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July 1998
Myocardial Infarction after Non-Cardiac Surgery.
Badner NH, Knill RL, Brown JE, Novick TV, Gelb AW. Anesthesiology. 1998; 88:572-878.
[ see abstract below ]
The most interesting aspect of this study is its finding that postoperative MIs occur early in the postoperative course. This is in sharp contrast to traditional teachings that most such MI's occur 2-3 days postoperatively.
The authors studied 323 patients with ischemic heart disease (CAD) undergoing non-cardiac surgery. Criteria for CAD were well defined, and would meet the criteria in anyone's practice. Patients had a clinical assessment, enzymatic studies and EKG's daily. MI diagnostic criteria were also rigorous and well defined.
Eighteen of 323 patients (5.6%) had an MI. This is consistent with previous reports of a 5% rate among at-risk patients. Only 3 of 18 exhibited chest pain during their MI. However, other clinical symptoms occurred in 10, including atrial fibrillation, pulmonary edema, and hypotension. Seven of the 18 patients with MIs had no clinical symptoms, which is consistent with previous reports that 40-60% of postoperative MIs are silent. Of the eighteen patients with MI, 17% died, a marked decrease from the previous reports that postoperative MI's are fatal in 50% of cases.
The authors found that different criteria for diagnosing MI's yielded markedly different results in the number of postoperative MI's (p<.0001). They compared four diagnostic regimens using combinations of clinical symptoms, EKG, CPK, and Troponin-T. Eliminating the need for EKG findings and relying primarily on enzymes, the postoperative MI rate could have been as high as 20%. The differing sensitivities of diagnostic criteria, and the long-term meaning of these different rates of diagnosis have yet to be established.
The most unexpected finding was that almost 50% of the MIs occurred on the day of surgery, and 75% occurred by postoperative day 1. The first postoperative night was the time of peak incidence. Also of note was that non-Q waves predominated over Q wave infarcts. Patients with silent vs. symptomatic MIs had similar one year outcomes, implying that they are probably of equal significance.
This study sheds some new light on how, when, and where we diagnose postoperative MIs in our cardiac patients undergoing non-cardiac surgery.
Return to the Current Literature Review Front Page, or read the abstract:
ABSTRACT
Background: In this study, the authors intensively monitored isoenzyme and electric activity of the heart for the first 7 days after noncardiac surgery in a large group of patients at risk for postoperative myocardial infarction (PMI).
Methods: After institutional review board approval and written informed consent were received, 323 patients, aged 50 yr or older, who had ischemic heart disease and presented for noncardiac surgery, were enrolled in this prospective, blinded study. After operation, patients had daily clinical assessments, electrocardiograms, and measurements of creatine kinase (CK), CK-2 (mass and activity), and Troponin-T on the operative night, twice daily on postoperative days 1-4, and then daily on days 5-7. A diagnosis of PMI was made if the total CK was >174 U/l and in the presence of two of the following: (1) CK-2/CK (mass or activity) >5%, (2) new Q waves lasting >=0.04 s and 1 mm deep in at least two contiguous leads, (3) Troponin-T was >0.2 µpyrophosphate scan.
Results: Eighteen of the 323 patients (5.6%) had a PMI, of which 3 (17%) were fatal. Only 3 of 18 patients had chest pain, whereas 10 of 18 patients (56%) had other clinical findings. The electrocardiographic classification of the PMI was Q wave in 6, non-Q wave in 10, and indeterminate in 2. The PMIs occurred on the day of operation in 8, on day one in 6, on day two in 3, and on day four in 1 patient.
Conclusions: This study determined that PMI was an early event, only occasionally associated with chest pain, and usually non-Q wave in nature.
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