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

Abstract

otational blood flow (“chiral asymmetry”) is acommon feature of blood flow in the distal aorticarch and descending thoracic aorta during the car-diac cycle (1). Although this pattern of flow hasbeen disputed (2), Koh et al. (3) have demonstratedthat chiral asymmetry is often exaggerated duringcardiopulmonary bypass (CPB). These authors sug-gest that this exaggeration of rotational flow mightbe a mechanism of atheroembolism during CPB. Inthis report, the development of exaggerated rota-tional flow in the distal aortic arch and descendingthoracic aorta is demonstrated in a patient under-going CPB and the impact of this flow on thestability of an atheromatous plaque in the descend-ing thoracic aorta is illustrated.The patient was a 70-yr-old male undergoingsemi-elective coronary artery bypass grafting. Acomposite image obtained after initiation of CPB butbefore aortic cross-clamping is shown in Figure 1.The color Doppler image in the upper left quadrantis a short-axis view of the distal aortic arch. At aNyquist limit of 151 cm/s, note the red:blue sepa-ration across the aortic lumen with the axis ofseparation being between 6 and 12 o’clock. This isconsistent with clockwise rotational flow in thisregion. The pulsed wave Doppler image in thelower right quadrant confirms the presence of rota-tional flow when the sample volume is movedsteadily from the 3 o’clock to the 9 o’clock positionacross the aortic lumen. As the sample volumecrosses the center of the lumen, the direction of flowchanges from “away from the transducer” (belowzero) to “towards the transducer” (above zero). Theaverage mean transverse (tangential) velocity at theluminal periphery in regions “1” and “2” is 70cm/s, corresponding to a rotational frequency of8–9 Hz given an aortic diameter of 2.60 cm as perthe following equation: