Heart (L1 and L2) Flashcards
What is 1st degree heart block?
abnormal prolongation in P-R interval (greater than normal 0.20 seconds) - AV nodal conduction time is too long
What is 3rd degree heart block?
complete AV nodal block w/ no consistent P-R interval
What is 2nd degree heart block?
some atrial impulses fail to reach ventricles; not all P waves followed by QRS complexes (=dropped beats)
Describe the difference b/t Mobitz Type I and Type II of 2nd degree heart blocks.
Type I- defect of AV node; progressive increases in P-R interval until dropped beat, then cycle re-starts
Type II- defect of His-Purkinje system; fixed # of non-conducted P waves for every successfully conducted QRS (PR intervals prolonged by same amount, then dropped beat)
What are the main autonomic neurotransmitters affecting heart rate?
acetylcholine (parasympathetic) and norepinephrine (sympathetic)
Where do depolarizations in the heart start?
Depolarizations start at the SA node and spread through the atria. (the point: the heart is NOT stimulated by nerves, but the ANS can speed or slow heart rate)
Explain the term “healing over.”
It is an increase in internal resistance resulting from a decrease in # of open gap junctions, which is caused by an increase in cytosolic calcium or hydrogen ions (decrease in pH). Neighboring cells essentially “pull in” gap junctions to prevent damage from spreading.
What is the slow, positive increase in voltage across a SA nodal cell membranes known as?
pacemaker potential; this spontaneous depolarization triggers the AP (SA nodal cells do not have a true resting state)
What is the main pacemaker in the heart?
SA node
What are the two main factors that determine cardiac conduction rate?
1) Space (length) constant - lambda
2) Rate of rise AND amplitude of action potential
What are the possible causes of a slurred QRS complex?
hyperkalemia, ischemia, ventricular tachycardia, PVC
What are the possible causes of a notched QRS complex?
blockages in left and/or right bundle branches (ventricles not contracting in a coordinated manner)
What takes up a large percentage of the volume of the cardiac myocyte?
mitochondria! (~40%)
Why do Purkinje fibers need to be fast?
They need to active the cells of the ventricle all at once (~100 msec), which allows for coordinated ejection of blood vs. random sloshing of blood.
Refers to failure of conduction somewhere in the cardiac conduction pathway.
heart block
Does the sequence of electrical events in an EKG correspond to the action potential?
no!
The sodium-potassium pump is specifically inhibited by _______.
digitalis
Identify the key components of sodium-calcium exchange.
- Exchanges 3 sodium for 1 calcium ion
- Can move in two directions; the forward direction brings 3 sodium ions in and extrudes 1 calcium ion to maintain low intracellular [calcium]
- Driven by sodium gradient across membrane (thus, indirectly affected by Na-K pump alterations)
Explain the process of “inward rectification” behavior associated with potassium.
- K+ in the heart affects its own permeability… K+ channels sense [K+], thereby increasing permeability with an increase in [K+] and decreasing permeability with a decrease in [K+]
- As potassium levels drop, K+ membrane permeability is decreased (less K+ leaking out corresponds to a less negative membrane potential)
- Essentially, this a way for the cell to conserve K+
Why are K+ channels turned off during heart depolarization?
This is so that K+ ions stop fighting the upstroke of the AP, allowing the cell to remain in a depolarized state for a long enough duration. (it would be a waste of energy if K+ efflux were competing against Ca2+ influx during the plateau of the AP)
