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Keywords:

  • aortic valve calcification;
  • mitral annular calcification;
  • mitral valve calcification;
  • warfarin

Abstract

  1. Top of page
  2. Abstract
  3. Methods
  4. Results
  5. Discussion
  6. Disclosure of Conflict of Interests
  7. References

Summary. Background: Warfarin affects the synthesis and function of the matrix Gla-protein, a vitamin K-dependent protein, which is a potent inhibitor of tissue calcification. Objectives: To investigate the incidence of mitral valve calcium (MVC), mitral annular calcium (MAC) and aortic valve calcium (AVC) in patients with non-valvular atrial fibrillation (AF) treated with warfarin vs. no warfarin. Patients and methods: Of 1155 patients, mean age 74 years, with AF, 725 (63%) were treated with warfarin and 430 (37%) without warfarin. The incidence of MVC, MAC and AVC was investigated in these 1155 patients with two-dimensional echocardiograms. Unadjusted logistic regression analysis was conducted to examine the association between the use of warfarin and the incidence of MVC, MAC or AVC. Logistic regression analyses were also conducted to investigate whether the relationship stands after adjustment for confounding risk factors such as age, sex, race, ejection fraction, smoking, hypertension, diabetes, dyslipidemia, coronary artery disease (CAD), glomerular filtration rate, calcium, phosphorus, calcium-phosphorus product, alkaline phosphatase, use of aspirin, beta blockers, angiotensin-converting enzyme inhibitors or angiotensin receptor blockers, and statins. Results: There was a significant association between the use of warfarin and the risk of calcification [unadjusted odds ratio = 1.71, 95% CI = (1.34–2.18)]. The association still stands after adjustment for confounding risk factors. MVC, MAC or AVC was present in 473 of 725 patients (65%) on warfarin vs. 225 of 430 patients (52%) not on warfarin (P < 0.0001). Whether this is a causal relationship remains unknown. Conclusions: Use of warfarin in patients with AF is associated with an increased prevalence of MVC, MAC or AVC.

Vitamin K antagonists (VKA) are commonly used as anticoagulants. VKA exert their anticoagulant effect by inhibiting the carboxylation of glutamic acid residues (Glu) into γ-carboxyglutamic acid (Gla) during the bio-synthesis of coagulation factors II, VII, IX and X. However, there are other Gla-proteins affected by vitamin K and its antagonists, including the naturally occurring anticoagulant proteins C, S and Z, the bone Gla-protein osteocalcin, the calcification inhibiting matrix Gla-protein (MGP), growth arrest specific gene 6 protein (Gas6), and trans-membrane Gla-proteins (TMGPs). The matrix protein Gla is vitamin K-dependent and functions as an inhibitor of calcification in tissues. Clinically important effects of inhibition of formation of these Gla-proteins by VKA include a paradoxical hypercoagulable state induced by the rapid fall of protein C as compared with the slower fall of factors II, IX and X when rapid oral anticoagulation is attempted and the well-known fetal bone calcification abnormalities associated with VKA use in pregnancy [1]. It has been suggested that the fetal bone anomaly called chondrodysplasia punctata is caused by incomplete carboxylation of MGP, resulting in excessive cartilage calcification, nasal and distal digital hypoplasia, and epiphyseal stippling [2].

Animal experimentation has demonstrated that either the lack of MGP or the use of VKAs has effects on cardiovascular calcification. A study found that mice lacking MGP developed spontaneous calcification of arteries and cartilage and died of vascular rupture 2 months later. This identified MGP as the first recognized inhibitor of calcification in vivo [3]. A study by Price et al. [4] showed that high doses of warfarin cause focal calcification of the elastic lamellae in the media of major arteries and in aortic heart valves in the rat. These investigators found that the calcification of arteries induced by warfarin was similar to that seen in the MGP-deficient mouse and suggested that warfarin induces arterial calcification by inhibiting γ-carboxylation of MGP, thereby inactivating the putative calcification-inhibitory activity of the protein. Later Price et al. [5] showed that concurrent warfarin administration increased the extent of calcification in the media of vitamin D-treated rats. Sweatt et al. [6] elucidated the interaction of MGP and bone morphogenetic protein2 (BMP-2). Using immunohistochemistry, these investigators showed that calcified lesions in the aortic wall of aging rats contained elevated concentrations of MGP that was poorly γ-carboxylated and did not bind BMP-2. These investigators demonstrated that the BMP-2/MGP complex exists in vivo, consistent with a role for MGP as a BMP-2 inhibitor. They postulated that age-related arterial calcification may be a consequence of under-gamma-carboxylation of MGP, allowing unopposed BMP-2 activity.

These background data led us to hypothesize that the incidence of aortic valve calcification, mitral valve calcification and mitral annulus calcification might be associated with the use of warfarin. Therefore, we performed a retrospective study in a non-valvular atrial fibrillation patient population that had undergone echocardiography at our institution to evaluate a possible association between use of warfarin and valvular calcification.

Methods

  1. Top of page
  2. Abstract
  3. Methods
  4. Results
  5. Discussion
  6. Disclosure of Conflict of Interests
  7. References

The presence of calcium on the mitral valve, the mitral annulus and aortic valve was studied in patients with non-valvular atrial fibrillation. Patients treated with warfarin were compared with comparable patients who did not receive warfarin. Studies were carried out in 725 patients treated with warfarin vs. 430 who did not receive warfarin. The patients were evaluated using two-dimensional echocardiograms. Valvular calcium was present in 473 patients on warfarin as compared with 225 patients not receiving warfarin. A wide variety of biochemical and epidemiological parameters were investigated.

Student’s t-tests were used to analyze continuous variables between both groups. Chi-square tests and Fisher’s exact tests were used to analyze dichotomous variables between both groups. Unadjusted and adjusted logistic regression analysis was used to investigate the association between the use of warfarin and the incidence of MVC, MAC or AVC.

Results

  1. Top of page
  2. Abstract
  3. Methods
  4. Results
  5. Discussion
  6. Disclosure of Conflict of Interests
  7. References

Of 1155 patients, 725 (63%) were receiving warfarin and 430 (37%) were not receiving warfarin. Table 1 lists the baseline characteristics of both groups. Table 2 shows the incidence of MVC, MAC, AVC and MVC or MAC or AVC in the warfarin and the no warfarin groups. Table 2 also lists levels of statistical significance, odds ratios and confidence intervals. Table 3 shows odds ratios along with the corresponding 95% confidence intervals for the effect of warfarin use on the incidence of MVC, MAC or AVC after adjustment for confounding factors.

Table 1.   Baseline demographic characteristics
VariablesNo warfarin (n = 430)Warfarin (n = 725)
  1. ACEI, angiotensin-converting enzyme inhibitors; ARBs, angiotensin receptor blockers.

Sex (%)
 Men263 (61)442 (61)
 Women167 (39)283 (39)
Ethnicity (%)
 Caucasian364 (85)617 (85)
 Black39 (9)51 (7)
 Hispanics23 (5)44 (6)
 Asians4 (1)13 (2)
Mean age, years (SD)74 (14)74 (12)
Left ventricular ejection fraction (%)
 Normal305 (71)473 (65)
 Abnormal125 (29)252 (35)
Diabetes mellitus (%)54 (13)250 (34)
Hypertension (%)202 (47)439 (61)
Dyslipidemia (%)227 (53)361 (50)
Smoking (%)132 (31)212 (29)
Use of aspirin (%)207 (48)179 (25)
Use of beta blocker (%)187 (43)396 (55)
Use of ACEI (%)75 (17)250 (34)
Use of ARBs (%)18 (4)66 (9)
Use of ACEI or ARBs (%)91 (21)280 (39)
Use of statins (%)211 (49)353 (49)
Mean glomerular filtration rate, mL/min/(1.73 m2) (SD)68 (43)65 (40)
Mean serum alkaline phosphatase, U L−1 (SD)111 (80)111 (93)
Mean serum calcium, mg dL−1 (SD)9.1 (4.1)9.0 (0.8)
Mean serum phosphate, mg dL−1 (SD)3.3 (1.3)3.2 (0.8)
Mean serum calcium-phosphate product (SD)30 (15)29 (7)
Table 2.   Incidence of mitral valve calcification, mitral annular calcification, aortic valve calcification, and mitral valve or mitral annular or aortic valve calcification in the warfarin and no warfarin groups
VariablesNo warfarin (n = 430), %Warfarin (n = 725), %P-valueOdds ratio95% CI
  1. MVC, mitral valve calcification; MAC, mitral annular calcification; AVC, aortic valve calcification.

MVC36 (8)89 (12)0.0391.531.02–2.30
MAC140 (33)275 (38)0.0661.270.99–1.63
AVC166 (39)351 (48)0.0011.491.17–1.90
MVC or MAC or AVC225 (52)473 (65)< 0.00011.711.34–2.18
Table 3.   Odds ratios for the effect of warfarin use on the incidence of mitral valve or mitral annular or aortic valve calcification after adjustment for confounding factors
Confounding factorsOdds ratio95% CI
None1.711.34–2.18
Age, sex, race1.911.47–2.49
Age, sex, race, glomerular filtration rate, serum alkaline phosphatase, serum calcium, serum phosphate, serum calcium-phosphate product1.931.48–2.52
Age, sex, race, use of statin, use of aspirin, use of beta blocker, use of ACEI or ARBs2.031.50–2.75
Age, sex, race, diabetes mellitus, hypertension, coronary artery disease2.591.92–3.51

MVC was present in 89 of 725 patients (12%) on warfarin vs. 36 of 430 patients (8%) not on warfarin (odds ratio = 1.53, 95% CI = 1.02–2.30). MAC was present in 275 of 725 patients (38%) on warfarin vs. 140 of 430 patients (33%) not on warfarin (odds ratio = 1.27, 95% CI = 0.99–1.63). AVC was present in 351 of 725 patients (48%) on warfarin vs. 166 of 430 patients (39%) not on warfarin (odds ratio = 1.49, 95% CI = 1.17–1.90). MVC, MAC or AVC was present in 473 of 725 patients (65%) on warfarin vs. 225 of 430 patients (52%) not on warfarin (odds ratio = 1.71, 95% CI = 1.34–2.18). Warfarin users still had a higher incidence of MVC, MAC or AVC (odds ratio = 2.59, 95% CI = 1.92–3.51) than non-warfarin users after controlling for the confounding effect of age, sex, race, diabetes mellitus, hypertension and coronary artery disease (Table 3).

Discussion

  1. Top of page
  2. Abstract
  3. Methods
  4. Results
  5. Discussion
  6. Disclosure of Conflict of Interests
  7. References

The data from animal experimentation have led investigators to examine the effects of warfarin risks in humans. A case series of 16 patients with cutaneous necrosis from calcific uremic arteriolopathy identified warfarin as the risk factor [7]. In two of these patients, substitution of low-molecular weight heparin for warfarin therapy resulted in clinical improvement. A study in patients with renal failure led to the postulation that long-term use of warfarin might lead to arterial calcification and suggested further investigation [8].

Spronk et al. [9] found that MGP accumulated at the borders of vascular calcification in human tissue specimens. These investigators suggested that undercarboxylated MGP is biologically inactive and that poor vascular vitamin K status may be a risk factor for vascular calcification. Schurgers et al. [10] investigated whether long-term oral anticoagulant treatment may induce calcification in humans. These investigators measured the grade of aortic valve calcification in valves removed from patients undergoing surgical valve replacement. Calcifications in valves from patients receiving preoperative oral anticoagulant treatment were significantly (2-fold) larger than in patients not receiving preoperative oral anticoagulants. These investigators concluded that oral anticoagulants may induce cardiovascular calcification as an adverse side-effect.

Schori and Stungis [11] reported a case of arterial calcification in a person who had long-term treatment with warfarin and suggested that physicians prescribing long-term warfarin treatment should consider arterial calcification as one of its potential consequences. Koos et al. [12] reported on the association of oral anticoagulation with AVC and coronary artery calcium assessed by multislice spiral computed tomography. These investigators found that patients on oral anticoagulant therapy had increased coronary artery calcium and AVC compared with patients without anticoagulation treatment. These investigators concluded that oral anticoagulation may be associated with increased AVC and coronary artery calcium in patients with AVC, presumably due to decreased activation of the matrix Gla-protein.

Holden et al. [13] carried out a retrospective cohort study designed to determine the association between long-term exposure to warfarin and severity of AVC in hemodialysis patients. Although the odds ratio of falling into a higher category of AVC following 18 months of warfarin was not statistically significant (P = 0.055), there was an association between lifetime months of warfarin exposure and severity of AVC (P = 0.004) that was independent of dialysis use, calcium and calcitriol intake. These investigators suggested that warfarin use may be associated with severity of AVC in hemodialysis patients.

The data from the present study are consistent with the published data [7–13]. Similar to these studies, these are not results from a prospective randomized trial. Warfarin and other vitamin K antagonists are essential drugs for many individuals and also carry a significant risk of causing bleeding. Additionally, satisfactory substitutes for vitamin K antagonist anticoagulants are not yet available. Thus, a randomized prospective trial is not feasible at this time.

Another approach to elucidating the role of vitamin K and/or warfarin in extra osseous calcification would be to look at the vitamin K intake and incidence of arterial disease and/or calcification in individuals not requiring anticoagulation. This approach has been taken by Gast et al. [14], who found no relation between vitamin K-1 intake and coronary heart disease. These investigators did find that a high intake of menaquinones, especially MK-7, MK-8 and MK-9, could protect against coronary heart disease. These investigators concluded that more research is necessary to define optimal intake levels of vitamin K intake for the prevention of coronary heart disease.

Schurgers et al. [15] have suggested that an optimal intake of vitamin K is necessary to minimize the risk of vascular calcification. Beulens et al. [16] have studied a postmenopausal population of women using a questionnaire about food intake. These investigators found that high dietary menaquinone intake, but probably not phylloquinone, was associated with reduced coronary artery calcification and concluded that adequate menaquinone intake could be important to prevent cardiovascular disease. Cranenburg et al. [17] have developed an assay for the circulating inactive form of matrix Gla-protein (ucMGP) as a biomarker for cardiovascular calcification that might be used to monitor the possible therapeutic use of vitamin K. These investigators state that vitamin K therapy has the potential of increasing the activity of MGP, possibly reducing the development of calcification.

Spronk et al. [18] have shown that menaquinone-4 is more effective than vitamin K-1 in prevention of arterial calcifications in rats. Wallin et al. [19] have demonstrated similar findings in tissue culture. Further support for the role of vitamin K in human vascular calcification comes from the work of Teichert et al. [20], who found that the T-allele of the vitamin K epoxide reductase complex subunit 1 (VKORC1 1173C_T) polymorphism was associated with a significantly higher risk of aortic calcification in whites. Braam et al. [21] reported that in a randomized placebo-controlled study, the addition of vitamin K to a food supplement of vitamin D and minerals resulted in improved elastic properties of blood vessels in postmenopausal women. No measures of calcification were reported [21]. In the Rotterdam study, Geleijnse et al. [22] reported an inverse relationship between aortic calcification and dietary intake of menaquinone (vitamin K2) but not phylloquinone (vitamin K1).

Warfarin is currently the only approved oral anticoagulant in the United States of America and was the only coumarin used in this study, which may not be generalizable to other VKA. The other currently available drugs for long-term home treatment are injectable low molecular weight heparin (LMWH) and an injectable factor Xa inhibitor. Warfarin’s action can be monitored by an inexpensive laboratory test: the internationalized normal ratio (INR). Due to long-term use and experience, clinicians can manage warfarin easily compared with the other available drugs. It has proven benefit in preventing strokes in atrial fibrillation patients, recurrent deep venous thrombosis and pulmonary embolism, and hence, reducing mortality in patient populations at risk for thromboembolic disease. Unlike LMWH, it has the advantage of fairly quick reversibility of its action in case of bleeding. Another advantage is that it can be safely used in patients with low creatinine clearance. Additionally, even if warfarin use does confer a certain amount of increased calcification, it is not clear that this is clinically significant, and even if it is, whether this disutility outweighs the utility of stroke prevention.

Our study has other limitations. We do not have data about the chief complaints that brought the patients to medical attention. Though the groups are equally matched for age, sex and race, there is a difference in incidence of diabetes, hypertension and CAD in the warfarin group compared with the no warfarin group. These factors are themselves known to cause calcification. Calcification was most strongly associated with CAD, which was greater in the warfarin group, and this may have been a significant confounding factor for warfarin’s association with calcification. Also we could not measure whether the patients had calcification before initiation of warfarin therapy. Being a retrospective chart review study, we could not assess whether the difference in calcification between the warfarin and the no warfarin group contributed to clinically significant morbidity and mortality in patients.

In conclusion, we report a clear association between prior warfarin use and the incidence of calcification of MVC, MAC or AVC. This association still stands after adjustment for many confounding risk factors. These data indicate that warfarin use may have a significant poorly recognized adverse effect. Further studies are needed to confirm and quantify this risk. The use of VKA has always been difficult because of complex pharmacodynamics, a narrow therapeutic window, numerous drug–drug and drug–food interactions and multiple adverse effects. This adds to the need to find alternatives to the use of oral VKA.

Disclosure of Conflict of Interests

  1. Top of page
  2. Abstract
  3. Methods
  4. Results
  5. Discussion
  6. Disclosure of Conflict of Interests
  7. References

The authors state that they have no conflict of interest.

References

  1. Top of page
  2. Abstract
  3. Methods
  4. Results
  5. Discussion
  6. Disclosure of Conflict of Interests
  7. References
  • 1
    Pettifor JM, Benson R. Congenital malformations associated with the administration of oral anticoagulants during pregnancy. J Pediatr 1975; 86: 45962.
  • 2
    Howe AM, Lipson AH, De Silva M, Ouvrier R, Webster WS. Severe cervical dysplasia and nasal cartilage calcification following prenatal warfarin exposure. Am J Med Genet 1997; 71: 3916.
  • 3
    Luo G, Ducy P, McKee MD, Pinero GJ, Loyer E, Behringer RR, Karsenty G. Spontaneous calcification of arteries and cartilage in mice lacking matrix GLA protein. Nature 1997; 385: 7881.
  • 4
    Price PA, Faus SA, Williamson MK. Warfarin causes rapid calcification of the elastic lamellae in rat arteries and heart valves. Arterioscler Thromb Vasc Biol 1998; 18: 14007.
  • 5
    Price PA, Faus SA, Williamson MK. Warfarin-induced artery calcification is accelerated by growth and Vitamin D. Arterioscler Thromb Vasc Biol 2000; 20: 31727.
  • 6
    Sweatt A, Sane DC, Hutson SM, Wallin R. Matrix Gla protein (MGP) and bone morphogenetic protein-2 in aortic calcified lesions of aging rats. J Thromb Haemost 2003; 1: 17885.
  • 7
    Coates T, Kirkland GS, Dymock RB, Murphy BF, Brealey JK, Mathew TH, Disney AP. Cutaneous necrosis from calcific uremic arteriolopathy. Am J Kidney Dis 1998; 32: 5148.
  • 8
    Farzaneh-Far A, Proudfoot D, Shanahan C, Weissberg PL. Vascular and valvar calcification: recent advances. Heart 2001; 85: 137.
  • 9
    Spronk HMH, Soute BAM, Schurgers LJ, Cleutjens JPM, Thijssen HHW, De Mey JGR, Vermeer C. Matrix Gla protein accumulates at the border of regions of calcification and normal tissue in the media of the arterial vessel wall. Biochem Biophys Res Commun 2001; 289: 48590.
  • 10
    Schurgers LJ, Aebert H, Vermeer C, Bültmann B, Janzen J. Oral anticoagulant treatment: friend or foe in cardiovascular disease? Blood 2004; 104: 32312.
  • 11
    Schori TR, Stungis GE. Long-term warfarin treatment may induce arterial calcification in humans: case report. Clin Invest Med 2004; 27: 1079.
  • 12
    Koos R, Mahnken AH, Mühlenbruch G, Brandenburg V, Pflueger B, Wildberger JE, Kühl HP. Relation of oral anticoagulation to cardiac valvular and coronary calcium assessed by multislice spiral computed tomography. Am J Cardiol 2005; 96: 7479.
  • 13
    Holden RM, Sanfilippo AS, Hopman WM, Zimmerman D, Garland JS, Ross A. Warfarin and aortic valve calcification in hemodialysis patients. J Nephrol 2007; 20: 41722.
  • 14
    Gast GC, De Roos NM, Sluijs I, Bots ML, Beulens JW, Geleijnse JM, Witteman JC, Grobbee DE, Peeters PH, Van Der Schouw YT. A high menaquinone intake reduces the incidence of coronary heart disease. Nutr Metab Cardiovasc Dis 2009; 19: 50410.
  • 15
    Schurgers LJ, Cranenburg ECM, Vermeer C. Matrix Gla-protein: the calcification inhibitor in need of vitamin K. Thromb Haemost 2008; 100: 593603.
  • 16
    Beulens JW, Bots ML, Atsma F, Bartelink ML, Prokop M, Geleijnse JM, Witteman JC, Grobbee DE, Van Der Schouw YT. High dietary menaquinone intake is associated with reduced coronary calcification. Atherosclerosis 2009; 203: 48993.
  • 17
    Cranenburg EC, Vermeer C, Koos R, Boumans ML, Hackeng TM, Bouwman FG, Kwaijtaal M, Brandenburg VM, Ketteler M, Schurgers LJ. The circulating inactive form of matrix Gla protein (ucMGP) as a biomarker for cardiovascular calcification. J Vasc Res 2008; 45: 42736.
  • 18
    Spronk HMH, Soute BAM, Schurgers LJ, Thijssen HHW, De Mey JGR, Vermeer CJ. Tissue-specific utilization of menaquinone-4 results in the prevention of arterial calcification in warfarin-treated rats. J Vasc Res 2003; 40: 5317.
  • 19
    Wallin R, Schurgers L, Wajih N. Effects of the blood coagulation vitamin K as an inhibitor of arterial calcification. Thromb Res 2008; 122: 4117.
  • 20
    Teichert M, Visser LE, Van Schaik RH, Hofman A, Uitterlinden AG, De Smet PA, Witteman JC, Stricker BH. Vitamin K epoxide reductase complex subunit 1 (VKORC1) polymorphism and aortic calcification: the Rotterdam Study. Arterioscler Thromb Vasc Biol 2008; 28: 7716.
  • 21
    Braam LA, Hoeks AP, Brouns F, Hamulyák K, Gerichhausen MJ, Vermeer C. Beneficial effects of Vitamin D and K on the elastic properties of the vessel wall in postmenopausal women: a follow-up study. Thromb Haemost 2004; 91: 37380.
  • 22
    Geleijnse JM, Vermeer C, Grobbee DE, Schurgers LJ, Knapen MH, Van Der Meer IM, Hofman A, Witteman JC. Dietary intake of menaquinone is associated with a reduced risk of coronary heart disease: the Rotterdam Study. J Nutr 2004; 134: 31005.