Estimating Bilateral Atrial Function by Cardiovascular Magnetic Resonance Feature Tracking in Patients with Paroxysmal Atrial Fibrillation

Trial remodeling is considered the most critical mechanism for atrial fibrillation. Functional changes in left atrial strain occur before structural changes closely related to structural remodeling and myocardial fibrosis in the left atrium. Cardiac magnetic resonance feature tracking is a novel non-invasive post-processing technique that can evaluate left atrial strain and strain rate with high accuracy and reproducibility.

The endocardium and epicardium of the atrial diastole and systole must be manually demarcated while examining the atrial strain. Care should be taken to choose the appropriate phase. CMRFT is preferred for clinical assessment of atrial strain, as it is a flexible parameter measurement with high reproducibility, soft tissue resolution and without the need for new sequence acquisition.

Begin with the cardiac magnetic resonance scanning of the patient's sinus rhythm. Locate the long axis Cine images and short axis using a three plane localization method. To do so, acquire the orthogonal multislice localizers in the hearts transverse, sagittal and coronal slices.

Obtain a two chamber localizer by selecting a transverse slice or positioning line at the middle of the ventricle from the transverse images. Set the slice vertically on the transverse image parallel to the septum and through the apex of the left ventricle. Then position the slice vertically on the two chamber localizer through the apex of the heart and the center of the mitral valve to acquire the four chamber localizer.

To obtain the short axis localizer situate the slice perpendicular to the septum on the four chamber localizer at a right angle to the long axis on the two chamber localizer. Based on the localizers, generate the standard views. To do so, use an automatically appearing slice to obtain a four chamber view.

Place it through the center of the left ventricle and vertically on the septum on the short axis localizer and click apply. On the four chamber view, position the slice parallel to the septum adjusted it to the center of the left ventricle on the short axis localizers and obtain the two chamber view. Get a three chamber view by positioning the slice through the center of the aorta and the left atrium on the short axis localizers.

Ensure the slice passes through the apex of the LV on the four chamber view. To collect the short axis views, position the slices vertically on the septum and parallel to the mitral annulus on the four chamber view. Then arrange the slices vertically on the connection line between the apex of the left ventricle and the center of the mitral annulus on the two chamber view.

Next, the two chamber view of the right ventricle is acquired by placing the slice parallel to the septum and shifting the slice into the center of the right ventricle on the short axis view without cutting the left ventricle into parts. Capture CMR Cine sequences of the two and four chamber views of both the ventricles the three chamber view and the short access view of the left ventricle using a retrospective ECG gated balanced steady state free precision sequence on a three Tesla MR Scanner. To perform ventricular function analysis, click on pax.

Input the patient ID and search current patient to find the images, transfer the images to the cardiovascular post-processing workstation by clicking on retrieve. Use the function multiplayer module. Choose the short access Cine of the ventricle and click on the detect LVRV contours at EDES phases to analyze the ventricular function.

To proceed with left atrial function analysis use the tissue tracking feature tracking module and measure the left atrium volumes and left ventricle strains in the four, three and two chamber Cine CMR images. At the end of the left atrial systole and diastole manually contour the endocardial and epicardial left atrium borders exclude the pulmonary veins and left atrial appendage from the LA outline. Once contouring is complete, ensure that the ROI series segment number selection key is shown as six.

Click on the perform strain analysis for automatic tracking of onscreen pixels during the entire cardiac cycle. Ensure automatic calculations of the left atrial volume and time curve, the global and segmental strain and the strain rate. To perform right atrial function analysis, obtain the right atrial volumes and strains using the tissue tracking feature tracking module with the four and two chamber right ventricle Cine CMR images.

Manually contour the endocardial and epicardial right atrium borders at the end of the right atrial systole and diastole. Exclude the vena cava and right atrial appendage from the outline. To complete the right atrial function analysis, obtain the functional demonstrated previously during the left atrial function analysis.

In the CMR scanning study, the MRI scans of 243 individuals were assessed and 71 patients with atrial fibrillation with CMR imaging were recruited for the study. Based on the exclusion criteria, 21 patients with paroxysmal atrial fibrillation who were granted an MRI scan with the sinus rhythm were selected for the study. The control group consisted of 19 age and gender matched individuals with normal CMR.

In these patients, the parameters of left and right atrial function and the standard characteristics of left and right ventricular function were examined. The atrial strain parameters included longitudinal strain and strain rate of reservoir conduit and booster pump phases. The segmental strain parameter analysis on the four and two chamber views showed that the left and right atrium's global longitudinal strain during the atrial fibrillation group's reservoir phase was significantly lower than in the control group.

In the four and two chamber views, the longitudinal strain of each segment of the left atrium was significantly lower than in the control group. Care should be taken to choose the appropriate phase and ensure the atrial appendage is excluded from the atrial contour. The operator must estimate the atrial and diastole based on experience.

The added Cine sequence of right ventricular two chamber and two long axis Cine make the result of the right atrial function more accurate than a single long axis.