ECG Findings in the Clinical Context
Without specific patient details provided in the question, I must address the most likely ECG findings based on the evidence for acute coronary syndromes and related conditions.
Most Likely ECG Finding: ST Depression
Based on the clinical guidelines for acute coronary syndromes, ST depression is the most common ECG finding in non-ST-elevation acute coronary syndrome (NSTE-ACS) and represents subendocardial ischemia. 1
Key Diagnostic Patterns
ST depression (especially horizontal or downsloping) is highly suggestive of NSTE-ACS and occurs more frequently than other ECG abnormalities in patients presenting with acute coronary symptoms. 1
- ST depression ≥0.5 mm (0.05 mV) during symptoms at rest strongly suggests ischemia and underlying severe coronary artery disease 1
- Horizontal or downsloping ST depression carries greater diagnostic significance than upsloping depression 1
- ST depression may occur in multiple leads and often indicates subendocardial ischemia from subocclusion of an epicardial artery or distal embolization 2
Comparison with Other ECG Findings
ST elevation occurs specifically in STEMI with acute transmural ischemia from complete coronary occlusion, representing a distinct clinical entity requiring immediate reperfusion therapy 1
Peaked T waves (hyperacute T waves) represent the earliest ECG manifestation of acute coronary occlusion but are transient and rapidly evolve to ST elevation within minutes to hours 3
QT prolongation is not a primary manifestation of acute coronary syndrome, though it may occur with certain medications, electrolyte abnormalities, or central nervous system events 1, 4
Clinical Context and Risk Stratification
- Transient ST changes (≥0.5 mm) during symptoms strongly suggest ischemia 1
- ST depression combined with elevated cardiac biomarkers confirms NSTE-ACS diagnosis 1
- Patients with ST depression have intermediate risk compared to those with ST elevation (higher risk) or normal ECGs (lower risk) 4
Evolution of ECG Changes
The ECG pattern in acute coronary syndrome is dynamic and changes over time, with ST depression potentially evolving to ST elevation if complete occlusion develops, or resolving with successful treatment. 5, 2
- ST depression may represent reciprocal changes from ST elevation in opposite leads 1
- Evolution of ST-T depression patterns can indicate progression from non-STEMI to STEMI 1
Common Pitfalls
- Do not dismiss ST depression <0.5 mm as definitively benign, as nonspecific ST-T changes still warrant clinical correlation 1
- ST depression may be secondary to non-ischemic causes including left ventricular hypertrophy, cardiomyopathies, and medications 2
- Always compare with prior ECGs to identify new changes, as chronic ST depression may represent old infarction or structural heart disease 1