When anesthesiologists evaluate the perioperative risk of Japanese patients with ischemic heart disease (IHD) preoperatively, the most important issue is that such evaluations are generally based on non-Japanese data. Despite different incidences of IHD, we do not have data derived from a Japanese database. To solve this problem, the Cardiac Ischemia and Anesthesia Research Committee in the Tokyo area began to collect data from cardiac patients in 1997. Two studies were conducted in 1997. In the first study, 3.9% of 8,358 patients undergoing noncardiac surgery displayed IHD; in the second study of 7,288 patients, the incidence was 3.1% (1,2). The incidence of perioperative cardiac complications in patients displaying IHD was 16.4% in the first study and 13.2% in the second, with an incidence of perioperative myocardial infarction of approximately 1%. In a review published in 1995, Mangano and Goldman (3) reported that approximately 30% of patients undergoing noncardiac surgery in the United States displayed IHD; this is nearly 10 times the proportion observed in Japan. However, the incidence of perioperative cardiac complications in IHD patients was 12.5%, and the incidence of perioperative myocardial infarction was 1% to 3.1% in the United States (3). Neither of these differed greatly from the rates observed in Japan.
We therefore decided to ascertain the prognostic factors associated with perioperative cardiac complications in the IHD patients in Japan. Consequently, we conducted a prospective study of patients undergoing general surgery who were classified as having intermediate risk for perioperative complications according to the American College of Cardiology/American Heart Association (ACC/AHA) Guidelines for Perioperative Cardiovascular Evaluation for Noncardiac Surgery (4).
We collected data from 11 Cardiac Ischemia and Anesthesia Research Committee hospitals between March 1999 and December 2000 prospectively. After each IRB approval, patients with intermediate clinical predictors of cardiac risk who were receiving intermediate risk surgical procedures based on ACC/AHA guidelines were included in the study. The factors indicating suspected IHD of intermediate risk included 1) the presence of stable angina, 2) a history of myocardial infarction, 3) the presence of compensated heart failure, 4) the presence of diabetes mellitus, or 5) electrocardiogram (ECG) abnormalities. For the intermediate risk surgical procedures we selected 1) intraperitoneal surgery without thoracotomy, 2) an endoscopic laparotomy not involving vascular surgery, or 3) intrathoracic surgery not involving vascular surgery. Subjects fulfilling these criteria who agreed to participate in a research study were included as study subjects. We did not permit active pretreatment for cardiac risk unless the cardiac events occurred during the operation.
Approximately 66 variables were examined and summarized. These included variables related to patient baseline characteristics, anesthetic management (general, spinal or epidural, general plus epidural), surgical invasiveness, perioperative hemodynamics, and drugs used. We defined hypotension as systolic blood pressure <80 mm Hg, bradycardia as <40 bpm, and tachycardia as more than 120 bpm. In addition, the Coronary Risk Index (CRI) scores of Ishiguro and Seki et al. (5,6) were calculated. This allows for simple evaluation of coronary artery lesion severity from a routine examination and exercise ECG performed both at the initial patient interview and preoperatively. The CRI was made by analyzing coronary risk factors and angiographic findings in 717 Japanese patients who underwent coronary angiographies, then subjecting these data to multivariate analysis to arrive at a score (5). The higher the index score, the greater the likelihood that the patient has significant stenosis of the coronary arteries. The actual CRI scores used in the present study are shown in Table 1.
Between postoperative days 3 and 5, troponin T test (Boehringer Mannheim) and 12-lead ECG tests were performed to determine whether myocardial damage was present postoperatively. The troponin T test can qualitatively detect myocardial troponin in the blood. The sensitivity of this test is 0.02 ng/mL, and it is not affected by troponin T of muscle less than 500 ng/mL. A value greater than 0.1 ng/mL indicates myocardial damage. Troponin T was donated by Sanwa Chemical.
Cardiac complications we defined were from minor events such as non-life threatening arrhythmia, ST-T change, and hypotension to major events such as myocardial infarction and cardiac death.
The statistical analysis involved a simple analysis of the study variables and the presence or absence of perioperative complications using the Mann-Whitney test with Bonferroni’s correction for multiple comparisons and the factor analysis. In addition, logistic regression analysis was performed to examine the magnitude of the effect of each variable on perioperative complications. P value <0.05 was considered significant.
Two-hundred-thirty-seven patients at 11 facilities were included in the study. Table 2 shows cardiac complications which were experienced by 43 of these patients (18.1%): 22 (9.3%) intraoperatively and 25 (10.5%) postoperatively; 4 patients experienced complications both intraoperatively and postoperatively. An investigation of the factors that contributed to the perioperative complications indicated that hypertension played a role in intraoperative complications, and factor analysis also suggested that anesthesia duration was a factor (Table 3). Twelve likelihood factors were examined and suggested factors related to the occurrence of postoperative complications including a history of myocardial infarction or heart failure, a presence of cerebral or peripheral vascular disorders, CRI grade, and a history of surgical intervention. Factor analysis also indicated that a history of heart failure, CRI grade, and a history of intervention were factors in postoperative cardiac complications (Table 4).
Logistic regression analysis (stepwise) was then performed to examine the extent to which each factor played a role in cardiac complications. Factors contributing to intraoperative cardiac complications were hypertension (odds ratio = 2.911; P < 0.02) and anesthesia duration (odds ratio = 1.003; P < 0.009) (Table 3). Implicated factors contributing to postoperative complications from among five factors selected using the Mann-Whitney U-test and factor analysis were a history of heart failure (odds ratio = 6.884; P < 0.004), a history of intervention (odds ratio = 2.884; P < 0.002), and CRI grade (odds ratio = 2.884; P < 0.01) (Table 4).
One patient showed a positive troponin T test and suffered from myocardial infarction postoperatively.
Our previous studies (1,2) revealed that the number of Japanese IHD patients undergoing noncardiac surgery were one-tenth of those in Europe and America, but the incidence of perioperative myocardial infarction of these patients was similar. We examined perioperative cardiac complications with moderately invasive surgery in patients with intermediate risk according to the ACC/AHA guidelines in an effort to discern the baseline factors that play a role in such complications. In compiling the study results, an examination of the interim findings revealed that the factors that played a role in intraoperative complications clearly differed from those that contributed to postoperative complications. Consequently, the investigation was conducted by considering intraoperative and postoperative complications separately.
In this study we found that hypertension was the most important factor for intraoperative management. This is consistent with reports that hypertension, or a history of hypertension, was one of the risk factors for cardiovascular death (7,8). Anesthesia duration was also a risk factor but the odds ratio was very small (close to one). This does not seem to be an important factor in the intraoperative period. Although the surgical operation is stressful for the patients, anesthetic technique can help.
Factors that contributed to postoperative complications included a history of myocardial infarction, a history of cardiac failure, a history of a cerebral or peripheral vascular disorders, CRI grade, and a history of intervention. All of these risk factors reflect coronary artery lesion severity or cardiac dysfunction. This indicates that patients with coronary risk factors, a history of cerebral or peripheral vascular disorders, or diminished cardiac function, such as heart failure, are susceptible to postoperative cardiac complications. In addition, the results of this study appear to be consistent with previous reports (3,4) from Europe and the United States in terms of links between myocardial ischemia and postoperative complications.
There was no significant difference regarding anesthetic management. Because the number of patients was limited, we could not evaluate the effects of anesthetic drugs on outcome in this study. Concerning the complexity of the surgical procedures, there was also no significant difference in complications. We wanted to determine whether myocardial damage was present during the following 3 to 5 days. However, a positive troponin T test was seen in only 1 patient who had experienced an obvious myocardial infarction. The lack of positive troponin T tests, even in patients with clear ECG changes, suggests that the troponin T test can diagnose the occurrence of myocardial infarction over a short time period but may not be an appropriate screening test for mild myocardial damage.
CRI is an index derived from coronary risk factors and imaging findings in patients who undergo coronary arteriography, and is used in Japan to predict whether patients have coronary diseases based on the results of medical inquiry, preoperative laboratory tests, and exercise ECG. A higher score indicates a higher probability of a significant coronary constriction. With a cutoff score of 15 points, the sensitivity and specificity of CRI were 86.3% and 79.9%, respectively. These are clinically acceptable figures. However, CRI cannot be used to predict perioperative cardiac morbidity. The results of the present study also show that preoperative CRI scores for coronary diseases are not significantly correlated to the perioperative cardiac morbidity. Lee et al. (9) prepared the Revised CRI after evaluating the conventional CRI, which included many items. The results identified the following six risk factors: 1) high risk surgery (thoracotomy, laparotomy, vascular surgery above the inguinal region), 2) history of IHD, 3) history of congestive heart failure, 4) history of cerebrovascular disease, 5) diabetes requiring insulin therapy, and 6) renal failure (creatinine >2.0). Similar findings were observed when we compared our results with these factors.
In a review published in 1995, Mangano and Goldman (3) reported that approximately 30% of patients undergoing noncardiac surgery in the United States displayed IHD, nearly 10 times the proportion observed in Japan. Therefore, data collection from intermediate risk patients in Japan seems to be more difficult than in the United States. Although we evaluated a limited number of patients, we believe this study presents valid Japanese data.
In conclusion, perioperative cardiac complications are generally infrequent among Japanese people; among intermediate-risk patients, however, the incidence of perioperative cardiac complications and risk factors are similar to those of European and American patients.
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