New classification of aortic dissection during the cardiac cycle as pulsating type and static type evaluated by electrocardiogram-gated multislice CT
Introduction
Aortic dissection (AD) is an emergency, critical and life-threatening disease [1], [2], [3], [4], [5], [6], [7], [8]. The DeBakey [9], [10] and Stanford classifications [6], [11] are available for physicians to accurately classify AD using computed tomography (CT) [5], [6] or magnetic resonance imaging (MRI) [12] and to choose the appropriate therapeutic treatment. But these modalities, especially CT, usually involve acquisition of static images [5]. Motion artifacts of ascending aorta itself or of an intimal flap, which cause cardiac pulsation, impair image quality in AD [13]. As a result, selection of treatment appropriate for AD may not occur, thereby missing the presence of AD in ascending aorta.
Therefore electrocardiogram (ECG)-gated CT acquisitions are recommended for evaluation of AD [14], to eliminate the influence of motion artifact by cardiac pulsation, even when the main target of the diagnosis is not coronary artery but thoracic aorta (especially the ascending aorta).
Furthermore, in ECG-gated CT acquisition we can simultaneously obtain pleural volume data at any cardiac phase in the ECG [15] and in four-dimensional images, we can see that true lumen (TL) gets larger while false lumen (FL) gets smaller (pulsating type) in some subjects with a double-barrel type AD with patent FL (Fig. 1); however, in others TL and FL do not change (static type) in a cardiac cycle. Nonetheless, the definition of pulsating type and the clinical significance of differences between pulsating and static types has not been predictive of future occurrence of an aortic rupture or aortic enlargement.
In this study, we have characterized and sought definition of these types, together with evaluation of their clinical significance.
Section snippets
Materials and methods
Twenty subjects (10 with descending thoracic AD with blood flow in both TL and FL and 10 controls without AD) were enrolled. The backgrounds of all 20 subjects are shown in Table 1.
Enhanced ECG-gated MSCT (Light Speed Ultra 16, GE) covered the thorax with slices of 1.25 mm thickness, and reconstructed every 10% from 0–90% of the R–R interval (total 10 phases) of the ECG. Two experienced physicians measured the luminal area of the descending thoracic aorta in 10 controls and TL and FL areas of
Results
Ten controls showed maximum lumen area as follows: (mean ± standard deviation, SD) at levels 1) 541 ± 87 mm2, 2) 449 ± 88 mm2 and 3) 445 ± 78 mm2 which were all significantly larger than minimum lumen areas (mean ± SD) at levels 1) 483 ± 94 mm2, 2) 413 ± 92 mm2 and 3) 397 ± 77 mm2 (all P < 0.01). Ratios of maximum area to minimum area (Mean % ± 2 SD) were 113 ± 9, 109 ± 10, and 112 ± 9, respectively at levels 1), 2), and 3) (Fig. 3). Therefore, normal descending aorta was significantly enlarged during a cardiac cycle,
Discussion
Concerning the presence of AD in ascending aorta, the Stanford criteria are already established [11]. Stanford A type, which includes AD in the ascending aorta, must be treated surgically [16], [17], whereas Stanford B type [6], which does not include AD in the ascending aorta, can be managed conservatively by pharmacological treatment with agents such as beta blockers to reduce blood pressure and pain control [18], [19].
The DeBakey classification [9] of AD in descending aorta characterises a
Reliability of our definition of pulsating type
In this study, we advocated a new concept involving presence of pulsation of TL in AD. We further established a provisional classification of AD subjects as pulsating or static type when the maximum area of TL was > 125% of the minimum area of TL at any of the 3 levels. We set a criterion level of 125% with reference to data obtained from the 10 controls for the following reasons: in controls the normal descending aorta was significantly enlarged during the cardiac cycle, but the ratio of
Conclusion
In AD, TL and FL show 2 types of area change in a cardiac cycle, those which are pulsating and static type. The pulsating type is more common if present in the acute phase from onset, or if entry is not located at the distal portion of descending thoracic aorta with retrograde flow in FL. This pulsating type might be exposed to pressure from cardiac pulsation and contribute to luminal enlargement. This new classification of AD may be useful to differentiate unstable AD affected by cardiac
Acknowledgement
The authors of this manuscript have certified that they comply with the Principles of Ethical Publishing in the International Journal of Cardiology [47].
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