Exam #2: Electrocardiography Flashcards
What is depolarization?
Switching of charges on the cell membrane; positive outside relative to negative inside
How is current related to depolarization & repolarization? How is this related to the ECG tracing?
- Current only flows when there is a depolarization or repolarization event
- The ECG electrode can only detect current
By convention, flow of a positive ion away from the positive pole of an electrode appears as what? What about the opposite?
- Away= negative deflection
- Toward= positive deflection
Away= down Toward= up
What is the electrocardiogram?
A summation of all the depolarizations and repolarizations occurring in cardiac cells
What is the p-wave? What is the normal duration of the p-wave?
- A summation of atrial myocyte depolarization
- 0.06-0.11 sec
What step theoretically comes before atrial depolarization?
SA node generation of impulse that CANNOT be seen on ECG
What does the PR interval correspond to? What is the normal duration of a PR interval?
- Atrial myocyte plateau phase (Ca++ IN & K+ OUT)
- 0.12-0.2 sec
What causes the QRS complex? What is the normal duration of a QRS complex?
- Ventricular depolarization
- 0.03-0.12 sec
What is the Q of the QRS? Define Q-wave.
Septal depolarization, which is positive current moving away from the positive electrode
Any negative defection before the R-wave is a Q-wave
What is the R of the QRS?
Ventricular muscle depolarization spreading toward electrode
What is the S of the QRS?
Ventricular muscle depolarization spreading away from the electrode
What is the ST segment?
Plateau phase of the ventricular myocyte
What is the T-wave?
Ventricular myocyte repolarization
Is atrial repolarization viewed?
NO, it is buried in the QRS
What is the chart speed of an ECG tracing?
25 mm/sec
How much time passes between 5mm?
0.2 sec (1 large box)