Major noncardiac surgery was defined by procedures performed in the operating room requiring general, spinal, or epidural anesthesia. The type of surgery was classified and categorized according to the surgical risk, determined using the ACC/AHA classification.1 High-risk surgeries included vascular surgeries, which have a cardiac risk often >5%. Intermediate-risk surgery is defined as surgery with a cardiac risk of 1%–5%, and included head and neck surgery, intraperitoneal and intrathoracic surgery, orthopaedic surgery, and prostate surgery. In our study patients, major gastrointestinal surgery (laparotomy, advanced bowel surgery, gastric surgery), major gynecological cancer surgery (abdominal hysterectomy and oophorectomy for cancer), major open or transurethral urological surgery (cystectomy, radical nephrectomy, total prostatectomy), head and neck surgery, and hip or knee arthroplasty were included. Intrathoracic surgery is not performed in our institution. Patients requiring emergency surgery (surgery required within 24 hours) or those undergoing minor-grade surgery were excluded. Risk assessment, preoperative preparation and drug therapy, and postoperative follow-up were completed according to current ACC/AHA guidelines.1
For each patient, preoperative risk factors of morbidity and mortality, patient characteristics, preoperative medication, and intraoperative data were prospectively evaluated. In the preoperative period, classification of the ASA was used as a composite index of a patient's general status.2 The Revised Cardiac Risk Index was used for prediction of cardiac risk based on 6 prognostic factors: high-risk type of surgery (defined as intraperitoneal, intrathoracic, or suprainguinal vascular procedures), ischemic heart disease, congestive heart failure, history of cerebrovascular disease, insulin therapy for diabetes mellitus (DM), and preoperative serum creatinine >2.0 mg/dL. Each of the prognostic factors was assigned as 1 point.3 Anesthetic management, monitoring, and other aspects of perioperative management were at the discretion of the attending physician.
Resting 12-lead ECGs recorded at a speed of 25 mm/second were taken 1 day before surgery, on the first 5 postoperative days, and whenever clinically indicated. To avoid interobserver variability, 2 blinded investigators independently analyzed ECG data. All ECGs were analyzed for the Minnesota classification,4 heart rate, QRS duration, QT interval, and left ventricular hypertrophy (LVH). Atrial fibrillation (AF) was defined by characteristic absolute irregularity of R-R intervals and concurrent loss of identifiable P waves in the ECG recordings.5 Mean QT-interval duration for 3 consecutive beats in leads II and V4 was calculated. Each QT interval was measured from the beginning of the QRS complex to visual return of the T wave to the isoelectric line. If U waves were present, the QT interval was measured to the nadir of the curve between the T and U waves. The QT interval was corrected for the heart rate with the use of 2 formulae: (1) Bazett's formula, QTcB = QT/√R-R,6 and (2) Hodges' formula, QTcH = QT + 1.75 (rate − 60).7 The intra- and interobserver variability were 5% and 6%, respectively, for measurements of QTc. Patients with bundle branch block (BBB;n = 71) and implantable devices (n = 6) were also excluded. ST-segment abnormalities were defined by using the following criteria: ST-J depression of ≥1 mm (Minnesota code 4-1); ST-J depression of 0.5–0.9 mm horizontal or sloping down (Minnesota code 4-2); ST segment sloping down and reaching ≥0.5 mm below baseline in leads I, II, aVL, aVF, and V1 through V6 (Minnesota code 4-3); or an ST-segment elevation of ≥1 mm in leads I, II, III, aVL, aVF, V5, and V6 or of ≥2 mm in leads V1 through V4 (Minnesota code 4-4).
Presence of LVH was defined by means of code 3.1 (Left: R amplitude >26 mm in either V5 or V6, or R amplitude >20.0 mm in any of leads I, II, III, and aVF, or R amplitude >12.0 mm in lead aVL measured only on second-to-last complete normal beat) and one of the following codes: 5.1 (T amplitude negative 5.0 mm or more in lead II, or in lead aVF when QRS is mainly upright), 5.2 (T amplitude negative or diphasic with negative phase at least 1.0 mm but not as deep as described in 5.1), or 5.3 (T amplitude flat, negative, or diphasic (negative-positive type only) with <1.0 mm negative phase in lead II; not coded in lead aVF). Frequent premature ventricular complexes were defined as >1 complex in 10 beats. Sinus tachycardia was defined as a heart rate >100 beats per minute, and sinus bradycardia was defined as a heart rate <50 beats per minute.
Electrocardiographic results showing AF, left or right BBB, LVH, frequent premature ventricular complexes, pacemaker rhythm, Q wave, ST-segment changes, or sinus tachycardia or bradycardia were classified as abnormal.
All patients underwent preoperative transthoracic 2-dimensional echocardiography. Standard parasternal and apical views were obtained in the left lateral decubitus position using available equipment (Vivid 3 Pro; GE Vingmed, Milwaukee, WI). Left ventricular ejection fraction (LVEF) was measured by transthoracic echocardiography using modified Simpson's rule.
Cardiac biomarkers (creatine kinase MB and troponin I) were evaluated 1 day before surgery, on the first 5 postoperative days, and whenever clinically indicated. Perioperative myocardial ischemia was diagnosed if cardiac troponin I was exceeding the 99th percentile of a normal reference population on the first or second day after surgery or if there was a new flat or downsloping ST-segment depression of >0.1 mV that lasted for ≥1 minute in the continuous ECG recording.
Patients were followed up by the consulting physician until discharge after surgery. The PCEs were defined as the occurrence of severe arrhythmias requiring treatment, cardiac death (death caused by acute myocardial infarction [MI], significant cardiac arrhythmias, refractory congestive heart failure, or as a death occurring suddenly without another explanation), acute heart failure, acute coronary syndrome (nonfatal acute MI or unstable angina), pulmonary thromboembolism, nonfatal cardiac arrest, and cardioembolic stroke. Perioperative MI was defined according to the universal definition of MI.8