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a Division of Cardiovascular Surgery, Mayo Clinic, Rochester, Minnesota
b Division of Cardiovascular Diseases, Mayo Clinic, Rochester, Minnesota
c Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, Minnesota
Accepted for publication January 17, 2008.
* Address correspondence to Dr Schaff, Division of Cardiovascular Surgery, Mayo Clinic, 200 First St SW, Rochester, MN 55905 (Email: schaff{at}mayo.edu).
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Abstract |
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Methods: We instituted an education program on a self-testing device before hospital discharge in 50 adult patients (median age, 54 years; 66% men) undergoing cardiac valve replacement with mechanical prostheses. Patients were monitored for 1 month to assess their ability to self-test and the accuracy of the INR measurements.
Results: Self-testing instruction began on postoperative day 4 (range, 1 to 8 days). Each patient had an average of 3.5 teaching sessions; each session lasted approximately 20 minutes. One month after discharge, all patients (98%) but 1 were able to self-test. No patient required interval instruction. One bleeding episode occurred in a patient whose INR exceeded the therapeutic range. Once warfarin doses were stabilized, 5 patients had subtherapeutic INR values on self-testing. The mean INR test result obtained from the coagulometer correlated well with values obtained by laboratory determination (r = 0.79).
Conclusions: This evaluation of an in-hospital education program demonstrates that patients are able to learn INR self-testing and that most will continue to use the method without the need for interval instruction. Improved anticoagulation management by early introduction of INR self-testing should reduce thromboembolic and hemorrhagic complications after valve replacement.
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Introduction |
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Unfortunately, bleeding after implantation of mechanical valves remains an important cause of valve-related death [4]. It has been shown that the risk of bleeding is directly proportional to the intensity of anticoagulant therapy [5] and the amount of time the international normalized ratio (INR) is outside of the therapeutic target range [6]. More frequent INR measurement reduces the rate of major hemorrhagic events, and patient self-testing with a coagulometer is now available for patients with prosthetic heart valves. Indeed, studies from Europe indicate that INR management by self-testing can reduce hemorrhagic complications after valve replacement by as much as 50% [7, 8]. The reduction in bleeding events is most likely from stricter control of the INR [9].
Because the rates of thromboembolism and bleeding are greatest in the first postoperative months, early introduction of INR self-testing to improve management of anticoagulation might be expected to reduce complications during this critical period. Typically, INR self-testing instruction for recipients of mechanical heart valves begins several weeks after hospital discharge and may require a month to complete [10]. In the United States, payers frequently do not cover the costs associated with INR self-testing until a patient has been on a stable dose of warfarin for 90 days. In the present study, we evaluated the feasibility of an in-hospital educational program for self-testing of INR in patients recovering from valve replacement.
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Material and Methods |
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Study Protocol
The goal of this study was to determine the efficacy of early postoperative instruction in INR self-testing for patients recovering from cardiac operations. Specifically, we monitored how many recipients of mechanical heart valves could be taught INR self-testing in the hospital and how many were able to continue self-testing for 1 month after discharge. We developed a structured education program patterned after established protocols [11] that was taught by a dedicated teaching nurse or physician. The program had four steps:
Self-testing instruction was initiated as soon as the patient's clinical status allowed and was completed before hospital discharge. The self-testing educational program was in addition to the standard anticoagulation education provided to all of our patients who receive a mechanical heart valve. The standard anticoagulation education includes a class, a video, and an informational booklet.
In addition to INR self-testing, INR values were also determined by a reference laboratory. This dual INR testing was intended only for the 1-month duration of the study. After the study the patients were given the option of continuing with self-testing or testing in the usual fashion.
All alterations to the dose of warfarin were based on blood drawn and processed in the standard fashion by the Mayo Clinic laboratory and, after hospital discharge, by the laboratory chosen by the managing physician.
Once patients were dismissed from the hospital, the referring physician assumed management of anticoagulation. Each time a patient was asked to have his or her INR checked by the managing physician, the patient also performed a self-test. In addition, the patients were instructed to self-test each Monday even if an INR test had not been ordered by the managing clinician. The patients were monitored for 1 month and were contacted by telephone after 2 weeks, to make sure they had enough supplies, and at the end of the study month. Once the study was completed, the patients returned a study-specific survey along with the INR log sheet on which they had recorded the INR results of both self-tests and laboratory tests.
Safeguards were installed for out-of-range INR self-tests. If a result from self-testing was 1.0 INR units away from the therapeutic range prescribed by the patient's managing physician, and an INR test by a standard laboratory was not scheduled, the patient was instructed to call the managing physician or the study coordinator. The patients were also instructed to call if they had any symptoms consistent with bleeding or a thromboembolic event.
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Results |
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The 50 subjects received 54 mechanical heart valves, with 54% being implanted into the aortic position. Concomitant procedures occurred in 52%, with coronary artery bypass grafting being the most common other procedure (11 patients). Median lengths of stay were 7.6 days (range 4 to 15 days) in the hospital and 2 days (range, 1 to 7 days) in the intensive care unit. The goal INR therapeutic range was set in accordance with established guidelines [12].
The clinical status of the patients dictated when self-testing instruction was initiated. For most patients, instruction began on postoperative day 4 (range, 1 to 8 days). Each patient received an average of 3.5 teaching sessions (range, 1 to 6). Each session lasted an average of 20 minutes for an average if 65 minutes (range, 20 to 150 minutes) of self-testing instruction before hospital discharge. Before going home, all patients were able to demonstrate their ability to self-test and record the result.
At the end of the study month, 49 of the 50 patients (98%) were able to obtain an INR result from the INRatio coagulometer. This was determined by personal communication with each subject at the end of the study. The single patient who did not perform self-testing stopped at the insistence of his managing physician.
Among patients who achieved a stable dose of warfarin, six instances occurred in which the self-testing value was 1 or more INR units above or below the therapeutic range. Five of these were low INR results by self-testing that were confirmed by the reference laboratory. The sixth subject reported a self-test INR of 6.7, but the reference laboratory returned a confirmatory INR of 3.2. The next day, the INRatio coagulometer again reported a high INR, while the reference laboratory again reported an INR within the prescribed therapeutic range. Later that same day, the patient was treated by the local emergency room for severe epistaxis. The INR determined by the emergency department was very similar to the INR that was had been reported by the coagulometer.
The INR logs were returned by 30 patients, and comparisons were made between the INR test results obtained from the INRatio coagulometer and the standard laboratories. The median number of times a patient attempted self-testing the first month after dismissal was 11 (range, 3 to 21). The median number of test strips used the first month was 15 (range, 5 to 23). The average INR obtained by self-testing while the patient was in the hospital was 2.58 ± 1.53 compared with 1.84 ± 0.59 from the Mayo Clinic's laboratory (r = 0.55, p = 0.005). The mean INR test result between the coagulometer was 2.98 ± 0.55; whereas, the average result obtained by multiple outside laboratories was 2.79 ± 0.96 (r = 0.79, p < 0.001).
Bland-Altman plots were obtained by plotting the differences in the INR result of the coagulometer against the mean for the Mayo Clinic's laboratory INR result (Fig 3) and the INR result from the outside laboratories (Fig 4). These demonstrate agreement of the INR results obtained by the coagulometer with the INR results obtained by the Mayo Clinic's laboratory as well as those of the outside laboratories.
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Comment |
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Encouraging patients to become active participants in their health care is possible and beneficial; for example, patients with diabetes mellitus or hypertension who self-monitor or self-adjust medication dosages, or both, have major improvements in medication compliance, clinical outcomes, and quality of life [13, 14]. Postoperative instruction, unfortunately, has not been considered an opportune time for patient instruction primarily due to concerns with altered neurocognitive function as a result of cardiopulmonary bypass, analgesic medications, and the rigors of routine convalescence.
The postoperative period, however, may be an ideal "teachable moment" as patients and family members focus on beginning healthy lifestyle changes. Physicians and their allied health staff are also immediately available to answer questions and resolve concerns. In the present study, despite having undergone cardiopulmonary bypass only a few days earlier, most patients felt well enough to begin INR self-testing instruction. All of the patients who completed the instruction protocol were able to perform INR self-testing at hospital dismissal. We found that most patients preferred self-testing and found it easier than having their INR checked in the usual fashion.
Because a higher frequency of bleeding is reported early after the initiation of warfarin therapy, achieving stricter INR control early after initiation of long-term anticoagulation may reduce bleeding events. In one study, for example, the frequency of major bleeding was 3.0% the first month after initiation of warfarin therapy, 0.8% per month for the next 11 months, and then reduced to 0.3% per month thereafter [15]. A greater proportion of time spent within the therapeutic INR range can be achieved by institution of patient self-testing. Also, INR self-management permits lower anticoagulation levels after mechanical heart valve replacement [16], with further reduction in the risk of bleeding.
Early institution of INR self-testing may reduce the number of thromboembolic events. The peak incidence of thromboembolism occurs during the first 3 months after valve replacement, after which time the per-annum incidence of thromboembolism remains relatively constant [17]. This is probably a reflection of the lack of endothelialization of the newly implanted prosthetic materials. Another contributing factor could be subtherapeutic INR levels predisposing to the development of valvar thrombus formation. Most of the patients in the present study with tests outside of the therapeutic range were below the goal range. Because the relationship between time in therapeutic range and clinical outcomes is strong [6], improving the time in therapeutic range with more frequent testing early after valve replacement may decrease early thromboembolic events.
Enhanced patient safety using INR self-testing ultimately requires an accurate and precise coagulometer. Interdevice variability of INR values does occur and is primarily due to differences in device mechanics, test strip reagents, and the sensitivity of the thromboplastin used. Although the aim of the present study was not to evaluate the performance characteristics of the INRatio device, a greater degree of correlation was observed between the outside laboratories and the INRatio coagulometer compared with the meter and the Mayo Clinic's laboratory. One potential reason for this observation is the heparin infusion that all of the patients received while being bridged to warfarin. Heparin interacts with the reagents on the test strip, thus increasing the likelihood of the test not working or the result to be inaccurate. For this reason, patients who are receiving a heparin infusion and being taught self-testing should rely on venipuncture while warfarin therapy is being initiated.
Bland-Altman graphs demonstrated agreement of INR results obtained by the coagulometer with those results obtained by the Mayo Clinic's laboratories and the outside laboratories. Bland-Altman analysis is a statistical method that allows for the comparison of two different measurement techniques [18]. The Bland-Altman graph plots the difference between the two techniques against their averages. The limits of agreement are defined by two standard deviations, which describe the range for 95% of the comparison points. It is superior to the correlation coefficient for defining the level of agreement between two measurement techniques. This is especially true when the techniques are measuring a value for which there is no systematic calibration method, such as the INR value.
An important obstacle to early patient self-testing is reimbursement. Currently, payment for INR self-testing is withheld by the Centers for Medicare & Medicaid Services (CMS) until a patient has been on a stable dose of oral anticoagulation for 90 days. Unfortunately, the first 90 days may be the period during which strict INR control by patient-self testing is most beneficial. In the United States, estimates are that less than 1% of patients being managed by anticoagulation clinics use self-testing to obtain INR results, and almost 60% of anticoagulation clinics prohibited INR self-testing for enrolled patients [12]. Cost is the reason most often cited for not offering INR self-testing to patients. Although the initial costs of self-testing are higher than cost of laboratory monitoring, several studies suggest that self-testing is more cost effective in the long-term [18].
Anticoagulation after implantation of mechanical heart valves remains the Scylla and Charybdis of postoperative management. Encouraging patients to become stakeholders in their health care by teaching them how to perform INR self-testing may reduce their risk of postoperative thromboembolism or bleeding. Centers that offer postoperative self-management instruction usually begin several weeks after discharge, losing any benefit offered by point-of-care testing. We have shown that it is possible for recipients of mechanical heart valves to learn INR self-testing before leaving the hospital and that they are able to continue testing during the first postoperative month. Early introduction of INR self-testing is possible and may reduce postoperative complications.
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References |
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