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ORIGINAL ARTICLE |
Department of Cardiovascular and Thoracic Surgery, GB Pant Hospital, Maulana Azad Medical College, New Delhi, India
Sumit Narang, MS Tel: +91 129 4086920 Fax: +91 11 26672594 Email: sumit_narang{at}yahoo.com, House No. 127, Sector 7 A, Faridabad, Haryana 121006, India.
ABSTRACT
Thrombogenicity of blood is known to have seasonal variations. The clinical implications of seasonal variations in the anticoagulation profile of patients with mechanical valves was assessed. Data of patients implanted with a mechanical heart valve for more than 3 months were collected at follow-up or on presentation to the emergency department. The mean time from the previous follow-up examination was 3.6 ± 0.3 months. The number of patients with an international normalized ratio >3.5 and the incidence of hemorrhagic events peaked in hottest part of the year (June–July), with 128 cases of prolonged clotting and 43 hemorrhagic events in this period. The number of patients with rapid clotting and the incidence of embolic events peaked in coldest part of the year (December–January), with 120 cases of international normalized ratio <1.5 and 37 embolic events in this period. There was a significant correlation between temperature and thrombogenicity in patients with prosthetic heart valves on long-term anticoagulation.
Key Words: Anticoagulants • Heart Valve Prosthesis • Seasons
INTRODUCTION
Seasonal variation in the thrombogenicity of blood is well known.2,3 This was found to be associated with seasonal variations in the rates of myocardial infarction, deep vein thrombosis, and pulmonary embolism, with more of these events occurring in the colder months of the year.4–17 Patients with mechanical heart valves who require long-term anticoagulation might also be affected by seasonal variations in thrombogenicity. This study was conducted to asses the clinical implications of seasonal variations in the anticoagulation profile of patients with mechanical valves.
PATIENTS AND METHODS
Data were collected from patients implanted with a mechanical heart valve for longer than 3 months and who were on chronic anticoagulation with warfarin with regular follow-up in our outpatient department, as well as those visiting the emergency department, between August 2005 and July 2007. The international normalized ratio (INR) and other details were recorded using a standard questionnaire. All patients were routinely advised to have their anticoagulation status checked at least once every 2 months, thus the year was divided into 6 periods of 2 months for analysis. All incidences of deranged clotting (INR >3.5 or <1.5) detected at outpatient clinics and all hemorrhagic and embolic complications presenting at the emergency department were recorded. No patient was counted twice; outpatient records were excluded if the patient presented to the emergency department. Patients taking any medication known to have a significant interaction with oral anticoagulants, those not following dietary advice, and alcoholics were excluded from the study. There were 2,220 patients in the dataset, 196 were excluded because of diet, drugs, or alcohol use. Patients with deranged clotting profiles with or without hemorrhagic or embolic complications were managed according to standard guidelines.
Statistical analyses were performed using the analysis of variance test. A p value <0.05 was considered significant.
RESULTS
The mean period between follow-up examinations in these patients was 3.6 ± 0.3 months. The mean maximum and minimum temperatures and humidity in each time period are given in Table 1
. The number of patients with INR >3.5 at outpatient clinics and the incidence hemorrhagic complications are given in Table 2. The number of patients with INR >3.5 and hemorrhagic events peaked in the hottest part of the year (June–July), with 128 cases of INR >3.5 (per 1,000 patients) and 43 hemorrhagic events (per 1,000 patients) during this period, leading to 18 hospital admissions and 6 deaths. The number of patients with INR <1.5 and the incidence of embolic events peaked in coldest part of the year (December–January) with 120 cases of INR <1.5 and 37 embolic events per 1,000 patients during this period, leading to 21 hospital admissions and 5 deaths (Table 3).
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Patients with mechanical heart valves require chronic anticoagulation. Seasonal variations in the incidence of prosthetic valve thrombosis have been shown, with the incidence peaking in the coldest part of the year.16 Other factors implicated in affecting anticoagulation profiles include diet, drugs taken for concurrent illness, and alcohol intake.17 In this study, patients taking any medication known to have a significant interaction with oral anticoagulants, those not following dietary advice, and chronic smokers and alcoholics were excluded. However, the effect of changes in diet in different seasons cannot be completely excluded, and the activity levels of the patients were not controlled.
The temperature was lowest in December–January and peaked in June–July. Humidity peaked in August–September and lowest in April–May. Thus temperature changes seem to correlate with variations in the anticoagulation profile and the related complications. Embolic episodes peaked in the coldest period, while hemorrhagic episodes peaked in warmest part of the year. These events coincided with changes in coagulation profiles found at outpatient clinics. No such correlation was observed with humidity. These findings raise the issue of how patients should be managed to maintain a clotting profile within a safe range to avoid complications. Furthermore, the mean duration between INR checks was 3.6 ± 0.3 months, despite advice to have checks every 2 months. This underscores the poor patient compliance and need for a better anticoagulation control system. One suggestion is to make patients aware of this information and recommend that they have their anticoagulant status checked more frequently, such as once a month, as well as within a few days of sharp changes in temperature, with a regular checkup at the outpatient department every 3 months. Patient self-testing and self-management has been shown to provide better control in various studies in Western populations;2 however, this may not be so successful in our patients with less awareness and education.
It was concluded from this study that there is a seasonal variation in clotting profiles of patients with prosthetic heart valves on chronic anticoagulation, possibly due to temperature variations. Because these seasonal effects cannot be controlled, patients should have their anticoagulation profile checked more frequently to maintain it within the desired range of INR (2.0–3.5). This might reduce the number of hemorrhagic or embolic complications.
ACKNOWLEDGMENTS
We acknowledge the assistance of Dr Ruchika Narang, MBBS, PhD, in analyzing data and in compilation of this manuscript.
REFERENCES
Asian Cardiovasc Thorac Ann 2009;
17:25-28
© 2009 by SAGE Publications
DOI: 10.1177/0218492309102625
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