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Chapter 49
Principles of Electrocardiography
| Question | Answer |
|---|---|
| Atria | two upper chamber of the heart |
| Atrioventricular node (AV) | part of the cardiac conduction system between the atria and the ventricles |
| Bundle of His | specialized muscle fibers that conduct electrical impulses form AV node to ventricular myocardium |
| Cardiac Arrest | condition of cardiac contraction stops completely |
| Cardio version | use of electroshock to convert an abnormal rhythm to a normal one |
| Defibrillator | machine that delivers an electroshock |
| Diastole | relaxation of the chambers of the heart |
| Ectopic | origination outside the normal tissue |
| Infarction | area of tissue that has died from lack of blood supply |
| Ischemia | decreases blood flow to a body part caused by blockage of supplying artery |
| Myocardial | pertaining to the heart muscle |
| Palpitations | a pounding of the heart |
| Sino atrial Node (SA) | the pace maker of the heart |
| Systole | contraction of the heart |
| Ventricles | two lower chambers of the heart |
| History of electrocardiography | Willem Einthoven developed techniques to record the electrical activity of the heart in the late 1800s. He called this recording the Electro Kardio Gramm, hence the acronym EKG; newer preferred term is ECG |
| Electrical conduction system of the heart | cardiac cycle include all events that occur in the heart in one heart beat (systole/diastole), During systole both atria and ventricles contract and empty the blood. During diastole, the cardiac phase of the heart chambers refill w/ blood |
| Cardiac cycle | for a healthy adult lasts approximately 0.8 seconds |
| Electrocardiograph | records both the intensity of the electrical impulses and the actual time it takes for each part of the cardiac cycle to occur |
| Sinoatrial Node (SA) | also called the pacemaker; located in the upper back wall of the right atrium at the junction of the superior, controls rate of heart contractions at 60-100bpm. Starts w/ the SA generating an impulse that travels across the muscle of the atria |
| Atrioventricular node (AV) | stimulated by SA, located in the posterior, superior portion of the right atrial septal wall directly behind tricuspid valve; |
| Bundle of His | electrical impulse then is transmitted to a group of conduction fibers, locater in upper part of the interventricular septal wall ending in the Purkinje fibers |
| Purkinje fibers | spread across the apex of the hear through he myocardium stimulating ventricular contraction |
| Normal sinus rhythm (NSR) | regular heart rate that falls within the range of 60-80bpm |
| Sinus bradycardia (slow) | below 60bpm |
| Sinus tachycardia (fast) | above 100bpm |
| Arrhythmia | irregular rhythm, conditions that interrupt the conduction pathway |
| Trained Athletes | may have slower than 60bpm when not exercising, if the SA fails to initialize the AV junction can take over as the main pacemaker of the heart |
| AV junction | surrounds the AV node (the AV node is not able to initialize its own impulses), and has a regular rate of 40-60bpm |
| Junctional rhythms | are characterized by a missing or inverted P-wave, if both the SA/AV junctions fail the ventricles can fire the electrical impulses themselves at the rate of 20-40bpm, will have a QRS complex greater than 120ms |
| Polarization | is the resting state of the myocardial wall, |
| Depolarization | when electrical system of the heart stimulates a myocardial cell, resulting in the contraction |
| Repolarization | the heart muscle cells must return to a resting state before they can be electrically stimulated again |
| P- Wave | first deflection, occurs during the Contraction of the atria |
| PR segment | return to baseline after atrial contraction |
| QRS complex | contraction of both ventricles |
| ST segment | time between the end of the ventricular contraction and the beginning of the ventricular recovery |
| T- wave | repolarization of the ventricles |
| QS interval | between the beginnings of the QRS complex through the T wave |
| U wave | occasionally seen as a small wave from after the T wave |
| Six channel ECG machines | leads places at specific anatomic locations |
| Multichannel ECG tracing | take seconds to perform and can be placed into the chart w/o mounting |
| Single channel ECG machines | older machines that record the 12 lead one at a time |
| Horizontal lines (ECG) | on the paper permit the determination of the relative strength of the heart beat, the paper is heat and pressure sensitive; handled carefully to avoid making any additional markings |
| Horizontal axis | of the paper represents time; |
| Vertical axis | represents amplitude |
| Small square | measures 1mm |
| Vertical and Horizontal lines | every fifth line is darker than the other lines creating a larger square measuring 5mm on each side |
| Small square | one small 1mm square passes the stylus (writer) every 0.04sec; |
| Large square | one large square 5mm passes the stylus (writer) every 0.2sec; in one second 5 large squares pass through the stylus (writer) |
| Electrodes | four are placed one each on the arms and legs Six are placed on the chest; most offices use single use, self stick, disposable that are packaged w/ conductive jelly at center |
| Electrode leads/wires | ten color coded and labeled lead wires ending in a small metal clip are attached; the leads carry the cardiac electrical impulses into the machine; records electrical activity of heart between two electrodes, pos/neg |
| Depolarization | occurs toward he positive electrode the deflection is upright, if it moves toward the negative electrode it is deflected downward |
| ECG | records views of the hear on both a frontal and transversal plane |
| Standard/ Bipolar leads | the first three leads recorded lead one- records right and left arm lead two- records right arm and left leg lead three- records left arm and left leg |
| Unipolar leads | single positive electrode that used the right leg for grounding |
| aVr | records activity of the atria from the right shoulder |
| aVI | records activity of the lateral wall left ventricle from the left shoulder |
| aVf | records activity of the inferior surface of the left ventricle from the left leg |
| Transverse | plane view of the heart, QRS complex is a negative deflection on V1 and V2 view, measure the electrical activity among six specific pts on the chest wall and a point with in the heart |
| V1 rode | is in the fourth intercostal space |
| V2 rode | fourth intercostal space, just to the left of the sternum |
| V3 rode | midway between V2 and V4 |
| V4 rode | fifth intercostal space |
| V5 rode | horizontal to V4 in the left anterior axillary line |
| V6 rode | horizontal to V4 in the left midaxillary line |
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iceheart