Circannual variations in the international normalized ratio (INR) among mechanical heart valve surgery patients on life-long warfarin

Abstract

Introduction: The aim of our study was to explore if there exists a circannual rhythm in INR as fluctuations in anti-coagulation can have serious consequences in patients with mechanical heart valve prosthesis. Methodology: This is a retrospective study performed in patients with stable INR value for at least 30 days post heart valve surgery in the period 2015–2016 attending a nurse-managed, cardiologist-supervised anti-coagulation clinic at King Abdul Aziz Cardiac Center.we determined average seasonal INR values for each patient, separately for aortic and mitral valve replacement patients. Data were analyzed using JMP Version 7.1, p < 0.05 considered significant. Results are expressed as mean ± SEM, differences between means were analyzed using Wilcoxon-rank sums test and chi-square as appropriate. Seasonal changes in INR were analyzed using analysis of variance of repeated measures (MANOVA), adjusting for potential confounders. Results: Data Collected for 397 patients (mean age 50 ± 0.7 years, 56% male) with a total of 6,220 INRs; 4149 in the high target (2.5–3.5) and 2021 in the low target (2–3) patients. There was no significant difference in the number of INR determinations performed across seasons. INR decreased significantly with time, from the highest value in the summer at 2.8 ± 0.07 to lowest in winter at 2.6 ± 0.02 (p < 0.0001), irrespective of the target INR (p = 0.36). There was no significant interaction between time-related changes in INR and age, gender, INR target, renal impairment, concomitant anti-platelet treatment except for smoking, which showed a significant interaction with INR variation over time (p < 0.001). Conclusion: To the best of our knowledge. This is the first study in the Middle-East extending European and North-American data on circannual changes in INR. Our results confirm the existence of such a rhythm; however the mechanism is unknown. Our findings recognize winter as a challenging season for maintaining optimum anti-coagulation, possibly requiring higher number of outpatient visits and INR determinations, with implications for health care costs.