Electrocardiography Flashcards
What abnormalities can an ECG detect?
Conduction - issues with e- signals
Structural - e.g. hypertrophy
Perfusion - blood flow changes
What are the advantages of an ECG?
Cheap,
Reproducible,
Quick
What are electrodes
patches you place on patient’s skin
What are cables
connection between electrode and machine
What are leads
Views of the heart from electrodes and cables
12 leads
What deflections are towards the +/-ve electrode
Upward deflection -> +ve
Downwards deflection -> -ve
What is represented by the isoelectric line
No change in voltage
What is denoted by the steepness of the deflection
Velocity of action potential
What is denoted by the width of deflection
X axis = time .: shows duration of event
In the cardiac cycle, what does the P wave represent?
Atrial Systole (atrial contraction)
In the cardiac cycle, what does the QRS complex represent?
Ventricular Systole (ventricular contraction)
In the cardiac cycle, what does the T wave represent?
Diastole (relaxation of ventricles, repolarisation)
Why is repolarisation of the atria not seen
Hidden within the QRS complex
Why does the AVN cause a slow speed of transduction
Allow time for ventricular filling after atrial contraction
What structure is involved in the Q wave, and what is its function?
Bundle branches - Septal depolarisation
Describe the vector of the Q wave
Towards negative electrode, so downward deflection
What structure is involved in the R wave, and what is its function?
Purkinje Fibres - ventricular septal depolarisation
Describe the vector of the R wave
Towards positive electrode (apex of heart), upward deflection
What structure is involved in the S wave, and what is its function?
Purkinje fibres - late ventricular depolarisation (outer ventricle walls)
Describe the vector of the S wave
Towards negative electrode (cardiac great vessels), downward deflection
Describe the direction of Lead I
1 L: Right Arm to Left Arm
Describe the direction of Lead II
2 Ls: Right Arm to Left Leg
Describe the direction of Lead III
3 Ls: Left Arm to Left Leg
What plane does Lead I/II/III use
Coronal
What view does Lead I give
Lateral
What view does Lead II/III give
Inferior
What plane do the V electrodes use?
Axial/horizontal
What is the position of V1?
Right sternal border in the 4th intercostal space
What is the position of V2?
Left sternal border in the 4th intercostal space
What is the position of V4?
Mid-clavicular line in the 5th intercostal space
What is the position of V3?
Halfway between V2 and V4 (diagonal)
What is the position of V5?
Anterior axillary line at the same level as V4
What is the position of V6?
Mid-axillary line at the same level as V4
What does the width of one big box on an ECG show?
0.2s
What does the width of one little box on an ECG show?
0.04s
What are the three active peripheral leads?
aVR, aVL, aVF
Describe the location of these peripheral leads and how this relates to their naming
aVR (augmented vector right - from Right hand)
aVL (augmented vector left - from Left hand)
aVF (augmented vector foot - from the foot of the inverted triangle)
Which leads use a coronal plane
Limb leads (I/II/III/aVL/aVR/aVF)
Which leads use a Horizontal plane
Chest leads (V1-6)
What leads give an inferior view
RCA
Lead I/II/aVF
What leads give an lateral view
LCx
Lead I/aVL/V5/V6
What leads give an antero septal view
LAD
Lead V1/2
anterior - V3/V4
What is the cardiac axis
Net direction of e- activity during depolarisation (R wave)
Where would a normal cardiac axis be between?
90 and -30 degrees
What region shows left axis deviation
-90º to -30º
What region shows right axis deviation
90º to 180º
what region shows extreme deviation
-90º to -180º
How would you calculate the cardiac axis using Lead II and aVL?
STEP 1 - work out net deflection of Lead II (highest amplitude + lowest amplitude (negative) /// STEP 2 - work out the net deflection of aVL /// STEP 3 - draw a right angle triangle - hypotenuse is cardiac axis, adjacent is lead II, opposite is aVL /// STEP 3 - figure out SOHCAHTOA - should be tan but just double check /// STEP 4 - Do the SOHCAHTOA
find some qs and practice
