Electrocardiogram Flashcards
define an Electrocardiogram
Summation of all the depolarizations and repolarizations in a cardiac cycle
Define the P wave
Summation of:
- lots of atrial myocytes depolarization
- Positive charge moving towards electrode causes Upward deflection
- generation of SA node it not detectable
- 1-2 Small boxes in length
Define the QRS complex
Summation of lots of ventricular myocytes depolarizing
- Q = slight negative deflection - small due to correspondence with septal depolarization
- R = positive (upward) deflection - ventricular muscle depolarizing spreading towards electrode
- S = negative (downward) deflection - ventricular muscles depolarizing spreading AWAY from electrode.
- -> 1-3 small boxes in length
What is occurring between P wave and QRS complex? (P-R interval)
Plateau of action potential caused by prolonged opening of Calcium channels results in no net movement of ions and thus no current is measured on ECG between P and QRS waves
–> 1-3 small boxes
Define T wave
Summation of:
- lots of ventricular cells REPOLARIZING
- reversal of charge movement makes direction of QRS and T waves similar.
- -> variable in length
What is occuring between S and T waves (S-T segment)
Corresponds to all the PHase 2’s of ventricular muscle
- plateau in AP caused by calcium channels
- -> variable in length (roughly half of R-R interval)
Define Q-T interval
ventricular action potential duration (initiation of ventricular depolarization to end of ventricular repolarization
–> variable (with HR) (gets shorter with high HR)
Define the six Frontal plane leads (limb leads)
Standard Leads (bipolar leads) - I = negative electrode on right wrist with positive electrode on left wrist - II = Negative electrode on right wrist with positive electrode on left ankle - III = Negative electrode on left wrist with positive electrode on left Ankle Unipolar Limb Leads: - aVR = augmented voltage - right arm (+) - aVL = augmented voltage - left arm (+) - aVF = augmented voltage - left foot (+)
Describe the (Transverse/Horizontal plane) chest lead placement
V1: 4th intercostal space, R sternal border (Right atria)
V2: 4th intercostal space, L sternal border
V4: 5th L intercostal space in midclavicular line
V3: Between V2 and V4
V5: in line with V4, in anterior axillary line (L. Ventricle)
V6: in line with V4 and V5, in midaxillary line (L. ventricle)
What to look for in a ECG
- Rate and regularity
- Mean QRS axis in the frontal plane
- Rhythm (intervals, waveform morphologies)
How is rate determined and normal value.
determined from R-R interval generally. (#large boxes divided by 300)
- Bradycardia = RESTING HR under 60 bpm
- Tachycardia = RESTING HR over 100bpm
What are some key points about vector analysis
- voltage recorded in the ECG will be GREATEST when the vector is PARALLEL to lead
- voltage recorded in the ECG will be LEAST when vector is PERPENDICULAR to lead
What would an increased QRS voltage be due too?
- Hypertrophy (more muscle that is depolarizing)
- Thin chest (can detect voltages better
What would a decrease QRS voltage be due to?
- Previous MI (less muscle, also wide QRS)
- Fluid in pericardium or pleural space (dampens signal that reaches outside surface of body)
- Large chest size, pulmonary emphysema insulate charge and reduce what reaches the surface
Describe how to find the approximation of axis of the QRS
1) look at lead I and aVF
2) “normal” vector was 60 degrees which would make leads I and aVF normally positive
- Right axis deviation = I neg; aVF positive
- Left axis deviation = I positive; aVF negative
- Indeterminant axis = Both negative
* *How do you check your approximation??**
Define Lead I
- Lead I runs from RA to LA, positive pole on LA
- Atrial depolarization will yield small positive deflection in lead I due to the vector pointing down and to the left
- Ventricular depolarization will lead a larger positive deflection in lead I due to vector point down and to left.
Define Lead II
- Runs from RA to LL, Positive pole on LL
- SAME atrial depolarization vector will yield a small positive in lead II
- SAME ventricular depolarization vector will yield a larger positive deflection in lead II (since vector is MORE Parallel to lead II)
Define Lead III
- lead III runs from the LA to the LL, positive pole on the LL
- Vectors can be almost perpendicular to the axis of this lead so the deflections of the superimposed vectors are small
Define Lead aVR
- lead aVR is a positive axis to RA
- “negative” pole is the grounding axis perpendicular to RA axis (looks a lot like lead III)
- SAME atrial depolarization will yield a small NEGATIVE deflection in lead aVR
- SAME ventricular depolarization will yield a BIGGER NEGATIVE deflection in lead aVR
Define Lead aVF
- lead aVF is a positive axis to LL (foot)
- Negative axis looks like Lead I
- SAME atrial depolarization will yield a small POSITIVE deflection in lead aVF (positive charge moving towards positive pole)
- SAME ventricular depolarization will yield a POSITIVE deflection in lead aVF
Define Lead AVL
- Lead aVL is a positive axis to LA
- NEGATIVE axis looks like lead II
- SAME atrial depolarization will yield small positive deflection in lead aVL (axis of atrial depolarization almost perpendicular)
- SAME ventricular depolarization will yield a small positive deflection (almost perpendicular)
