Pt 1 Care of Patients w/Dysrhythmias Flashcards
Properties of Cardiac Cells
- Automaticity
- Excitability
- Conductivity
- Contractility
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Is the ability to respond mechanically to an impulse
Contractility
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Is the ability to initiate an impulse spontaneously & continuously
Automaticity
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Is the ability to be electrically stimulated
Excitability
?
Is the ability to transmit an impulse along a membrane in an orderly manner
Conductivity
Conduction System of the Heart
A normal cardiac impulse begins in the __ __ in the upper right atrium.
It spreads over the atrial myocardium via interatrial pathways & internodal pathways, causing atrial contraction.
sinoatrial node (SA)
The impulse then travels to the __ __, through the bundle of His, and down the left and right bundle branches.
It ends in the __ __, which transmit the impulse to the ventricles.
atrioventricular node (AV)
Purkinje fibers
Electrolytes & Dysrhythmias
- Na, K, Ca, Mg
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Imbalances of this electrolyte are the most common electrolyte-associated cardiac arrhythmias
Potassium
Potassium
- Plays a role in both nerve conduction & the heart’s ability to send an electrical impulse
- Low lvls can cause relatively stable arrhythmias, while high lvls can quickly lead to lethal arrhythmias
- Na, Mg, & Ca imbalances also place heart @ risk for arrhythmias
AHA
→ Arrhythmias caused by these electrolytes only occur when electrolyte lvls are extremely high or low - lvls that are typically incompatible w/human functioning, leading to death
Cardiac Conduction System
Atrial activity is represented by the __ __
P wave
Ventricular activity is represented by the __ __
QRS complex
Sinoatrial node
> Electrical impulses __-__ beats/min
__ __ on ECG
60-100
P wave
Atrioventricular junction
> __ __ on ECG
Contraction known as “atrial kick”
__-__ bpm
PR interval
40-60
Bundle of His
> Right & left bundle branch system
__-__ bpm
20-40
ECG Monitoring
- P wave represents atrial activity
- PR interval is measured from the beginning of the P wave to the beginning of the QRS complex
- Represents the time taken for the impulse to spread through the atria, AV node, bundle of His, bundle branches, & Purkinje fibers to a point immediately preceding ventricular contraction
QRS represents __ __?
ventricular activity
QRS complex has 3 distinct waves
Q wave is the first negative (downward) deflection after P wave, short & narrow, & not present in several leads
R wave is first positive (upward) deflection in the QRS complex
S wave is the first negative (downward) deflection after the R wave
QRS interval is measured from the beginning to end of QRS complex
- Represents time taken for depolarization (contraction) of both ventricles (___)
systole
ST segment is measured from the S wave of the QRS complex to the beginning of T wave
Represents time between ventricular depolarization & repolarization (___)
diastole
**Should be isoelectric (flat)
ST segments should be flat, and when they begin to rise that’s how the EKG tracing represents an ST elevation MI (STEMI)**
T wave represents time for ventricular ___
It can represent potassium levels & oxygenation problems
repolarization
Q-T interval is measured from the beginning of the QRS complex to the end of the T wave
Represents the time taken for entire electrical depolarization & repolarization of ventricles
Can be important to assess as a side effect of rx’s (prolonged QT intervals) [i.e., Haldol]
Normal time for PR interval: -
0.12 - 0.20
Normal QRS: -
**0.04 - 0.10
! If these times exceed these measurements that means there’s a delay in conduction**
Electrocardiographic Waveforms
Assessment of Cardiac Rhythm
- Interpret the rhythm AND evaluate the clinical status of the pt
- Is the patient hemodynamically stable?
- Determine the cause of dysrhythmia
- Treat the patient, not the monitor!
When Things Go Wrong = Dysrhythmias
- Disorder of impulse formation, conduction of impulses, or both
- SA node = normal pacemaker of heart (60-100 bpm)
- Secondary pacemakers = AV node (40-60 bpm)
- His-Purkinje fibers (20-40 bpm)
If the SA node fires more slowly than a 2° PM, the electrical signals from 2° PM may “escape”
2° PM will then fire automatically @ its intrinsic rate
These 2° PM’s may start from the AV node @ a rate of 40-60x/min or the His-Purkinje system @ at a rate of 20-40x/min
Another way that 2° PM’s can start is when they fire more rapidly than the normal PM of the SA node
Triggered beats (early or late) may come from an __ __ or accessory pathway (area outside the normal conduction pathway) in the atria, AV node, or ventricles
Results in a dysrhythmia, which replaces the normal sinus rhythm
ectopic focus
Impulse started by SA node or an ectopic focus must be conducted to the entire heart
Property of myocardial tissue that allows it to be depolarized by a stimulus is ___
excitability
This is an important part of the transmission of the impulse from one cell to another
Lvl of excitability is determined by the length of time after depolarization that the tissues can be re-stimulated
Recovery period >stimulation is the __ __ or period
refractory phase
When the normal impulse is changed, blocked, excited, or depressed, irregular heart rhythms (dysrhythmias) occur
When dysrhythmias occur, cardiac output and therefore perfusion may suffer
Normal
- Rate 60-100
- Rhythm: regular
- P waves present, consistent & have ratio of 1 P wave to 1 QRS
- PR interval 0.12 - 0.20
- QRS duration 0.04 - 0.10
Abnormal
- Rate <60 or >100
- Rhythm: irregular
- P waves absent, inconsistent, or have ratio > 1:1 w/QRS
- PR interval <0.12 or >0.20
- QRS duration <0.04 or >0.10
