Patients will be analyzed by the monitoring method assigned. Patients will contribute to patient years during the time they are in the study For patient year analysis the following patients will be censored at the last day the patient had a complete assessment for study outcomes within the intended treatment duration. Patients who did not have a thromboembolic or bleeding event during the time of the predefined randomized test duration, patients lost to follow-up patients who died because of other reasons than thromboembolic events patients who withdrew informed consent before the end of the predefined treatment duration and who did not have an efficacy or safety outcome. The per-protocol-population (PPP) will consist of all randomized patients without any major deviation from the protocol. The following deviations will lead to exclusion from the PP population: Patients not tested according to allocation or no VKA treatment received at all 11.3 Study population/sample size and power/ demographics and patient characteristics Baseline characteristics: Demographic characteristics (including age, sex, indications for anticoagulation, concomitant drug use) will be summarized by treatment group using descriptive statistics and the groups will be compared with regard to baseline characteristics using traditional statistical methods. As, all major clinical events are likely to be admitted to Landspitali, the only acute care hospital in the Reykjavik area, loss to follow-up is expected to be negligible. Therefore, no adjustment of sample size is considered necessary. Patients excluded from the analysis population in the per protocol analysis will be listed by test method and reason for exclusion. The number and percentage of randomized patients who discontinued from the study prematurely will be tabulated by main reason for discontinuation and treatment group.