The Role of ECG in the Diagnosis and Risk Stratification of Acute Coronary Syndromes: an Old but Indispensable Tool

Since its inception in 1902 by Willem Einthoven, the electrocardiogram (ECG) has fundamentally undergone minimal technological advances. Nevertheless, its clinical utility is critical, and it remains an essential tool to diagnose, risk stratify, and guide reperfusion and invasive strategies in patients with suspected acute coronary syndromes. ECG reading can be demanding, with many healthcare professionals lacking the necessary expertise to accurately interpret them. This is exacerbated by the need to constantly revisit old dogmas pertinent to the interpretation of ECGs. Notably, ECG leads record the global electrical activity of the heart toward and away from each electrode rather than local events. The long-held central paradigm that the various ECG leads record local events underneath specific electrodes should therefore be reassessed. For example, ST segment elevation in leads V1 and V2 usually denote antero-apical rather than septal infarction, often a misnomer utilized by the majority of clinicians. The ECG diagnosis of ST-elevation myocardial infarction (STEMI) is sometimes challenging and discerning it from non-ST-elevation myocardial infarction (NSTEMI) is of paramount importance to implement timely acute reperfusion therapy. In fact, when qualifications for emergency reperfusion therapy are based on STEMI ECG criteria, nearly one-third of cases with acute coronary occlusion are missed. Diagnostic ST elevation in the absence of left ventricular (LV) hypertrophy or left bundle-branch block (LBBB) is defined by a specific set of sex-specific criteria for new ST elevation at the J point in contiguous precordial or limb leads. However, other ECG criteria need to be kept in mind. These include, but are not limited to, new or presumably new left bundle branch block (LBBB), which is often considered as an STEMI-equivalent; ST depression in two or more precordial leads (V1–V4), denoting a true inferolateral transmural myocardial infarction; and the infrequent presentation with hyperacute T-wave changes. As our understanding of the pathology of ischemic reperfusion injury has evolved and following the introduction of new imaging modalities such as cardiac magnetic resonance imaging, we need to re-assess the old dogmas pertinent to the interpretation of ECGs and update the terms and classifications.