@article {Marstrande001670, author = {Peter Marstrand and Kasim Almatlouh and J{\o}rgen K Kanters and Claus Graff and Alex H{\o}rby Christensen and Henning Bundgaard and Juliane Theilade}, title = {Effect of moderate potassium-elevating treatment in long QT syndrome: the TriQarr Potassium Study}, volume = {8}, number = {2}, elocation-id = {e001670}, year = {2021}, doi = {10.1136/openhrt-2021-001670}, publisher = {Archives of Disease in childhood}, abstract = {Background In long QT syndrome (LQTS), beta blockers prevent arrhythmias. As a supplement, means to increase potassium has been suggested. We set to investigate the effect of moderate potassium elevation on cardiac repolarisation.Methods Patients with LQTS with a disease-causing KCNQ1 or KCNH2 variant were included. In addition to usual beta-blocker treatment, patients were prescribed (1) 50 mg spironolactone (low dose) or (2) 100 mg spironolactone and 3 g potassium chloride per day (high dose+). Electrocardiographic measures were obtained at baseline and after 7 days of treatment.Results Twenty patients were enrolled (10 low dose and 10 high dose+). One patient was excluded due to severe influenza-like symptoms, and 5 of 19 patients completing the study had mild side effects. Plasma potassium in low dose did not increase in response to treatment (4.26{\textpm}0.22 to 4.05{\textpm}0.19 mmol/L, p=0.07). Also, no change was observed in resting QTcF (QT interval corrected using Fridericia{\textquoteright}s formula) before versus after treatment (478{\textpm}7 vs 479{\textpm}7 ms, p=0.9). In high dose+, potassium increased significantly from 4.08{\textpm}0.29 to 4.48{\textpm}0.54 mmol/L (p=0.001). However, no difference in QTcF was observed comparing before (472{\textpm}8 ms) versus after (469{\textpm}8 ms) (p=0.66) high dose+ treatment. No patients developed hyperkalaemia.Conclusion In patients with LQTS, high dose+ treatment increased plasma potassium by 0.4 mmol/L without cases of hyperkalaemia. However, the potassium increase did not shorten the QT interval and several patients had side effects. Considering the QT interval as a proxy for arrhythmic risk, our data do not support that potassium-elevating treatment has a role as antiarrhythmic prophylaxis in patients with LQTS with normal-range potassium levels.Trial registration number NCT03291145.No data are available. All data relevant to the study are included in the article or uploaded as supplementary information.}, URL = {https://openheart.bmj.com/content/8/2/e001670}, eprint = {https://openheart.bmj.com/content/8/2/e001670.full.pdf}, journal = {Open Heart} }