This study highlights the characteristics of LF-LG AS focusing on CT findings. The AVACT and aortic annulus were larger in classic LF-LG AS compared to those in high-gradient severe AS and 27.8% of classic LF-LG AS patients presented AVACT≥1.2 cm2. High BNP, preoperative AF, classic LF-LG AS, and smaller aortic root were associated with MACCE after AVR.
Classic LF-LG AS patients demonstrated higher ESVI and EDVI, lower LVEF, larger AVAecho and AVACT, and larger aortic annulus compared to high-gradient severe AS. The key messages of this study are demonstrated in Figure 4. In a previous study, patients with severe AS had significantly larger aortic annulus and ST junction diameters compared with those measured in control groups.16 This could be attributed to aortic root remodelling: as severe AS progresses ESVI and EDVI increase to compensate, and dilated LV cavity may lead to dilatation of the aortic annulus. Failure to compensate may result in heart failure. Since the BNP was higher in classic LF-LG AS and the group presented poor outcome compared to high-gradient severe AS, classic LF-LG AS may be a compensation failure of high-gradient severe AS. Paradoxical LF-LG AS presented preserved ESVI, EDVI, and LVEF, although AVAecho and AVACT were larger than in high-gradient severe AS.
In this study, we used cut-off value of AVACT<1.2 cm2 as this value was suggested for severe AS in a previous study.14 However, in classic LF-LG AS group, approximately one third of the patients exhibited AVACT≥1.2 cm2. AVC was lower in the AVACT≥1.2 cm2 compared to that of AVACT<1.2cm2 group, and in this group, moderate AS patients might be misclassified as severe AS and vice versa. This can also be applied to paradoxical LF-LG patients, despite 14.5% of these patients presenting AVACT≥1.2 cm2. Although we could not derive the role of AVACT in diagnosing LF-LG AS patients, further studies whether AVACT could be used to discriminate true LF-LG AS are would be of value.
The outcome of AS after AVR was associated with preoperative high BNP levels, AF, classic LF-LG AS, and small aortic root. The plasma BNP level was associated with LV dysfunction in AS, and was a well-known predictor of poor outcome in patients with AS overall and after AVR.17–19 AF is also a dominant predictor in both asymptomatic and symptomatic patients with moderate to severe AS, and after AVR.20–22 Classic LF-LG AS was associated with worse outcomes after AVR compared those observed in high-gradient AS patients, although LF-LG AS patients have displayed survival benefits with AVR.3 Finally, small aortic root measured on CT was an independent prognostic factor. This finding should be interpreted cautiously. When AS severity progresses, the increased LV cavity volume may increase the size of the aortic annulus and sinus of Valsalva. However, a small aortic root has also been associated with increased ischemic cardiovascular events and mortality in patients with AS,23 possibly reflecting impaired root remodelling process and atherosclerotic changes.
Our study has several limitations. Because this is a retrospective study using a patient cohort that underwent AVR, patients not indicated for surgery due to poor general conditions or comorbidities or who declined operation were not included. The selection bias may affect the outcome assessment, and AVR itself was not used as an outcome parameter. Instead, we used MACCE after AVR. Therefore, the outcomes of this study may not directly infer the outcomes of AS population managed with diverse treatment options. Further studies with AS managed by conservative treatment, surgical AVR, and transcatheter AVR could be of value to evaluate overall outcomes of AS patients. Second, because the small number of LF-LG AS patients, we could not observe the role of AVACT for reclassification of LF-LG AS. However, we showed the CT characteristics of LF-LG AS: AVACT and aortic annulus were larger in classic LF-LG AS compared to those in high-gradient severe AS. This finding may be explained by the aortic root remodelling which is associated with the dilated LV. Third, although classic LF-LG patients showed higher overall mortality and a large aortic annulus, a small aortic root was one of the factors associated with MACCE. Both decreased LV function in classic LF-LG AS and impaired aortic root remodelling may contribute to the outcome, respectively, but further studies are necessary to provide more evidences.
In conclusion, classic LF-LG AS presented larger AVACT and aortic annulus than high-gradient severe AS. Old age, high BNP, AF, classic LF-LG AS and small aortic root on CT were associated with MACCE after AVR. These findings suggest the potential role of cardiac CT in classification and outcome assessment of severe AS.