Currently, there are no standard diagnostic criteria for perioperative MI in patients undergoing noncardiac surgery. Optimal diagnostic criteria must consider the unique features of perioperative MIs, in particular that a large proportion are clinically silent. We propose diagnostic criteria for perioperative MIs () that we have adapted from a recent consensus document of the joint European Society of Cardiology / American College of Cardiology (ESC/ ACC) committee that redefined nonperioperative MI16
The first of our criteria requires a typical rise in troponin or a typical fall of an elevated troponin level detected at its peak after surgery in a patient without a documented alternative explanation for an elevated troponin level (e.g., pulmonary embolism) or — only if troponin measurement is unavailable — a rapid rise and fall of CK-MB. We encourage physicians to use troponin measurement, because perioperative CK-MB measurements are prone to false-positive and false-negative values. Surgical trauma can result in the release of CK-MB from skeletal muscle and a false-positive CK-MB value for MI.17,18,19
A substantial proportion of perioperative MIs occur in the first 2 days after surgery, when serum CK values are high secondary to surgical trauma. These high CK values can result in a low, and thus false-negative, ratio of CK-MB to total CK.19,20
Given the limitations of CK-MB measurement in the perioperative setting, physicians should only use CK-MB if troponin measurement is unavailable at their centre.
As troponin values rise, their variability, as measured by the coefficient of variation, decreases. The ESC/ACC guidelines define an increased troponin level as “a measurement exceeding the 99th percentile of a reference control group.” At the same time, however, they specify that the coefficient of variation at the 99th percentile should be 10% or less. Unfortunately, no available troponin assay meets the 10% coefficient of variation criterion at the 99th percentile — higher levels (above the 99th percentile) are required to meet this criterion.21,22
In keeping with previous suggestions,21,23
until the assays are improved to meet the ESC/ACC recommendation, we define an increased troponin level as the lowest value that has a coefficient of variation equal to 10% (Appendix 1
New Q-wave changes (≥ 30 ms) present in any 2 contiguous leads fulfill the definition of the development of pathological Q waves. We define electrocardiogram (ECG) changes indicative of ischemia as ST-segment elevation (≥ 2 mm in leads V1, V2 or V3 and ≥ 1 mm in the other leads) or ST-segment depression (≥ 1 mm) in at least 2 contiguous leads, or symmetric inversion of T waves (≥ 1 mm) in at least 2 contiguous leads. Coronary artery intervention includes percutaneous coronary intervention or coronary artery bypass grafting (CABG).
Because many patients will not experience symptoms, clinicians may still miss the correct diagnosis in patients with an elevated troponin level after surgery who have experienced an MI. Some of these patients will have an uninterpretable ECG (e.g., paced, left bundle-branch block, chronic ST-segment changes); some will have an infarct in a territory (e.g., posterior) where the conventional ECG lacks sensitivity;24
and some will have significant ST-segment changes that resolve by the time the ECG is repeated the following day. To avoid missing the diagnosis of MI, we have added to the first criterion the finding of a new or presumed new wall-motion abnormality on echocardiography or a new or presumed new fixed cardiac defect on radionuclide imaging.
When physicians encounter a patient who has an elevated troponin level after surgery without either ischemic symptoms or a diagnostic ECG, the differential diagnosis includes MI and noncardiac causes (e.g., pulmonary embolism). Because MI is a probable cause of an elevated troponin level in this situation, physicians should consider obtaining an echocardiogram or radionuclide imaging.
Although physiologic studies suggest that an imaging study may be insensitive (an injury involving > 20% of myocardial wall thickness may be required to detect a wall-motion abnormality on echocardiography, and an injury of myocardial tissue > 10 g may be required to detect a radionuclide perfusion defect),16
at least 1 clinical study has suggested that echocardiography has a high sensitivity: 108 patients had troponin levels measured before surgery and every 6 hours for the first 36 hours after surgery, as well as echocardiography before surgery and 3–5 days after surgery.19
Echocardiography demonstrated a new wall-motion abnormality in all but 1 of the 9 patients who experienced an MI based on the diagnostic criteria of an elevated troponin level and significant ECG changes. This study also suggested excellent specificity for echocardiography. None of the remaining 99 patients had a new wall-motion abnormality. These results suggest that a wall-motion abnormality detected on an imaging study in the absence of a prior study suggests the diagnosis of perioperative MI, and a demonstrably new abnormality increases the likelihood further and thus supports our definition of a perioperative MI.
Further research is needed to evaluate the diagnostic criteria we propose.