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What is automaticity?
- Ability of cardiac pacemaker cells to spontaneously initiate an electrical impulse without being stimulated by a nerve.
- Is nice because it acts as a backup if a node drops out.
- Can be bad if a rogue cell initiates a new heart beat.
- *very unique to cardiac cells.
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What is excitability?
Ability of cardiac muscle cells to respond to an outside stimulus.
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Conductivity?
Ability to pass electricial current from cell to cell.
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Contractility?
Abilty of cell to respond with contraction by shortening.
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True/False: Brain and heart can utilize ATP for energy for repolarization of cells.
- False.
- Heart and brain can only use O2 for repolarization which is why escemia is so bad for them.
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How is calcium involved in action potentials?
Ca+ is involved in contractility.
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Which elyte acts as an acid?
Potassium. (K+)
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Why is sodium important to cardiac action potentials?
- Because sodium is the first to cross the membrane to depolarize the cell.
- Digoxine is the most popular sodium channel drug.
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What do action potentials during depolarization look like?
 - ECG is just an average of all action potentials at any give time.
- DOES NOT MEASURE ACTUAL, MECHANICAL FUNCTION, ONLY ELECTRICAL ACTIVITY.
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What do you need to know about the SA node?
- Rate = 60-100
- Clinically known as "sinus," i.e., NSR (normal sinus rhythm.)
- May create P wave.
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What do you need to know about the AV node?
- Normal rate = 40-60/min
- Acts as a filter to prevent overstim from SA
- Will appear on ECG when no P wave but has a narrow QRS.
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What is Atrial kick?
Atrium squirts blood into ventricles creating "extra" volume in ventricles-->^cardiac output.
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What do you need to know about IVR
(Idioventricular pacer cells)
- 20-40/min
- Does not play into atrial kick.
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What can a pt look like when he/she has low cardiac output?
- Do not rely on BP as measure of CO
- Skin is cool (no circulation to SQ tissue)
- Skin has gray tone
- Diaphoresis, “cool clammy” feel
- May or may not have ↑ JVD (good thing to document).
- Low urine output
- Change in LOC
- Orthostatic BP
- Positional Orthopnea
- Rhythm disturbances
- May have chest pain or discomfort
- Tachycardia if not on Beta-Blocker type drug
Assessment skills are vital to put the picture together.
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