Flashcards in Exam #2: Electrocardiography Deck (42):
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
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?
How much time passes between 5mm?
0.2 sec (1 large box)
How much time passes between 1mm?
0.04 sec (1 small box)
What corresponds to 1.0 mV?
10mm (2x large boxes vertically)
Where is lead I?
+ left arm to - right arm
Where is lead II?
+ left foot to - right arm
Where is lead III?
+ left foot to - left arm
Where the standard limb leads bipolar or unipolar? What about the augmented limb leads?
Where is aVR?
+ right arm
Where is aVL?
+ left arm
Where is aVF?
+ left foot
Draw the hexaxial lead system.
List the placement of the precordial leads.
V1= R. sternal border 4th intercostal space
V2= L. sternal border, 4th intercostal space
V4= Midclavicular, left 5th intercostal space
V3= between V2 & V4
V5= anterior axillary line, in line with V4
V6= in line with V4 & V5, midclavicular
List the R-R rate as determined by counting "large boxes."
What causes left axis deviation?
End of deep expiration
Hypertrophy (systemic, valvular disease, congenital)
LBBB (occurs with wide QRS)
What causes right axis deviation?
End of deep inspiration
Moving to standing
Hypertrophy (pulmonary valve stenosis, pulmonary HTN, congenital)
RBBB (with wide QRS)
What is the normal PR-interval?
3-5 small boxes
What is the normal QRS duration?
<1-3 small boxes
What is the normal QT interval?
What causes increased voltage of QRS?
What causes decreased voltage of QRS?
Fluid in pericardium or pleural space
What are the clinical manifestations of hyperkalemia on ECG?
Tall, peaked T-waves
What are the clinical manifestations of hypokalemia on ECG?
Decreased T-wave amplitude
What is the pathophysiology underlying a PR interval that is longer than normal?
1st degree AV block
What is the pathophysiology underlying a PR interval that is shorter than normal?
Junctional rhythm or accessory pathway between the atria & ventricles
What is the pathophysiology underlying a few very large & wide QRS complexes appearing in a lead with mostly normal QRS complexes?
What is the pathophysiology underlying all very large & wide QRS complexes?