Physiological basis for ECG Flashcards
what does the ECG measure
Potential DIFFERENCES between recording electrodes generated by electrical currents projecting from the heart to body surface during depolarization and repolarization
measures the sum of electrical potentials generated by the conduction of electrical depolarization and repolarization in the heart as projected to the body surface
what do different EKG leads do?
view electircal vectors of the heart from different angles, providing information about electrical activity in different regions
what info can EKG’s give
LOTS
Hypertrophy and Enlargement Rate and Rhythm Abnormalities Conduction Abnormalities Ischemia and Infarction Electrolyte Disturbances, Drug Effects, etc.
what 3 things contribute to reproducible rate and rhythm observed on the ECG
automaticity
conduction system
functional synctium (cell to cell via gap junctions)
what is the p wave
atrial depolarization
begins at the SA node and spreads toward the AV node
right atrium begins to depolarize before the left
***immediately precedes atrial contraction
what is the QRS complex
ventricular depolarization (atria repolarizing simultaneously)
IMMEDIATELy precedes ventricular contraction
atria remain contracted until repolarization
ventricles remain contracted until after the T wave of repolarization
what is the T wave
ventricular repolarization
if the first deflection is downward
Q wave
the first upward deflection is
the R wave
second upward deflection
R primary
the first downward deflection following an upward deflection
S wave
if the entire configuration consists solely of one downward deflection
QS wave
if the first wave of the complex is an R wave, the following downward deflection is ….
an S wave NOT a Q wave
if there is a downward deflection only then it is a
Q wave if is the first wave of the complex
in which direction does repolarization normally travel?
begins at the last area that was depolarized, travels toward the base of the heart in the opposite direction of depolarization
slower than ventricular depolarization
5 large squares =
1 second
so one little square is 0.2 seconds
2 large squares vertically
1 mV
what is the PR interval? why is it important?
represents the time from the start of atrial depolarization to the start of ventricular depolarization
includes AV node delay time for filling
normally 0.12-0.2 seconds (just over 2 small squares)
important for identifying conduction blocks
what is the ST segment and why is it important clinically?
Represents time from end of ventricular depolarization to start of ventricular repolarization
Generally horizontal or gently up-sloping in all leads
***Deviation from isoelectric line indicates myocardial ischemia or injury
what does ST elevation indicate
MI
acute pericarditis
LVH
hyperkalemia , etc.
what is the QT interval
beginning of ventricular depolarization to end of ventricular repolarization
includes all electrical events occurring in the ventricles
HR dependent
more time in repolarization phase (t wave is wider than QRS)
what are the causes of long QT syndrome?
Congenital:
-mutant Na (failure to inactivate)
K+ (Defective repolarization)
Acquired:
-electrolyte imbalances, pharmacological, etc.
what is the length of the QT interval
less than or equal to 0.44 seconds
what are the two ways of determining heart rate
counting boxes 300–> 150–> 100 –> 75–> 60 –> 50–> 43–> 38–> 33–> 30)
or by estimating HR by number of R-R intervals in 6 secs x 10
(#R-R/6 sec x 10) = bpm
(3 seconds between each tick)
