ABC | Volume 110, Nº4, April 2018

Case Report Marinheiro et al Primary ventricular fibrillation in a patient with mild hypercalcemia Arq Bras Cardiol. 2018; 110(4):393-396 SQTS (short ST segment and prolonged T peak - T end interval and T peak - T end / QT ratio), 7 make SQTS diagnosis less probable. It is unclear if short QT interval can be intermittent or whether fluctuating QT intervals are of clinical significance in patients with SQTS. 8 Of note, a case of sudden cardiac death associated with intermittent short QT interval has been described. 9 Mazzanti et al. 10 proposed that SQTS and Brugada Syndrome (BrS) may have some features in common and intermittent pattern of short QT interval (same as ST elevation in right precordial leads) seems reasonable. The presence of short action potential duration, as well as abbreviated repolarization, suggests that the R-on-T phenomenon may precipitate arrhythmogenesis in SQTS. Obviously, performing genetic testing could be considered. Five genes have been linked to SQTS (KCNH2, KCNQ1, KCNJ2, CACNA1C and CACNB2b), but the yield of genetic screening remains low (20% overall). 10 In other words, the chances of a gene mutation be identified and confirm the diagnosis is low and a negative test does not rule out SQTS since there are mutations unidentified. Besides, our patient had no offspring or siblings so it was considered that genetic test would not add relevant information or change therapeutic management. The good response to quinidine in the follow-up supports the diagnosis of SQTS since quinidine can reduce arrhythmic events in this entity. 5 The authors admit that alternative diagnosis can be considered. The occurrence of malignant ventricular arrhythmias in patients with PVCs with short coupling interval has been extensively reported. In these cases, PVCs have the same morphology suggesting one focal origin. Left bundle branch morphology and left axis were identified as most commonly related to VF, 11 which is usually not induced by an EP study. Verapamil is reported to be effective in suppressing these arrhythmias, while quinidine, β -blockers and amiodarone are ineffective. In our patient, quinidine is effective, PVCs had distinct morphologies and initially PVCs were suppressed by isoproterenol, which is not a consistent finding in these cases. Of note, transient metabolic or electrolytic disorders can influence PVC susceptibility to degenerate in VF 12 so hypercalcemia could have contributed to this phenomenon. The initial diagnosis was rethought several months later when PHPT was confirmed although it is not clear if the arrhythmic events can be caused by mild hypercalcemia. Other reported cases described more severe hypercalcemia associated with arrhythmias. Alternatively, mild hypercalcemia could have been a trigger to ventricular arrhythmias in the case of SQTS or PVCs with short coupling. In fact, the patient had higher levels of calcium while on therapy with quinidine and no arrhythmias occurred. To establish a cause-effect relationship it is necessary to demonstrate that calcium perfusion would cause VF in EPS as described by Chang et al. 11 However it would imply repeating EPS with calcium perfusion and facing a potential electrical storm which could be difficult to control as it had been in the first episode. For these reasons, the authors considered it inappropriate. Conclusion The authors report a case of electrical storm possibly related to SQTS taking into account the presence of short QT interval and isoproterenol and quinidine efficacy. 13 However, it is not clear why short QT interval was present only in the first ECG and secondary causes could not be completely ruled out since mild hypercalcemia was present. Up until now there are no reports regarding mild hypercalcemia as a cause of arrhythmic storm. The final diagnosis is still not certain but EPS with calcium perfusion could be dangerous and genetic testing yield in SQTS is too low to justify its use. Although without a definitive diagnosis, the authors emphasize the importance of excluding all reversible causes, especially in case of subtle hydroelectrolytic disorders like the one presented above. Author contributions Conception and design of the research: Marinheiro R, Sardinha F, Gonçalves S, Serra S; Acquisition of data: Marinheiro R, Sardinha F; Analysis and interpretation of the data: Marinheiro R, Parreira L, Sardinha F; Writing of the manuscript: Marinheiro R, Parreira L; Critical revision of the manuscript for intellectual content: Parreira L, Amador P. Potential Conflict of Interest No potential conflict of interest relevant to this article was reported. Sources of Funding There were no external funding sources for this study. Study Association This study is not associatedwith any thesis or dissertationwork. 395