Review of myocardial viability using Nuclear Medicine imaging in rare cardiac malposition of dextrocardia - understanding right approach.

Imaging of dextrocardia in human needs understanding orientation of heart chambers and walls. There are many types of cardiac malpositions as dextrocardia (with or without situs inversus), mesocardia and levocardia. The myocardial perfusion Scintigraphy (MPS) of dextrocardia has been explained in case reports and imaging atlas; however the myocardial viability assessment using Nuclear Medicine imaging techniques is less documented in literature. Methods: Two cases of dextrocardia with situs inversus and one case of mesocardia were included in the study to assess the myocardial viability using 99m Tc Sestamibi rest perfusion scintigraphy and 18 Fluorine Fluorodeoxy glucose positron emission tomography (18 F FDG PET). Cardiac Single Photon Emission Computed Tomography (SPECT) images of dextrocardia with situs inversus were acquired using 'feet in supine' position with 1800 arc from Left anterior oblique (LAO) to right posterior oblique (RPO); whereas right lateral to left lateral arc was used for mesocardia. The processing and reconstruction was done by entering the same patient position and repeated after entering 'feet first prone' position. The two reconstructed images were compared for orientation of walls and cardiac chambers. Results: The first processing using 'feet first supine' position revealed interchanged septum and lateral wall in reconstructed images in dextrocardia with situs inversus. The same was corrected after changing patient position to 'prone' for rest perfusion and PET raw data during processing. The display of cardiac slices in various axes matched conventional nomenclature of septum and lateral wall leading to easy interpretation. However this change was not required in mesocardia; where location of chambers of heart was not interchanged. Conclusion: The acquisition protocol of SPECT being semicircular orbit needs careful selection of arc by keeping the patient position as 'feet first supine' for various types of dextrocardia. The processing and reconstruction of data by changing patient position to prone was found to be most useful method to match the septal and lateral wall orientation for interpretation of images.