| A | B |
|---|
| automaticity | ability of the heart to initiate an electrical impulse without being stimulated by a source |
| conductivity | ability of the heart cells to receive and transmit and electrical impulse |
| contractility | ability of the heart muscle cells to shorten in response to an electrical stimulus |
| excitability/irritability | ability of the heart muscles cells to respond to an impulse or stimulus |
| sympathetic | part of the Automatic Nervous System (ANS) that causes an increase in the heart rate |
| parasympathetic | part of the Automatic Nervous System (ANS) that helps slow the heart rate |
| Bachmann's bundle (pathway) | structure that relays the electrical impulse from the SA node to the left atrium in a normal heart |
| SA Node (sinoatrial node/pacemaker) | area of specialized cells in the upper right atrium that initiates the heartbeat |
| AV node (atrioventricular node) | delays the electrical impulse to allow the atria to complete their contraction |
| bundle of his (AV bundle) | located next to the AV node; provides transfer of the electrical impulse from the atria to the ventricles |
| bundle branches | left and right branches of the bundle of his that conduct impulses down either side of the interventricular septum to the left and right ventricles |
| Purkinje fibers | the fibers within the heart that distribute electrical impulses from cell to cell throughout the ventricles |
| Purkinje network | spreads the electrical impulse throughout the ventricles by means of the Purkinje fibers |
| polarization | state of cellular rest inn which the inside of negatively charge and the outside is positively charged |
| depolarization | electrical activation of the cells of the heart that initiates contraction of the heart muscle |
| action potential | the change in the electrical potential of the heart muscle when it is stimulated |
| repolarization | the return of heart muscle cells to their resting electrical state, causing the heart muscle to relax |
| P wave | the return of heart muscle cells to their resting electrical state, causing the heart muscle to relax |
| QRS complex | ventricular depolarization and resulting ventricular contraction; atrial repolarization occurs but cannot be seen |
| T wave | ventricular depolarization |
| U wave | repolarization of the bundle of His and Purkinje fibers; maybe seen if electrolyte imbalances |
| PR interval | beginning of atrial depolarization to the beginning of ventricular depolarization |
| QT interval | period of time from the start of ventricular depolarizaiton to the end of ventricular repolarization |
| ST segment | time between ventricular depolarization and the beginning of ventricular repolarization |
| ischemia | occurs when there is a sudden loss or reduction in blood supply that is oxygenated to a region of the heart tissue; can occur for a number of reasons |
| J wave | represents the end of the QRS complex and ventricular depolarization; important when measuring the length of the QRS complex and interpreting the ECG tracing. |
| 0.12 to 0.20 second | normal PR interval |
| 0.06 to 0.1 second | normal QRS complex |
