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Electrocardiograms (ECG) are used to measure the electrical activity of the heart and diagnose arrhythmias.

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12 – Lead ECG Heart arrhythmia diagnosis More specific than a 4-lead ECG configuration 10 electrodes placed on patient using anatomical landmarks Four on limbs; six on chest

Existing Devices Laerdal 12-Lead Task Trainer Visible placement Expensive (over $8000) Armstrong 12-Lead ECG Placement Trainer Mark placement with magnets Not effective for testing: 

Existing Devices Laerdal 12-Lead Task Trainer Visible placement Expensive (over $8000) Armstrong 12-Lead ECG Placement Trainer Mark placement with magnets Not effective for testing

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A normal adult 12-lead ECG Normal adult 12-lead ECG The diagnosis of the normal electrocardiogram is made by excluding any recognised abnormality. It's description is therefore quite lengthy.normal sinus rhythm each P wave is followed by a QRS P waves normal for the subject P wave rate 60 - 100 bpm with <10% variation rate <60 = sinus bradycardia rate >100 = sinus tachycardia variation >10% = sinus arrhythmia

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normal QRS axis normal P waves height < 2.5 mm in lead II width < 0.11 s in lead II for abnormal P waves see right atrial hypertrophy , left atrial hypertrophy , atrial premature beat , hyperkalaemia normal PR interval 0.12 to 0.20 s (3 - 5 small squares) for short PR segment consider Wolff-Parkinson-White syndrome or Lown - Ganong -Levine syndrome (other causes - Duchenne muscular dystrophy, type II glycogen storage disease ( Pompe's ), HOCM) for long PR interval see first degree heart block and ' trifasicular ' block

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normal QRS complex < 0.12 s duration (3 small squares) for abnormally wide QRS consider right or left bundle branch block, ventricular rhythm, hyperkalaemia , etc. no pathological Q waves no evidence of left or right ventricular hypertrophy

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normal QT interval Calculate the corrected QT interval ( QTc ) by dividing the QT interval by the square root of the preceeding R - R interval. Normal = 0.42 s. Causes of long QT interval myocardial infarction, myocarditis , diffuse myocardial disease hypocalcaemia, hypothyrodism subarachnoid haemorrhage , intracerebral haemorrhage drugs (e.g. sotalol , amiodarone ) hereditary Romano Ward syndrome ( autosomal dominant) Jervill + Lange Nielson syndrome ( autosomal recessive) associated with sensorineural deafness

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normal ST segment no elevation or depression causes of elevation include acute MI (e.g. anterior , inferior ), left bundle branch block , normal variants (e.g. athletic heart, Edeiken pattern, high-take off), acute pericarditis causes of depression include myocardial ischaemia , digoxin effect , ventricular hypertrophy , acute posterior MI , pulmonary embolus , left bundle branch block

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normal T wave causes of tall T waves include hyperkalaemia , hyperacute myocardial infarction and left bundle branch block causes of small, flattened or inverted T waves are numerous and include ischaemia , age, race, hyperventilation, anxiety, drinking iced water, LVH , drugs (e.g. digoxin ), pericarditis , PE , intraventricular conduction delay (e.g. RBBB )and electrolyte disturbance. normal U wave

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Acute inferior myocardial infarction ST elevation in the inferior leads II, III and aVFreciprocal ST depression in the anterior leads See also acute anterior MI . Right Bundle Branch Block and sinus bradycardia are also present.

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Acute anterior myocardial infarction ST elevation in the anterior leads V1 - 6, I and aVLreciprocal ST depression in the inferior leads

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Acute posterior myocardial infarction ( hyperacute ) the mirror image of acute injury in leads V1 - 3(fully evolved) tall R wave, tall upright T wave in leads V1 -3usually associated with inferior and/or lateral wall MI

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Old inferior myocardial infarction a Q wave in lead III wider than 1 mm (1 small square) anda Q wave in lead aVF wider than 0.5 mm anda Q wave of any size in lead II

Acute myocardial infarction in the presence of left bundle branch block Features suggesting acute MI ST changes in the same direction as the QRS (as shown here)ST elevation more than you'd expect from LBBB alone (e.g. > 5 mm in leads V1 - 3)Q waves in two consecutive lateral leads (indicating anteroseptal MI) : 

Acute myocardial infarction in the presence of left bundle branch block Features suggesting acute MI ST changes in the same direction as the QRS (as shown here)ST elevation more than you'd expect from LBBB alone (e.g. > 5 mm in leads V1 - 3)Q waves in two consecutive lateral leads (indicating anteroseptal MI)

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Acute myocardial infarction in the presence of left bundle branch block Features suggesting acute MI ST changes in the same direction as the QRS (as shown here)ST elevation more than you'd expect from LBBB alone (e.g. > 5 mm in leads V1 - 3)Q waves in two consecutive lateral leads (indicating anteroseptal MI)

hypertrophy patterns : 

hypertrophy patterns

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Left ventricular hypertrophy (LVH) There are many different criteria for LVH. Sokolow + Lyon (Am Heart J, 1949;37:161) S V1+ R V5 or V6 > 35 mm Cornell criteria (Circulation, 1987;3: 565-72) SV3 + R avl > 28 mm in men SV3 + R avl > 20 mm in women Framingham criteria (Circulation,1990; 81:815-820) R avl > 11mm, R V4-6 > 25mm S V1-3 > 25 mm, S V1 or V2 + R V5 or V6 > 35 mm, R I + S III > 25 mm Romhilt + Estes (Am Heart J, 1986:75:752-58) Point score system Left atrial abnormality (dilatation or hypertrophy) M shaped P wave in lead II prominent terminal negative component to P wave in lead V1 (shown here) See also - mitral stenosis

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Mitral Stenosis There is atrial fibrillation . No P waves are visible. The rhythm is irregularly irregular (random). There is the suggestion of right ventricular hypertrophy. Right axis deviation and deep S waves in the lateral leads. Another important feature of right ventricular hypertrophy not shown here is a dominant R wave in lead V1. The combination of Atrial Fibrillation and Right Axis Deviation on the ECG suggests the possibility of mitral stenosis . See also - aortic stenosis .

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Right atrial hypertrophy A P wave in lead II taller then 2.5 mm (2.5 small squares).The P wave is usually pointed

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Long QT interval The QT interval normally varies with heart rate - becoming shorter at faster rates. It is usually corrected using the cycle length (R-R interval) as shown opposite. normal QTc = 0.42 seconds Romano-Ward syndrome is an autosomal dominantly inherited form of long QT interval and there is a risk of recurrent ventricular tachycardia, particularly Torsade de Pointes . Ventricular premature beats (VPBs) 2 ventricular premature beats are also shown in this ECG They are broad occur earlier than normal and are followed by a full compensatory pause (the distance between the normal beats before and after the VPB is equal to twice the normal cycle length).

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Acute pulmonary embolus The following, often transient, changes may be seen in a large pulmonary embolus. an S1Q3T3 pattern a prominent S wave in lead I a Q wave and inverted T wave in lead III sinus tachycardia T wave inversion in leads V1 - V3 Right Bundle Branch Block low amplitude deflections

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Hyperkalaemia The following changes may be seen in hyperkalaemia small or absent P waves atrial fibrillation wide QRS shortened or absent ST segment wide, tall and tented T waves ventricular fibrillation

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Hypokalaemia The following changes may be seen in hypokalaemia . small or absent T waves prominent U waves (see diagram) first or second degree AV block slight depression of the ST segment

Using leads I and aVF the axis can be calculated to within one of the four quadrants at a glance: 

U sing leads I and aVF the axis can be calculated to within one of the four quadrants at a glance

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I f the axis is in the "left" quadrant take your second glance at lead II. both I and aVF + ve = normal axis both I and aVF - ve = axis in the Northwest Territory lead I - ve and aVF + ve = right axis deviation lead I + ve and aVF - ve lead II + ve = normal axis lead II - ve = left axis deviation

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library contents | ECG axis | ECG history | ECGs by Example The electrical axis at a glance ... 2 glances actually.

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causes of a Northwest axis (no man's land) emphysema hyperkalaemia lead transposition artificial cardiac pacing ventricular tachycardia causes of right axis deviation normal finding in children and tall thin adults right ventricular hypertrophy chronic lung disease even without pulmonary hypertension anterolateral myocardial infarction left posterior hemiblock pulmonary embolus Wolff-Parkinson-White syndrome - left sided accessory pathway atrial septal defect ventricular septal defect

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. causes of left axis deviation left anterior hemiblock Q waves of inferior myocardial infarction artificial cardiac pacing emphysema hyperkalaemia Wolff-Parkinson-White syndrome - right sided accessory pathway tricuspid atresia ostium primum ASD injection of contrast into left coronary artery note: left ventricular hypertrophy is not a cause left axis deviation