<p style="font-weight: 400;"><span>High-resolution microCT imaging can provide an accurate detection of hypo-attenuating leaflet thickening (HALT) and is capable of determining leaflet thickening rate when compared to histological analysis, new data reveal.</span></p> <p style="font-weight: 400;"><span>However, the same study showed that microCT imaging cannot accurately differentiate thrombus morphology, said Aloke Finn, MD, from CVPath Institute Inc., Gaithersburg, Maryland, said.</span></p> <p style="font-weight: 400;"><span>Speaking at Transcatheter Cardiovascular Therapeutics (TCT) 2022 in Boston, Finn noted that the gold standard for diagnosis of subclinical leaflet thrombosis after surgical or transcatheter aortic valve replacement (TAVR) is 4-dimensional computed tomography (4DCT) scan, where the characteristic finding on is a hypo-attenuating opacity at the base of valve leaflets, or HALT. </span></p> <p style="font-weight: 400;"><span>He noted that HALT identified on functional cardiac CT can affect valve function and clinical outcomes; thus, identifying HALT may be important for improving long term durability of transcatheter aortic valves. </span></p> <p style="font-weight: 400;"><span>“High resolution imaging such as microCT may yield further insight into the pathophysiology of HALT and is likely to be able to distinguish different stages of HALT, which is not capable at this point with regular CT,” he said, noting that thrombus morphology evolves over time, from a loose mesh of fibrin and platelets in the acute stage to a compact structure of acellular and cellular components – generally called an organizing thrombus – and eventually to infiltration by smooth muscle cells and collagen – organized thrombus – that is resistant to treatment.</span></p> <p style="font-weight: 400;"><span>“Here for the first time, we compared microCT changes of HALT with histologic changes of valve thrombosis and characterization over time,” he said. </span></p> <p style="font-weight: 400;"><span> </span></p> <p style="font-weight: 400;"><strong><span>Study setup</span></strong></p> <p style="font-weight: 400;"><span>The HALT study compared the microCT findings of HALT with histologic findings of acute,</span></p> <p style="font-weight: 400;"><span>organizing, and organized thrombosis. In total, 123 explanted self-expanding transcatheter aortic valves were assessed from a population of more than 7,500 participants from 11 clinical trials across surgical risk groups, said Finn, noting that explanted valves represented <2% of all patients.</span></p> <p style="font-weight: 400;"><span>He added that histological leaflet thickening was evaluated in 320 leaflets from 110 cases, including cases with severe intrinsic calcification, while microCT was only analyzed in 106 leaflets from 36 cases and excluded severe intrinsic calcification.</span></p> <p style="font-weight: 400;"><span>Baseline characteristics of patients were similar for both groups, with statistical differences in age, sex, and baseline history of antiplatelet therapy or anticoagulants. However, there were significant differences in the duration of implant (66 days for histology group vs. 125 days for microCT group; p<0.001); Society of Thoracic Surgeons (STS) predicted risk of mortality (PROM), with the histology group scoring an average 8.6% and the microCT 5.7% (p=0.008); and the type of value used, where the histology group skewed heavily toward use of the CoreValve (histology group: 82% CoreValve, 16% Evolut R, 2% Evolut PRO; microCT group: 58% CoreValve, 36% Evolut R, 6% Evolut PRO; p=0.016).</span></p> <p style="font-weight: 400;"><span>HALT on microCT was defined as increased leaflet thickness (>normal) and graded based on length of leaflet involvement (visual assessment)</span></p> <p style="font-weight: 400;"><span> </span></p> <p style="font-weight: 400;"><strong><span>Key findings</span></strong></p> <p style="font-weight: 400;"><span>Finn reported that microCT was “very good at detecting the presence or the absence of HALT” in addition to determining leaflet thickening rate. </span></p> <p style="font-weight: 400;"><span>Approximately 45% of leaflets showed at least some degree of leaflet thickening, with the prevalence of leaflet thickening (defined as Grade 1 – 4 based on the length of involvement of visible leaflet thickening). </span></p> <p style="font-weight: 400;"><span>However, microCT was not effective at differentiating leaflet thickening types, he said. </span></p> <p style="font-weight: 400;"><span>Furthermore, the study reported that leaflet thickening was observed more frequently in implants of longer duration, noting that all thrombi were acute at <30 days, while most organizing thrombi occurred after 30 days, and thrombi were most organized after 1 year. </span></p> <p style="font-weight: 400;"><span>Indeed, the study reported that the median (Q1-Q3) duration of implant for each type of thrombus was: 16 days (interquartile range [IQR]: 10-66) for acute thrombi, 373 days (IQR: 93-916) for organizing thrombi and 1,014 days (IQR: 619-1,293) for organized thrombi.</span></p> <p style="font-weight: 400;"><span>Finn said the findings underscore the need for early detection of HALT in patients: “Because at greater than 1 year, basically, you have organized thrombi which are unlikely to resolve with anticoagulant therapy.”</span></p> <p style="font-weight: 400;"><span>He added that while higher resolution imaging like microCT may be useful for detection of HALT, there is a need to be able to detect thrombi type.</span></p> <p style="font-weight: 400;"><span>“I think the importance comes to knowing whether the thrombi are already organized or whether they're acute. Acute thrombi will resolve, as you know, with anticoagulation,” he said.</span></p> <p style="font-weight: 400;"><strong><span>Image Credit: Jason Wermers/CRTonline.org</span></strong></p>