An unusual cause of tachyarrhythmia in an otherwise healthy young man

A 32-year-old man referred to the cardiology clinic for palpitations was found to have paroxysmal supraventricular tachycardia (SVT) on 24-hour Holter monitoring. His general and cardiac examinations were unremarkable. A transthoracic echocardiographic study to exclude structural heart disease was performed and showed an abnormal structure in relation to the right ventricular (RV) free wall; however, poor echocardiographic windows precluded proper characterisation. Cardiac MR (CMR) was therefore performed. Cine images (figure 1 and online supplementary videos 1 and 2) demonstrated the abnormal structure. Dynamic pass of contrast (rest perfusion module) showed the sequence of intracavitary enhancement across different cardiac chambers in the horizontal long-axis plane (figure 1 and online supplementary video 3).heartjnl;103/18/1472/F1F1F1Figure 1Still frames from balanced steady state free precession images in the horizontal long-axis plane (A,B). Still frames from the dynamic pass of contrast in the horizontal long-axis and the short axis following contrast injection into the right arm (C,D). Images in the horizontal long-axis plane at the basal level using T2-weighted short-tau inversion recovery (E) and half Fourier single-shot turbo spin echo (F).DC1SP110.1136/heartjnl-2017-311485.supp1Supplementary data DC2SP210.1136/heartjnl-2017-311485.supp2Supplementary data DC3SP310.1136/heartjnl-2017-311485.supp3Supplementary data QUESTION: The abnormal structure is most likely which of the following?Pericardial cystRight atrial appendage aneurysmRight ventricular aneurysmJuxtaposed left atrial appendageAccessory right ventricular chamber.