EKG - The QT Interval Flashcards
Shortly after depolarization
the ventricles then
repolarize, which causes a
wave of repolarization to
appear on the EKG,
represented by the _____
T Wave
What is the ST segment showing?
After the ventricles are depolarized (represented by the QRS Complex), the
myocardial cells experience a brief refractory period (ST Segment) during which time they
are resistant to another stimulation.
the QT Interval measures ______
the duration of time from the beginning of
ventricular depolarization to the end of
ventricular repolarization
How to measure the QT interval
count the number of little boxes starting at the
beginning of the QRS and stopping at the end of the T-wave.
A normal QT Interval varies and depends on the _____
HR and patient’s gender.
T/F The QT Interval gets shorter as the heart rate gets faster
T (Variable)
QTc Equation
QTc = QT / the square root of the R - R Interval
QTc
Corrected QT
(adjusts for heart rate)
“normal QTc by gender
○ Men - Less than 0.43 seconds
○ Women- Less than 0.45 seconds
Most sources consider anything “greater
than ____” to be a prolonged
QT Interva
0.45 seconds
The isoelectric line is the time
when ______
the myocardial cells are restabilizing and reconstructing the resting membrane potentials
QT prolongation ____ the isoelectric line
shortens, which can be dangerous because:
If a depolarizing event (like a
PVC) occurs when the
ventricles are attempting to
repolarize (T wave), this can
trigger a dangerous
arrhythmia, like V-Tach.
Congenital reasons for QT prolongation
■ Several inherited disorders of cardiac repolarization are associated with
QT prolongation. All individuals in these families need to be screened.
■ If the inherited abnormality is found, beta blockers and sometimes
implantable defibrillators are recommended because of the risk for
sudden death from ventricular tachycardia.
■ These patients must also be restricted from competitive sports (although
modest exercise may be okay depending on results of exercise stress
testing) and must never take drugs that can prolong the QT Interval.
Acquired reasons (Antiarrhythmic drugs) for QT Prolongation
■ Many antiarrhythmic drugs at their therapeutic doses (ironically):
● Flecainide
● Quinidine
● Procainamide
● Amiodarone
● Disopyramide (Norpace)
● Nicardipine
● Sotalol (Betapace)
Non antiarrhythmic drugs that can cause QT prolongation (more FYI)
● Terfenadine and Astemizole (old antihistamines)
● Benadryl and Vistaril
● Zofran, Phenergan, and Anzemet
● Macrolide antibiotics, Fluoroquinolones, Sulfa, Chloroquine
● Tricyclics and Prozac
● Tizanidine, Oxytocin, Methadone
