High-risk ECG patterns in ACS—Need for guideline revision

Abstract

The current guidelines advocate distinct approaches (urgent reperfusion therapy) to patients with suspected acute coronary syndromes (ACS) presenting with ST elevation (STE) versus patients without STE on their electrocardiogram (ECG). This is based on the paradigm that STE represents ongoing transmural ischemia due to an acute occlusion of an epicardial coronary artery whereas the significance of other ECG findings is more contentious. The role of urgent coronary angiography in patients without STE is less clear and initial stabilization with conservative treatment is recommended. However, in some cases the distinction between STEMI and non-STE-ACS is difficult. Acute occlusion of a coronary artery may cause less than the current recommended threshold STE. On the other hand, many patients may have STE secondary to nonischemic etiology. In many patients with non-STE-ACS the coronary artery is not completely occluded at the time of presentation and there are rapid fluctuations in the severity of ischemia and hence, dynamic changes are observed in the ECG. Several ECG patterns associated with particular coronary anatomy and high-risk prognosis have been identified. Patients with ACS presenting with these high-risk patterns should probably be referred for coronary angiography with the possibility of urgent intervention with the goal of prevention of ischemic complications, rather than for immediate myocardial salvage, as in classic STEMI.

Introduction

The current guidelines make a clear distinction in the triage and initial management of patients presenting with symptoms suggestive of acute coronary syndrome (ACS) with and without ST elevation (STE) in their presenting ECG.1., 2. STE is thought to manifest ongoing transmural ischemia due to an acute occlusion of a coronary artery. Emergent reperfusion therapy is indicated to “save” myocardium and limit the ischemic damage. Tremendous effort has been invested to shorten the time from initiation of symptoms (or presentation) to reperfusion. The current guidelines suggest that patients presenting without STE can be initially managed conservatively and coronary angiography can be performed later to prevent reinfarction, but not to save myocardium.

However, many patients presenting with chest pain may have STE secondary to nonischemic etiologies.³ Many classic patterns of nonischemic STE can be easily identified (early repolarization, normal pattern, pericarditis, etc). However, it should be remembered that the magnitude and distribution of these nonischemic STE patterns may dramatically change over time. For example, the magnitude of STE secondary to early repolarization tends to diminish with tachycardia, whereas STE secondary to aneurysm or left bundle branch block may increase with tachycardia. On the other hand, some patients with an acute occlusion of a coronary artery with ongoing ischemia may have borderline STE or no STE at all.² The European guidelines suggest that ongoing suspicion of myocardial ischemia, despite medical therapy, is an indication for emergency coronary angiography, even in patients presenting without STE.²

In theory, patients presenting with STE have ongoing ischemia and ongoing necrosis that should be stopped by emergency revascularization. On the other hand, patients with ACS without STE may show diverse angiographic and clinical findings that may signify incomplete and dynamic occlusions. In many patients, symptoms diminish by the time of presentation. In these patients, the ECG is not expected to show acute ischemic changes or localize the site of coronary thrombus. In such instances, the ECG may show the “footprints” of previous ischemia—(terminal) T-wave inversions with insignificant ST deviation. However, if an ECG is recorded during an episode of active symptoms, dynamic changes indicating ischemia can be detected. Thus, it is crucial to interpret the ECG while knowing the clinical data and especially whether or not the patient was symptomatic when the recording was done. Currently, the severity and/or quality of symptoms cannot be stored in the digital database. Future ECG machines should include a method to enter this information, along with the demographic data when the ECG is recorded.

Several high-risk ECG patterns have been described in patients with non-STE-ACS.⁴ These patterns can be divided into those with ongoing ischemia (that do not result in STE) and those without ongoing ischemia (reperfusion of a culprit lesion with high-risk features) (Table 1):