ISSN : 1301-5680
e-ISSN : 2149-8156
Turkish Journal of Thoracic and Cardiovascular Surgery     
Do patients with mechanical heart valves have the appropriate knowledge regarding warfarin therapy and can they adhere to the correct dosage?
Department of Surgical Nursing, Ege University Faculty of Nursing, İzmir, Turkey
DOI : 10.5606/tgkdc.dergisi.2015.10390


Background: This study aims to determine the knowledge level regarding warfarin therapy and adherence to therapy of patients with mechanical heart valve.

Methods: This descriptive study included 114 patients (56 males, 58 females; mean age 53.0±13.5 years; range 18 to 80 years) who received warfarin therapy for at least three months at the Department of Cardiovascular Surgery of Ege University Medical Faculty Hospital between 4 October 2012 and 30 May 2013. Patients who agreed to participate in the study were older than 18 years of age and literate. Data were collected by using sociodemographic profiles and a questionnaire form on knowledge of and adherence to warfarin therapy. A score of 1 (one) was given to patients’ correct answers, and 0 (zero) was given to incorrect or “I don’t know” answers for each item on the scale, and mean scores were obtained. Patients’ adherence to warfarin was measured by four questions involving (i) regular use of the medication as prescribed by doctors, (ii) forgetting to take the medication, (iii) delaying for more than 24 hours, and (iv) frequency of overuse. The answers to these four questions were evaluated based on a 100 mm visual analog scale.

Results: Patients’ mean score regarding anticoagulant therapy was 9.8±3.9 (lowest: 2, highest: 20) out of 22. Of the patients, 62.3% (n=71) stated that they used warfarin precisely as prescribed by doctors (100%).

Conclusion: It was determined that patients with mechanical heart valve and using warfarin had low level of knowledge regarding warfarin therapy and that they experienced problems in terms of their adherence to the medication.


Replacing a diseased heart valve with a mechanical prosthesis is a routine procedure with low perioperative morbidity and mortality rates.[1] However, the potential risk of thromboembolism postoperatively is still a major concern.[1] For this reason, patients are required to receive lifelong oral anticoagulant therapy,[1-4] with warfarin (Coumadin, Zentiva Sağlık Ürünleri Sanayi ve Tic. A.Ş. Levent, İstanbul) being the normal drug of choice.[5] Unfortunately, because of its narrow therapeutic range, warfarin causes various complications, the most serious of which is bleeding.[5-7] Despite its wide usage, most patients are not aware of warfarin’s side effects, and they do not know that laboratory follow-up tests [e.g., international normalized ratio (INR) and prothrombin time (PT)], and warfarin-food interactions can inhibit the effectiveness of this medication.[5,7-10]

Nurses have a key role in a patient’s adherence to treatment and the evaluation of its efficacy since they are in close contact with them 24 hours a day. Hence, a more effective nursing approach to individuals receiving warfarin therapy may improve the adherence to treatment and either avoid or minimize certain side effects.[5,11] The goal of this research was to determine the patients’ knowledge level regarding warfarin therapy and assess their ability to adhere to the proposed treatment regimen.


This descriptive study included 114 patients (56 males and 58 females; mean age 53.0±13.5 years; range 18 to 80 years) who received warfarin therapy at the Department of Cardiovascular Surgery of Ege University Medical Faculty Hospital for at least three months between October 4, 2012 and May 30, 2013. All of the patients who agreed to participate in the study were over the age of 18 and literate. No sampling method was used. All of the participants, except those who were pregnant, were included within the scope of the research. The total number of patients who underwent mechanical heart valve replacement at the same hospital in 2011 was 78.

For data collection, we used a questionnaire form developed by researchers in accordance with the related literature.[10,12,13] This included a total of 47 questions to determine the patients’ sociodemographic data as well as their level of knowledge regarding warfarin and their ability to adhere to this drug treatment. To ensure the content validity of the questionnaire, seven experts in the field were consulted and asked to evaluate the items in terms of their appropriateness to Turkish society, linguistic clarity, and comprehensibility. For a proper consideration of the experts’ views, a content validity index (CVI) was used, and each question was scored on a scale ranging from 1 (“not appropriate”) to 4 (“very appropriate”). Any necessary changes were then made in accordance with the expert views, and the form was then updated. Next, a pre-application was conducted with 10 patients who had similar characteristics to the sample, and to test the clarity, comprehensibility, and functionality of the items, they were informed about the process beforehand. After this was completed, the questionnaire was further updated to obtain the finished product.

The form included 21 multiple-choice questions that measured the patients’ knowledge with regard to warfarin therapy. Each question had four possible options, but only one of these was correct. To avoid random answers, an “I don’t know” option was added to the others; thus, each question had five options. The average scores were calculated by assigning a score of 1 to the correct answers and a score of 0 to the incorrect or “I don’t know” answers. The minimum score patients could receive was 0 while the maximum was 21. Then the total scores were evaluated and put into one of three categories: high (16-21 points), moderate (8-15 points), or low (0-7 points).

The patients’ adherence to warfarin dosage was assessed via four questions which focused on regularly using the medication as prescribed by doctors, forgetting to take the medication, delaying to take it for more than 24 hours, and overusing the drug.

The data was collected via face-to-face interviews conducted by the researchers, and after the patients answered the questions, they were given the correct answers. The interviews lasted 30 minutes on average.

Before the research was conducted, the study was approved by the Scientific Ethics Committee of Ege University, Nursing Faculty and the institution where the research would be conducted. In addition, the patients were informed about the details of the study, and we obtained verbal consent from all of the volunteer participants for their participation.

Statistical analysis
The data was analyzed using the SPSS for Windows version 16.0 software program (SPSS Inc., Chicago, IL, USA). Descriptive statistics were presented as number, percentage, and mean, and compliance of the quantitative variables with the normal distribution was assessed using the Shapiro-Wilk test. Additionally, an independent sample t-test was used for the normally distributed variables. For those that were not normally distributed, Spearman’s correlation analysis and analysis of variance (ANOVA) were used, and for nominal and ordinal variables, a chi-square test was also performed. A p value of <0.05 was considered to be statistically significant.


The sociodemographic characteristics and the data related to the patients’ warfarin usage are given in Tables 1 and 2, respectively.

Table 1: Patient distribution by their sociodemographic characteristics

Table 2: Patient distribution by warfarin usage

The patients’ average knowledge score regarding the anticoagulant therapy was 9.3±3.7 out of 21 points (lowest: 2; highest: 19). Based on the total scores, 29.8% of the patients (n=34) had low scores while 65.8% (n=75) had moderate and 4.4% (n=5) had high scores. The patients’ answers to the questions related to anticoagulant therapy are given in Table 3.

Table 3: Patient distribution based on their answers to questions regarding their knowledge of anticoagulant therapy

No statistically significant difference was detected between the patients’ complications and their knowledge of warfarin therapy [t=0.086, degrees of freedom (df)=112; p=0.932). We also found a negative correlation between the patients’ age and their knowledge of warfarin. However, this did not reach statistical significance (r= -0.028 p=0.764).

Furthermore, we determined that there was no statistically significant difference between the patients’ gender ( t= - 0.821; d f=105.35; p =0.413), m arital s tatus (t= - 1.318; d f=112; p =0.190), p lace o f r esidence (t=1.932; df=112; p=0.056), duration of warfarin usage (p=0.948), amount of education received regarding the use of warfarin (t= -0.146; df=112; p=0.884), and their knowledge of warfarin therapy. On the other hand, a statistically significant difference was found between the educational status of the patients and their knowledge level (p=0.001) as we determined that the university graduates (12.6±2.1) had a higher level of knowledge than the primary (8.6±3.7) and high school graduates (9.5±3.5).

Our findings also showed that 62.3% (n=71) of the patients stated that they used warfarin precisely as it was prescribed by doctors (100% adherence). Only one patient stated that they did not adhere to the doctors’ advice (0 adherence) (Table 4).

Table 4: Patient distribution based on their answers to questions related to their adherence to anticoagulant therapy

In addition, 41.2% (n=47) said that they had not experienced delays in taking their warfarin within the previous month (100% adherence), whereas only 7.0% (n=8) stated that they had experienced frequent delays in taking their medication (0% adherence) (Table 4). Moreover, 62.3% (n=71) said that they had never forgotten to take their warfarin within the previous month (100% adherence) while just a single patient (0.8%) stated that they always forgot (0% adherence) (Table 4). Finally, 29.8% (n=34) of the patients answered that they had taken an overdose of warfarin within the previous month (0% adherence) (Table 4).

No statistically significant differences were found between the complications experienced by the participating patients and the education they received regarding warfarin usage (x2=1.170; p=0.279), alcohol consumption (x2=0.343; p=0.558) and their use of medications other than warfarin (x2=3.803; p=0.051). However, we did identify a statistically significant difference between the complications experienced by the participating patients and the duration of warfarin usage (x2=14.938; p=0.001). We also found that 12.9% of the patients who had used warfarin for less than a year (n=4), 52.4% of those who had used it for 1-5 years (n=33), and 55.0% of those who had used it for more than five years (n=11) had experienced complications, but no statistically significant differences were detected between these complications and the patients’ knowledge levels related to their normal INR levels (x2=0.330; p=0.566) and their last INR levels (x2=0.773; p=0.379).


In this study, we determined that 14.9% of the participating patients (n=17) had no knowledge of how much warfarin they were receiving. In the study conducted by Mercan and Enç[14] with 114 individuals, 81.6% who did not know their warfarin dosage, so our results were much lower compared to theirs. In our study, we believe that this lack of knowledge was caused by the tendency of the patients to focus on the number of tablets rather than the number of milligrams they were taking, and the fact that 84.2% of our patients identified the different warfarin doses by their colors supports this belief. The tendency of individuals to identify their medication by tablet types without any knowledge of the correct dosage may mean they take the wrong medication at the wrong time, which could cause various complications. In the case study by Nural et al.,[15] they reported that a 53-year-old male patient lost his life after developing diffuse alveolar hemorrhage due to an overdose of warfarin. This was a direct result of taking two different doses of warfarin without knowing that they were the same medication. Therefore, doctors and nurses should make sure that their patients adequately understand their medication doses before they are discharged.

In the literature, it has been noted that home testing of INR or even self-management methods that allow for patient self-dosing and self-testing via standardized protocols are quite beneficial.[1,3] In contrast, our study indicated that only 2.6% of the patients performed self-testing of INR levels at home. Hence, further studies are needed to investigate the reasons for our low result.

Approximately half of the patients included in our study (42.1%) stated that they experienced complications related to warfarin usage. In the literature, bleeding is still the most common complications in mechanical heart valve patients.[1] Furthermore, interaction with other medications plays a major role in this condition. In support of this idea, we found that almost all of our patients (95.6%, n=109) regularly used medications other than warfarin.

In addition, the literature shows that mechanical heart valve patients and their families should be educated regarding the use of warfarin and how to manage the different dosage amounts.[3] Only 64% of the patients (n=73) in our study stated that they had received education related to warfarin usage, and 63% of these (n=46) said this education came from physicians while 37% said it came from nurses. In the study by Mercan and Enç[14] they found that 22.8% of their study participants had received educational information regarding the use of warfarin, with 76.9% receiving this information from physicians and 7.7% from nurses. The rate of patients in our study who were informed about warfarin usage by nurses was higher than in the Mercan and Enç study;[14] hence, we believe that they should realize that patient and discharge education are among their primary responsibilities.

This study identified some deficiencies related to the patients’ knowledge about warfarin usage. It is essential that they have a high knowledge level regarding the need to adhere to their therapy in order to prevent complications. In the study conducted by Van Damme et al.[10] that focused on mechanical heart valve patients, the average knowledge score concerning warfarin therapy was 7 out of 10 points, whereas in our study, the patients’ average score was 9.3±3.7 out of 21 points (lowest: 2; highest: 19). This lack of knowledge can negatively impact the patients’ ability to adhere to their medication, which can lead to the development of complications; thus, our findings offer proof that mechanical valve heart patients need to be better education with regard to the use of warfarin.

A great majority of the patients in our study (78.9%, n=90) knew that the INR test measured blood clotting; however, they (78.9%, n=90) did not know that a high level of INR indicated a high risk of bleeding and that a low level of INR indicated a high risk of blood clot formation. This could also be interpreted as a lack of knowledge on the part of the patients with regard to warfarin usage. Furthermore, more than half of our patients (67.5%, n=77) did not know that they should regularly watch for signs and symbols of bleeding, which is the most common side effect associated with this type of therapy. In their study, Tang et al.[16] emphasized that those individuals who were warfarin users needed to be informed about the side effects of this medication, and Cheah and Marten[17] also pointed out this need as well.

Furthermore, warfarin-food interaction is an issue that requires significant consideration.[14,18] The literature points out that patients should be informed of possible changes in the INR in response to the use of herbal/dietary supplements or the chronic use of alcohol in large quantities.[19] Our findings indicated that a significant portion of the patients were not informed about which food groups would adversely interact with the warfarin. Hu et al.[20] determined that the major deficiency in their patients’ knowledge was related to nutrition and vitamin K sources, and Mercan and Enç[14] found that none of their patients who were admitted to the emergency room because of complaints of bleeding due to warfarin usage had been informed about warfarin-food interaction. When our findings are compared with the literature, it must be acknowledged that mechanical heart valve patients are in need of education regarding warfarin-food interaction.

We anticipated that the patients who had received education related to warfarin would have higher scores on the questionnaire, but our results showed that more studies are needed to investigate the efficacy of the education given to these patients. Our other finding that conflicted with the literature[21] was that there was no meaningful difference between the patients’ age and their experience with complications, but this might have been due to the small sample size in our study.

Low adherence to treatment may lead to negative clinical outcomes, hospitalization, increased health care costs, and mortality.[22] Since warfarin is a highly efficacious drug, a proper level of anticoagulation is difficult to maintain.[8] Therefore, a high level of adherence is crucial for the treatment to succeed. However, it is known that even patients who receive education regarding the importance of adherence to their warfarin therapy have difficulty in maintaining their medication regimens, and this poor adherence can have a significant effect on anticoagulation control.[8] As a result of our research, some problems were detected related to our patients’ ability to adhere to their medication. The rate of patients who used warfarin precisely as it was prescribed by the doctors (i.e., those who fully adhered to the therapy) was only 62.3% (n=71). Van Damme et al.[10] also noted that only 72.2% of their patients had 100% adherence. We hypothesize that these low rates stem from the patients’ insufficient knowledge of warfarin therapy.

For patients who are prescribed this drug, it is vitally important that they take the warfarin at the same time every day. More than half of our patients (58.8%) stated that they failed to follow a regular intake of their medication. In other words, there had been a delay in taking their warfarin within the previous month. However, only a few of our study participants (7%, n=8) expressed that they frequently delayed taking their medication. Another factor that affects a patient’s ability to adhere to their drug regimen is forgetting to take a dose, and a significant portion of our patients (37.7%) said that there were days within the previous month when they forgot to take their medication. Kimmel et al.[8] found that one-two missed doses a week caused a reduction in anticoagulation. Moreover, when INR levels fall a bit below the therapeutic range, it increases the risk of thromboembolism. Furthermore, this condition may lead to the need for higher dosage levels, new tests, a re-consultation with a physician, and incorrect dosage intake.

Although cases of overdosage are not very common, when this occurs, it is known to cause over-anticoagulation. In a previous study, 40% of the patients demonstrated poor adherence, which was clinically significant.[8] As an adherence factor, the rate of overdosage in that study within the previous month was low (28.2%), yet it is still an issue that should be emphasized in patient education since it may lead to bleeding complications.


In this study, we determined that the patients who underwent heart valve replacement and took warfarin had a low level of knowledge regarding warfarin therapy and that they experienced problems in terms of their adherence to their medication. However, because of the sample size used in our study, further studies should be undertaken on a larger number of patients to investigate these issues more thoroughly.

Declaration of conflicting interests
The authors declared no conflicts of interest with respect to the authorship and/or publication of this article.

The authors received no financial support for the research and/or authorship of this article.


1) Christensen TD, Andersen NT, Attermann J, Hjortdal VE, Maegaard M, Hasenkam JM. Mechanical heart valve patients can manage oral anticoagulant therapy themselves. Eur J Cardiothorac Surg 2003;23:292-8.

2) Shrestha P, Koirala B, Shrestha N, Thapa P. A study on complication and monitoring of warfarin in post-valve surgery. JNMA J Nepal Med Assoc 2009;48:111-5.

3) Leeper B. Valvular disease and surgery. In: Carlson KK, editor. Advanced critical care nursing. St. Louis: Elsevier; 2009. p. 322-46.

4) Koertke H, Zittermann A, Tenderich G, Wagner O, El-Arousy M, Krian A. Low-dose oral anticoagulation in patients with mechanical heart valve prostheses: final report from the early self-management anticoagulation trial II. European Heart Journal 2007;28:2479-84.

5) Oterhals K, Deaton C, De Geest S, Jaarsma T, Lenzen M, Moons P, et al. European cardiac nurses’ current practice and knowledge on anticoagulation therapy. Eur J Cardiovasc Nurs 2014;13:261-9.

6) Hamby L, Weeks WB, Malikowski C. Complications of warfarin therapy: Causes, costs, and the role of the anticoagulation clinic. Eff Clin Prac 2000;3:179-84.

7) 2010 BC Guideline warfarin therapy management. Available at: pdf [Accessed: May 5, 2014]

8) Kimmel S, Chen Z, Price M, Parker CS, Metlay JP, Christie JD, et al. The influence of patient adherence on anticoagulation control with warfarin results from the international normalized ratio adherence and genetics (IN-RANGE) study. Arch Intern Med 2007;167:229-35.

9) Cruess DG, O’Leary K, Platt AB, Kimmel SE. Improving patient adherence to warfarin therapy. JCOM 2010;17:505-9.

10) Van Damme S, Van Deyk K, Budts W, Verhamme P, Moons P. Patient knowledge of and adherence to oral anticoagulation therapy after mechanical heart-valve replacement for congenital or acquired valve defects. Heart Lung 2011;40:139-46.

11) Subramanym P, Ranganayakulu D. The management of oral anti coagulant therapy in patient point of view. Int J Pharm Sci Bio 2010;1:169-173.

12) Briggs AL, Jackson TR, Bruce S, Shapiro NL. The development and performance validation of a tool to assess patient anticoagulation knowledge. Social and Administrative Pharmacy 2005;1:40-59.

13) Carvalho ARS, Dantas RAS, Pelegrino FM, Corbi ISA. Adaptation and validation of an oral anticoagulation measurement of treatment adherence instrument. Rev Lat Am Enfermagem 2010;18:301-8.

14) Mercan S, Enç N. Warfarin kullanan bireylerin eğitim gereksinimleri. Türk Kardiyol Dern Türk Kardiyol Dern Kardiyovasküler Hemşirelik Dergisi 2011;2:12-7.

15) Nural SM, Baydın A, Karataş AD, Elmalı M. Yüksek doz warfarin kullanımı sonucu gelişen yaygın alveolar hemoraji. Türk Toraks Dergisi 2007;7:68-71.

16) Tang EO, Lai C, Lee K, Wong R, Cheng G, Chan T. Relationship between patients' warfarin knowledge and anticoagulation control. The Annals of Pharmacotherapy 2003;37:34-9.

17) Cheah GM, Marten KH. Coumadin knowledge deficits: do recently hospitalized patients know how to safely manage the medication. Home Health Nurse 2003;21:94-100.

18) Göz M. Warfarin-gıda etkileşmesi; Olgu sunumu ve literatürün gözden geçirilmesi. Türk Göğüs Kalp Dama 2006;4:320-4.

19) Ageno W, Gallus AS, Wittkowsky A, Crowther M, Hylek EM, Palareti G. Oral anticoagulant therapy: Antithrombotic therapy and prevention of thrombosis, 9th ed. American College of Chest Physicians Evidence- Based Clinical Practice Guidelines. Chest. 2012;141(2 Suppl):44-88.

20) Hu A, Chow CM, Dao D, Errett L, Keith M. Factors influencing patient knowledge of warfarin therapy after mechanical heart valve replacement. J Cardiovasc Nurs 2006;21:169-75.

21) El Ghousain HE, Thomas M, Varghese SJ, Hegazi MO, Kumar R. Long term oral anticoagulant therapy with warfarin: experience with local patient population in kuwait. Indıan J Hematol Blood Transfus 2014;30:111-9.

22) Berben L, Bogert L, Leventhal ME, Fridlund B, Jaarsma T, Norekvål TM, et al. Which interventions are used by health care professionals to enhance medication adherence in cardiovascular patients? A survey of current clinical practice. Eur J Cardiovasc Nurs 2011;10:14-21.

Keywords : Adherence; anticoagulant; knowledge level; mechanical heart valve

Viewed : 4774
Downloaded : 1182