Clinical study: myocardial infarction
Myocardial infarction after vascular surgery: the role of prolonged, stress-induced, ST depression-type ischemia

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Abstract

OBJECTIVES

The goal of this study was to investigate the nature of the association between silent ischemia and postoperative myocardial infarction (PMI).

BACKGROUND

Silent ischemia predicts cardiac morbidity and mortality in both ambulatory and postoperative patients. Whether silent stress-induced ischemia is merely a marker of extensive coronary artery disease or has a closer association with infarction has not been determined.

METHODS

In 185 consecutive patients undergoing vascular surgery, we correlated ischemia duration, as detected on a continuous 12-lead ST-trend monitoring during the period 48 h to 72 h after surgery, with cardiac troponin-I (cTn-I) measured in the first three postoperative days and with postoperative cardiac outcome. Postoperative myocardial infarction was defined as cTn-I >3.1 ng/ml accompanied by either typical symptoms or new ischemic electrocardiogram (ECG) findings.

RESULTS

During 11,132 patient-hours of monitoring, 38 patients (20.5%) had 66 transient ischemic events, all but one denoted by ST-segment depression. Twelve patients (6.5%) sustained PMI; one of those patients died. All infarctions were non-Q-wave and were detected by a rise in cTn-I during or immediately after prolonged, ST depression-type ischemia. The average duration of ischemia in patients with PMI was 226 ± 164 min (range: 29 to 625), compared with 38 ± 26 min (p = 0.0000) in 26 patients with ischemia but not infarction. Peak cTn-I strongly correlated with the longest, as well as cumulative, ischemia duration (r = 0.83 and r = 0.78, respectively). Ischemic ECG changes were completely reversible in all but one patient who had persistent new T wave inversion. All ischemic events culminating in PMI were preceded by an increase in heart rate (Δ heart rate = 32 ± 15 beats/min), and most (67%) of them began at the end of surgery and emergence from anesthesia.

CONCLUSIONS

Prolonged, ST depression-type ischemia progresses to MI and is strongly associated with the majority of cardiac complications after vascular surgery.

Abbreviations

CAD
coronary artery disease
CI
confidence interval
CK
creatine kinase
cTn-I
cardiac troponin-I
ECG
electrocardiogram
LVH
left ventricular hypertrophy
MI
myocardial infarction
PMI
postoperative myocardial infarction
ROC
receiver-operator characteristic curve

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Supported by Chief Scientist, Ministry of Health of Israel (Grant no. 2828); Hebrew-University, Hadassah Hospital Combined Research Grant; Marquette Electronics, Inc., Office of Grants.