The ST Segment

S-T Segment

The ST segment is the flat, isoelectric section of the ECG between the end of the S wave (the J point) and the beginning of the T wave.

  • The ST Segment represents the interval between ventricular depolarization and repolarization.
  • The most important cause of ST segment abnormality (elevation or depression) is myocardial ischaemia or infarction.
ECG basics: waves, segments and intervals LITFL ECG library

Causes of ST Segment Elevation


Morphology of the Elevated ST segment

Myocardial Infarction

ECG Complex ST segment elevation

Acute STEMI may produce ST elevation with either concave, convex or obliquely straight morphology.


ST Segment Morphology in Other Conditions

ECG-Complex-ST-segment-elevation-in-pericarditis BER LBBB
ECG-Complex-ST-segment-elevation-in- Brugada

Patterns of ST Elevation

Acute ST elevation myocardial infarction (STEMI)

ST segment elevation and Q-wave formation in contiguous leads. Follow the links above to find out more about the different STEMI patterns.:


There is usually reciprocal ST depression in the electrically opposite leads. For example, STE in the high lateral leads I + aVL typically produces reciprocal ST depression in lead III (see example below).

ECG Anterior STEMI evolving

Coronary Vasospasm (Prinzmetal’s angina)

  • This causes a pattern of ST elevation that is very similar to acute STEMI — i.e. localised ST elevation with reciprocal ST depression occurring during episodes of chest pain.
  • However, unlike acute STEMI the ECG changes are transient, reversible with vasodilators and not usually associated with myocardial necrosis.
  • It may be impossible to differentiate these two conditions based on the ECG alone.

Pericarditis

Acute Pericarditis causes widespread concave (“saddleback”) ST segment elevation with PR segment depression in multiple leads, typically involving I, II, III, aVF, aVL, and V2-6.

ECG Pericarditis ST changes
  • Concave “saddleback” ST elevation in leads I, II, III, aVF, V5-6 with depressed PR segments.
  • There is reciprocal ST depression and PR elevation in leads aVR and V1.
  • Spodick’s sign was first described by David H. Spodick in 1974 as a downward sloping TP segment with specificity for acute pericarditis.

Benign Early Repolarization

Benign Early Repolarization (BER) causes mild ST elevation with tall T-waves mainly in the precordial leads. BER is a normal variant commonly seen in young, healthy patients. There is often notching of the J-point — the “fish-hook” pattern.

The ST changes may be more prominent at slower heart rates and disappear in the presence of tachycardia.

ECG BER vs pericarditis 2

There is slight concave ST elevation in the precordial and inferior leads with notching of the J-point (the “fish-hook” pattern)


Left Bundle Branch Block (LBBB)

In Left bundle branch block (LBBB), the ST segments and T waves show “appropriate discordance” — i.e. they are directed opposite to the main vector of the QRS complex.

This produces ST elevation and upright T waves in leads with a negative QRS complex (dominant S wave), while producing ST depression and T wave inversion in leads with a positive QRS complex (dominant R wave).

ECG Left Bundle Branch Block LBBB
  • Note the ST elevation in leads with deep S waves — most apparent in V1-3.
  • Also note the ST depression in leads with tall R waves — most apparent in I and aVL.

Left Ventricular Hypertrophy (LVH)

Left Ventricular Hypertrophy (LVH) causes a similar pattern of repolarization abnormalities as LBBB, with ST elevation in the leads with deep S-waves (usually V1-3) and ST depression/T-wave inversion in the leads with tall R waves (I, aVL, V5-6).

ECG Left ventricular hypertrophy LVH

Ventricular Aneurysm

This is an ECG pattern of Ventricular Aneurysm – residual ST elevation and deep Q waves seen in patients with previous myocardial infarction. It is associated with extensive myocardial damage and paradoxical movement of the left ventricular wall during systole.

ECG Ventricular Aneurysm
  • There is ST elevation with deep Q waves and inverted T waves in V1-3.
  • This pattern suggests the presence of a left ventricular aneurysm due to a prior anteroseptal MI.

Brugada Syndrome

Brugada Syndrome is an inherited channelopathy (a disease of myocardial sodium channels) that leads to paroxysmal ventricular arrhythmias and sudden cardiac death in young patients.

The tell-tale sign on the resting ECG is the “Brugada sign” — ST elevation and partial RBBB in V1-2 with a “coved” morphology.

ECG Brugada Syndrome Type 1

There is ST elevation and partial RBBB in V1-2 with a coved morphology — the “Brugada sign”.


Ventricular Paced Rhythm

Ventricular pacing (with a pacing wire in the right ventricle) causes ST segment abnormalities identical to that seen in LBBB. There is appropriate discordance, with the ST segment and T wave directed opposite to the main vector of the QRS complex.

ECG Ventricular Paced Rhythm AV sequential pacing

Raised Intracranial Pressure

Raised Intracranial Pressure (ICP) (e.g. due to intracranial haemorrhage, traumatic brain injury) may cause ST elevation or depression that simulates myocardial ischaemia or pericarditis.

More commonly, raised ICP is associated with widespread, deep T-wave inversions (“cerebral T waves“).

ECG Catecholamine storm Raised ICP ST changes

Widespread ST elevation with concave (pericarditis-like) morphology in a patient with severe traumatic brain injury.


Takotsubo Cardiomyopathy

Takotsubo Cardiomyopathy: A STEMI mimic producing ischaemic chest pain, ECG changes +/- elevated cardiac enzymes with characteristic regional wall motion abnormalities on echocardiography.

Typically occurs in the context of severe emotional distress (“broken heart syndrome“). Commonly associated with new ECG changes (ST elevation or T wave inversion) or moderate troponin rise.

ECG Tako-Tsubo Cardiomyopathy

Less Common Causes of ST segment Elevation


Transient ST elevation after DC cardioversion from VF

ECG Rhythm strip post DCCV cardioversion

J waves in hypothermia simulating ST elevation

J waves Osborn Wave hypothermia temp 30°C

Causes of ST Depression


Morphology of ST Depression

  • ST depression can be either upsloping, downsloping, or horizontal.
  • Horizontal or downsloping ST depression ≥ 0.5 mm at the J-point in ≥ 2 contiguous leads indicates myocardial ischaemia (according to the 2007 Task Force Criteria).
  • Upsloping ST depression in the precordial leads with prominent De Winter T waves is highly specific for occlusion of the LAD.
  • Reciprocal change has a morphology that resembles “upside down” ST elevation and is seen in leads electrically opposite to the site of infarction.
  • Posterior MI manifests as horizontal ST depression in V1-3 and is associated with upright T waves and tall R waves.

ST Segment depression
ST segment depression upsloping downsloping horizontal

ST segment morphology in myocardial ischaemia

ECG Complex ST Morphology 1

Reciprocal change

ECG-Complex-ST-Morphology-Reciprocal-change

ST segment morphology in posterior MI

ECG Complex ST Morphology Posterior AMI

Patterns of ST depression

Myocardial Ischaemia

ST depression due to subendocardial ischaemia may be present in a variable number of leads and with variable morphology. It is often most prominent in the left precordial leads V4-6 plus leads I, II and aVL.

Widespread ST depression with ST elevation in aVR is seen in left main coronary artery occlusion and severe triple vessel disease.

ECG left main coronary artery occlusion LMCA

NB. ST depression localised to the inferior or high lateral leads is more likely to represent reciprocal change than subendocardial ischaemia. The corresponding ST elevation may be subtle and difficult to see, but should be sought. This concept is discussed further here.


Reciprocal Change

ST elevation during acute STEMI is associated with simultaneous ST depression in the electrically opposite leads:

ECG Inferior AMI Reciprocal ST depression
  • Reciprocal ST depression in aVL with inferior STEMI

ECG lateral AMI Reciprocal ST depression
  • Reciprocal ST depression in III and aVF with high lateral STEMI

Posterior Myocardial Infarction

Acute posterior STEMI causes ST depression in the anterior leads V1-3, along with dominant R waves (“Q-wave equivalent”) and upright T waves. There is ST elevation in the posterior leads V7-9.

ECG Posterior STEMI St changes 2

De Winter T Waves

De Winter T waves: a pattern of up-sloping ST depression with symmetrically peaked T waves in the precordial leads is considered to be a STEMI equivalent, and is highly specific for an acute occlusion of the LAD.

ECG de Winter waves

Digoxin Effect

Digoxin Effect: Treatment with digoxin causes downsloping ST depression with a “sagging” morphology, reminiscent of Salvador Dali’s moustache.

ECG Digoxin Effect Salvador Dali

Hypokalaemia

Hypokalaemia causes widespread downsloping ST depression with T-wave flattening/inversion, prominent U waves and a prolonged QU interval.

ECG Hypokalaemia ST changes

Right ventricular hypertrophy (RVH)

Right ventricular hypertrophy (RVH) causes ST depression and T-wave inversion in the right precordial leads V1-3.

ECG Right ventricular hypertrophy RVH

Right Bundle Branch Block (RBBB)

Right Bundle Branch Block (RBBB) may produce a similar pattern of repolarisation abnormalities to RVH, with ST depression and T wave inversion in V1-3.

ECG RBBB Right bundle branch block ST changes

Supraventricular tachycardia (SVT)

Supraventricular tachycardia (e.g. AVNRT) typically causes widespread horizontal ST depression, most prominent in the left precordial leads (V4-6).

This rate-related ST depression does not necessarily indicate the presence of myocardial ischaemia, provided that it resolves with treatment.

ECG AVNRT AV-nodal re-entry tachycardia ST depression 2
Orthodromic AVRT

References
  • Edhouse J, Brady WJ, Morris F. ABC of clinical electrocardiography: Acute myocardial infarction-Part II. BMJ. 2002 Apr 20;324(7343):963-6. Review. PubMed PMID: 11964344; PubMed Central PMCID: PMC1122906. Full text.
  • Smith SW. T/QRS ratio best distinguishes ventricular aneurysm from anterior myocardial infarction. Am J Emerg Med. 2005 May;23(3):279-87. PubMed PMID: 15915398.

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Emergency Physician in Prehospital and Retrieval Medicine in Sydney, Australia. He has a passion for ECG interpretation and medical education | ECG Library |

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