Source of funding: The Swedish Medical Products Agency, Selander’s fund, the Swedish Heart-Lung Foundation, the Swedish Research Council, Uppsala County Council Research Fund, and Thuréus foundation. The funding agencies had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; and preparation, review, or approval of the manuscript.
Ethical approval: Granted from the regional ethical review board, Uppsala, Sweden (2011/231).
Contributors: M.K. conceived the study, interpreted the data, and drafted the manuscript. P.H. contributed to the design of the study, collected the data from the Medical Products Agency, and also obtained the ethical approval. Both authors critically revised the manuscript for important intellectual content and approved the final version.
Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.