1What causes a positive deflection on an EKG?
Flow of positive charges/depolorizaiton towards a positive electrode OR!! flow of negative charges or repolorization towards a negative electrode
When cells depolarize towards the positive electrode/away from the negative electrode; Na and K ions move through gap junctions from cell to cell, propagating electrical signcal through the tissue. This action changes the resting (slightly negative) cell, with the charge turning it positive. This flow of positive charges moving towards the positive electrode causes the positive deflection (line spikes up then returns DOWN towards isoelectric line)
2What causes a negative deflection on an EKG?
Flow of positive charges/depolarization from a positive electrode towards a negative electrode/away from the positive electrode (line then returns up towards isoelectric line)
3Describe the positioning of electrodes with lead II
- negative electrode on R arm
- positive electrode on L leg
4What is happenning when the isoelectric line in maintained on the EKG? (No movement on the EKG)
- no net movement of electrical activity OR
- electrical activity is occurring perpendicular to the axis of that lead
5When is the PR segment? And the PR interval?
PR segment = end of P-wave to very beginning of QRS
PR interval = beginning of P-wave to very beginning of QRS
6Normal PR interval
<0.2 sec (<1 large box)
7Normal QRS
<0.12 sec
--> narrow = normal
8What is the QT-interval? What is normal?
Time from the beginning of the Q-wave to the end of the T-wave; prolonged QT-interval increases risk for torsades de pointes
- males <430 millisec
- females <460 millisec
9What is represented by the P-wave?
Firing of the SA node with "mean" energy towards AV node
10What does the Q-wave represent?
Q-wave represents septal depolarization, which is done largely by the L bundle branch
11What happens to the Q wave and R wave throughout the precordial leads?
From V1 to V6, the Q wave increases in amplitude and the R wave decreases in amplitude
12What portion of the heart is viewed by lead I?
high lateral wall of left ventricle
13What leads view the right ventricle?
V1-V3 and avR
14What leads view the inferior wall of the heart?
leads II, III, and avF
15What leads view the septal wall of the heart
Leads V1 and V2
16What leads view the right ventricle?
Leads avR, V1, and V2
17What leads view the anterior wall of the heart?
V3 and V4
18What leads view the anteroseptal area of the heart?
V1 through V4
19What leads view the lateral wall of the heart?
leads I, aVL, V5, and V6
20How much time is represented by 5 mm of EKG paper?
0.2 sec (one large box)
21How much time is represented by 1 mm of EKG paper?
0.04 sec (one small box)
22Discuss the system approach to 12-lead EKG interpretation
Check the rhythm strip first!
1. Rate
- rhythm strip (~10 sec), R waves x 6
- box method: 300 / r-r interval in LARGE squares
2. Rhythm - regular or irregular
- R-R interval constant or not?
3. QRS - narrow or wide
- < or > 0.12 sec
4. Sinus p-waves present
- upright P-wave in Lead II? Inverted P-wave in avR? Every P followed by QRS?
5. P-R interval (normal is <0.2 sec)
- normal, prolonged, constant, variable, progressively longer?
23What measurement is considered STEMI?
- 1mm ST-E in 2 contiguous leads EXCEPT V2 and V3
--> in leads V2 and V3, 2 mm of ST-E is required
24What measurement is considered ST-depression?
- need 0.5 mm ST-D in 2 contiguous leads
- horizontal ST-D is most concerning for ischemia; however, upsloping ST-D with peaked T-waves in V1-V3 is concerning for proximal LAD occlusion
- DDx: NSTEMI, post MI, LBBB, LVH with strain pattern, reciprocal changes, digoxin toxicity