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45 Cards in this Set
- Front
- Back
What are the normal axis values?
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-30 to +90
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If there was left axis deviation, where would the axis lie?
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-30 to -90
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If there was right axis deviation, where would the axis lie?
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+90 to +180
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What does the electrical axis represent?
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Average direction of the heart's electrical activity during ventricular depolarisation
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What leads are used to determine the electrical axis?
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Leads:
I II III aVr aVl |
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Describe the quadrant method
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On the basis of QRS deflection in lead I and aVf
Lead I shows whether the impulses are moving right or left Lead aVf shows whether the impulses are moving up or down |
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Describe the degree method
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1. Review all 6 leads, identify the one that contains either the smallest QRS complex/ complex with equal deflection above and below the baseline.
2. Use the Hexaxial diagram to identify the lead at 90 degrees to this lead 3. Is this lead mostly negative or positive? |
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Name 5 factors the influence the location of the axis
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1. Heart's position in the chest
2. Heart size 3. Patient's body size/ type 4. Conduction pathways 5. Force of electrical impulses being generated |
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In which direction does the electrical axis swing when there is damage or necrosis?
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Away from the damaged area, therefore that area of the heart will be the last to be depolarised.
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What kind of deviation will infants and children have?
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Right axis deviation
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What kind of deviation will pregnant women have?
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Left axis deviation
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Name 6 causes of right axis deviation
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1. RBBB
2. Left posterior hemiblock 3. Lateral wall MI 4. Emphysema 5. RV hypertrophy 6. NORMAL |
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Name 8 causes of Left axis deviation
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1. LV hypertrophy
2. Inferior wall MI 3. Left anterior hemiblock 4. LBBB 5. Ageing 6. Mechanical shifts 7. WPW syndrome 8. NORMAL |
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Name 3 causes of mechanical shifts
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1. Ascites
2. Pregnancy 3. Tumours |
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Why is left axis deviation common in the elderly?
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From fibrosis of the anterior fascicle of the left bundle branch
From thickness of the left ventricular wall (increased) |
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In which leads is the P wave always positive and negative?
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Always positive in Lead I and II
Always negative in aVr |
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How many small squares should a P wave be in duration and amplitude?
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Less than 3 small squares in duration
Less than 2.5 small squares in amplitude |
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In which lead is the P wave normally biphasic?
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Lead V1
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What happens to the P waves in right atrial enlargement?
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They become tall and pointed (P pulmonale)
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What happens to the P waves in left atrial enlargement?
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They become notched/ bifid (m shaped) (p mitrale)
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What is the normal PR interval?
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0.12-0.20ms (3-5 small squares)
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What causes the PR interval?
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Atrial depolarisation and delay in AV junction (AVN/ bundle of HIS)
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What does a long PR interval indicate?
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1st degree heart block
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What does a short PR interval indicate?
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Accessory pathway/ WPW syndrome
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Where might non- pathological Q waves present?
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I
III aVl V5 V6 |
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How big is a pathological Q wave?
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More than 2mm deep and more than 1mm wide
OR 25% the amplitude of the subsequent R wave |
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What does a pathological Q wave suggest?
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Previous MI
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Name 4 conditions that have a tall R wave in V1
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1. Right ventricular hypertrophy
2. Posterior MI 3. Type A WPW syndrome 4. RBBB (A tall R wave in children in lead V1 is NORMAL) |
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In which leads can you recognise left ventricular hypertrophy?
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V1 = tall S wave
V5/6 = tall R wave (more than 35mm) aVl = R wave (more than 11mm) BASICALLY: QRS voltage increases with LVH |
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What happens to the QRS complex in bundle branch block?
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It widens (above 0.12ms)
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What happens to the QRS complex in RBBB?
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In leads overlying the right ventricle (V1 and V2) the QRS complex looks like RABBIT ears or an M
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What happens to the QRS complex in LBBB?
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In V1 and V2 there are broad, deep S waves
Looks like a W |
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What is the acronym for RBBB and LBBB?
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RBBB= MaRRoW - M in V1 and W in V6
LBBB= WiLLiaM - W in V1 and M in V6 |
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What is the J point?
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Point between the QRS and ST segment
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What does an elevation of the ST segment represent?
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Acute MI
Greater than 1 small square in 2 leads |
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Give 3 causes of ST depression
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1. Ischaemia
2. LVH with strain 3. Digitalis toxicity |
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What does T wave inversion suggest?
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MI
Ischaemia |
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What are the changes seen in MI/ Ischaemia?
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Q waves
ST segment elevation/ depression T wave inversion |
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What does the QT interval represent?
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The total duration of depolarisation and reploarisation
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What happens to the QT interval when heart rate increases?
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It decreases
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What should the QTc be?
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Less than 0.44s in males
Less than 0.46s in females |
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What is the risk with a prolonged QT interval?
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Ventricular arrhythmia
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What is a U wave?
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They are related to after depolarisations which follow repolarisation
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What should the look like?
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Small, round and symmetrical
Positive in lead II with an amplitude of less than 2mm (The direction should be the same as the T wave) |
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When is the U wave more prominent?
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At slow heart rates
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