]

This article has been cited by other articles:

				M. Swaminathan, H. P. Grocott, G. B. Mackensen, M. V. Podgoreanu, D. D. Glower, and J. P. Mathew The "Sandblasting" Effect of Aortic Cannula on Arch Atheroma During Cardiopulmonary Bypass Anesth. Analg., June 1, 2007; 104(6): 1350 - 1351. [Full Text] [PDF]

This Article Full Text (PDF) Data Supplement Alert me when this article is cited Alert me if a correction is posted Services Email this article to a colleague Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (2) Citing Articles via Google Scholar Google Scholar Articles by Pybus, D. A. Search for Related Content PubMed PubMed Citation Articles by Pybus, D. A. Related Collections Cardiovascular Equipment Complications Monitoring (Cardiac)