ECG

Question 1

What is an ECG?

Answer 1

Electrocardiogram records the electrical activity of the heart muscle over time

Question 2

What can ECG recording monitor?

Answer 2

Heart Rate
Evaluate effects of disease or injury on heart function
Evaluate pacemaker function
Evaluate responses to medications
Record a baseline heart rhythm before, during and after testing or procedures

Question 3

What is the relationship between the standard limb leads known as?

Answer 3

Einthoven’s Law

Question 4

Explain Cardiac Vectors?

Answer 4

Electrical currents traveling in the heart can be recorded as waveforms as a part of an ECG. The direction of these electrical vectors will determine whether a positive (upright) or negative (downward) deflection is recorded.

A current may also flow perpendicular (neither to a positive or a negative pole) to a lead. In this case, a biphasic deflection occurs. A biphasic deflection is one that equals zero when the value of the positive and negative vectors are added.

Question 5

Explain Cardiac Vectors?

Answer 5

Electrical currents traveling in the heart can be recorded as waveforms as a part of an ECG. The direction of these electrical vectors will determine whether a positive (upright) or negative (downward) deflection is recorded.

A current may also flow perpendicular (neither to a positive or a negative pole) to a lead. In this case, a biphasic deflection occurs. A biphasic deflection is one that equals zero when the value of the positive and negative vectors are added.

Question 6

Describe an Artefact in an ECG?

Answer 6

Any interference resulting in suboptimal acquisition of data
Eg. Patient Moving (Gross movements, tremors, shivering), AC interference (alternating currents), loose electrodes, dry electrodes, cardiac compressions, etc.

Question 7

What data is created in an ECG?

Answer 7

Creates a 10-second view of the heart’s electrical activity (presented graphically)
Electrodes have detected an electrical current and this has been amplified, displayed and is arranged with sequenced leads and rhythm strip.

Question 8

What does the graph paper the ECG is printed on tell us?

Answer 8

A standard ECG runs at a paper speed of 25mm/sec
Each small block of ECG is 1mm^2
At a paper speed of 25mm/sec, one small black of ECG translates into 0.04secs (40ms)
Five small blocks make up 1 large block, which translates to 0.20 sec (200ms)
There are 5 large blocks per second

A diagnostic quality 12 lead ECG is calibrated at 10mm/mV, so 1mm translates into 0.1mV

Question 9

Describe the relationship between leads and electrode placement?

Answer 9

Created by either one or two electrodes, a lead provides a particular view of the electrical activity between 2 points (poles)
Each lead consists of a positive pole & a negative pole which provides an electrical picture of the heart

• A current flowing towards a positive pole causes a positive deflection
• A current flowing away from a positive pole causes a negative deflection
• A current flowing perpendicular to the lead may show a biphasic waveform or none at all

Question 10

What planes are used to view the heart?

Answer 10

Frontal (Vertical) Plane

Horizontal Plane

Question 11

Describe Biploar Leads

Answer 11

These leads compare the electrical potentials between two electrodes ( + & - ) The axis of the lead is determined by the position of the two electrodes. There are three bipolar leads - also known as the “Standard Limb Leads”
(Leads I, II, III)

Question 12

Describe Unipolar Leads?

Answer 12

These leads compare the electrical potentials between a positive (extremity) electrode and the zero potential reference point (obtained by adding the electrical potentials from all three standard limb leads)

There are three unipolar leads: aVR, aVL, and aVF
The letter A stands for augmented, the letter V indicates a unipolar lead, and the inferior letters indicate the position the electrode is placed (R = Right shoulder, L = Left shoulder, F = Left Leg/Foot)

Question 13

Explain Einthoven’s Triangle?

Answer 13

The three standard limb leads form what is known as Einthoven’s Triangle.

A schematic depiction of the relationship between leads I, II and III.
As the positive electrodes of the three standard limb leads are electrically about the same distance from the center of the heart (zero potential reference point), an equilateral triangle can be formed in the body’s frontal plane using the three axes.

Expressed mathimatically as:
Lead I + Lead III = Lead II

Question 14

Describe Precordial Unipolar Leads?

Answer 14

The precordial leads measure the difference in electrical potential between a chest electrode and the central terminal.
The precordiall leads are on a horizontal plane and give information about electrical currents traveling anteriorly and posteriorly as well ad right and left.
These leads are V1, V2, V3, V4, V5, V6

Question 15

Describe the position the electrodes are placed in?

Answer 15

V1 = 4th intercostal space to the right of the sternum
V2 = 4th intercostal space to the left of the sternum
V3 = Midway between V2 and V4
V4 = 5th intercostal space left mid-clavicular line
V5 = Left anterior axillary line between V4 & V5 at the same level as  V4
V6 = Left mid-axillary line, same as V4

aVL =
aVR =
aVF =

Lead I =
Lead II =
Lead III =