Nordgren: The Electrocardiogram

Question 1

What is the most widely used cardiac imaging technique?

Answer 1

Echocardiography

-non invasive and provides 2 and 3 dimensional images of the heart

Question 2

How does echocardiography work?

Answer 2

Images are made by sending a pulse of ultrasound (sound waves) into tissue using an ultrasound transducer. The sound reflects and echoes off of parts of the tissue. The echo is recorded and displayed as an image.

Question 3

The longer time between wave transmission and the return of the reflected wave is indicative of…

Answer 3

A deeper structure.

Question 4

What is doppler electrocardiography?

Answer 4

Measures and visualizes the speed and direction of the blood flow.

Question 5

What is the doppler effect?

Answer 5

The apparent change in the f of a wave caused by relative motion between the source of the wave and the observer. As sound waves move toward an observer there is an increase in the perceived f/pitch d/t compression of the wave front. As the sound waves move aaway, there is a decrease in perceived f/pitch.

Question 6

How do you read a color doppler?

Answer 6

red- blood moving toward the probe

blue- blood moving away from the probe

Question 7

What is cardiac angiography?

Answer 7

Used to visualize the interior of the heart chambers and the blood vessels. (looks for blockage/narrowing of the lumen). This is done by injecting a radio-opaque contrast agent into the blood vessel and using x ray based techniques like flluoroscopy to read it.

Question 8

What is MUGA?

Answer 8

Multigated acquision scan (radionuclide ventriculography)

An intravenous injection of a radioactive isotope (usually technetium) that labels RBC and an image is created using a gamma camera. It provides an image of the heart pumping blood.

Question 9

How are ESV and ESP used to assess contractility?

Answer 9

You can get ESV using several imaging techniques, and ESP is obtained from arterial pressure recorded at the point of aortic valve closure. You can then plot them on a PV loop. A decrease in contractility may be caused by heart disease and is associated with a downward shift of the ESPVR line.

Question 10

What is a normal EF?

Answer 10

55%

Question 11

What usually accompanies heart failure?

Answer 11

Reduced EF

Question 12

What is the Fick principle?

Answer 12

Calculates the rate at which a substance is being added or removed from the blood as it passes through an organ.

Question 13

What is the equation for the Fick principle?

Answer 13

Q (flow rate)= Xtc (amt of substance consumed)/ ([Xa- what goes in]- [Xv- what goes out])

Resulting in a measurement of cardiac output.

Question 14

What is the cardiac index?

Answer 14

Relates cardiac function to the size of the individual.

CI=CO/BSA

Question 15

What is an ECG used for?

Answer 15

1. It’s used to evaluate cardiac electrical properties:
   excitation rate, excitation rhythm, impulse conduction
2. The results of current propagated through the extracellular fluid (currents are generated by a wave of excitation that travels through the heart)

Question 16

What is the conduction time through the atria and AV node?

Answer 16

120-200 msec

Question 17

How long does ventricular depolarization take?

Answer 17

60-100 msec

Question 18

What is the total duration of ventricular systole?

Answer 18

<380 msec at normal HR= 60 bpm

Question 19

What are the three ECG regions of no voltage?

Answer 19

1. End of the PR interval
2. ST segment
3. Time between T wave and next impulse generated by the SA node

Question 20

What causes no voltage at the end of the PR interval?

Answer 20

Depolarization wave reaches a non-muscular (non-excitable) border between the atria and ventricles. The atrial muscle cells are depolarized (phase 2), the ventricular cells are still resting. The electrical field created during the passage through the AV node is too small to see.

Question 21

Why is there no voltage in the ST segment?

Answer 21

There are no rapid changes in membrane potential occuring anywhere. The atrial cells returned to resting and ventricular cells depolarized (phase 2).

Question 22

What might you observe in the ST segment if there is a myocardial injury or inadequate blood flow?

Answer 22

A depressed or elevated ST segment

Question 23

What is einthoven’s Triangle?

Answer 23

Recording electrodes are placed on R and L arms and on the L leg creating a triangle around the heart. An ECG trace then records the voltage difference between two points on this triangle using bipolar limb leads.

Question 24

What is recorded by an ECG?

Answer 24

The net dipole of a cardiac impulse (the spreading wave of depolarization).

Question 25

What determines the magnitude of the dipole?

Answer 25

1. How many cells are depolarizing

2. Consistency of individual dipole orientation

Question 26

What does an upward deflection on an ECG tell you?

Answer 26

The wave of depolarization is moving TOWARD the + electrode.

Question 27

What does a downward deflection on an ECG tell yoU?

Answer 27

The wave of depolarization is moving AWAY from the + electrode.

Question 28

What causes ventricular depolarization?

Answer 28

Rapid and large changes in the direction and net dipole.

Question 29

Where does ventricular depolarization begin?

Answer 29

Depolarization begins LEFT of the intraventricular septum.

Question 30

What ventricular cells are the first to repolarize?

Answer 30

the last to depolarize

Question 31

Why is a T wave a POSITIVE deflection?

Answer 31

The net cardiac dipole is oreinted in the same direction during repolarization as during depolarization. A negative wave front approaching a negative lead–> double negative signal that is translated as a positive deflection.

Question 32

What is the mean electrical axis?

Answer 32

The orientation of the cardiac dipole during the most intense phase of ventricular depolarization (R wave).

Question 33

What is a normal axial deviation?

Answer 33

0-90

Question 34

What can cause left axis deviation <0 degrees?

Answer 34

1. Physical displascement of heart to the left
2. left ventricular hypertrophy
3. loss of electrical activity to the right ventricle

Question 35

What can cause right axis deviation > 90 degrees?

Answer 35

1. Physical displacement of heart to the right
2. right ventricular hypertrophy
3. loss of electrical activity to the left venticle

Question 36

How do you calculate MEA using R waves?

Answer 36

Find the largest R wave and follow that diplole. If the wave is negative than the dipole is in the opposite direction.

Question 37

How do you calculate MEA using vectorcardiography?

Answer 37

Graphical representation of ALL the net dipole amplitudes throughout hte entire length of the cardiac cycle. Follow hte ECG and trace all the dipole head orientations around hte axial reference system.

Question 38

What are augmented leads?

Answer 38

Unipolar limb leads. One positive electrode is referenced against a combination of other electrodes.

Question 39

How do you use the equiphasic approach to calculate MEA?

Answer 39

1. Determine which leads contains the most equiphasic QRS complex.
2. Determine which lead lies 90 deges away from the most equiphasic lead and look at the tracing.
3. If the QRS complex is predominantly + then the direction of this lead is approximatley the QRS axis. If hte QRS is predominantly negative, then the QRS axis is 180 degrees away from teh direction of this lead.

Question 40

What is a 6 lead ECG?

Answer 40

Records electrical activity of hte heart as it appears from a frontal plane using bipolar and augmented unipolar leads.

Question 41

What is a 12 lead ECG?

Answer 41

An additional 6 chest or precordial unipolar lead that looks at electrical activity in the transverse plane. Placed along the chest wall and designated as V1 through V6.