Association Between the INR and Warfarin Dose in Patients With Mechanical Prosthetic Heart Valves

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Background Although several algorithms have been proposed to predict individual warfarin doses, the relationships between the international normalized ratio (INR) and cumulative warfarin dose remain to be determined. Objectives The aim of this study was to explore the correlation between the INR and the cumulative dosage of warfarin within a week in patients who have undergone mechanical heart valve replacement. Methods A retrospective study was conducted at the First Affiliated Hospital of Shantou University Medical College in southern China. Fifty‐two patients who underwent mechanical heart valve replacement between January 2016 and December 2022 were included. The daily warfarin dose, cumulative dosage of warfarin within a week, and INR value were recorded. A simple linear regression model was used to analyze the correlation between the INR and cumulative warfarin dosage within a week. Results Of the 52 patients who underwent mechanical heart valve replacement, 19 were male, and 33 were female. Twenty‐three and 18 patients had undergone mitral valve replacement and aortic valve replacement, respectively. Eleven patients underwent both mitral and aortic valve replacement. There was a strong linear correlation in 35 patients (67.31%), with a correlation coefficient (adjusted R 2 ≥ 0.7) identified between the INR and the cumulative dosage of warfarin within a week. The patients with weak correlations (adjusted R 2 < 0.7) were more likely to be female and have lower left ventricular ejection fractions, fewer days and lower cumulative warfarin doses at the first time of therapeutic INR. Multivariate logistic regression analysis revealed that none of these factors significantly affected the relationship between the INR and cumulative warfarin dose. Conclusion Our study revealed a strong linear correlation between the INR and the cumulative dosage of warfarin within a week in most patients with mechanical prosthetic heart valves.

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