Ions
Electrically charged particles.
Polarized
Possessing an electrical charge.
Depolarization
The wave of electrical current that changes the resting negatively charged cardiac cell to a positively charged one.
Sodium-Potassium Pump
The active transport system that returns the cardiac cell to its resting, electrically negative state following depolarization.
Repolarization
The wave of electrical current that returns the cardiac cell to its resting, electrically negative state.
Transmembrane Potential
The electrical charge at the cell membrane.
QRS Complex Appearance
Is a spiked waveform that represents depolarization of the ventricular myocardium.
ST Segment
Is a flat line on the EKG that follows the QRS complex and represents a period of electrical silence.
T Wave Appearance
Is a broad rounded wave that follows the ST segment and represents ventricular repolarization.
Refractory
Means resistant to.
Absolute
The cell cannot accept another impulse because it's still dealing with the last one. Absolutely no stimulus, no matter how strong, will result in another depolarization.
Relative
A strong stimulus will result in depolarization.
Supernormal Period
Even a weak stimulus will cause depolarization. The cardiac cell is "hyper." Stimulation at this time can result in very fast, dangerous rhythms.
What are the 3 Refractory Periods?
-Absolute
-Relative
-Supernormal Period
P Wave
Represents atrial depolarization.
Normal P Wave
Is small, rounds, and upright, but many things can alter the P wave shape.
Ta Wave
Represents atrial repolarization - usually not seen, as it occurs at the same time as the QRS complex.
QRS Complex
Represents ventricular depolarization.
T Wave
Represents ventricular repolarization.
U Wave
If present, the U wave follows the T wave. It should be shallow and rounded, the same deflection as the T wave.
U Wave Represents
Late ventricular repolarization and is not normally seen.
PR Segment
Is the flat lines between the P wave and the QRS and between the QRS and T waves.
Each P-QRS-T sequence is what?
One heartbeat.
Baseline or Isoelectric Line
The flat line between the T wave of one beat and the P wave of the next beat.
Q Wave
A negative deflection that occurs before a positive deflection.
Deflection means what?
Wave.
R Wave
Any positive deflection. There can be more than one.
R Prime
A second R wave; written R'.
S Wave
A negative deflection that follows an R wave.
QS Wave
A negative deflection with no positive deflection at all.
Conduction System
A network of specialized cells whose job is to create and conduct the electrical impulses that control the cardiac cycle.
Pacemaker
The intrinsic or artificial focus that propagates or initiates the cardiac impulse.
Sinus Node
The normal pacemaker of the heart.
Interatrial Tracts
Pathways that carry electrical impulses from the sinus node through the atrial tissue.
Atrial Tissue
Tissue in the atria.
Escape
A safety mechanism in which a lower pacemaker fires at its slower inherent rate when he faster, predominant pacemaker fails.
AV Node
The group of specialized cells in the conduction system that slows impulse transmission to allow atrial contraction to occur.
Bundle of His
A confluence of conduction fibers between the AV node and the bundle branches.
Bundle Branches
Conduction pathways extending from the bundle of His in the lower right atrium to the Purkinje fibers in the ventricles. There is a right and a left bundle branch.
Purkinje Fibers
Fibers at the terminal ends of the bundle branches. Responsible for transmitting the impulses into the ventricular myocardium.
Ventricle
The lower pumping chambers of the heart.
Automaticity
The ability to create an impulse without outside stimulation.
Conductivity
The ability to pass this impulse along to neighboring cells.
Excitability
The ability to respond to this stimulus by depolarizing.
Contractility
The ability to contract and do work.
Escape Rhythm
Is a series of escape beats.
Usurpation
To take control away from; also called irritability.
Heart Rhythn
A pattern of successive depolarizations.
Arrhythmias
Abnormal heart rhythms.
Intervals
Measurements of time between EKG waves and complexes.
Amplitude
The height of the waves and complexes on the EKG.
12-Lead EKG
Is a printout of the heart's electrical activity viewed from 12 different angles as seen in 12 different leads
Lead
An electrocardiographic picture of the heart.
Rhythm Strip
A printout of one or two leads at a time, done on special rolls of paper.
Identifying Data
Such as name, date, time, and room number
Interpretive Data
Such as heart rate.
PR Interval
Measures the time it takes for the impulse to get from the atria to the ventricles. Normal PR interval is 0.12 to 0.20 seconds. It's measured from the beginning of the P wave to the beginning of the QRS and includes the P wave and the PR segment. The P wa
QRS Interval
Measures the time it takes to depolarize the ventricles. Normal QRS interval is less than 0.12 seconds, usually between 0.06 to 0.10 seconds. It measured from the beginning of the QRS to the end of QRS.
QT Interval
Measures depolarization and repolarization time of the ventricles. The QT interval is measured from the beginning of the QRS to the end of the T wave and includes the QRS complex and the T wave. At normal heart rates of 60 to 100, the W interval should be