DSA #1: Origin of Heartbeat/ECG

Question 1

The first set of leads developed were the?

Answer 1

Standard limb leads, also knows as the bipolar leads

Question 2

What is the charge of the bipolar lead of the right arm?

Answer 2

Always negative (-)

Question 3

What is the charge of the bipolar lead of the left leg?

Answer 3

Always positive (+)

Question 4

What is the charge of the bipolar lead of the left arm?

Answer 4

Whatever’s left

Question 5

What are the bipolar lead I connections?

Answer 5

1 “L”: Left arm to right arm

Question 6

What are the bipolar lead II connections?

Answer 6

2 “L’s”: Left Leg to right arm

Question 7

What are the bipolar lead III connections?

Answer 7

3 “L’s”: Left Leg to Left arm

Question 8

What were augmented unipolar leads designed for?

Answer 8

To increase the size of the signals (heart’s electrical activity) and giving s new views of that activity

Question 9

How do augmented unipolar leads compare to standard limb leads?

Answer 9

Use the same electrodes as you used for the standard limb leads. The only thing that changes is how these electrodes are connected.

Question 10

How are the three electrodes utilized in augmented unipolar leads?

Answer 10

Two of the three electrodes we had used are tied together and brought to the ground. The remaining electrode become the exploring or active lead.

Question 11

What is one of the limitations of either the augmented unipolar leads or the standard limb leads?

Answer 11

They all look at the heart from the same plane (the coronal)

Question 12

What came into use so that we could view the heart from the transverse or horizontal plane?

Answer 12

The six chest leads

Question 13

How does current flow in unipolar leads?

Answer 13

Current moving towards an active electrode produces a positive deflection, away a negative deflection.

Question 14

What is the P wave?

Answer 14

SA nodal depolarization; atrial depolarization

Question 15

What is the PR interval?

Answer 15

Depolarization travels from SA node through AV node via internodal pathway (getting to the AV node is quick!)

Question 16

What is the QRS complex?

Answer 16

Ventricular depolarization (includes bundle branches and purkinje fibers)

Question 17

What is the T wave?

Answer 17

Ventricular repolarization

Question 18

What is the QT interval?

Answer 18

Total time the ventricles spend depolarized. Measured from beginning of QRS complex to end of T wave

Question 19

What is the ST segment?

Answer 19

The tme between the end of the QRS complex and the beginning of the T wave. Along with the QRS complex, during this time the ventricle is in the absolute refractory period.

Question 20

What does the x-axis and y-axis indicate on an ECG?

Answer 20

x-axis: time

y-axis: voltage

Question 21

Why does the T-wave appear to moving in the same direction as the QRS complex did (upwards), despite the fact it represents the opposite electrical event?

Answer 21

Repolarization is heading the opposite direction (“two” negatives) and electronics perceive two negatives as a positive (+).

Question 22

What is the normal range for the PR interval (secs)?

Answer 22

0.12 - 0.20 seconds

Question 23

What is the normal range fro QRS duration?

Answer 23

up to 0.10 sec

Question 24

What is the normal range for the QT interval; and what must it be corrected for?

Answer 24

up to 0.43 sec (must be corrected for heart rate)

Question 25

What is the normal range for R-R interval (heart rate); what does it represent?

Answer 25

• Time between beats, used to calculate heart rate
• 0.6 - 1.0 sec

(heart rate: 60 - 100 bpm)

Question 26

What is the normal range for mean electrical axis?

Answer 26

-30 to +110 degrees is the widest normal range

(0 to +90 is considered normal by most)

Question 27

How much time does each square represent on the x-axis of the ECG?

Answer 27

25 mm/sec, 1 sq = 1mm so 1 sq = 1/25 = 0.04 sec

Question 28

How are calculations made on a ECG?

Answer 28

1. Figure out which seqment you are looking for
2. Count the number of squares in the segment
3. (# squares) x (0.04 sec/square)

Question 29

What would be calculated between the blue lines?

Answer 29

The PR interval

Question 30

What would be calculated between the blue lines?

Answer 30

The QRS duration

Question 31

What would be calculated between the blue lines?

Answer 31

The QT interval

Question 32

What would be calculated between the blue lines?

Answer 32

The R-R interval

*The time between two QRS complexes = instataneous heart rate

Question 33

What does the mean electrical axis tell us?

Answer 33

The net direction the depolarization or repolarization is heading, typically used for the ventricles.

Question 34

To calculate the mean electrical axis of the ventricles, what is used?

Answer 34

The QRS complex; indicating net direcion of the depolarization of the ventricles

*Normal: 0 to 90 degrees

Question 35

In a patient with left ventricular hypertrophy but a normal conduction pathway, what would you expect to see on an ECG?

Answer 35

Increase the amplitude (height) of the QRS complex

*Remember hypertrophy refers to having more muscle cells (or bigger ones), leading to more current flow during depolarization.

Question 36

What event on an ECG represents phase 0 of the ventricular action potential?

Answer 36

QRS complex

Question 37

During what part of the ECG is the ventricular condunctance for calcium the highest?

Answer 37

ST segment