ECG basic

Question 1

What are leads?

Answer 1

Leads are view of the heart

They are a perspective of electrical activity from a given direction.

Question 2

what does the P, QRS and T wave measure?

Answer 2

P= The electrical signal that stimulates contraction of the atria ( atrial systole).
QRS= The electrical signal that stimulates contraction of the ventricles ( ventricular systole)
T= the electrical signal that signifies relaxation of the ventricles. Bigger than P wave.

Question 3

what are leads I, II and III

Answer 3

They are your primary bipolar leads.

Question 4

What are leads aVF, aVL and aVF?

Answer 4

are your augmented leads

Question 5

Why do we have los of different leads?

Answer 5

Each lead gives you a different view of the heart, so when we see a change in one of the leads it tells us where about the problem is in the heart.

Question 6

Were do we put the leads?

Answer 6

Lead I (one L) ; Right Arm to Left
Lead II (two L’s): Right Arm to Left Leg
Lead III (three L’s): Left Arm to Left Leg

Question 7

where do each of the electrodes go?

Answer 7

V1
Right sternal border
In the 4th intercostal space
V2
Left sternal border
In the 4th intercostal space
V3
Halfway between V2 and V4
V4
Mid-clavicular line
In the 5th intercostal space
V5
Anterior axillary line
at the level of V4
V6
Mid-axillary line
at the level of V4

Question 8

What are the normal ranges on an ECG?

Answer 8

R-R interval: 0.6-1.2
as R-R interval gets smaller, heart rate gets faster
P wave duration: 80 ms

P-R interval: 120-200 ms
QRS duration: less than 120ms
QT interval: 420 ms
T wave duration: 160 ms
Heart rate: 60-100 bpm

Question 9

How to work out/ do calculations?

Answer 9

-Each square is 0.04 s parallel to the x axis.

-

Question 10

How to work out QRS axis?

Answer 10

• Need a lead view
• Need a 90 degree view so aVL, aVF, aVR
• we can use Lead I and aVF, or Lead II and aVL, or Lead III and aVR

1. Work out how many squares in the y direction for lead II both top and bottom and work out Net deflection
2. Now look t the 90 degree angle, work out net deflection again
3. so cardiac axis is:
   tan theta= opposite/ adjacent
   and then do tan inverse to work out the angle.
   and then subtract from 60.
   Do aVL/lead II.

Question 11

Describe the measurement on an ECG?

Answer 11

5 x 5 square.

Along the x-axis:
each small square is 0.04, and the whole length is 0.2s

Along the y axis:
each square is 0.1 mV
The whole length is 0.5 mV

Question 12

Describe the conduction system?

Answer 12

• The SA node spontaneously depolarises to trigger cardiac cycle
• Specialist conductive pathways conduct through atria and to AV node
• AV node slows transmission
• Bundle of His & branches (composed of Purkinje fibres) insulate signal and carry to bottom of ventricles
• Purkinje fibres then spread through myocardium (from endocardium to epicardium) to apex then up to base of ventricles

Question 13

How to record ECG, where do the parts go?

Answer 13

• Sticky electrodes need special placement on limbs (RA, LA and LL; Einthoven’s triangle) and chest (V1-V6; using anatomical landmarks)
• Cables attach to electrodes to transmit signal to recorder
• Leads are visual representations of cardiac activity in the coronal and horizontal planes
• All leads have a fixed cathode (+ve) and some have a fixed anode (I, II, III) and some have a virtual anode (aVR, aVL, aVF, V1-V6)

Question 14

How do you read an ECG?

Answer 14

• Lead II is the most commonly used single lead
• Specific durations and amplitudes of specific waveforms can provide information about the heart
• Cardiac axis gives the net vector of the R-wave, which is usually the largest electrical event as it is the biggest amount of muscle – normal range is -30 to +90 degrees