Lecture 24: Wave Forms Flashcards
Each cycle of cardiac contraction and relaxation begins when
the sinus node depolarizes spontaneously
Is the beginning visible on the ECG
nope
P wave
- A recording of the spread of depolarization through the atrial myocardium from start to finish
- Predominantly represents the right atrial depolarization because the sinus node is located there and depolarizes before the left
Once atrial depolarization is complete, the ECG
becomes electrically silent (AV delay)
The AV delay allows for
the atria to finish contracting and emptying their volume of blood before the ventricles begin to contract,
Vagal (parasympathetic) stimulation of AV node
Slows the current
Sympathetic stimulation of AV node
accelerates the current
Ventricular conduction system
Consists of the bundle of his, bundle branches, and terminal purkinje fibers
After the AV delay
the current goes down the ventricular conduction system
Atrial repolarization is overshadowed by
the QRS complex
Q wave
Represents the depolarization of the interventricular septum
R and S wave
Represent the depolarization of the right and left ventricles
T wave represents
Ventricular repolarization
Why does the T wave have a longer duration than the QRS complex?
Repolarization does not proceed as a synchronized propagated wave
Timing of repolarization is a function of properties of
individual cells such as numbers of particular K+ channels
U wave
Rarely seen and believed to be due to slow repolarization of the papillary muscles
PR segment
- Area from the end of P wave to beginning of QRS segment
- Flat portion of ECG that corresponds to AV node conduction
PR interval
- Includes P wave and PR segment
- Reflects depolarization of L and R atria and the spread of the impulse through the AV node and ventricular conduction pathway
ST segment
- Segment between the end of the S wave and the T wave
- Isoelectric, indicating that all ventricular muscle is depolarized
- Correlates with the plateau of action potential, Ca influx via L-type Ca channels
- Time during which the ventricles are contracting and emptying
QT interval
- Represents the time from ventricular depolarization to repolarization
- Measures the total duration of ventricular activation
