All procedures performed in this study were in accordance with the ethical standards, approved by the ethics committee of our institute, and complied with the Declaration of Helsinki 1964 and its later amendments. Written informed consent was obtained from all individual participants included in this study.
The study design was prospective observational; it included thirty patients indicated for TAVI. Twenty patients (66.7%) had implanted Sapien valves, while the remaining 10 patients (33.3%) had implanted CoreValve. They were enrolled in a cardiac ECG-gated CT calcium score study and ECG-gated CT aortography between December 2019 and February 2021. Patients with rapid arrhythmia or unstable clinical conditions or those with contraindication to contrast administration (allergy or GFR less than 30 ml/min) were excluded.
Patient preparation and setup
The patients were instructed to fast 4–6 h prior to the study, and medications are not to be discontinued. Before the examination, the heart rate and rhythm were evaluated. All steps of the study were explained in detail for each patient (including the breath-holding instructions).
CT examination
All MSCT examinations were performed using a 256-slice scanner (iCT 256 Philips; Eindhoven, The Netherlands). The heart rate was checked on the monitor. The patient was positioned supine on the table with feet first. ECG leads are fixed at four corners of the pericardium. Calcium score was performed using the prospective ECG gating at 75% of the cardiac cycle, and the CT aortography was performed using the retrospective ECG gating. First, a localization scan (scanogram) was performed yielding an antero-posterior and lateral views of the chest.
1-CT calcium score The field of view was adjusted to cover the aortic root. Aortic valve calcium scoring (AVCS) was performed using (Agatston score) in the cranio-caudal direction while the patient is holding the breath in inspiration. Calcification was considered when CT density was above 130 HU. Acquisition parameters were as follows: ECG gated at 75% of the RR interval, 270 ms gantry rotation, 3 mm collimation, 80 mA, and 120 kV. To minimize the total effective patient radiation dose, the scan was conducted with a relatively low tube current (Fig. 1).
2-CT aortography The field of view was adjusted to cover the entire aorta including the aortic root, thoraco-abdominal aorta, and iliofemoral arteries. Acquisition parameters are as follows: retrospective ECG gating with dose modulation, 270 ms gantry rotation, 256 × 0.6 mm collimation, 330 mA, and 120 kV. The contrast (with an average volume of 80 cc) was injected via a wide bore (18 gauge) cannula in an antecubital vein with a rapid injection rate (5–6 cc/sec) using the automatic dual head injector. The contrast used was a non-ionic low osmolar iodine containing (Ultravist 370 mg/ml, Schering AG, Germany). 40 cc of chasing saline is injected at the same flush rate to make sure of the utilization of all the injected contrast. Image acquisition was done while the patient is holding the breath in inspiration.
Image analysis
An experienced radiologist and cardiologist, with more than 12 years of experience in cardiac CT reporting, both blinded to the clinical data, reviewed all CT studies, including the aortic valve calcium score and the CT aortography, in a consensus interpretation. The analysis was performed using a commercially accessible workstation, Vitrea 5 Core workstation (Vital Images, Minnetonka, MN).
Patient follow-up to detect complications
The patients were followed up clinically and by echocardiography every 3 months for 1 year, those who developed complications were enrolled for another CT study. Complications included paravalvular leak (PVL) and major adverse cardiac events (MACE).
MACE include myocardial infarction, heart failure, stroke, and cardiovascular death. They were diagnosed clinically and by different imaging modalities.
Measurements
All measurements were performed manually, using the ECG-synchronized images, during mid-to-end systole (35–45% of cardiac cycle). Initially, the LVOT was examined to exclude obstructing lesions. The aortic annulus was defined as the luminal contour within a virtual plane aligned with the most basal attachment points of the three aortic valve cusps. Quantification of annular diameters, area and perimeter was done manually with the cursor. The coronary ostial height measured in a perpendicular fashion to the annular plane. The STJ diameter was measured on the transverse double oblique. The ascending aorta diameter was measured on transverse double oblique plane at the level of the main pulmonary artery. The minimum diameter of the descending aorta was identified. Comments on the aortic course, tortuosity, and presence of aneurysms or atherosclerotic plaques were done. The minimum cross section diameter of the common iliac, external iliac, and common femoral arteries bilaterally was determined with a comment on tortuosity and calcifications.
Statistical methodology
For quantitative data, median, minimum, and maximum were used, while categorical data were summarized using frequency and relative frequency (%). The sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and diagnostic effectiveness of standard diagnostic indices were computed as reported by Galen [6]. The optimal cutoff value of several parameters for detecting complications was determined using a ROC curve and area under the curve analysis. The nonparametric Mann–Whitney test was used to make comparisons between quantitative variables [7]. The chi-square test was used to compare categorical data. When the anticipated frequency is less than 5, the exact test was utilized instead [7]. Regression analysis was conducted to predict complications [8]. Statistical significance was defined as a P value of less than 0.05.
