Perioperative Myocardial Infarction in Noncardiac Surgery: Focusing on Intraoperative and Postoperative Risk Factors Cardiac Unit, Department of Medicine, Prapokklao Hospital, Chantaburi Abstract Perioperative cardiac complications can be assessed before surgery with risk prediction indices but these indices have limited overall accuracy. These risk predictions could be improved by information obtained during and after surgery. Patients 30 years of age and older with myocardial infarction (MI) who had noncardiac surgery and were admitted to Prapokklao Hospital from October 2002 to September 2007 were evaluated retrospectively. The results showed that there were ten ST-elevation MI and fourteen non ST-elevation MI. The incidence of perioperative MI was 0.5:1000. The in-hospital mortality rate was 50%. Multivariate analysis revealed that intraoperative anemia and postoperative hypotension were independent predictors of perioperative MI (odds ratio 7.37, 95% CI 2.06-23.36, p 0.002 and odds ratio 5.37, 95% CI 1.47-19.64, p 0.011 respectively). In conclusion, intraoperative anemia and postoperative hypotension were independent predictors of perioperative MI. Therefore, besides risk assessment and therapy before surgery, the improvement of care during and after surgery focusing on these predictors may be useful for minimizing perioperative MI. Keywords: myocardial infarction, perioperative, noncardiac surgery, risk factors Thai heart J 2008; 21 : 023-027 E-Journal : http://www.thaiheartjournal.org Introduction Myocardial infarction (MI) is a major cause of perioperative morbidity and mortality in patients undergoing noncardiac surgery. The pathophysiology of perioperative MI differs somewhat from that of MI occurring in the usual setting. In the latter, rupture of a coronary arterial atherosclerotic plaque leads to platelet aggregation and thrombus formation. In contrast, plague rupture occurs in only about half of perioperative MI. The remainder are due to a prolonged imbalance between myocardial oxygen supply and demand in the setting of coronary artery disease (1-4). Though risk for cardiac complications can be assessed before surgery with risk prediction indices (5-9), these indices have limited overall accuracy (10). These risk predictions could be improved by information obtained during and after surgery. Anemia and hypotension which Correspondence: Cardiac Unit, Department of Medicine, Prapokklao Hospital, Chantaburi E-mail: iampiyapong@yahoo.com diminish myocardial oxygen supply might be useful for identifying those who are at risk for perioperative MI. The present study attempts to evaluate the association between the risk factors during and after surgery (intraoperative anemia, intraoperative hypotension, postoperative anemia, postoperative hypotension) and perioperative MI in noncardiac surgical patients. Methods This was a retrospective study conducted at Prapokklao Hospital. This study had hospital approval to do the research and collect the data. The study population included all patients 30 years of age or older who had noncardiac surgery during a five year period from October 2002 to September 2007. The cases were all patients who had acute MI during the perioperative period. The controls were non-mi patients with the same sex and operation. The ratio of cases to controls was 1:4 using the first 4 matched records for controls at the same time of cases. Perioperative was defined as the time from arrival in the operating suite to hospital discharge. ST elevation MI was diagnosed if the patient satisfied two criteria: 1) ST-elevation 0.1 mv in 2 consecutive leads or new left
bundle branch block and 2) serum troponin T 0.1 ng/ml or serum CK-MB 2 x upper normal limit. Non STelevation MI was diagnosed if the patient satisfied two criteria: 1) ST depression 0.1 mv or T wave inversion 0.1 mv in 2 consecutive leads and 2) serum troponin T 0.1 ng/ml or serum CK-MB 2 x upper normal limit. Intraoperative was defined as the time from the beginning of anesthesia until the patient was transferred from the operating theater to the recovery room. Postoperative was defined as the time between the patients being transferred from the operating theater to hospital discharge. Anemia was considered present when the hematocrit was 33 percent. Intraoperative hypotension was considered present when the systolic blood pressure was 90 mmhg and persisted more than 30 minutes. Postoperative hypotension was considered present when the systolic blood pressure was 90 mmhg and persisted more than 1 hour. A data record form was developed for review of the medical records. This form included information on demographic characteristics, principal diagnosis, type of operation, type of MI, discharge status, and American society of Anesthesiologists physical status classification (ASA-classification). Emergency or non-emergency operation, underlying cardiovascular disease, diabetes mellitus, intraoperative and postoperative blood pressure as well as hematocrit were recorded. Data were collected and analyzed. The Chi-Square test and Fischer s Exact test were used to compare categorical data. The unpaired t-test was used for quantitative data. For multivariate analysis, multiple logistic regression was used to determine the effect of each factor on MI after having been adjusted for other risk factors in the model. A p-value of less than 0.05 was considered significant. Results From October 2002 to September 2007, thirty cases were identified. Six cases were excluded due to disagreement in the diagnosis of MI. Twenty-four cases were eligible for further matching and analysis. The incidence of perioperative MI was 24 in 47710 cases or 0.5:1,000. Among the 24 included patients, 11 men and 13 woman, there were 10 cases (41.7%) with ST-elevation MI and 14 cases (58.3%) with non ST-elevation MI. Twelve patients died in the hospital. The overall in-hospital mortality rate was 50 percent. The mean age was 71.6 years (standard deviation 14 years). The clinical characteristics of patients are presented in Table 1. Risk of perioperative MI increased in elderly, patients with ischemic heart disease, ischemic stroke, diabetes, ASA classification e 3, and emergency surgery. When each variable was considered alone in a univariate analysis, it was found that all four factors (intraoperative anemia, intraoperative hypotension, postoperative anemia, postoperative hypotension) were associated with perioperative MI (Table 2). Taking into account all predictors simultaneously using a multiple logistic regression analysis revealed that intraoperative anemia and postoperative hypotension remained independent predictors of perioperative MI (Table 3). Discussion The incidence of perioperative MI in non cardiac surgery patients varies widely from less than 1 percent to 38 percent in some studies (11-18). The disparity results from methodological issues, in particular, the way in which patients were selected for study and the sensitivity and specificity of the tests used to diagnose MI. In this report, the incidence of preoperative MI was not high (0.5:1000) but the in-hospital mortality was very high (50%). This contrasts to a lower morality rate (15-20%) reported in other studies (19-22). In part, the high mortality rate found in our study could be a result of a high proportion of STelevation MI. Our study confirms the association between perioperative MI with underlying cardiovascular disease, diabetes, ASA classification and emergency surgery reported in other studies (5,8,10). Myocardial oxygen supply may be diminished by anemia and hypotension. In our study, intraoperative anemia and postoperative hypotension were independently associated with a higher incidence of perioperative MI. These factors have not been previously noted and are very interesting because these two factors can be prevented
Perioperative Myocardial Infarction in Noncardiac Surgery: Focusing on Intraoperative and Postoperative Risk Factors Table 1. Preoperative patient characteristics Perioperative No myocardial Odds ratio p-value myocardial infarction (95 % CI) infarction (n = 96 ) (n = 24) Age (yr) : X (SD) 71.6 (14) 60.2 (16) 0.002 Ischemic heart disease 9 (37.5 %) 7 (7.3 %) 7.63 (2.47-23.56) <0.001 Ischemic stroke 10 (41.7 %) 12 (12.5 %) 5.00 (1.81-13.76) 0.002 Diabetes mellitus 16 (66.7 %) 24 (25.0 %) 6.00 (2.28-15.77) <0.001 ASA class 3 17 (70.8 %) 27 (28.1 %) 6.20 (2.31-16.64) <0.001 Emergency surgery 16 (66.7 %) 40 (41.7 %) 2.80 (1.09-7.17) 0.028 Table 2. Univariable analysis of intraoperative and postoperative risk factors Perioperative No myocardial Odds ratio p-value myocardial infarction (95 % CI) infarction (n = 96 ) (n = 24) Intraoperative anemia 15 (62.5 %) 20 (20.8 % ) 6.33 (2.42-16.57) <0.001 Intraoperative hypotension 5 (20.8 %) 4 (4.2 %) 6.05 (1.49-24.65) 0.016 Postoperative anemia 11 (45.8 %) 16 (16.7 % ) 4.23 (1.61-11.11) 0.002 Postoperative hypotension 10 (41.7 %) 13 (13.5 %) 4.56 (1.68-12.40) 0.004 Table 3. Multivariable analysis of risk factors in comparison with univariable analysis Univariable analysis Multivariable analysis p-value OR Adjusted OR (95%CI) Intraoperative anemia 6.33 7.37 (2.06-23.36) 0.002 Intraoperative hypotension 6.05 3.01 (0.59-15.31) 0.185 Postoperative anemia 4.23 1.61 (0.47-5.55) 0.450 Postoperative hypotension 4.56 5.37 (1.47-19.64) 0.011 and modified. Besides risk assessment and therapy before surgery, the improvement of care during and after surgery focusing on these factors may be useful in minimizing perioperative MI. The incidence of perioperative MI was low. There were only 24 cases found in this study. This resulted in a wide 95% confidence interval of adjusted odds ratio. Moreover, the study variables in a multiple logistic regression model were also limited though there were other factors which may relate to perioperative MI. More extensive study of these predictors may be required. Conclusion The incidence of perioperative MI is low but the in-hospital mortality is very high. Intraoperative anemia
and postoperative hypotension were independent risk factors of perioperative MI. The improvement of care during and after surgery focusing on these preventable and modifiable risk factors may be useful for minimizing perioperative MI. Acknowledgment The author wishes to acknowledge Mrs. Pimon Mahutikit for searching the medical records and Dr.Urai Puvanakul for data analysis. References 1. Fuster V, Badimon L, Badimon JJ, Chesebro JH. The pathogenesis of coronary artery disease and the acute coronary syndromes. N Engl J Med 1992; 326: 242-50. 2. Cohen MC, Aretz TH. Histological analysis of coronary artery lesions in fatal postoperative myocardial infarction. Cardiovasc Pathol 1999; 8: 133-9. 3. Dawood MM, Gupta DK, Southern J, Walia A, Atkinson JB, Eagle KA. Pathology of fatal perioperative myocardial infarction: implications regarding pathophysiology and prevention. Int J Cardiol 1996; 57: 37-44. 4. Grayburn PA, Hillis LD. Cardiac events in patients undergoing noncardiac surgery: shifting the paradigm from noninvasive risk stratification to therapy. Ann Intern Med 2003; 138: 506-11. 5. Eagle DA, Brundage BH, Chaitman BR, et al. Guidelines for perioperative cardiovascular evaluation for noncardiac surgery. Report of the American College of Cardiology/American Heart Association Task Force on Practice Guideline (Comminttee on Perioperative Cardiovascular Evaluation for Noncardiac Surgery). J Am Coll Cardiol 1996; 27: 910-48. 6. Dripps RD. New classification of physical status. Anesthesiology 1963; 24: 111. 7. Lewin I, Lerner AG, Green SH, Del Guercio LR, Siegel JH. Physical class and physiologist status in the prediction of operative mortality in the aged sick. Ann Surg 1971; 174: 217-31. 8. Goldman L, Caldera DL, Nussbaum SR, et al. Multifactorial index of cardiac risk in noncardiac surgical procedures. N Engl J Med 1977; 297: 845-50. 9. Detsky AS, Abrams HB, Mclaughlin JR, et al. Predicting cardiac complications in patients undergoing non-cardiac surgery. J Gen Intern Med 1986; 1: 211-9. 10. Gilaert K, Laroceug BJ, Patrick LT. Prospective Evaluation of Cardiac Risk Indices for Patients Undergoing Noncardiac Surgery. Ann Intern Med 2000; 133: 356-9. 11. Becker RC, Underwood DA. Myocardial infarction in patients undergoing noncardiac surgery. Cleve Clin J Med 1987; 54: 25-8. 12. Ashton MC, Petersen JN, Wray PN, et al. The incidence of perioperative myocardial infarction in men undergoing noncardiac surgery. Ann Intern Med 1993; 118: 504-10. 13. Eagle KA, Rihal CS, Mickel MC, et al. Cardiac risk of noncardiac surgery: influence of coronary disease and type of surgery in 3368 operations. Circulation 1997; 96: 1882-7. 14. Landesberg G, Mosseri M, Zahger D, et al. Myocardial infarction following vascular surgery: the role of prolonged, stress-induced, ST-depression-type ischemia. J Am Coll Cardiol 2001; 37: 1839-45. 15. Landesberg G, Shatz V, Akopnik I, et al. Association of cardiac troponin, CK-MB, and postoperative myocardial ischemia with long-term survival after major vascular surgery. J Am Coll Cardiol 2003; 42: 1547-54. 16. Landesberg G, Mosseri M, Shatz V, et al. Cardiac troponin after major vascular surgery: the role of perioperative ischemia, preoperative thallium scanning, and coronary revascularization. J Am Coll Cardiol 2004; 44: 569-75. 17. Landesberg G, Luria MH, Cotev S, et al. Importance of longduration postoperative ST-segment depression in cardiac morbidity after vacular surgery. Lancet 1993; 341: 715-9. 18. Mangano DT, Hollenberg M, Fegert G, et al. Perioperative myocardial ischemia in patients undergoing noncardiac surgery: I. Incidence and severity during the 4-day perioperative period. J Am Coll Cardiol 1991; 17: 843-50. 19. Shan KB, Kleinman BS, Rao TL, Jacobs HK, Mestan K, Schaafsma M. Angina and other risk factors in patients with cardiac diseases undergoing noncardiac operations. Anesth Analg 1990; 70: 240-7. 20. Ashton CM, Petersen NJ, Wray NP, et al. The incidence of perioperative myocardial infarction in men undergoing noncardiac surgery. Ann Intern Med 1993; 118: 504-10. 21. Badner NK, Knill RL, Brown JE, Novick TV, Gelb AW. Myocardial infarction after noncardiac surgery. Anesthesiology 1998; 88: 572-8. 22. Kumar R, Mckinney WP, Raj G, Heudebert GR, Heller HJ, Koetting M, et al. Adverse cardiac events after surgery: assessing risk in a veteran population J Gen Intern Med 2001; 16: 507-18.
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