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51 Cards in this Set
- Front
- Back
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Cardiac Pacemaker Cells |
Non-contractile cardiac cells. Has unstable resting membrane potentials. |
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What do cardiac pacemaker cells do? |
Helps depolarize and contract heart in orderly sequential manner. Initiates and distributes impulses throughout the heart. |
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Pacemaker Potentials |
Also called Prepotentials. Unstable resting membrane potentials. Spontaneously developing local potential in pacemaker cells reaching threshold. |
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What Causes Pacemaker Potential? |
Due to opening of sodium channels and closing of potassium channels. |
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Depolorization |
Begins when the pacemaker potential reaches threshold. Influx of calcium ions. |
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Repolorization |
Calcium channels inactivate and potassium channels open. Allows efflux of potassium. Brings membrane potential back to negative voltage. |
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Sequence of Electrical Excitation |
1. SA node generates impulses 2. Impulses pause for 0.1s at AV node 3. AV bundles connects atria to ventricles 4. Bundle branches conduct impulses through interventricular system 5. The subendocardial conducting network depolorizes the contractile cells of both ventricles |
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What are the components of the cardiac conduction system? |
SA Node, AV Node, AV Bundle, Left and Right Bundle Branches, Purkinje Fibers |
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What does self-stimulating mean? |
Able to depolarize spontaneously and pace the heart. |
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Sinoatrial Nodes Pacemaker Cells generate..... |
Action potentials spontaneously and at regular intervals. |
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What is the initial step toward full heart contraction? |
SA nodes pacemaker cells generating action potentials. |
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Unlike other cardiac muscles, Ca2+ primarily..... |
Responsible for depolarization phase in pacemaker cells. |
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What node is quicker than others and sets the pace? |
SA node |
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Ectopic Foci Example |
Atrioventricular Bundle |
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How are Artificial Ectopic Focuses created? |
Changing the cardiac muscle cell membranes permeability |
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Electrocardiograph |
Can detect electrical currents generated by heart |
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Electrocardiogram |
ECG/EKG. Diagnostic tool. A graphic recording of Electrical activity. Composite of all action potentials at a given time. |
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How are ECG/EKGs performed? |
Electrodes placed on various points on body to measure voltage differences |
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Most common electrocardiogram? |
12 lead ECG |
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P Wave |
Depolarization of SA node and atria |
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T Wave |
Ventricular repolarization |
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P-R Interval |
Beginning of atrial excitation to beginning of ventricular excitation |
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S-T Segment |
Entire ventricular myocardium depolarized |
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Q-T Interval |
Beginning of Ventricular depolarization through ventricular repolarization |
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Sequence of Depolarization and Repolarization of Heart on an ECG |
1. Atrial depolarization initiated by the SA node 2. Atrial depolarization complete. There's a 0.1s delay at AV node. 3. Ventricular depolarization begins at apex. Atrial repolarization occurs 4. Ventricular depolarization complete 5. Ventricular repolarization begins at apex 6. Ventricular repolarization is complete |
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Sequence of Depolarization and Repolarization in Waves |
1. P Wave 2. Flat 3. QRS Complex 4. Flat 5. T Wave 6. Flat |
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Junctional Rythym |
SA node is nonfunctional. P waves are absent. AV node paces heart at 40-60 bpm. |
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Second-Degree Heart Block |
AV node fails to conduct some SA node impulses. More P waves than QRS. AV node fails to conduct some SA node impulses. More P waves than QRS. |
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Ventricular Fibrillation |
Electrical activity is disorganized. Action potentials occur randomly. Chaotic, abnormal ECG deflections. Acute heart attacks and after an electrical shock. |
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Asystole |
Cardiac arrest. No discernable electrical activity on EKG. Flatline with all waves. Occurs when heart develops arrhythmia that causes it to stop beating. Death within minutea. |
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How do pacemakers control heart rythyms? |
Utilize electrical pulses to cause heart to beat at normal rate. |
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Tachycardia |
Fast heart rate >100bpm |
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Bradycardia |
Slow heart rate <60bpm. |
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Components of Pacemakers |
Leads and pulse generator |
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What is a Pulse Generator? |
Sealed lithium battery. Makes electrical signals that make heart beat. |
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What is a Lead? |
Insulated flexible wires. |
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What does a Lead do? |
Conducts electrical signals between the heart and pulse generator. |
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Where is the pacemaker Lead located? |
One end is attached to pulse generator and one end is positioned in heart. |
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Fibrillation |
Rapid, irregular, out of phase heart contractions |
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What happens when the heart rate is removed from the SA node? |
Ventricles no longer pump correctly. Blood stops circulating. Possible brain death. |
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Defibrillation |
Electrically shocks the heart. Depolarizes the entire heart myocardium. |
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What happens when the hearts myocardium is depolarized? |
Wipe slate clean, SA node functions normally, sinus rythym re-established. |
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What is cardiac output? |
Volume of blood pumped out of each ventricle in one minute. |
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What influences cardiac output? |
Heart rate and stroke volume |
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How do you calculate cardiac output? |
Heart rate times stroke volume. Assume stroke volume of 70 ml/beat |
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How do you calculate your blood volume? |
Based on 33 ml/lb of body weight. |
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How often is your entire blood volume circulating through your heart at rest? |
3 times every minute. |
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QRS Complex |
Ventricular depolarization and atrial repolarization |
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Pacemakers |
Small devices used to control abnormal heart rythyms. |
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What fibrillation is attributed to cardiac arrest? |
Ventricular |
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What is stroke volume? |
Amount of blood through the heart per beat |
