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ePaper created 2014-10-06, 13:17:01 | version 1.33.00
explanatory power of r2 = 0.0419 for TTR and r2 = 0.0258 for the critical value rate, although it was statistically significant (P\0.0001 for both models). Correcting for all other patient characteristics, the use of CoaguChek XS had a positive effect of ?1.0% on the TTR and 0.002 fewer critical values per month compared with the use of INRatio2. While the effect on TTR was smaller in magnitude than in the univariate analysis (Table 1), in the multivariate analysis it was statistically significant (P = 0.008). The effect of the coagulometer on the rate of critical values remained not statistically significant. The effect of the choice of coagulometer on the TTR and critical value rate was smaller than the effect of female gender (-1.9% on TTR and ?0.048 on critical values per month, both P\0.001), and the choice of medication (phenprocoumon ?3.1% on TTR and -0.015 critical values per month, both P\0.001). A high target range (3.0–4.0) decreased the TTR significantly (-5.3%) and increased the critical events per month (?0.082, both P\0.001). A primary indication for mechanical heart valves increased the TTR by 3.0% (P\0.001) without a statistically significant effect on the frequency of critical values. Multivariate Analysis for Fatal Events The multivariate Cox regression analysis for the different parameters on patient survival showed that the choice of the device had no statistically significant influence (HR 1.05, 95% CI 0.65–1.70, P = 0.838) (Fig. 1). Similarly, most indications did not significantly influence the risk, while the target range and, most prominently, patient age at start, had statistically significant effects (a year higher age increased the HR by 8%, 95% CI 5–11%, P\0.001) (Fig. 2). DISCUSSION This retrospective analysis shows that the choice of coagulation monitor had no effect on clinical outcome of 4,326 Dutch patients treated with VKAs using self-monitoring. The results of the analysis provide a good insight to the quality of INR control in patients performing self-monitoring of INR values and, consequently, the clinical efficacy and safety of VKA treatment. In addition, the analysis provides unique data allowing us to compare the quality of INR control with two different INR monitors, INRatio2 and CoaguChek XS. Since major clinical events and deaths could not be verifiably attributed to a particular cause in the NTS data, no analysis of the rate of individual major thrombotic or hemorrhagic events could be completed. Therefore, it is not possible to compare the overall rate in the NTS data with rates reported in studies of new oral anticoagulant agents (NOACs), nor is it an objective of this analysis. In addition, this analysis is based on data collected in clinical practice, and not in the pre-specified and more tightly defined setting of randomized controlled trials. The major NOAC studies in atrial fibrillation suggest a general non-inferiority of NOACs versus warfarin with a reduction of hemorrhagic events (most notably of cerebral bleeding [27–30]). Interestingly some meta- analyses found in subgroup analyses a dependency of this effect on the quality of TTR control in the VKA group. Go´mez-Outes et al. [28] found that the positive effects of NOACs versus warfarin on non-hemorrhagic strokes and systemic embolic events and on mortality were present in centers that only achieved a TTR below 65% in the warfarin arm. Similarly Ruff et al. [31] showed in a recent meta-analysis that there was a trend for a lower risk reduction of NOACs on stroke and systemic Adv Ther