Discussion

ACS includes a spectrum of illness, encompassing several types of NSTEMIs (non-ST segment elevation myocardial infarctions) and STEMIs (ST segment elevation myocardial infarctions).² NSTEMIs result when there has been enough ischemia to the myocardium that myocardial cells are injured and begin to leak intracellular contents that may be measured in the blood (eg, troponin, creatine kinase, etc.).^1,3 In contrast, STEMIs result most commonly from total occlusion of a coronary vessel, typically from a ruptured atherosclerotic plaque. STEMIs are suspected by a specific set of criteria on ECG tracings, including:⁴

• New ST elevation at the J point in two contiguous leads with f >0.1 mV in all leads other than leads V2–V3
• For leads V2–V3, ≥0.2 mV in men ≥40 years, ≥0.25mV in men <40 years, or ≥0.15 mV in women
• New left bundle branch block (in some cases, especially with Sgarbossa criteria)⁵

Regardless of the cause, restoring perfusion and oxygen supply to the myocardium is critical and time-dependent, making rapid diagnosis essential.

Although there are relatively clear diagnostic criteria to indicate STEMI, actual ECG findings can vary widely depending on the characteristics of the infarct (ie, size, severity, and timing) as well as when the ECG was obtained. In the patient described above, at the time of presentation, STEMI criteria were absent.

Riley and colleagues conducted a retrospective study in 2013 that evaluated 41,560 patients from 432 sites and found that 11 percent of patients who were ultimately diagnosed with STEMI did not meet STEMI criteria at the time of the initial ECG. They noted that 72.4 percent of this group developed diagnostic ECGs for STEMI on repeat testing obtained within 90 minutes. Further analysis of these populations showed no significant difference in the timing of the initial ECG being obtained in relation to symptom onset and no significant difference in coronary artery disease risk factors between the population who had initially diagnostic ECGs for STEMI and those who did not.⁶

Meanwhile, a paradigm shift in ACS may be under way. Meyers and colleagues conducted a retrospective study that reviewed a prospectively collected population of 467 ACS patients. The researchers compared two paradigms: occlusion with STEMI and occlusion without STEMI. Occlusion myocardial infarction (OMI) was defined as acute with either Thrombolysis in Myocardial Infarction (TIMI) 0–2 flow or TIMI 3 flow plus peak troponin T >1.0 ng/mL. The results demonstrated that among 108 OMIs, only 60 percent met the usual STEMI criteria. Therefore, the study suggested that about 40 percent of OMIs did not present with STEMI criteria; those with STEMI plus OMI were more likely to go to a catheterization lab sooner than STEMI without OMI, though adverse outcomes were similar.⁷

Summary

This case describes a patient who presented with symptoms concerning for ACS. Repeat ECGs and troponin demonstrated myocardial ischemia that was not previously apparent.

It is widely known that ACS may be present without an initial increase in cardiac troponin if there has not been sufficient time. Many patients may be experiencing an acute STEMI without classic diagnostic ECG changes. Because the time to reperfusion is critical, it is important to obtain serial ECGs to reevaluate patients presenting with ACS symptoms.⁸

New studies have challenged the STEMI/NSTEMI model to include additional patterns in order to prevent delay in intervention of occlusion without STEMI.