Lecture 24: Wave Forms

Question 1

Each cycle of cardiac contraction and relaxation begins when

Answer 1

the sinus node depolarizes spontaneously

Question 2

Is the beginning visible on the ECG

Answer 2

nope

Question 3

P wave

Answer 3

• A recording of the spread of depolarization through the atrial myocardium from start to finish
• Predominantly represents the right atrial depolarization because the sinus node is located there and depolarizes before the left

Question 4

Once atrial depolarization is complete, the ECG

Answer 4

becomes electrically silent (AV delay)

Question 5

The AV delay allows for

Answer 5

the atria to finish contracting and emptying their volume of blood before the ventricles begin to contract,

Question 6

Vagal (parasympathetic) stimulation of AV node

Answer 6

Slows the current

Question 7

Sympathetic stimulation of AV node

Answer 7

accelerates the current

Question 8

Ventricular conduction system

Answer 8

Consists of the bundle of his, bundle branches, and terminal purkinje fibers

Question 9

After the AV delay

Answer 9

the current goes down the ventricular conduction system

Question 10

Atrial repolarization is overshadowed by

Answer 10

the QRS complex

Question 11

Q wave

Answer 11

Represents the depolarization of the interventricular septum

Question 12

R and S wave

Answer 12

Represent the depolarization of the right and left ventricles

Question 13

T wave represents

Answer 13

Ventricular repolarization

Question 14

Why does the T wave have a longer duration than the QRS complex?

Answer 14

Repolarization does not proceed as a synchronized propagated wave

Question 15

Timing of repolarization is a function of properties of

Answer 15

individual cells such as numbers of particular K+ channels

Question 16

U wave

Answer 16

Rarely seen and believed to be due to slow repolarization of the papillary muscles

Question 17

PR segment

Answer 17

• Area from the end of P wave to beginning of QRS segment

- Flat portion of ECG that corresponds to AV node conduction

Question 18

PR interval

Answer 18

• Includes P wave and PR segment
• Reflects depolarization of L and R atria and the spread of the impulse through the AV node and ventricular conduction pathway

Question 19

ST segment

Answer 19

• Segment between the end of the S wave and the T wave
• Isoelectric, indicating that all ventricular muscle is depolarized
• Correlates with the plateau of action potential, Ca influx via L-type Ca channels
• Time during which the ventricles are contracting and emptying

Question 20

QT interval

Answer 20

• Represents the time from ventricular depolarization to repolarization
• Measures the total duration of ventricular activation