Strength and limitations
The randomized controlled design strengthens the causal inference of the findings. The present study was open labelled and therefore patients in the control group could have been motivated to increase their potassium intake independent of the trial. This is not likely to be an important factor as p-K levels in the control group were unchanged from baseline to follow-up. The study was limited by a low sample size and larger trials are needed to confirm the findings. Further, the study was designed as an all-comer trial of patients with low-normal- to moderately reduced left ventricular ejection fraction. Thus, the cohort is heterogeneous which could affect the generalizability of the results. The primary analysis is not conclusive on whether the effects seen with the intervention on myocardial function is caused by changes in potassium homeostasis per se or the effects of MRAs. However, the sensitivity analysis of patients only receiving potassium supplements showing similar results strengthens confidence in the main hypothesis.