From August 1st, 2014 to July 31st, 2015, patients with mitral valve prolapse by physical examination and trans-thoracic echocardiography were recruited. Then, valve repair surgery was carried out and re-examined by CT scan at 3 months after initial diagnosis. Exclusion criteria: patients with renal insufficiency (serum creatinine> 1.5 mg/dl), thyroid diseases, iodine allergy, progressive heart failure, atrial fibrillation and other types of arhythmia, pregnant women, those with previous history of myocardial infarction, heart ischemia or other diseases occurring in recent 3 months and those unwilling to participate in this study were excluded. The diagnosis of mitral valve prolapse was confirmed by two experienced physicians, who reviewed the results of trans-thoracic echocardiography. If the heart rate was > 70 times/min before the examination, β-receptor blocking pharmacon (25–50 mg metoprolol) was injected to control the heart rate at 65 times/min. A total of 90 eiligible patients completed the study. Written informed consents were obtained from all patients or family members.
Trans-thoracic echocardiography and data acquisition
Conventional trans-thoracic echocardiography was performed by experienced physician (GE Vingmed Ultrasound, VIVID-3, General Electrics, USA). Mitral valve prolapse was defined as valve cusp displacement > 2 mm or the parasternal direction of the long axis tended to the left atrial direction. Mitral valve leaflet thickness was measured under two- to four-chamber view similar to CT scan. The severe degree of mitral regurgitation, end-diastole and end-systole of left ventricular volume, ejection fraction, peak pulmonary arterial pressure and other parameters were also measured.
Patients were processed by 64-row CT inspection after 3 months of trans-thoracic echocardiography (GE. Light speed. VCT, General Electrics, USA). The related parameters were set as followed: level alignment was 2 × 32 × 0.6 mm; profile acquisition was 64 × 0.6 mm; pitch of screw thread was 0.2; slew time was 350 ms; tube voltage was 120 kV; tube current time was 600 mAs. A 70-100 ml nonionic iodine contrast agent was applied in the detection, washed by 40 ml physiological saline and administered via intravenous dripping at a rate of 3 ml/ seconds along the elbow vein. The bolus technique was utilized to calculate the scanning delay.
CT data acquisition
Besides the function of coronary artery with CT examination, the thickness and motion range of mitral valve leaflet were collected, which was 25–30% data during R-R period, because the motion range of valve cusp in this section reached the maximal value. The data was processed by the late stage of multi-planar reconstruction, we defined three-chamber plane generated in the direction of parasternal longitudinal axis wasdefined as passing through the left ventricular long axis and left ventricular outflow tract, equivalent to the left coronal oblique angle. Two-chamber plane was defined as the left ventricular geometric center vertical long axis direction, equivalent to the sagittal oblique view passing through the ventriculus sinister, left atrium and center of mitral valve. Four-chamber plane was generated by the recombining of left ventricular short axis, which was located in the middle of the left ventricle. It was defined as a transitional plane passing through the left ventricular center, diaphragm and right ventricular free wall. During the systole period (25–30% R-R period), the maximum vertical distance was recorded between the mitral valve leaflet and annulus plane under three-chamber view, equivalent to the long axis view of trans-thoracic echocardiography. Left ventricular offset was defined as negative value, and its left atrial offset was defined as positive value. The thickness of valve cusp was measured under two- to four-chamber view, excluding the calcified part. The explanation of checking image was finished by two experienced clinicians, who were blind to the results of trans-thoracic echocardiography.
SPSS 20.0 statistical software was utilized for data analysis. The data were expressed as mean ± standard deviation (SD). Continuous variables were statistically compared by t-test. Classified variables were compared by chi-square test or Fisher exact test. The correlation analysis was processed by Pearson’s correlation analysis examination. The ROC curve was adopted to detect the cut-off point. The sensitivity, specificity, false positive, false negative and other parameters were detected and measured. A P value of less than 0.05 was considered as statistical significance.