title: Risk of Post-TKA Acute Myocardial Infarction in Patients With a History of Myocardial Infarction or Coronary Stent.
abstract: BACKGROUND
  Acute myocardial infarction (AMI) is one of the most important perioperative complications of total knee arthroplasty (TKA). Although risk-stratification tools exist for the prediction of cardiac complications including AMI after noncardiac surgery, such stratification does not differentiate the patients with a coronary stent alone, AMI without a stent, or AMI with a stent. The risk of postoperative AMI in these patient groups may vary. Several studies have recommended suitable times for noncardiac surgery in patients with a coronary stent; however, they do not differentiate between the patients with AMI and no AMI. The suitable time of noncardiac surgery for patients with AMI and stent may vary from those with a stent alone. Moreover, a study to evaluate the risk of AMI within 1 year in an Asian population with a history of AMI or coronary stent who underwent TKA has not been reported.
  
  
  OBJECTIVE
  (1) What are the risks of AMI within 1 year of TKA in patients who have had a stent alone, AMI without a stent, or AMI with a stent as compared with patients without an AMI/stent? (2) For patients with AMI/stent placement, when can TKA be performed where the risk of subsequent AMI normalizes? (3) What comorbidities are associated with post-TKA AMI? (4) Is the risk of AMI within 1 year after surgery in patients undergoing TKA without a history of AMI/stent higher than that in patients with no surgery?
  
  
  METHODS
  This study is a retrospective study of the medical claim records of 128,216 patients who underwent TKA between 1997 and 2010 in Taiwan. The records were retrieved from the research database of the Bureau of National Health Insurance in Taiwan, which maintains the records of 99.68% of the Taiwan population. The patients who had a history of AMI or coronary stent placement within the year before TKA were compared with the patients who had not experienced AMI or stent placement before TKA. The control subjects were matched according to sex, age, Charlson score, and year of surgery. There were 2413 patients in each group. The patients with a history of AMI or stent placement and the timing of TKA after coronary event were further stratified as with a coronary stent alone, AMI without a stent, and AMI with a stent. The effects of the comorbidities of renal failure, diabetes, liver failure, and hypertension were also analyzed individually. The risk of AMI within 1 year after TKA was investigated using bivariate analysis and the Cox proportional hazard model. To compare the risk of AMI within 1 year of surgery in the patients with a history of TKA and no AMI/stent with the population without a history of surgery, a similar bivariate analysis and the Cox proportional hazard model were applied to their matched case and control groups, each containing 110,980 patients.
  
  
  RESULTS
  In the adjusted model, using no AMI/stent before TKA as a reference, patients having undergone AMI + stent had the highest risk (hazard ratio [HR], 5.23; 95% confidence interval [CI], 1.81-15.14; p = 0.002), AMI alone without a stent had less risk (HR, 4.88; 95% CI, 1.49-16.01; p = 0.009), and stent alone with AMI had the lowest risk (HR, 3.16; 95% CI, 1.29-7.71; p = 0.012). In all patients, risk of AMI after TKA was not different than reference values after 1 year of initial AMI or stent (stent: HR, 1.67; 95% CI, 0.71-3.94; p = 0.239; AMI: HR, 1.88; 95% CI, 0.42-8.49; p = 0.412; AMI + stent: HR, 1.91; 95% CI, 0.53-6.89; p = 0.321). The risk of post-TKA AMI was elevated within 1 year of the previous episode of AMI/stent (0-180 days: HR, 8.42; 95% CI, 3.03-23.41; p < 0.001; 181-365 days: HR, 7.52; 95% CI, 2.47-22.88; p < 0.001). Only chronic renal failure under hemodialysis was associated with increased risk of AMI within 1 year of TKA (adjusted HR, 4.34; 95% CI, 1.22-15.43; p = 0.023). Patients undergoing TKA with no history of AMI/stent had a lower risk of AMI within 1 year of TKA compared with the patients with no history of surgery (adjusted HR, 0.92; 95% CI, 0.86-0.99; p = 0.016).
  
  
  CONCLUSIONS
  This study found the risk of post-TKA AMI remains high within 1 year in patients with a history of AMI/stent. It is recommended that an elective TKA should be performed at least 1 year after an episode of AMI or stent placement. Stents do not provide protection against post-TKA AMI within 6 months of the AMI and patients with AMI + stent have a higher risk of AMI than those with only AMI. Patients of AMI/stent on hemodialysis have a very high risk of post-TKA AMI. However, the risk of AMI is lower in post-TKA patients compared with those with no TKA.
  
  
  METHODS
  Level III, prognostic study.
authors.affiliation: Chang Bing Show Chwan Memorial Hospital, Changhua, Taiwan, Republic of China.|IRCAD-Taiwan, Changhua, Taiwan, Republic of China.
authors.forename: Atul
authors.initials: A
authors.lastname: Kumar
authors.affiliation: China Medical University, Taichung, Taiwan, Republic of China.
authors.forename: Wen-Chen
authors.initials: WC
authors.lastname: Tsai
authors.affiliation: Chang Bing Show Chwan Memorial Hospital, Changhua, Taiwan, Republic of China.
authors.forename: Tai-Sheng
authors.initials: TS
authors.lastname: Tan
authors.affiliation: China Medical University, Taichung, Taiwan, Republic of China.
authors.forename: Li-Ting
authors.initials: LT
authors.lastname: Chiu
authors.affiliation: Asia University, Taichung, Taiwan, Republic of China.
authors.forename: Pei-Tseng
authors.initials: PT
authors.lastname: Kung
authors.affiliation: Show Chwan Memorial Hospital, 542, Sec 1 Chung-shan Road, Changhua County, 505, Taiwan, Republic of China.
authors.forename: Ching-Kan
authors.initials: CK
authors.lastname: Lo
authors.affiliation: Show Chwan Memorial Hospital, 542, Sec 1 Chung-shan Road, Changhua County, 505, Taiwan, Republic of China. showjoeku@gmail.com.
authors.forename: Ming-Chou
authors.initials: MC
authors.lastname: Ku
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects*; D016009:Chi-Square Distribution; D015897:Comorbidity; D003324:Coronary Artery Disease / Q000175:diagnosis / Q000628:therapy*; D016208:Databases, Factual; D005260:Female; D006621:Hip Joint / Q000601:surgery*; D006801:Humans; D008297:Male; D008499:Medical Records; D008875:Middle Aged; D015999:Multivariate Analysis; D009203:Myocardial Infarction / Q000175:diagnosis / Q000209:etiology / Q000628:therapy*; D062645:Percutaneous Coronary Intervention / Q000009:adverse effects / Q000295:instrumentation*; D057216:Propensity Score; D016016:Proportional Hazards Models; D012008:Recurrence; D012189:Retrospective Studies; D018570:Risk Assessment; D012307:Risk Factors; D015607:Stents; D013624:Taiwan; D013997:Time Factors; D016896:Treatment Outcome