Chapter 36 Dysrhythmias Flashcards
Cardiac Axis
The direction of electrical current flow in the heart.
Lead Axis
An imaginary line between the (-) and (+) leads
P wave
atrial depolarization
.11 sec
PR Segment
Isoelectric line from end of P wave to beginning of QRS complex
the electrical impulse is traveling trough the AV node where its delayed.
PR Interval
Measured from beginning of P wave to end of PR segment
It reps the time required for atrial depolarization as well as the impulse delay at AV node and travel time to purkinje fibers
measures between .12 and .20 sec
QRS Complex
Depolarization of ventricles.12 sec
Q wave
first negative deflection, not present in all leads, usually small = initial ventricular septal depolarization
if abnormally present, = myocardial necrosis
R Wave
First Positive deflection of QRS
S wave
a neg deflection following the R wave
QRS duration
time required for depolarization of both ventricles
Measured from beginning of QRS complex to the J point (qrs ends and st begins)
measures between 0.4-0.10 sec
ST Segment
normally isoelectric line representing ventricular repolarization
it occurs from the J point to the beginning of the T wave
ST elevation or depression may indicate myocardial injury, ischemia, infarction, conduction abnormalities or meds
T wave
Ventricular repolarization
U wave
if present, follows the T wave and may result from slow repolarization of ventricular purkinje fibers.
an abnormal U wave may represent electrolyte abnormality (hypokalemia)
QT inteval
total time required for ventricular depolarization an repolarization
Measured from beginning of QRS complex to end of T wave
.39 sec + or - .4 sec
6 sec strip method
quick method to determine the mean heart rate
least accurate, but choice method for irregular rhythms
count # of QRS complexes in 6 sec strip and multiply by ten = rate for full min.
Big Block method
accurate if QRS comp. are regular and evenly spaced
Count big blocks between R to R and divide into 300
Sinus arrhythmia
a variant of NSR
results from changes in intrathoracic pressure during breathing
the HR increases with inhalation and decreases during exhalation
observed in healthy children and adults
Tachydysrhythmia
HR >100
decreases diastolic time and coronary perfusion time
a continued rise in HR decreases the ventricular filling time, decreasing the stroke vol.
so, CO and BP will begin to decrease
increases the work of the heart, increasing myocardial O2 demand
Bradydysrhythmias
HR <60
Slower HR reduces myocardial O2 demand
a prolonged diastole allows better coronary perfusion time
if HR is too slow= decreased CO, BP and less coronary perfusion
Premature complexes
occur when a cell group other than the SA node, becomes irritable and fires an impulse before the nxt sunus impulse is produced
the abnormal focus is called an ectopic focus, may be generated by atrial, junctional, or ventricular tissue.
If too frequent, pt may experience ss of decreased CO
Escape rhythms
may occur when SA node fails to discharge, or is blocked, or when sinus impulse fails to depolarize the vents because of an AV nodal block.
Escape rhythms/complexes serve as escape pacemaker and are seen after a pause
may originate from av junctional or ventricular tissue
they stop when the SA node or the AV node can function normally
