Prognostic value of 12-lead electrocardiogram and peak troponin I level after vascular surgery

Transcription

1 Prognostic value of 12-lead electrocardiogram and peak troponin I level after vascular surgery Santiago Garcia, MD, a Nicholas Marston, MD, a Yader Sandoval, MD, b Gordon Pierpont, MD, PhD, a Selcuk Adabag, MD, MS, a Jorge Brenes, MD, b Steven Santilli, MD, PhD, c and Edward O. McFalls, MD, PhD, a Minneapolis, Minn Objective: The aim of this investigation was to determine if the presence of ischemic electrocardiographic (ECG) changes in patients undergoing vascular surgery provides incremental prognostic information about the long-term risk of death compared with a single peak troponin level within 48 hours after surgery. Methods: This was a retrospective analysis of 337 patients undergoing moderate-risk to high-risk vascular surgery at our institution whose ECG and biomarker data were complete. Peak cardiac troponin (ctn) I values that exceeded the upper reference limit (URL) were categorized as low-positive ( ), at or exceeding the URL but less than three times the URL, or high-positive ( ), at or exceeding three times the URL. ECGs were classified as ischemic or nonischemic. The primary outcome was death at 1 year after the vascular operation. Independent predictors of long-term mortality were determined by Cox proportional hazards regression analysis. Results: The most common vascular problem was an expanding abdominal aortic aneurysm (n 185 [55%]). With regard to ctni, 53 patients (16%) were classified as high ( ) and 82 (24%) as low ( ). The ECG in 21 patients (6%) showed evidence of myocardial ischemia. An increase in 1-year mortality of 3% for normal, 11% for low ( ), and 17% for high ( ) (P <.01) was seen with incremental ctn values. Independent predictors of long-term mortality were age (odds ratio [OR], 1.05, 95% confidence interval [CI], ; P <.01), stratified troponin (OR, 1.62; 95% CI, ; P <.01), tissue loss (OR, 3.30; 95% CI, ; P <.01), stratified Revised Cardiac Risk Index (OR, 1.32; 95% CI, ; P <.07), and statin use (OR, 0.62; 95% CI, ; P.04). The presence of ischemia on ECG was not a predictor of long-term mortality. Conclusions: In the presence of an elevated ctn I, the ECG is not an independent predictor of long-term mortality after vascular surgery. These results support a strategy of routine surveillance of ctns after vascular surgery for the detection of cardiac events and postoperative risk stratification. (J Vasc Surg 2013;57: ) The electrocardiogram (ECG) is considered an essential component of the diagnostic evaluation of a suspected myocardial infarction (MI), as recommended by a joint European Society of Cardiology/American College of Cardiology Foundation/American Heart Association/World Heart Federation Task Force. 1 This is particularly relevant after noncardiac operations, where patients are heavily sedated and episodes of myocardial ischemia remain subclinical. 2-5 Although 24-hour ECG monitoring may increase the capacity to diagnose transient myocardial ischemic events, the technology may be insensitive to many patients, 2,6 including those individuals who ultimately are diagnosed with a postoperative MI. 7,8 It is not surprising that clinicians rely on a rise and fall of specific cardiac From the Department of Medicine, Division of Cardiology, a and Department of Surgery, Division of Vascular Surgery, c Minneapolis VA Medical Center and University of Minnesota; and the Department of Medicine, Hennepin County Medical Center. b Dr Garcia is supported by a VA Career Development Award of the Office of Research and Development (1IK2CX ). Author conflict of interest: none. Reprint requests: Santiago Garcia, MD, Minneapolis VA Medical Center, One Veterans Dr (111-C), Minneapolis, MN ( garci205@ umn.edu). The editors and reviewers of this article have no relevant financial relationships to disclose per the JVS policy that requires reviewers to decline review of any manuscript for which they may have a conflict of interest /$36.00 Published by Elsevier Inc. on behalf of the Society for Vascular Surgery biomarkers in the first several days after surgery as a means of optimal risk stratification in the postoperative period. 2,7 Cardiac troponin (ctn) has gained widespread acceptance as a highly sensitive and specific biomarker of myocardial necrosis. 6,9,10 After a noncardiac operation, an elevated ctn level is an identifier of increased mortality 6-11 and, as shown in a recent meta-analysis, independently predicts long-term risk of death. 12 Although the presence of new ECG changes has been used as a means of adjudicating the presence or absence of an MI in patients with an elevated troponin level, 1,3 no study has tested the independent value of the ECG beyond that offered by the specific troponin elevation. Accordingly, in this study, we tested whether the presence of ischemic ECG changes in patients undergoing high-risk vascular surgery, provides incremental prognostic information about the long-term risk of death compared with a single peak troponin level 48 hours after surgery. METHODS This study was approved by the Human Studies Committee and the Research and Development Committee of the Minneapolis Veterans Affairs Medical Center. Individual consent was waived. Study patients. Between January 2005 and December 2009, 545 consecutive patients underwent vascular surgery at the Minneapolis VA Medical Center, and their relevant clinical and surgical variables were collected in a

2 JOURNAL OF VASCULAR SURGERY Volume 57, Number 1 Garcia et al 167 database. The study cohort for the present retrospective analysis comprised 337 patients (61% of total) who underwent a qualifying vascular operation during the study period. Qualifying vascular operations included endovascular (EVAR) and open abdominal aortic repairs, lower limb revascularization, and carotid endarterectomy. All procedures, including EVAR, were performed under general anesthesia. We excluded 96 patients with incomplete biomarker or ECG data and 112 patients who underwent amputations or lower-risk percutaneous revascularization procedures such as carotid or lower limb stenting. Patients clinical risk scores were estimated by quantifying the Revised Cardiac Risk Index (RCRI). 13 Briefly, the RCRI is calculated by giving a score of 0 (absent) or 1 (present) to the following clinical variables: history of coronary artery disease, insulin-dependent diabetes, history of congestive heart failure, history of cerebrovascular disease, high-risk surgery, and renal insufficiency (creatinine 2 mg/dl). Troponin assays and myocardial perfusion imaging. Blood samples were obtained in all patients 48 hours after surgery, and troponin I levels were determined by the Dade Behring Dimension Analyzer (Siemens Healthcare Diagnostics Inc, Tarrytown, NY). The peak troponin I level was considered abnormal if it exceeded the upper reference limit (URL), based on the 99th percentile of a normal population, as specified by the manufacturer guidelines. The lower limit of detection was 0.03 g/l, and the 20% and 10% total imprecision were determined at 0.1 and 0.3 g/l, respectively. 14 Values were categorized as lowpositive (low [ ]) at or exceeding the URL but less than three times the URL, or high-positive (high [ ]) at three or more times the URL. This analytic strategy has been published before. 15 When available, each single-photon emission computed tomography (SPECT) imaging test with a myocardial perfusion defect was visually semiquantitated. Defect size was determined by polar map analysis and categorized according to the percentage of the left ventricular wall involved as small, 10%; medium, 10% to 20%; and large, 20%. Twelve-lead ECG. A 12-lead ECG was obtained before the operation and daily for 3 postoperative days. Two board-certified cardiologists (S.G., G.P.), who were blinded to the troponin values and clinical outcomes, reviewed the ECG tracings and classified them as ischemic (ST-segment depression 1 mm, or 2 mm T-wave inversion in at least contiguous leads) or nonischemic. In the event of a paced rhythm or left bundle branch block, tracings were deemed uninterpretable and the ECG was designated as nondiagnostic. The interobserver agreement rate for ECG reading was 93%. In cases where a discordant reading was present, the senior cardiologist reading (G.P.) provided the analysis. Outcome. The primary outcome was death at 1 year after the vascular operation. Survival was determined from the time of the vascular operation, and deaths were retrieved through the Department of Veterans Affairs Beneficiary Information and Electronic Records Locator Subsystem. Secondary outcomes included 30-day and 2.5-year mortality. Statistics. Data are presented as mean standard deviation or as percentages. Continuous variables were compared with the t-test when normally distributed and by a nonparametric test when skewed. Categoric variables were compared with 2 test. Predictors of the long-term risk of death were determined by Cox proportional hazards regression analysis with backward elimination. A Cox regression analysis model was used to analyze univariate clinical variables that were associated with increased mortality at 1 year (P.05) and variables associated with increased mortality risk in other studies, including preoperative cardiac risk, as estimated by the RCRI (three or more risks), 13,16 advanced arterial-occlusive disease, defined by tissue loss with nonhealing ulcers, 17,18 high-risk vascular surgery involving abdominal operations with aortic cross-clamp, 19 presence of ischemic ECG changes, 8 peak postoperative troponin levels (three or more times the URL of the specific troponin assay), 1,15 age, and preoperative statin treatment. 20 Individual risk factors included in the RCRI were not included. Survival curves were generated using the product-limit method, and intergroup differences were evaluated using the log-rank test. Odds ratios (OR) and hazard ratios (HRs) with their respective 95% confidence intervals (CI) are presented. Differences for all tests were considered significant at P.05. SPSS 11 software (SPSS Inc, Chicago, Ill) was used for statistical analysis. RESULTS Study cohort. A total of 337 patients underwent vascular surgery, and one or more troponin values were drawn 48 hours of surgery in all patients. The mean age of the population was 69 8 years, and the mean RCRI was An expanding abdominal aneurysm was present in 185 patients (55%), which was the most common indication for vascular surgery. Other indications were severe symptomatic carotid artery disease in 77 (23%) and critical limb ischemia, including severe claudication in 20 (6%), rest pain in 22 (6.5%), and nonhealing ulcers or tissue loss in 20 (6%). Preoperative medication use included aspirin in 76%, -blockers in 73%, and statins in 71%. Elevated postoperative troponin levels and outcomes. Troponin levels exceeded the URL of the assay in 135 patients; of whom, 53 (16%) were classified as high ( ) and 82 (24%) as low ( ). Of those patients with an elevated level, nearly 90% had a rise and fall of the troponin I level that was 30% of the baseline value, consistent with a perioperative cardiac event. As reported in Table I, those patients with an elevated ctn level were older, had a higher preoperative RCRI, and were more likely to have a moderate to large perfusion defect on SPECT before the operation. An elevated troponin level predicted increased risk of death (Fig 1; Table II). Compared with those patients with a negative postoperative ctn, patients with a low ( ) and a high ( ) ctn level had an increased risk of death at 1 year

3 168 Garcia et al JOURNAL OF VASCULAR SURGERY January 2013 Table I. Baseline clinical variables according to troponin levels (N 337) Variable a (n 202) (n 82) (n 53) Negative Low ( ) High ( ) P Age, years Hyperlipidemia 158 (78) 63 (76) 44 (83).67 Insulin-dependent DM 15 (7) 6 (7) 7 (13).37 Chronic kidney disease 18 (9) 22 (21) 16 (20).008 Cerebrovascular disease 53 (26) 26 (31) 8 (15).09 COPD 47 (23) 21 (25) 14 (26).85 Coronary artery disease 87 (43) 44 (53) 34 (64).01 Prior Myocardial infarction 43 (21) 21 (25) 19 (35).01 Congestive heart failure 13 (6) 13 (15) 12 (22).01 RCRI score RCRI variables present (29) 16 (20) 8 (15) 2 99 (49) 38 (46) 24 (45) 3 44 (22) 28 (34) 21 (40) Abnormal pre-op SPECT b 53 (26) 28 (34) 33 (62).01 Perfusion defect Reversible 37 (18) 20 (24) 24 (45).01 Fixed 21 (10) 18 (22) 17 (32).01 Moderate or large 25 (12) 20 (24) 21 (40).01 Urgent or emergency 27 (13) 9 (11) 13 (24).07 Open AAA repair 33 (16) 21 (25) 17 (32).02 EVAR 82 (40) 28 (34) 14 (26).13 Infrainguinal PAD 37 (18) 13 (16) 15 (28).17 Carotid surgery 50 (24) 20 (24) 7 (13).19 Tissue loss 11 (5) 6 (5) 5 (9).49 Ischemic ECG changes 6 (3) 5 (6) 10 (18).01 Medications Aspirin 157 (77) 67 (81) 34 (62).05 -blockers 124 (61) 53 (64) 39 (73).25 Statins 145 (71) 60 (73) 35 (66).64 AAA, Abdominal aortic aneurysm; COPD, chronic obstructive pulmonary disease; DM, diabetes mellitus; ECG, electrocardiogram; PAD, peripheral arterial disease; RCRI, revised cardiac risk index; SPECT, single-photon emission computed tomography. a Continuous data are presented as mean standard deviation, and categoric data as number (%). b Abnormal SPECT refers to reversible and fixed perfusion defects. Some patients have both types of defect and that explains why the sum of reversible and fixed perfusion defects exceeds the total number of abnormal SPECTs. (3% vs 11% vs 17%, respectively; P.01) and at 2.5 years (7% vs 16% vs 28%; P.01; Table II) after vascular surgery. Use of cardiac medications during long-term follow-up was high, including aspirin in 86%, -blockers in 74.5%, and statins in 71%. Among diabetic patients, the mean glycated hemoglobin was 6.63% 1.37%. Postoperative ECG changes and outcomes. New ischemic changes were detected in 21 of the 337 patients (6%) and were more prevalent (18%) in those patients with a high ( ) ctn level (Table I). At 1 year after surgery, the mortality rate was nonsignificantly higher for patients with vs those without new ischemic ECG changes (14% vs 6%; P.18). All patients with an ischemic ECG tracing and who died at 1 year after surgery had an elevated postoperative ctn level (Fig 2). The presence of ischemic ECG changes did not increase the long-term mortality risk in any of the troponin subsets (Fig 3). Cox proportional-hazards model. As shown in Fig 4, independent predictors of long-term mortality after vascular surgery were age (OR, 1.05; 95% CI, ; P.01), stratified troponin (OR, 1.62; 95% CI, ; P.01), tissue loss (OR, 3.30; 95% CI, ; P.01), stratified RCRI (OR, 1.32; 95% CI, ; P.07), and statin use (OR, 0.62; 95% CI, ; P.04). Urgent and emergency operations, abnormal preoperative SPECT, ischemia on ECG, and aortic cross-clamp operations were not included in the model. DISCUSSION The principal finding of this study is that an elevated troponin level after vascular surgery predicts late mortality and that the addition of the ECG for identifying high-risk patients after surgery does not add additional prognostic information beyond that supplied by peak ctn elevation. Although the diagnosis of MI may be dependent on one or more correlates of myocardial ischemia, including the use of the ECG as a means of detecting ischemia, the absence of those clinical variables does not minimize the importance of a rise and fall of the troponin level as an independent predictor of death. In the present study, biochemical evidence of myocardial ischemia or necrosis, or both, as determined by a ctn level above the URL of the specific assay, was observed in a high percentage (40%) of patients undergoing vascular

4 JOURNAL OF VASCULAR SURGERY Volume 57, Number 1 Garcia et al 169 Fig 1. Kaplan-Meier survival curves according to peak cardiac troponin I (ctni) after vascular surgery. Normal ctni (blue line, group 0), low ( ) (red line, group 1), and high ( ) (orange line, group 2). SE, Standard error. Table II. Postoperative, 1-year, and 2.5-year mortality according to peak ctn levels (N 337) Mortality Negative Low ( ) High ( ) (n 202) (n 82) (n 53) No. (%) No. (%) No. (%) P 30 days 2 (1) 1 (1) 1 (2).86 1 year 6 (3) 9 (11) 9 (17) years 14 (7) 13 (16) 15 (28).01 ctn, Cardiac troponin. Fig 3. One-year mortality after vascular surgery was assessed relative to postoperative troponin status and ischemic electrocardiographic changes. Results were not statistically significant. Fig 2. Flow chart describes survival status 1 year after vascular surgery as it relates to postoperative ischemic electrocardiographic (ECG) changes and troponin status. surgery. In contrast, only a fraction of the study cohort (6%) had evidence of myocardial ischemia on a postoperative ECG tracing. Even among those patients with an elevated troponin level, less than one in four had evidence of myocardial ischemia on ECG. Conversely, all of the patients with ischemic ECG changes and who died 1 year after vascular surgery had an elevated ctn after surgery. The findings from the logistic regression mode show that a low ( ) and a high ( ) ctn elevation were both predictors of 1-year mortality, whereas the presence of an ischemic ECG, independent of the ctn level, was not predictive of longterm outcomes. The most recent American College of Cardiology/ American Heart Association perioperative guidelines state

5 170 Garcia et al JOURNAL OF VASCULAR SURGERY January 2013 Fig 4. Clinical predictors of long-term mortality after vascular surgery are shown in Cox proportional hazards regression analysis. RCRI, Revised Cardiac Risk Index. that in patients with high or intermediate clinical risk who have known or suspected coronary artery disease undergoing high-risk or intermediate-risk surgical procedures, performing an ECG at baseline, immediately after the surgical procedure, and daily on the first 2 days after surgery appears to be the most cost-effective strategy for detecting perioperative MI. 21 Our results indicate that a strategy of systematic surveillance of postoperative cardiac events based on the peak postoperative ctn level provides more rationale because of the higher degree of sensitivity and the improved accuracy to predict long-term death compared with the results of postoperative 12-lead ECG tracings alone. The findings from the present study are consistent with those from Rinfret et al, 22 who reviewed outcomes in 3570 patients undergoing major noncardiac surgery and found that 8% had evidence of myocardial ischemia postoperatively. As with our study findings, those authors showed that the incidence of a major postoperative cardiac complication was higher in patients with ischemic ECG changes than in those without ECG changes (7% vs 2%). 22 Because data involving biomarker elevations were not available in their study, whether additional prognostic information would have proved beneficial for predicting long-term risk of death is unclear. Using a different strategy involving ECG tracings, Bottiger et al 8 investigated 55 patients undergoing noncardiac surgery and found that continuous 3-channel Holter monitoring was more sensitive than intermittent 12-lead ECG recordings for the detection of myocardial ischemia (53% vs 44%). 8 However, the concordance of abnormalities on the Holter monitor with elevations in troponin I was modest and was reported to be 70%. Unlike a spontaneous MI, in which patients present with sudden onset of chest pain as a result of a ruptured plaque in the coronary artery, 23 the pathophysiology of a postoperative MI is unclear and may result from an imbalance between oxygen supply and demand. 2 Several studies that used continuous ECG monitoring in high-risk vascular patients undergoing surgery indicated that tachycardia-related ST-segment depression is common in the postoperative period and that these events predict those individuals at increased risk of short-term and long-term mortality. 5,6 Landesberg et al 6 showed that the peak troponin elevation, used as a surrogate marker for myocardial damage, correlates well with the duration of ST-segment depression. The specific clinical conditions that trigger an elevated troponin level during the postoperative period are complex but are likely related to increased adrenergic stimulation. 24,25 In fact, the magnitude of the rise in catecholamines is higher among patients with elevated troponin levels, 26 which would suggest an association between the sympathetic system and myocardial necrosis, with a supply-and-demand mismatch that is likely mediated by wide fluctuations in heart rate, diastolic perfusion pressure, and myocardial wall stress. Nearly 90% of ischemic events detected by Holter monitoring occur in the operating or recovery rooms at a time that postoperative hemodynamic conditions are most unstable. 8 Because continuous ECG monitoring may not be available during these vulnerable periods, the low predictive accuracy of the 12- lead ECG as a means of detecting ischemic events is not surprising. After noncardiac operations, when adverse cardiac events are likely to be clinically subtle, the value of a rise and fall of a specific cardiac biomarker for predicting long-term outcomes is a critical tool. Our study results show that systematic surveillance of peak ctn levels should be a strong consideration for optimal risk stratification after high-risk noncardiac operations such as vascular surgery. The incremental value of looking for ECG changes, as a means of detecting clinical correlates of ischemia, can grossly underestimate those patients at increased risk of death, and the ECG by itself provides no incremental value in predicting outcomes in this specific population with vascular disease, independent of the biomarker. Our practice is to routinely

6 JOURNAL OF VASCULAR SURGERY Volume 57, Number 1 Garcia et al 171 sample ctn before (baseline) and after the vascular operation every 8 hours for the first 24 hours. Among patients with a rise and fall in ctn, a cardiac consultation is obtained for optimization of medical therapies and to guide selection of cardiac imaging. Our study has several limitations that are worth noting. First, we have limited information regarding adequacy of risk factors control after the vascular operation, which is an important determinant of long-term mortality. Second, we are unable to provide cause-specific mortality data. Third, we only included patients with complete biomarker and electrocardiographic data. We cannot exclude the possibility of selection bias, whereby lower-risk patients, in whom ctns were not measured, were excluded. Finally, all patients in our cohort were men. Caution is required when extrapolating these results to women. CONCLUSIONS The optimal means of risk stratifying patients in the postoperative period, after high-risk noncardiac operations, must include surveillance of specific cardiac biomarkers within the first 48 hours after surgery. Although the addition of the ECG may provide supplementary information about an associated clinical correlate of ischemia, the low sensitivity of the ECG for identifying patients at increased risk of death limits its utility in clinical practice. AUTHOR CONTRIBUTIONS Conception and design: SG, EM, SA, GP, SS Analysis and interpretation: SG, SA, EM, SS Data collection: NM, YS, JB, Writing the article: SG, SA, EM, SS, YS, NM Critical revision of the article: SS, GP, YS, JB, EM, SA Final approval of the article: SG, NM, SA, GP, YS, JB, SS, EM Statistical analysis: SG, SA Obtained funding: SG, EM Overall responsibility: SG REFERENCES 1. Thygesen K, Alpert JS, White HD, et al; Joint ESC/ACCF/AHA/ WHF Task Force for the Redefinition of Myocardial Infarction. 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