2 - ECG Flashcards
Why does the <3 have to contract?
To pump to very vital vascular beds/circulation
When someone presents chest pain, what do you in a fully equipped hospital setting and why?
ECG! To dx if cardiac or non-cardiac chest pain
What will be represented in the ECGοΌ
Fast response AP/summation of electrical activity generated by enormous no of individuals cardiac cellsοΌmyocytesοΌin the atria and ventricles
Normal cardiac cell membranes are capable of
- Polarized under RMP
- Rapidly discharge (depolarize)
- Conduct/propagate electrical currents
- *certain cells (sinus node),depolarize and repolarize automatically
Determine the phases of the fast response AP in an ECG tracing
Phase 0-1 = QRS
Phase 2 = ST segment
Phase 3 = T wave inscription
Phase 4 = TQ segment
Position of Limb Leads? Augmented Limb Leads?
Draw Hexaxial Reference System
What view of the heart will you get from limb leads? Precordial/chest leads?
Limb leads - frontal view
Chest/Precordial leads - horizontal view
Placing of precordial/chest leads
V1 - 4th ICS, just to the right of the sternum
V2 - 4th ICS, just to the left of the sternum
V4 - 5th ICS, left midclavicular line
V3 - between V2 and V4
V5 - anterior axillary at same levels as V4
V6 - midaxillary at same level as V4
Aspects of the Heart Monitored by the ECG leads?
2, 3, aVF = inferior
V5, V6, aVL = lateral
V2-V4 = anterior/septal
V1-V2 = Posterior wall
What does each horizontal line represent in an ECG tracing? Vertical?
1 horizontal = 0.04 s or 40 ms
1 vertical = 0.1 mV
What should you do first when you look at an ECG tracing? Before analysis
Look at calibration!
Should be 10 mm = 1 mV amplitude
Additional leads in children? Why do we need additional leads?
V3R, V4R (Right)
V7 (Left)
We need more leads because children are normally physiologically RV dominant = there could be some degree of RV enlargement or hypertrophy after birth
Why?
>In utero, RV is working as hard as your left since the resistance in the pulmonary vascular bed is also high)
What does a positive deflection indicate? Negative? Biphasic?
A. Positive deflection
- mean wave of depolarization spreads towards the leadβs positive poles
B. Downward/Negative deflection
- mean is away the + pole or towards the - pole
- e.g. aVR
C. Biphasic
- mean depolarization path is directed at right angles (perpendicular) to any lead axis
Segments
PR
ST
TP
Intervals
- PR
- start of P to start of Q - QRS
- Start to end of QRS - QT
- Start of QRS to end of T - R-R
P wave
- What stimulates depolarization?
- What does this represent?
- Characteristics of a normal P wave
- Abnormalities in P wave and PR interval may be due to?
- Normal values
PR segment
- Describe in location in graph?
- Represents what?
PR interval
- Normal values
- Location in the graph
- Encompasses/represents?
P wave.
- None! Automaticity
- Atrial depolarization
- Smooth and rounded
- Heart blocks/circuit conduction block in the pathway so delayed conduction of AP in the ventricles
- Normal values: Duration: less than 0.11s or 3 small sq; Amplitude: 0.5-2.5 mm
PR segment 1. End of P to the start of QRS 2. Physiologic delay in the AV node Importance: 1. To ensure ventricles are fully filled; 2. To ensure the atria has pumped everything *Normal values may vary
PR interval
- ~0.12-0.20s (3-5 small sq)
- Start of P to start of QRS
- Encompasses the beginning of excitation of atria and ventricles
QRS complex
- Normal values
- Location in the graph
- Represents?
- If the Q wave is higher than 1 mm? Normal Q wave duration?
- Normal: Duration: not more than 3 small sq (<0.10 s); Amplitude of Q wave : lower than 1 mm
- Beginning to the end of ventricular depolarization complex (QRS)
- Ventricular depolarization
- Possibly MI
- Normal Q wave: Less than 0.015s but if more than 0.03s = definite abnormal rdg
+ Amplitude:
aVL = < 2 mm
Lead I = < 3 mm
Lead II and aVF = < 4 mm
Importance of tallest R wave/QRS complex?
At this particular lead, the ventricular contraction is strongest (usually in Lead II) so it has something to do with the direction of the axis
The tracing of the ST segment is typically ____
Flat/within the baseline (or else, possibly myocardial ischemia leading to MI)
What is a J point?
Junction at which your ventricular starts to repolarize
What does nonspecific sttp wave changes mean?
Not significant.
T wave
- Normal value
- Represents what?
- If abnormal, which electrolyte could have caused it?
- 0.10-0.25 sec; amplitude: <5 mm
- Ventricular Repolarization
- K+
QT interval
- Normal values
- Represents?
- What must be done to this value?
- <0.44 sec (10-11 boxes)
- Measures total ventricular activity
- Must be corrected (QTc)
>Bazzettβs Formula: QTc/(R-R)^Β½
>Hodges method: QTc (msec) = QT (msec) + 1.75 (HR - 60)
U wave
- Normal value
- Is it always seen?
- Mechanisms why it occurs?
- Less than 1 small box (less than 0.1 mV)
- Often seen at slow HR but not always seen
- SUGGESTED mechs:
A. Delayed repolarization
B. Late repolarization
C. Long AP
Calc HR using
- QRS counting method
- R-R interval
- R waves/QRS complexes in 30 large squares or 6 sec) x 10; can be used even in arrhythmic patients
- R-R
>Using big sq: 300/R-R interval
>Using small sq: 1500/R-R interval
Origin of electrical activity
SA node
Criteria to know if rhythm is sinus?
- Each QRS is preceded by a P wave
- Constant PR interval
- P axis is w/in 0-90 degrees
Normal precordial
In adults, R wave progression
In children, malaki yung R sa V1 and V2 because R dominant
What is the mean electrical/QRS axis?
General direction in the frontal plane toward which the QRS complex vector is predominantly pointed
How to calculate for the MEA?
- Quadrant Method (Lead I and aVF)
- Three Lead Analysis (Lead I, aVF + II)
- Isoelectric Method
Differences between Pediatric and Adult ECG
- HR
- RVH in fetus
- RAD
