Waveforms, segments, and intervals Flashcards
State which electrophysiological event corresponds to the P-wave, QRS complex, T-wave, and U-wave
- P: Atrial depolarization
- QRS: Ventricular Depolarization
- T: Ventricular repolarization
- U: Unknown
An unusually long P-wave may be a sign of ______
Left Atrial Enlargement
Define the boundaries of the PR segment
end of P-wave to beginning of QRS complex
Define the TP segment and explain its significance to ECG interpretation
- Segment running from the end of one T-wave to the beginning of the next P-wave
- Least likely part of ECG to be affected by pathology so serves as a reference for establishing a baseline
PR depression may be a sign of
pericarditis
Define an interval with relation to ECGs
intervals contain one or more waveforms +/- one or more segments
What are the endpoints of the PR interval?
beginning of P-wave to beginning of QRS complex (P-wave + PR segment)
Define the QT interval.
sum of the duration of the QRS complex, ST segement, and T-wave (beginning of QRS to end of T-wave)
What property of ECGs do intervals describe?
Duration (not amplitude!)
What is the normal duration of the PR interval?
120-200ms (3-5 small squares)
What is indicated by a shortened or prolonged PR interval? Define what is meant by shortened or prolonged PR.
- Shortened (<120ms or 3 small squares): indicates an abnormal pathway for conduction from atria to ventricles (as in LGL or WPW)
- Prolonged (>200ms or 5 small squares): indicates delayed AV conduction as in AV nodal block.
What is the normal duration of the QRS interval?
<120ms (3 small squares)
What is indicated by a QRS duration >120ms?
abnormal sequence of ventricular depolarization (as in BBB) or excessive ventricular mass (LVH)
A quick approximation for an appropriate QT interval is:
no more than 1/2 the RR interval
Factors that influence appropriate QT duration are:
Age, sex, heart rate
What is indicated by a prolonged QT interval?
a QT interval that is >1/2 the RR interval indicates prolonged ventricular depolarization (long QT), which may indicate ischemia or predispose to torsades des pointes
List appropriate durations for the PR, QRS, and QT intervals
- PR: 120-200ms
- QRS: <120ms
- QT: <1/2 RR
The “J” in J-point stand for ________. The J point is defined as
Junction.
The J point indicates where the QRS complex meets the ST segment
What is the Bazzett formula for QTc?
QTc= QT / √ RR
What are normal QTc intervals for men and women?
- QTc is prolonged if > 440ms in men or > 460ms in women
- QTc > 500 is associated with increased risk of torsades de pointes
- QTc is abnormally short if < 350ms
