02 - Basic Principles of the ECG Flashcards
With atrial depolarization, atrial contraction begins and correlates to which wave?
P
What is the pathway of the typical cardiac electrical activity?
SA node Right atrium AV node Bundle of His Purkinje fibers Ventricles
When atrial contraction finishes, the myocardium stops depolarizing and there is another isoelectric point in the ECG which is called
P-R interval
When depolarization moves from the apex of the ventricles toward the outflow tracts, this complex is generated?
QRS
Why is the QRS complex bigger than the P wave?
Ventricular myocardial muscle has greater mass
The first downward portion of the QRS complex corresponds to what electrical activity?
Septal depolarization
The first upward portion of the QRS complex corresponds to what electrical activity?
Left ventricle depolarization
The second downward portion of the QRS corresponds to what electrical activity?
Right ventricle depolarization
The second upward portion of the QRS corresponds to what electrical activity?
Return to baseline
What electrical event occurs when ventricular contraction finishes?
None
What is happening during the refractory period?
Depolarization can not occur while ion channels are balancing potassium and calcium
What is happening during ventricular relaxation? What wave does this correspond to?
Ventricular repolarization
T
Changes to the T wave are often due to
Ventricular tissue not being able to repolarize or relax correctly
Why is atrial repolarization/relaxation not shown on the EKG waveform?
It is usually swallowed up in the QRS complex
The SA node paces the heart at what rate? What is its height and width?
60-100 bpm
Height - 2.5 mm
Width - .11 sec
First half of the P wave is ______ depol while the second half is ______ depol
Right atrium
Left atrium
Slow conduction through the AV node is carried by
Calcium ion channels
The AV node responds to ______ from the sympathetic nerves and ______ from the vagus nerve
Stimulation
Inhibition
The PR interval measures? How many seconds does it last?
Beginning of atrial contraction to ventricular contraction
.12-.20 sec
Upon reaching the ventricular conducting system, depolarization is
Rapid
How long is the QRS complex?
.12 sec
What does a very wide or deep Q wave indicate?
MI that involves full depth of the myocardium and has left a scar
Physical contraction and pull back of the heart from the electrode during contraction
S wave - any neg deflection after R wave
Displacement of the ST segment indicates
Damage to the cardiac muscle or strain on ventricles
