Electrocardiographic changes in the ST segment and T waves have long been recognized as potent, if imperfect, indicators of ischemia and potential infarction (9
). Consensus guidelines issued in 2000 recommended useful thresholds for identifying ST and T wave changes as pathologic (2
), although multiple confounding factors including early repolarization, LBBB, pre-excitation syndromes, metabolic disturbances and myocarditis may complicate their application (1
). However, growing recognition of age and gender differences in ECG patterns and particularly in precordial ST segments (12
) suggested that ST amplitude was generally maximal in V2 and V3 and greater in men, particularly young men, than in women.
Macfarlane et al. developed criteria for ST elevation MI from a training set of 789 ECGs from patients presenting with chest pain as well as ECGs from a population of 1496 adult normals of both genders (13
). Based on their findings, they proposed criteria for ST elevation MI which enhanced both sensitivity and specificity in the test set when compared with the original ACC/ESC criteria. While Macfarlane’s proposed criteria took into account age, gender, and specific ECG leads, it was cumbersome to apply in clinical practice because a formula had to be used to determine unique criteria for each patient.
In 2007, a new joint expert consensus document on the universal definition of MI was issued by the ESC/ACCF/AHA and WHF that incorporated many of Macfarlane’s concepts but without the need to determine patient specific criteria. The new criteria lowered the threshold for ST elevation in lead V1 from greater than or equal to 0.2 mV to greater than or equal to 0.1 mV to diagnose ischemia. They also set different thresholds for ST segment elevation in V2 and V3 compared with all other leads and set lower ST thresholds for women than men in these leads (1
). In addition, ST depression of ≥0.05 mV in two contiguous leads was used as a revised criterion for ischemia. Recent recommendations for the standardization and interpretation of the ECG in acute ischemia/infarction go even further, calling for both age and gender specific criteria for ST elevation, as well as lead specific criteria for ST depression (17
In this analysis of subjects presenting to the ED with symptoms of possible cardiac ischemia and a nondiagnostic ECG, the 2007 ESC/ACCF/AHA/WHF ECG criteria identified substantially more patients ultimately diagnosed with an ACS. Moreover, sensitivity for ACS was increased with minimal or no effect on specificity, as no subjects identified as having diagnostic ischemic changes by revised ECG criteria left the hospital with a final diagnosis of noncardiac chest pain. Patients who had ECGs diagnostic of ischemia by revised, but not prior standard criteria, also had a trend toward increased 1 year mortality, highlighting the importance in accurately identifying these patients.
Our results should be interpreted in light of possible limitations in our study. Electrocardiograms were reviewed by a single cardiologist, although tracings were analyzed several months apart to minimize bias. Holter electrocardiograms were recorded using the Mason-Likar rather than standard lead configuration, although reported differences between the two have centered predominantly on a rightward shift in axis and changes in Q and S wave amplitudes, rather than effects on ST and T wave changes (18
). Moreover, our analysis used Holter electrocardiograms exclusively, so that the increased yield seen with the revised criteria for ischemia was based on identical tracings with the same lead configuration. Some patients were lost to longer term follow-up. The relatively small sample size may have limited power to detect the effect of the revised criteria on clinical outcomes. Nonetheless, in this analysis, revision of the ECG criteria for ischemia was associated with enhanced diagnostic performance and identified a subset of patients at higher risk. The revised criteria should be retained.