Term
| Pathophysiology of Arrhythmia |
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Definition
Coronary Ischemia
Tissue Hypoxia
Electrolyte disturbances
Over stimulation of sympathetic nervous system
Abnormal impulse formation or impulse conduction |
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Term
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Definition
Atrial Origin
Ventricular (More fatal) |
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Term
| Bradycardia is slowing of the heart, while tachycardia is rapid beating. |
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Definition
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Term
| Relationships between ion currents, cardiac action potentials, and the findings on surface ECG |
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Definition
| Figure 14-1 Relationships between ion currents, cardiac action potentials, and the findings on surface ECG. The normal heartbeat originates in the SA node. The impulse is conducted through internodal fibers to the AV node and then through the bundle of His, bundle branches, and Purkinje fibers to the ventricular muscle. On the ECG, the P wave represents atrial depolarization, the QRS complex represents ventricular depolarization, and the T wave represents ventricular repolarization. The PR interval is primarily related to the conduction time through the AV node, and the QT interval represents the time between ventricular depolarization and repolarization. In phase 0, ventricular depolarization is caused by sodium influx through the fast sodium channel. In phase 1, the membrane is transiently repolarized as a result of potassium efflux. In phase 2, the membrane potential is relatively stable because of the concurrent influx of calcium and efflux of potassium. In phase 3, repolarization is caused by continued potassium efflux as calcium influx declines. In phase 4, the ion balance is returned to normal by the action of the sodium pump (Na+,K+-adenosine triphosphatase [ATPase]). Calcium is removed from the cell by the sodium-calcium exchanger and the calcium ATPase (not shown). |
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Term
| Sinoatrial (SA) node cell |
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Definition
Resting membrane potential –55 mV
Depolarize to +10 mV
No plateau |
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Term
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Definition
resting membrane potential –85 mV
Depolarize to +45mV
Longer plateau |
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Term
| SA Node Action Potential and Ion Currents |
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Definition
SA nodal cells are depolarized slowly by the pacemaker current (If) (phase 4), which consists of an inward flow of sodium (mostly) and calcium ions
Depolarization to the threshold potential opens highly selective voltage-gated calcium channels
As the calcium channels close and potassium channels open (phase 3), the membrane potential repolarizes |
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