Cardiac Cell Properties
Pacemaker cell ability to initiate electrical impulse w/o being stimulated from another source
Automaticity
The period of recovery that cells need after being discharged before they are able to respond to a stimulus. This is the definition of what?
Refractoriness
Primary Pacemaker, initiates impulse that's normally conducted throughout the atria. Sinus Rhythm?
60-100 BPM
•Cardiac cells that are not normally associated with a pacemaker function begin to depolarize spontaneously
OR
•A pacemaker site other than the SA node increases its firing rate beyond that which is considered normal
Abnormal automaticity
The main 4 electrolytes that affect heart functions
Sodium, Potassium, Calcium, and Chloride
Ability of cardiac muscle cells to respond to an outside stimulus
Excitability (irritability)
Cells cannot be stimulated to conduct an electrical impulse, no matter how strong the stimulus
Absolute refractory period (ARP)
Receives impulse from SA node but delays the conduction allowing the Atria to pump blood to ventricles. Sinus Rhythm?
Atrioventricular (AV) Node
0 BPM
Abnormal electrical impulses occur during repolarization (after depolarizations), when cells are normally quiet
Requires a stimulus to initiate depolarization
Triggered activity
Describe differences between Depolarization and Repolarization
A cell is active or stimulated when depolarized
A cell is resting when repolarized
Ability of a cardiac cell to receive an electrical stimulus and conduct that impulse to an adjacent cardiac cell
Conductivity
Cardiac cells can be stimulated to depolarize if the stimulus is strong enough
Relative refractory period (RRP)
Receives impulse from AV node and is connected to it, relaying it to the next bundle branches. Sinus Rhythm?
Bundle of His (AV Bundle)
40-60 BPM
•Slowed—all impulses are conducted but it takes longer than normal to do so
•Intermittent—some (but not all) impulses are conducted
Partial Conduction block
What causes Abnormal Heart Rhythms (Dysrhythmias)?
Results from disorders of impulse formation, disorders of impulse conduction, or both
Ability of cardiac cells to shorten, causing cardiac muscle contraction in response to an electrical stimulus
Contractility
Includes the absolute refractory period and the first half of the relative refractory period
Effective refractory period
Receives impulse from Bundle of His, relays it to the last step. Sinus Rhythm?
Left and Right Bundle Branches
0 BPM
•No impulses are conducted through the affected area
Complete Conduction block
Describe the difference between Myocardial cells and Pacemaker cells
Myocardial cells
-Working or mechanical cells
-Responsible for contraction
Pacemaker cells
-Specialized cells of electrical conduction system
-Spontaneously generate and conduct impulses
Weaker-than-normal stimulus can cause cardiac cells to depolarize
Supernormal period
Receives impulse from Bundle Branches and relays it to ventricular myocardium. Sinus Rhythm?
Purkinje Fibers
20-40 BPM
An impulse returns to stimulate tissue that was previously depolarized
Reentry