Bedside interpretation: ECG, CXR, CT and labs

ECG interpretation in the ICU

Reviewed Nov 2026·4 references
New· views rounded down, updated weekly

A systematic 12-lead read, STEMI criteria and their mimics, troponin in critical illness, QTc risk and electrolyte patterns.

Definition
Use a fixed sequence for every ECG: rate, rhythm, axis, intervals (PR, QRS, QTc), P waves, QRS morphology, ST segments, T waves, and comparison with previous tracings. In the ICU most troponin rises are myocardial injury or type 2 MI rather than type 1 (plaque rupture) MI.

At the bedside

  1. 1

    Rate and rhythm

    Regular or irregular; P before every QRS; narrow vs broad complex (see cardiac-emergencies-arrhythmias module for management).

  2. 2

    Intervals

    PR 120-200 ms; QRS < 120 ms; QTc (Bazett, or Fridericia when HR > 100): > 500 ms or rise > 60 ms from baseline = high torsades risk.

  3. 3

    ST elevation (STEMI)

    New ST elevation at the J point in ≥ 2 contiguous leads: ≥ 1 mm in all leads except V2-V3, where ≥ 2 mm (men ≥ 40 y), ≥ 2.5 mm (men < 40 y), ≥ 1.5 mm (women).

  4. 4

    STEMI equivalents

    Posterior MI (ST depression V1-V3, tall R; check V7-V9), new LBBB with ischaemic symptoms or Sgarbossa criteria, de Winter T waves, diffuse ST depression with aVR elevation (left main / multivessel ischaemia).

  5. 5

    Mimics

    Pericarditis (diffuse concave ST elevation, PR depression), LV aneurysm, early repolarisation, hyperkalaemia, Brugada, Takotsubo, raised ICP (deep T inversion).

  6. 6

    Troponin

    Above the 99th percentile with a rise/fall = myocardial injury; MI requires ischaemic symptoms, ECG changes, imaging or angiographic evidence. Sepsis, PE, tachyarrhythmia, AKI and shock cause type 2 MI or non-ischaemic injury.

  7. 7

    Electrolytes

    Hyperkalaemia: peaked T → PR prolongation, P loss → broad QRS → sine wave. Hypokalaemia: U waves, ST depression. Hypocalcaemia: long QT. Hypercalcaemia: short QT.

Common ICU drugs that prolong QT

ClassExamples
AntiarrhythmicsAmiodarone, sotalol, procainamide
AntipsychoticsHaloperidol (IV), quetiapine, olanzapine
AntimicrobialsMacrolides, fluoroquinolones, azoles, chloroquine/hydroxychloroquine
Antiemetics/GIOndansetron, domperidone, metoclopramide
OthersMethadone, tricyclics, citalopram

Stop QT-prolonging drugs and correct K (to 4-5 mmol/L) and Mg when QTc > 500 ms.

Red flag · call your senior now
STEMI or STEMI-equivalent in an ICU patient: immediate cardiology discussion for reperfusion even if the admission diagnosis was non-cardiac.
Red flag
QTc > 500 ms with bradycardia, hypokalaemia or hypomagnesaemia: high risk of torsades.
Pitfall
Labelling every troponin rise in sepsis as 'NSTEMI' and starting dual antiplatelets.
Pitfall
Machine QTc in AF, bundle branch block or with wide U waves - measure manually.
Pearl
Always compare with the previous ECG - new changes matter more than absolute values.

Calculators for this topic

Corrected QT (Bazett)

QT ÷ √(RR in seconds). Over-corrects at fast heart rates.

References

  1. 1

    Thygesen K, Alpert JS, Jaffe AS, et al. Fourth universal definition of myocardial infarction (2018). Eur Heart J 2019;40:237-69.

  2. 2

    Byrne RA, Rossello X, Coughlan JJ, et al. 2023 ESC guidelines for the management of acute coronary syndromes. Eur Heart J 2023;44:3720-826.

  3. 3

    Drew BJ, Ackerman MJ, Funk M, et al. Prevention of torsade de pointes in hospital settings: a scientific statement from the American Heart Association and the American College of Cardiology Foundation. Circulation 2010;121:1047-60.

  4. 4

    Farkas J. The Internet Book of Critical Care (IBCC). EMCrit Project; continuously updated.

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Educational reference for trained clinicians. Check doses against your hospital protocol and the patient in front of you.