EKG

Question 1

What can an EKG tell?

Answer 1

1) anatomical orientation of the heart;
2) size of the chambers;
3) rhythm and conduction disturbances;
4) cardiac injury;
5) effects of drug or electrolyte disturbances

Question 2

What are the conventions of the x and y axes of an EKG?

Answer 2

x-axis = TIME each large box (5 mm) = 0.2 sec; each small box (1 mm) = 0.04 sec
y-axis = VOLTAGE  each large box (5 mm) = 0.5 mvolt; each small box (1 mm) = 0.1 mvolt

Question 3

What is the P wave?

Answer 3

atrial depolarization

Question 4

What is the QRS complex?

Answer 4

ventricular depolarization

Question 5

What is the T wave?

Answer 5

ventricular repolarization

Question 6

What is the RR interval determine?

Answer 6

Heart rate

Question 7

What does the PR interval determine?

Answer 7

The delay of an electrical impulse by the AV node that allows atrial emptying

Question 8

What does the QRS duration determine?

Answer 8

The health of the His/Purkinje system

Question 9

What does the QT interval determine?

Answer 9

The measure of an action potential width of ventricular myocytes

Question 10

What does the ST interval determine?

Answer 10

The plateau phase of an action potential in ventricular myocytes

Question 11

How can a heart rate be calculated?

Answer 11

60 sec/min // R-R rate (sec/beat)

Question 12

What is the electrical basis of EKG?

Answer 12

Electrodes detect direction in which a depolarization is happening (+ if towards the electrode or - if away from the electrode) and the intensity of the depolarization as a result of tissue mass–large tissues tend to have larger depolarizations

Question 13

Why is the T wave positive on an EKG?

Answer 13

Repolarization starts in the epicardium and works deep to the endocardium so the direction of the vector is opposite of the anticipated; with a negative vector and a negative electrical change, the overall magnitude of the vector is positive and points towards the electrode

Question 14

What are the three standard limb leads?

Answer 14

1) Right arm (-) to Left foot (+)
2) Right arm (-) to Left foot (+)
3) Left arm (-) to Left foot (+)

Question 15

What are the three augmented limb leads?

Answer 15

1) Right arm (+) and the sum of left arm and left foot (-)
2) Left arm (+) and the sum of left foot and right arm (-)
3) Left leg (+) and the sum of the right arm and left arm (-)

Question 16

What are the points of the Einthoven triangle?

Answer 16

The shoulders and umbilicus/groin

Question 17

What is the normal mean QRS axis and what are the two conditions necessary to fulfill it?

Answer 17

between -30 degrees and +90 degrees

QRS must be positive in Lead 1 and Lead 2

Question 18

How can the axis be determined?

Answer 18

1) Find the isoelectric lead. The vector is perpendicular to this lead.
2) Determine if the perpendicularity is positive or negative depending on nearby leads

Question 19

Factors that can cause an abnormal axis

Answer 19

1) Physical–posture, height, weight

2) Pathological–ventricular hypertrophy, myocardial damage, or bundle branch block

Question 20

What are precordial leads?

Answer 20

Leads placed transversely across the chest (V1-V6) to determine the vector within the chest; V4 is usually the isoelectric vector

Question 21

What is the most common cause of a long QT interval?

Answer 21

Genetic mutation of many ion channels (collectively termed congenital long QT syndromes), drugs, as well as metabolic and electrolyte disturbances

Question 22

What are clinical concerns for a long QT interval?

Answer 22

syncope and potentially fatal arrhythmias

Question 23

Which channel can have genetic mutations that affect the ability of a cell to repolarize?

Answer 23

KCNH2 (hERG)

Question 24

What is the consequence of a genetic mutation in hERG channels?

Answer 24

Ca++ channels can recover from inactivation before the tissue is repolarized and premature action potentials can fire