ECG Interpretation PDF

# ECG interpretation- from Ozmedicine ## Paper speed: - usually 25mm/sec which results in: - each "big" square = 0.2secs - each "small" square = 0.04secs ## Systematic ECG interpretation: The image depicts an ECG waveform, where the following components are labeled: - P wave - Q wave -...

# ECG interpretation- from Ozmedicine ## Paper speed: - usually 25mm/sec which results in: - each "big" square = 0.2secs - each "small" square = 0.04secs ## Systematic ECG interpretation: The image depicts an ECG waveform, where the following components are labeled: - P wave - Q wave - R wave - S wave - T wave - U wave - PR interval - ST segment - QRS complex - QT interval ## What is the rate? - Count the number of large squares in one RR interval and divide into 300: - 1.5 squares = 200 bpm - 2 squares = 150 bpm (could this be atrial flutter with 2:1 block) - 3 squares = 100 bpm (faster than this is tachycardia) - If irregular count complexes in 6 seconds (30 big squares) and multiply by 10 gives an approximate rate. ## What is the rhythm & how has the depolarisation been initiated? - **Regular:** - **Tachycardias:** - **Narrow complex:** - Sinus tachycardia - AV nodal reentrant tachycardia - Atrial tachycardia - Atrial flutter with fixed AV conduction - Wide complex (see wide complex tachycardia): - VT - Torsade de Pointes - SVT with BBB or aberrancy - Atrial flutter with WPW conduction - Pre-excited (circus movement) tachycardia (WPW anterograde conduction) - **Bradycardias:** - Sinus bradycardia - AV block - **Irregularly irregular:** - **AF:** - **Narrow complex** - **Broad complex** if WPW anterograde conduction or intraventricular conduction defect - **Atrial flutter with variable block** - **Regularly irregular:** - Multifocal atrial tachycardia - Tachycardia - **Irregular:** - VF ## What is the mean frontal QRS axis? - The mean frontal axis is the sum of all the ventricular forces during ventricular depolarisation - Normal axis is -30deg to +120deg - **Left axis deviation (LAD):** - More negative than -30deg to -90 - See left axis deviation (LAD) - Aetiology includes: - Left Bundle Branch Block (LBBB) or left ventricular hypertrophy (LVH) - LAHB - **Right axis deviation (RAD):** - More positive than +120deg to 180 - See right axis deviation (RAD) - Aetiology includes: - Right Bundle Branch Block (RBBB) or right ventricular hypertrophy (RVH) - **Rules of thumb:** - If there is an isoelectric complex in the limb leads then the axis is 90deg to that lead, check which way by looking at direction in other leads - If predominantly +ve in both I & II then it is normal - If -ve in I it is R axis deviation, -ve in II L axis - If predominantly -ve in all I, II & III then it is in "no man's land" ie NW quadrant & +ve in aVR: ventricular focus highly likely if leads are correctly placed - **Mathematical determination:** - Create a right angle triangle from 2 resultant vectors: - **Horizontal vector side determined by net sum of lead I complex:** - Length = net sum in mm (ie. subtract height of negatively directed components from height of positively directed components) - Direction of vector: to right if net sum is +ve - **Vertical side determined by net sum aVF is attached to arrow end of horizontal vector:** - Length = net sum in mm - Directed downwards if net sum +ve - The axis is the angle between the horizontal vector & the hypotenuse: ie. Inverse Tan (net sum aVF / net sum I) (nb. ensure + or - included here) ## P Wave shape: - P waves are best seen in leads II & V1 - If inverted in lead I and upright in aVR then arm leads are reversed or dextrocardia is present, but in dextrocardia there is loss of R waves in V4-6 - **P mitrale:** - Wide P waves >= 0.12secs - Notching of wide P wave in lead II with distance b/n peaks > 0.04sec - Biphasic P wave in V1 - if P-terminal force (depth of inversion x width) > 0.04 - **P pulmonale:** - Tall, peaked P waves: - Height in lead III > lead I - >= 3mm in an inferior ## P-R interval: - Normally 0.12-0.21sec - Shortened PR interval: - WPW - Normal variant - Low atrial or upper AV junctional rhythms - Accelerated AV conduction - Phaeochromocytoma - Glycogen storage disease - Fabry’s disease - Prolonged PR interval: - No dropped beats 1st degree heart block - Dropped beats: - Dropped beat after successive increasingly long PR interval - Wenckebach (Mobitz type I) - At least 2 regular, consecutive impulses conducted with same PR Mobitz type II - No conduction complete HB ## QRS width: - Normally < 0.12sec ## QRS height: - LVH ## QRS morphology: - **Tall R waves in V1:** - Thin chest wall or normal variant - RBBB - NB. slurred S wave in leads I, V5 & V6 - RVH - WPW - True posterior infarction - assoc. inf. AMI & no slurred S in V5/6, T wave upright in V1-2 - HOCM - Duchenne’s muscular dystrophy - Low placement of leads V1-2 - **RBBB:** RSR' or RSr' pattern in V1 or V2 (ie. M-shape): - QRS > 0.10sec and slurred S in leads I, V5/6 - Aetiology: - Normal variant - IHD - HT - RhHD - CHD esp. ASD, VSD, Fallot’s tetralogy - Pericarditis, myocarditis - QRS 0.09-0.10sec and slurred S in leads I, V5 or 6: - Incomplete RBBB: - < 1% of normal individuals - Secundum ASD (90% of these pts have incomplete RBBB) - QRS < 0.08sec and no slurred S in leads I, V5 or 6: - RSr' variant: - Aetiology: - 5% of normal individuals - Recording artifacts - Chest deformities - straight back syndrome, pectus excavatum - CHD eg. ASD & rarely VSD or coarctation aorta - Acquired heart disease - eg. MS - RVH - RV diastolic or volume overload - Cor pulmonale - Pulm. embolism - WPW - AVNRT - should have pseudo-S wave in leads II, III & avF - Duchenne’s muscular dystrophy - Late activation of outflow tract of RV eg. crista supraventricularis ## LBBB: - **ECG:** - QRS duration > 0.11sec - M shape in leads I, V5 or V6 - QS complex usually present in leads facing RV ie. V1 - ST elevation common in V1-4 with ST-T waves opposite in direction but <50% have small r wave in V1 - To terminal QRS direction - **Aetiology:** - Normal hearts but extremely rare in children - IHD - these pts have high incidence of LV dysfunction & CCF - Cardiomyopathy - Degenerative diseases - If present, cannot make diagnosis of LVH & Dx of AMI is difficult - see ECG Diagnosis of AMI - See LBBB ## Pathologic Q waves: - >25% of succeeding R waves - >0.04secs wide ## Q-T interval: - The QT interval on the ECG is measured from the start of QRS complex to end of the T wave - QTc refers to a QT interval "corrected" for the effect of differing heart rate to give a QT value as if the heart rate is 60bpm - If rate 60-100bpm, then QT should be less than half the RR interval - Bazett’s formula: QTc = QT / square root (RR interval) ## Prolonged QTc: - Prolonged QTc represents delayed repolarisation & predisposes to early after-depolarisations, re-entrant tachycardias, especially potentially fatal torsade de pointes VT which is most likely if bradycardia is present too. ## Shortened QTc: - Aetiology: - Hypercalcaemia - Hyperkalaemia - Digoxin intoxication ## ST segment: - **ST elevation:** - Aetiology: - AMI, variant angina - Benign early repolarisation - Pericarditis - Hyperkalaemia - Left Bundle Branch Block (LBBB) or left ventricular hypertrophy (LVH) (right precordial leads) - Mechanical (pericardiocentesis needle striking ventricle) - Electrical artefacts (artificial pacemaker, monitor) - Hypothermia - Ventricular aneurysm ## Inferior MI- ST elevation in II, III, AVF ## Anterior MI- ST elevation in V2, V3 ## Lateral MI- ST elevation in V4, V5, V6 ## L main MI- ST elevation in aVR ## T wave: - Normal T wave is asymmetric with steeper descending limb than ascending limb - Inverted T waves: - Myocardial ischaemia - Digoxin - Myocardial strain - Peaked T waves: - Aetiology: - Acute myocardial ischaemia (the hyperacute T wave) - symmetric wave form esp. if> 5-7mm height - Benign early repolarisation - Left Bundle Branch Block (LBBB) or left ventricular hypertrophy (LVH) (right precordial leads) - Hypertrophic cardiomyopathy - Hyperkalaemia - Subarachnoid haemorrhage (SAH) - Acute haemopericardium - Flattened T waves: - Aetiology: - Normal newborn infants - Digoxin - Hypothyroidism - Hypokalaemia - Pericarditis - Myocarditis - Myocardial ischaemia ## U wave: - May be prominent in hypokalaemia but may be present in normal pts