Exam 1 Flashcards
myocardial cells
muscle, property of contractility
Specialized cells
electrical activity, property of conduction
Conductivity
ability to transmit impulses from one area to another
Excitability (irritability)
capability of the cell to respond to a stimulus
Automaticity
capacity to initiate an impulse or stimulus
Rhythmicity
property of regularity of the intervals at which impulses are formed
Refractoriness
property of being unresponsive to an impulse
inside the cardiac cell
high K low Na, at rest (polarized)
outside the cardiac cell
low K high Na, at rest (polarized)
Absolute refractory period
- the time during the cardiac cycle in which the heart cannot respond to a stimulus (during depolarization)
- serves as a protective mechanism
Relative refractory period
- cell can respond to a strong stimulus
- The repolarization phase is in process but not quite completed (some cells are polarized and others are depolarized =vulnerable)
- T wave on the ECG
Supernormal Period
during this period the cardiac cells will respond to a weaker than normal stimulus (just before the cells have completely repolarized)
Nonrefractory period
the time when the heart is completely repolarized and ready to adequately and efficiently respond to another stimulus
Normal pathway for cardiac electrical conduction
originates in the SA node, backup pacemaker is the AV node, Bundle of HIS and Purkinje Fibers
SA node
normally where impulses originate
60 to 100 times per minute
AV node
- when the impulse reaches the A-V node, conduction is delayed 0.1 second allowing time for the atria to eject blood into the ventricle
- if the S-A node fails, the A-V junction can assume control at a rate of 40 to 60 per minute
the His-Purkinje system
- The Purkinje fibers allow a rapid spread of the impulse through the ventricular mass.
- If the S-A node and A-V junction fail to initiate an impulse, the His-Purkinje system takes over and pace the heart at a rate of 20 to 40 beats per minute
Lead II
- bipolar lead
- positive electrode is placed over the apex of the heart (in the left midclavicular line at the 4th or 5th intercostal space).
- negative electrode is placed beneath the clavicle to the right of the sternum near the 2nd intercostal space
Small box value
0.04 sec
Big box value
0.2 Seconds
P wave
Represents atrial depolarization
If present and upright in Lead II, normally indicates impulse originated in S-A node
PR interval (PRI)
Normal duration is 0.12- 0.20 second
Measured from the beginning of the P wave to the beginning of the QRS complex
Represents atrial depolarization and delay through the A-V node
QRS complex
Normal duration is less than 0.12 second
Measured from the beginning of the QRS to the end of the S wave
Represents ventricular depolarization
ST segment
Measured from the end of the QRS complex to the beginning of the T wave
Period between the completion of ventricular depolarization and beginning of ventricular repolarization
ST-segment elevation
acute myocardial injury, preinfarction, & pericarditis
ST-segment depression
myocardial ischemia
J-joint
end of QRS and beginning of ST segment
T wave
Represents ventricular repolarization (recovery phase)
Normally upright in Lead II
U waves
May or may not be visible.
Found after T wave
Prominent upright U waves are abnormal (Hypokalemia)
Method 1- 1500
1500 (number of small squares in 1 minute) divided by number of small boxes between 2 R waves
Method 2- 300
300 (number of large squares in 1 minute) divided by number of large boxes between 2 R waves
Method 3- 10
10 multiplied by number of Rs in 6 seconds
Artifact
ECG waveforms from sources outside the heart (interference seen on a monitor)
4 common causes: patient movement, loose or defective electrodes, improper grounding, faulty ECG apparatus
Normal sinus rhythm
PP and RR interval (rhythm)- regular PP and RR rate- 60-100/min P wave- upright in lead II PRI- 0.12-0.20 second QRS interval- less than 0.12 second
Sinus Dysrhythmias
Dysrhythmias originating in the sinoatrial (S-A) node.
Sinus Bradycardia looks
PP and RR interval (rhythm)- regular PP and RR rate- less than 60/min P wave- upright in lead II PRI- 0.12-0.20 second QRS interval- less than 0.12 second
Sinus Bradycardia Common etiology
damage to the S-A node, vagal stimulation, increased intracranial pressure, certain drugs (digoxin or beta-blockers), during sleep, normal in conditioned athletes
Sinus Bradycardia Clinical S&S
seldom symptomatic unless rate is markedly decreased, slow regular pulse, hypotension, dizziness, chest pain, or changes in level of consciousness
Sinus Tachycardia looks
PP and RR interval (rhythm)- regular PP and RR rate- greater than 100/min P wave- upright in lead II PRI- 0.12-0.20 second QRS interval- less than 0.12 second
Sinus Tachycardia Common etiology
exercise, pain, fever, CHF, shock, agitation, illicit drugs, caffeine, nicotine
Sinus Tachycardia Clinical S&S
vary with rate, rapid regular pulse, may sense palpitations, may experience dyspnea, may be asymptomatic
Sinus Arrhythmia looks
PP and RR interval (rhythm)- irregular PP and RRrate- varies (usually 60-100/min) P wave- upright in lead II PRI- 0.12-0.20 second QRS interval- less than 0.12 second
Sinus Arrhythmia Common etiology
common in children and young adults, increase in heart rate with inspiration, decrease in heart rate with expiration, usually considered benign
Sinus Arrhythmia Clinical S&S
irregular pulse, usually asymptomatic
Premature Atrial Complex (PAC)
Early beats from an ectopic focus in the atria
early, abnormally shaped P wave
P wave- may differ from sinus P wave; may be notched, peaked, diphasic, or lost in preceding ST segment or T wave
QRS interval- less than 0.12 second
Premature Atrial Complex (PAC) common etiology
atrial stretch (may be seen with valve disease, CHF, liver disease, pulmonary hypertension), mitral valve prolapse, emotional upheaval, nicotine, caffeine, digitalis
Premature Atrial Complex (PAC) clinical s &s
irregular pulse, patient usually unaware of PACs
what is Paroxysmal Supraventricular Tachycardia (PSVT)
A dysrhythmia originating in an ectopic focus anywhere above the bifurcation of the bundle of His
Often a PAC triggers a run of PSVT
Paraxysmal refers to an abrupt onset and termination
Paroxysmal Supraventricular Tachycardia (PSVT) looks
Heart rate 100-300 (some text say 140-250) beats/minute
Rhythm is regular or slightly irregular
P wave is often hidden in the T wave (such a fast rate)
QRS is usually normal
Paroxysmal Supraventricular Tachycardia (PSVT) common etiology
same as PACs
Paroxysmal Supraventricular Tachycardia (PSVT) clinical s&s
rapid regular pulse, may exhibit signs and symptoms of decreased cardiac output or CHF or even myocardial infarction (rapid rates decrease ventricular filling time, increase myocardial oxygen oxygen consumption, and decrease oxygen supply)
Atrial Flutter
PP intervals (rhythm)- regular
RR intervals (rhythm)- regular or irregular
PP rate- 250-350/min
RR rate- varies
P wave- sawtooth appearance (called F waves), more than one F wave is present for each QRS
PRI- unable to measure
QRS interval- less than 0.12 second (may be distorted by F wave)
Atrial Flutter common etiology
increased sympathetic tone, atrial stimulation, valvular disease, hyperthyroidism
Atrial Flutter Clinical S&S
depend on ventricular rate, may experience palpitations, angina, or dyspnea
Atrial Fibrillation looks
PP and RR interval (rhythm)- grossly irrregular
PP rate- greater than 350/min (unmeasurable)
RR rate- varies
P wave- no discernible P wave (atrial activity is characterized by undulations in the baseline)
PRI- unable to measure
QRS interval- less than 0.12 second
Atrial Fibrillation common etiology
ischemic heart disease, hypoxemia, hyperthyroidism, valvular disease
Atrial Fibrillation Clinical S&S
irregular pulse, may have pulse deficit (difference in apical rate and radial rate), depend on ventricular response, may experience palpitations, angina, or dyspnea, may cause decreased cardiac output, may develop emboli from atrial wall thrombus formation