EKG Conference

Question 1

The action potential duration is represented by what part of the EKG?

Answer 1

Q-T interval

• usually 230-450 msec

Question 2

What occurs during the P-R interval?

Answer 2

Depolarization of Atria, Bundle Branches, Purkinje & Bundle of His

Question 3

What is the term for the following:

1. Area of EKG that includes a waveform
2. No waveform

Answer 3

Interval

Segment

Question 4

When does the SA node depolarize on the EKG?

Answer 4

Before the P wave

Question 5

When is the plateau of the action potential, as reflected on the EKG?

Answer 5

S-T Segment (no waveform)

Question 6

If all the QRS complexes were tall, how would this be seen clinically?

Answer 6

HYPERTROPHY of the ventricles (in football players for example)

• seen via XRAY –> hypertrophy of the ventricles

Question 7

Everyone has the same Q-T interval. True or False?

Answer 7

False!

NO FIXED QT INTERVAL SINCE EVRYONE HAS A DIFFERENT BASE HR

Question 8

When does depolarization of the ventricles occur?

Answer 8

QRS complex

Question 9

How is the speed of the Action Potential reflected on an EKG?

Answer 9

the timing of QRS –> narrow QRS = fast AP

slurred QRS = slow AP

Question 10

What are the slow activating AP of the heart? When are these cells depolarized on the EKG?

Answer 10

1.Sa and AV node

1. Before the Pwave
2. During the middle of the p wave = AV Nodal (activated before atrial depolarization)

Question 11

How does the His Bundle enter the left and right bundle branches?

Answer 11

through the SEPTUM

• first place depolarization of the heart is spread (depolarization starts here as well)

Question 12

The EKG provides info on contractile ability and strength of the heart. True or False

Answer 12

FALSE!

• but we can infer from the EKG various changes

Question 13

What si the value in seconds of one small box? A large box?

Answer 13

Small - 0.04 seconds

Large - 0.2 seconds

Question 14

How do you calculate HR on EKG?

Answer 14

300/ # of boxes between each QRS

Question 15

What is the main change during a tachycardia?

Answer 15

HR

• diastole is decreased, so with length-interval relationship the systole is shortened so that diastole can be prolonged a little to allow increases filling

Question 16

What are the values for the following

1. P-R Interval
2. QRS
3. Q-T interval
4. Tachycardia
5. Bradycardia

Answer 16

1. 120-200 (.12 -0.2)
2. 70-100msec (0.07-0.1)
3. 230-450 (0.23-0.45)
4. cycle length less than 0.6 seconds (600 msec) & greater than 100 beats/min
5. cycle length greater than 1 second (1000 msec) & les than 60 beats/min

Question 17

Of the precordial leads, which is strongest and why?

Answer 17

V6

• closest to left ventricle so positive deflection is largest

Question 18

Describe the location of the precordial leads.
V1
V2
V3
V4
V5
V6

Answer 18

V1 - 4th intercostal space at the right sternal border
V2 - 4th intercostal space at the LEFT sternal border
V3 - is placed halfway between V2 and V4
V4 - 5th intercostal space at the left midclavicular line
V5 - same level as V4 at the left ANTERIOR axillary line
V6 - same level as V4 at the left midaxillary line

V1 and V2 = septal leads. Electrical activity of the inter-ventricular septum is best measured in these leads.

V3 and V4 = anterior leads. Electrical activity of the anterior (front) wall of the left ventricle is best measured in these leads.

V5 and V6 = left precordial or lateral precordial leads.

Question 19

A notched QRS is often the sign of what?

Answer 19

Bundle Branch block

ex: RBBB
- As conduction through the myocardium is slower than conduction through the Bundle of His-Purkinje fibres,
- since NOT conducting through His-Prukinje system (and through muscle) - the action potential is slower and QRS is widened!!
- The QRS complex often shows an extra deflection which reflects the rapid depolarisation of the left ventricle followed by the slower depolarisation of the right ventricle.

Question 20

Can an EAD or DAD be seen on an EKG?

Answer 20

NO!!!

• no membrane potentials seen directly on EKG

Question 21

What is the mnemonic to distinguish Left & Right bundle branch block?

Answer 21

A mnemonic to distinguish between ECG signatures of Left bundle branch block (LBBB) and right, is WiLLiaM MaRRoW; i.e., with LBBB, there is a W in lead V1 and an M in lead V6, whereas, with RBBB, there is an M in V1 and a W in V6.

Question 22

What are the:

1. Inferior Leads
2. Lateral Leads
3. Antero septal

Answer 22

1. Leads II, III, avF
2. V5, V6, avL, I
3. V1-V2 = septal
   V3-V4 = anterior

Question 23

In PVC, what has changed due to changes in AP?

Answer 23

Contractility

• Ca handling

Question 24

After a PVC, will arterial pressure be higher or lower? Why does a PAUSE occur?

Answer 24

HIGHER than normal

= increased after load

• SA blocked in AV node since ventricle is still in refractory period –> recovers after this pause
• increase contractility due to PESP

Question 25

What is the last part of the heart to be activated? The first?

Answer 25

1. Epicardial Surface (endo to epi)

2. Septum

Question 26

Why does repolarization cause a positive waveform? Where does repolarization start?

Answer 26

1. Vector of depolarization is in the same direction as the vector of depolarization

(even though it is an opposite electrical event)

2, EPICARDIAL SURFACE

Question 27

What Repolarizes first, epicardium or endocardium?

Answer 27

EPICARDIUM

• shorter AP & quicker depolarization because there is a K+ current
• epicardial cells have more iTo
  = shorter AP as a result

Question 28

What are two possible causes of Left and right axis deviation?

Answer 28

1. Hypertrophy of respective ventricle (L for LAD or R for RAD)
2. Bundle Brnach block

• right block = RAD
• left block = LAD

more negative than -30 = LAD

more positive than 90 = RAD