Cardiac Physiology Flashcards
Place in sequence and give the pacing of each of the following components of the internal conduction system:
AV node, myocardium, SA node
The SA node has the highest intrinsic rate of any cardiac tissue.
SA node = 60-70/ min
AV node = 50/ min
Myocardium = 30/ min
Describe the normal electrical activation of the heart.
Conduction begins at the sinoatrial node, then through the atria via the interatrial tract, also known as Bachman’s bundle. Also down the internodal tracts, to the atrioventricular node. At the AV node, electrical impulse pauses to prevent simultaneous contraction of the atria and ventricles. Then the impulse travels through the Bundle of His to the left and right bundle branches and out the Purkinje fibers.
Describe the wave of contraction (depolarization) within the myocardium.
The wave of contraction moves from the endocardium to the epicardium, evident by the design of the Purkinje fibers.
What is the absolute refractory state?
The absolute refractory state is that period when a muscle cell is not excitable. As it corresponds with the EKG, absolute refractory period begins at the Q wave and ends about halfway through the T-wave.
What does the P-wave represent?
The P wave represents atrial systole.
What does the P-R interval represent?
The P-R segment represents from atrial to ventricular depolarization.
What does the QRS complex represent?
The QRS complex represents ventricular systole (depolarization).
What does the T wave represent?
The T-wave represents ventricular diastole (repolarization).
What is the normal duration for the QRS complex?
.10 sec
What do the boxes on the EKG represent?
small box = .04 second
big box = .2 second
Five big boxes = one second
What is a normal R-R interval?
3-5 big boxes (60 – 100 bpm)
What is the normal value for PR interval?
Less than one big box on the EKG, less than .2 seconds.
