ECG - NSTEMI

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Typical ECG Findings in NSTEMI

Core Definition NSTEMI = myocardial infarction without persistent ST elevation on ECG but with troponin rise and ischaemic symptoms or ECG changes.

Key Message ECG is abnormal in ~80–90% of NSTEMI cases, but ~10–20% can have a completely normal or non-specific ECG → troponin is diagnostic. Changes are often dynamic → repeat ECG every 15–30 min if pain ongoing or high clinical suspicion.

Most Common & Typical ECG Changes

• ST-segment depression – most frequent and characteristic finding
• Horizontal or downsloping ≥0.5 mm (0.05 mV) in ≥2 contiguous leads
• Most common in lateral leads (I, aVL, V5–V6) or inferior leads (II, III, aVF)
• Can be widespread (anterior + lateral + inferior) in multivessel disease
• T-wave inversion – deep symmetric inversion (>2 mm) in ≥2 contiguous leads
• Common in anterior (V2–V4), lateral (I, aVL, V5–V6) or inferior leads
• Wellens' pattern (deeply inverted or biphasic T waves in V2–V3) indicates critical proximal LAD stenosis → urgent angiography
• Transient / brief ST elevation that resolves quickly before ECG capture
• Indicates unstable plaque with transient occlusion → still classified as NSTEMI if no persistent elevation
• Other supportive findings
• Hyperacute (tall, broad, peaked) T waves early in ischaemia
• Poor R-wave progression or loss of R waves (anterior infarction)
• New left bundle branch block (LBBB) with ischaemic symptoms → treat as STEMI equivalent
• Reciprocal ST depression opposite to subtle elevation
• Arrhythmias (sinus tachycardia, new atrial fibrillation, ventricular ectopics)

High-Risk ECG Patterns in NSTEMI

• Widespread ST depression in ≥3 leads + ST elevation in aVR → left main or triple-vessel disease
• Wellens' syndrome (deeply inverted or biphasic T waves V2–V3) → high-risk proximal LAD lesion
• Dynamic changes on serial ECGs (worsening depression, new T inversion)
• ST depression in multiple territories → multivessel ischaemia

Important Clinical Notes & Pitfalls

• Normal ECG does NOT exclude NSTEMI → always interpret with symptoms + troponin
• NSTEMI vs unstable angina → troponin elevation distinguishes (NSTEMI = troponin positive)
• Differentials for ST depression / T inversion: LVH with strain, digoxin effect, hypokalaemia, pulmonary embolism, takotsubo cardiomyopathy, myocarditis
• Always compare to previous ECGs if available
• Repeat ECG frequently during ongoing pain or if initial ECG non-diagnostic

Management Implications of ECG

• High-risk ECG (Wellens', widespread depression + aVR elevation, dynamic changes) → immediate invasive strategy (<2 hours to cath lab)
• Intermediate-risk → early invasive (<24 hours)
• Low-risk or non-specific changes → selective invasive or conservative approach

Clinical Pearl for Exams / OSCE / MCQ

• Most common ECG in NSTEMI → ST depression ± T-wave inversion in lateral or inferior leads
• Wellens' pattern or ST elevation in aVR + widespread depression → high-risk → urgent angiography
• Normal ECG does NOT rule out NSTEMI → rely on clinical picture + high-sensitivity troponin
• Always repeat ECG and compare serial changes in suspected ACS

Chest pain at rest and ECG shows Sinus bradycardia, ST depression widespread, T wave inversion V2-5. Wellens Syndrome

Sources (2026)

• ESC Guidelines: Acute Coronary Syndromes (2023, minor 2025 updates)
• AHA/ACC NSTE-ACS Guideline (2022, reaffirmed 2025)
• NICE CG95 / NG185: Chest pain of recent onset (updated 2025)
• Life in the Fast Lane ECG Library (2026 updates)
• UpToDate: ECG in NSTEMI (2026)