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Never Ever Miss an MI


The one finding on an ECG, which you can never afford to miss, and may cost dear life, if missed is Myocardial Infarction, i.e ST-T changes. Timely diagnosis with the simple ECG, which is cheap and easily available may save precious lives. Lets get started, Never ever to miss an MI.

Who needs an ECG:

There are many instances where We miss an MI, simply because We did not order for an ECG. Diabetics may not have chest pain, so called silent MI. Inferior wall MI may present with epigastric pain mimicking Peptic Ulcer disease. Its always better to "Make Sure" than to "Be Sure". Following are some instances, where we must order an ECG,
  • Any case with chest discomfort-left sided/crushing/radiating to arm or jaw/associated with sweating/palpitation
  • Sudden onset of pain in the epigastrium
  • Radiating pain in the left arm
  • Profuse Sweating
  • Palpitation/Breathlessness
  • Giddiness/Syncope
  • Hypotension/Hypertension
  • Old age and those with co-morbidities with any of the above symptoms
  • When your instinct asks for an ECG

Leads and Walls:

Before going into changes on an ECG, Lets look at which leads looks at which wall of the heart. There is no trick easier than memorising this.
  • V1, V2- Septal
  • V3, V4- Anterior
  • I, aVL, V5, V6- Lateral
  • II, III, aVF- Inferior

Quick Facts:

  • ST elevation- Transmural ischaemia/infarction
  • ST depression- Sub endocardial ischaemia/infarction
  • T wave inversion- Myocardial ischaemia
  • Pathological Q wave- Old infarct

ST Segment:

ST segment is the segment between QRS complex and T wave. It should be isoelectric i.e in-line with the baseline or TP segment.The J point is the critical point that determines ST elevation or depression.
If the J point is shifted one box above/below in atleast two contiguous limb leads and two boxes above/below in two contiguous chest leads, the ST segment is considered to be elevated/depressed.
Contiguous means the successive leads corresponding to a particular wall of the heart.
Example:
  • I, aVL are contiguous leads as they correspond to lateral wall.
  • I, II are not contiguous leads as I belong to lateral wall and II belong to inferior wall.
But in chest leads, the leads next to one another are considered contiguous.
Example:
  • V4 and V5 are called contiguous leads though V4 belongs to anterior wall and V5 belongs to lateral wall.

STEMI:

STEMI is ST Elevation Myocardial Infarction
It means transmural ischaemia/infarction i.e blood supply to the entire thickness of myocardium is interupted. It is a life threatening emergency and prompt diagnosis and immediate re-establishment of circulation through PCI (Percutaneous Coronary Intervention) or thrombolysis within the golden period is vital.
Ideally, the "door to balloon time" should be less than 90mins and the "door to needle time" should be less than 60minutes. Such is the seriousness of STEMI.

Diagnosis:

STEMI is diagnosed when, 

  1. ST segment (look at the J point) is 1mm above the baseline in contiguous limb leads and 2mm above baseline in contiguous chest leads.

      2. Hyper-Acute T waves.


      3. New onset Left Bundle Branch Block
      4. Reciprocal change may be seen in the opposite lead. Opposite of lateral wall is inferior wall and vice versa. For eg. ST elevation in lateral wall may be accompanied by ST depression in inferior wall.

Progress:

If the patient survives the acute complications of STEMI, changes occur in the ECG picture with passage of time.
  • The ST segment returns to baseline
  • Pathological T wave inversion develops
  • Pathological Q wave develops, which usually remains permanent and indicate old infarct.
Pathological T wave inversion:
  • It is symmetrical, i.e the downstroke and upstroke should be of same length
  • More than 3mm deep
  • T wave inversion in aVR and V1 are normal.

Pathological Q wave:
  • It is more than 1mm wide
  • More than 2mm deep
  • More than 25% depth of QRS complex.

Practise:

1.

ST elevation in I, aVL, V3, V4, V5, V6. Anterolateral STEMI. This shape of ST elevation in anterior leads is called tombstone pattern as it involves a large territory with a high likelihood of death if not diagnosed early.

2.

ST elevation in II, III, aVF with reciprocal 
changes in I, aVL. Inferior Wall STEMI.

3.

ST elevation in V2, V3, V4. Anteroseptal STEMI

4.

T wave inversion in V2, V3, V4, V5. Evolved Anterior Wall MI

NSTEMI:

NSTEMI is Non ST segment Elevation Myocardial Infarction. It indicates sub endocardial ischaemia or infarction caused due to partial occlusion of a blood vessel. Though it also requires PCI, it is less urgent than STEMI and is initially treated with anticoagulants and antiplatelets. Thrombolysis is ineffective or contraindicated in NSTEMI.
However if not identified and treated may lead to fatal arrhythmias or progress to STEMI.
 It is diagnosed by
  • Downsloping of ST segment (look at the J point) is 0.5mm below the baseline in two contiguous leads indicate ischaemia. More than 1mm is more specific and more than 2mm in more than 3 leads has high mortality rate.


  • T wave inversion should be atleast 1mm deep in atleast two contiguous leads with positive QRS complex.
  • Widespread ST depression with ST elevation in aVR suggests Left Main Coronary Artery occlusion (LMCA).
  • Unlike STEMI, pathological Q wave does not develop in NSTEMI.

Unstable Angina:

Unlike NSTEMI, Unstable Angina is not associated with infarction. The ST segment returns back to baseline once the pain is releived. Cardiac troponins are also not elevated.

Practise:

1.

T wave inversion in I, aVL, V3, V4, V5, V6- Anterolateral wall Ischaemia
2.

Wide spread ST depression with ST elevation in aVR. NSTEMI-LMCA occlusion.
Every ECG, You get in your hand is a study material. Study the ECG and practise diagnosing. Expertise comes with Practise. Keep Medizening..!

Dr.Praful JK, MBBS

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