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ECG

Terms in this set (27)

What are the 10 steps to analysing an ECG?
Rhythm; rate; QRS axis; P wave; PR interval; pathological Q waves; QRS normal; ST segment; T waves; QT interval
Where are the limb leads attached?
Earth - R leg
aVR - R arm, aVF - L leg, aVL - L arm
Where are the precordial chest leads attached?
V1 - 4th ICS, R sternal edge
V2 - 4th ICS, L sternal edge
V4 - 5th ICS, L mid-clavicular line
V6 - 5th ICS, L mid-axillary line
V3 between V2 and V4, V5 between V4 and V6 in 'anterior axillary line', 5th ICS
What view of the heart does each lead offer?
1 - left lateral, 2 - left lateral, 3 - inferior
aVR - RA, aVL - L lateral, aVF - inferior
V1 and V2 - RV
V3 and V4 - septum and anterior wall
V5 and V6 - anterior and lateral wall LV
What is the calibration of the ECG recording?
1 large square - 5 small squares - 200 ms (0.2s)
1 small square - 40 ms (0.04s)
1 mV - 1 cm (2 large squares)
What do the different parts of the ECG waves correspond to?
P - atrial depolarisation
QRS - ventricular depolarisation
T - ventricular repolarisation
What is the PR interval?
Conduction from SAN to the ventricles, 120 ms - mostly due to the delay at AVN
What is the normal size of the QRS complex?
<120 ms (3 small squares)
What lead is used for the rhythm strip?
Lead with the clearest P waves - usually II
How is the heart rate calculated?
Using the rhythm strip
- count the number of QRS complexes, times by 6 (10 second strip)
- number of large squares in R-R' interval divided by 300 (or small squares divided by 1500)
300, 150, 100, 75, 60, 50
What is the 'basis' of the ECG lead?
Upwards deflection - electricity/depolarisation spreading towards positive lead
Downwards deflection - depolarisation spreading away from positive/towards negative
How can the cardiac rhythm be described and upon what basis?
Regular or irregular QRS complexes, associated with P waves
Sinus, regular rhythm - each QRS preceded by P waves, normal PR interval
Irregular - regularly or irregularly irregular
What is an extrasystole?
An ectopic beat, premature depolarisation of the atria or ventricles
Atrial - premature abnormal P wave (possibly lost in preceding T wave); ventricle - premature abnormal QRS
What is bigeminy?
Alternating sinus and ectopic beats
What are the three main types of bradycardic conduction abnormalities?
Sinus b - p before QRS, slow rate
Junctional b - no p wave, normal QRS (abnorm close to AVN, therefore p wave buried by QRS)
AV block - depends on degree of disease and speed of AVN
What are the different types of AV block?
First degree - prolonged PR interval
Second degree - Mobitz 1 (progressive PR prolongation until non-conducted P wave); Mobitz 2 (PR interval constant, intermittent failure of P conduction)
Third degree/complete - no P conduction, independent and disassociated P and QRS rhythms
What are the two main differences between the BBB?
Abnormality in His conduction - prolongs QRS
RBBB - M in V1, W in V6
LBBB - W in V1, M in V6
What is the difference between the two types of tachycardias?
Wide QRS (>0.12s) - broad complex (ventricular)
Narrow QRS (normal) complex (supraventricular)
What are the types of SVTs?
Atrial fibrillation - irregularly irregular, chaotic baseline
Atrial flutter - regular, classic 'sawtooth' baseline - rate usually 300/min (QRS 150/min in 2:1 block)
Atrial tachycardia, AVN re-entry tachycardia - regular t
What is the normal QRS axis?
-30 to +90 degrees - direction of spread of depolarisation through heart
What causes axis deviation?
RAD - RV hypertrophy (increased strain on RHS)
LAD - LV hypertrophy, poor conduction
How can the P waves be altered?
Absent - heart block, AF
Tall and peaked - enlarged RA
Broad and bifid - enlarged LA
What sort of Q waves are considered pathological?
>2 small squares tall/>1 small square wide, >25% of the R wave - eg MI, LV hypertrophy, bbb
What can alter the ST segment from its usual isoelectric position?
Elevation - MI, pericarditis
Depression - ischaemia, drugs, LV hypertrophy
What can alter the T waves?
Tall - myocardial ischaemia, hyperkalaemia
Small - hypokalaemia, pericardial effusion, hypothyroidism
Inverted - MI/ischaemia, ventricular hypertrophy, digoxin toxicity
What can change the QT interval?
Short - hypercalcaemia, digoxin
Prolonged - drugs, hypocalcaemia, inherited LQTS
What are delta waves?
Small deflection at start of QRS in WPW - accessory pathway between a and v causes short PR interval, delta waves and broad QRS
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