6. Cardiac Conduction System & ECG Flashcards
Cells in the sinoatrial node and AV node are capable of _____.
spontaneous depolarization
How are SA and AV node cells able to spontaneously depolarize?
their phase 4 periods have slow depolarization due to the funny current and are thereby unstable
What kind of channels are absent in the SA and AV node cells?
sodium
Why is the SA node the usual cardiac pacemaker?
its cells have the fastest spontaneous depolarization rate, and the AV node cells’ delay allows the atrium to contract first
Why do Purkinje cells have such fast APs?
they have a large # of Na channels
What makes up a gap junction?
connexins
What is automaticity?
the ability to spontaneously depolarize
What is the P wave?
depolarization of the R and then L atrium
Where is the AV node located?
between the fibrous tricuspid and mitral valve rings that separate the atria from the ventricles
What is found between the fibrous tricuspid and mitral valve rings that separate the atria from the ventricles?
the AV node
Where does the depolarization wave go after the AV node?
through the bundle of His into the left and right bundle branches
What do the bundle branches divide into?
Purkinje fibers
What does the right Purkinje bundle divide into?
it doesn’t- it’s a single entity supplying the R ventricle
What does the left Purkinje bundle divide into?
anterior and posterior branches or fascicles
What does the QRS complex represent?
depolarization of the ventricles
What is the T wave?
repolarization of the ventricles
What is phase zero of the ventricular AP?
the fast sodium current causes rapid depolarization
What does phase two of the ventricular AP look like?
a long plateau and little change in voltage
What does the T wave on the EKG correspond to in the ventricular AP?
phase 3- a rapid decrease in voltage as potassium efflux continues
If the _____ is positive the T wave should be positive.
QRS
If the QRS is positive the _____ should be positive.
T wave
If the QRS is negative the _____ should be negative as well.
T wave
if the _____ is negative the T wave should be negative as well
QRS
Discordance between the ___ and ____ in any lead is pathological, reflecting abnormalities such as ischemia or ventricular hypertrophy.
QRS and T waves
