cardiac + arrhythmias Flashcards
4 properties of cardiac cells
automaticity
excitability
conductivity
contractility
automaticity
ability of cardiac pacemaker cells to spontaneously generate an electrical impulse
SA node, AV junction, Purkinje fibers
excitability
ability of cardiac cells to respond to an electrical impulse
depolarization occurs when cells become electrically excited
conductivity
ability of cardiac cells to transmit an electrical impulse to neighboring cardiac cells
contractility
ability of cardiac cells to shorten in response to electrical stimulation (mechanical event)
cardiac action potential
change in electrical charge inside the cardiac cell when it is stimulated
polarization
electrical state of cardiac cell membrane when cell is at rest
no electrical activity occuring
ECG is flat, isoelectric line
depolarization
electrical event that results in a contraction of cardiac muscle
P wave = atrial depolarization
QRS complex = ventricular depolarization
repolarization
restoration of polarized state of cell membrane
ST segment and T wave = ventricular repolarization
absolute refractory period
brief period during depolarization when the cells will not respond to further stimulation, no matter how strong the stimulus
relative refractory period
vulnerable period during which some cardiac cells have repolarized but may respond to a stronger-than-normal stimulus
can cause v-fib
“R on T phenomenon”
cardiac conduction system
SA node
AV node
Bundle of His
Purkinje fibers
SA node
pacemaker of the heart located in right atrium
generates impulses at 60-100 bpm
P wave = atrial depolarization
AV node
electrical pathway between atria and ventricles located in lower right atrium behind tricuspid valve
generates impulses at 40-60 bpm
isoelectric line after P wave
Bundle of His
where ventricular conduction system originates
penetrates AV valves then bifurcates into L/R branches to Purkinje fibers
QRS complex on ECG
generates impulses at 20-40 bpm
Purkinje fibers
can act as pacemaker if there are no impulses from SA or AV nodes
ECG leads
6 limb leads provide view of frontal plane of heart
6 chest leads provide view of horizontal plane of heart
speed of ECG monitors
25 mm/sec
vertical line of ECG
represents voltage/amplitude of waveforms
waveform
either a deflection upward or downward from baseline of ECG recording
segment
line between waveforms that usually falls on ECG baseline
interval
a waveform and an adjoining segment
complex
made up of multiple deflections, such as QRS
P wave
start of cardiac cycle
SA node fires and results in atrial depolarization
PR segment
after P wave, short segment that usually falls on isoelectric line
PR interval
P wave + PR segment following P wave
reflects atrial depolarization and impulse delay through AV junction (PR segment)
beginning of P to beginning of QRS complex
0.12-0.2 seconds
QRS complex
Q wave - first negative deflection after P wave
R wave - first positive deflection of the complex
S wave - downward deflection following R wave
depolarization of both ventricles
measured from where Q leaves baseline to where last wave levels out at baseline
<0.12 seconds
ST segment
isoelectric line between QRS and T wave
early repolarization of ventricles
considered elevated or depressed if it deviates above or below the isoelectric line by more than 1 mm
T wave
follows ST segment
represents ventricular repolarization
usually rounded
QT interval
QRS complex + ST segment + T wave
total time required for ventricular repolarization
0.38-0.42 seconds
7 steps to interpreting cardiac rhythm
- determine heart rhythm
- determine HR
- examine P waves
- examine P to QRS ratio
- measure PR interval
- examine QRS complex
- interpret the rhythm
heart rate
normal 60-100 bpm
atrial and ventricular rates should be the same
6-second method
large-box method
normal sinus rhythm (NSR)
originates at SA node
P to P and R to R intervals are regular
P waves are uniform and upright with ONE P wave preceding each QRS complex
sinus arrhythmia
AKA respiratory sinus arrhythmia
originates at SA node but is irregular with repetitive variation in cycle length
PR interval and QRS duration are normal and consistent
(not a true arrhythmia)
sinus bradycardia
originates in SA node but <60 bpm regular P to P and R to R intervals P waves are uniform and upright with one P wave per QRS complex PR interval is between 0.12-0.2 seconds QRS complex is <0.12 seconds
sinus tachycardia
originates in SA node at >100 bpm regular P to P and R to R intervals P waves are uniform and upright with one P wave per QRS complex PR interval is between 0.12-0.2 seconds QRS complex is <0.12 seconds
atrial dysrhythmias
originate in atria but outside of the SA node
P wave configuration will be upright, but shaped differently than P waves originating in SA node
premature atrial complexes (PACs)
early beats that most often originate from an irritable focus in the atria
single early beats with an underlying rhythm rather than an abnormal rhythm itself
P wave may be hidden in preceding T wave
causes of atrial dysrhythmias
emotional stress/anxiety fatigue nicotine, medications, alcohol, caffeine infection electrolyte imbalances CHF, myocardial ischemia
supraventricular tachycardia (SVT)
rapid dysrhythmia that originates above the ventricles in either the atria or the AV junction
>120 bpm (usually 150-250 bpm)
atrial flutter
regular atrial rhythm; ventricular rhythm may or may not be regular depending on AV conduction
initiated by irritable focus in atria
causes rapid depolarization (250-350 bpm)
usually no P wave, instead “flutter” waves with saw-toothed appearance
atrial fibrillation
occurs from rapid firing of multiple irritable foci in atria
no effective atrial contraction bc no uniform wave of depolarization
decreased cardiac output
atrial rate 350-600 bpm
no P wave, instead fib waves with wavy baseline
atrial kick
blood pushed out of the atria into the ventricles after they depolarize and contract together
lost in A-fib
atrial dysrhythmia collaborative care
rate control with chronic anticoagulation (usually Coumadin)
beta blockers and calcium channel blockers for rate control
digoxin if no response to BBs or CCBs
cardioversion
TEE
ventricular dysrhythmias
originate in ventricles
ventricles may take over as the pacemaker for the heart if:
SA node fails to discharge an impulse
impulse is blocked and does not reach the ventricles
SA node and AV node are pacing slower than impulse generation of ventricles
an irritable site in one of the ventricles produces a rapid rhythm
premature ventricular complexes (PVCs)
an early beat with an underlying rhythm initiated by an irritable focus in one of the ventricles
no PR interval
no P wave
may be unifocal or multifocal
unifocal PVCs
look the same and originate from the same irritable focus in the ventricles
multifocal PVCs
look different and may originate from different irritable foci in the ventricles
ventricular escape rhythm
AKA idioventricular rhythm
occurs in ventricles with no association in atria
may exist when both SA and AV nodes fail to pace the heart or when their impulses are blocked
P waves usually absent
ventricular tachycardia
AKA VT, VTach
run of 3+ PVCs in succession ventricular rate 110-250 bpm regular rhythm P waves absent or hidden in QRS wide QRS
ventricular fibrillation
severe electrical chaos in ventricles
multiple irritable foci firing in erratic, disorganized manner
no ventricular contraction
no cardiac output/systemic perfusion
fatal within minutes without intervention
Torsades de pointes
type of ventricular tachycardia that can become ventricular fibrillation
ventricular asystole
AKA cardiac standstill
no ventricular activity
no cardiac output
flatline ECG
pulseless electrical activity (PEA)
organized electrical activity is present
pulseless due to absent mechanical activity or inability of heart to fill/contract
poor prognosis unless reversible cause is rapidly ascertained and treated
defibrillation
unsynchronized shocks that use higher energy level than cardioversion
used for shockable pulseless arrests including VF, VT
must call “all clear” before delivering shock
cardioversion
synchronized with pt’s QRS complex
must use “synchronize” button on defibrillator
shock occurs on R wave
cardioversion indications
unstable SVT
atrial fibrillation
atrial flutter
ventricular tachycardia (with a pulse)
pacemaker
device designed to assist in stimulating the heart when the natural pacemaker is too slow or its impulses are blocked from reaching the ventricles
external temporary pacemaker
used in emergency situations for pts with unstable bradycardia
most defibrillators can perform this function
AKA transcutaneous pacing
internal temporary pacemaker
AKA transvenous or epicardial pacing
insertion of pacing wire into either right atrium or right ventricle via central venous catheter
epicardial pacing wires may be placed during an open chest cardiac procedure
permanent pacemaker
used to resolve dysrhythmias that are not temporary
involves placing one or more wires into the heart chambers
demand (synchronous) pacing
synchronized with pt’s HR
fixed-rate (asynchronous)
fires continually at a preset rate regardless of pt’s intrinsic HR
failure to pace
pacemaker fails to deliver an electrical stimulus
absence of pacer spikes on ECG
pt may become bradycardic and hypotensive
failure to sense
pacer fails to recognize pt’s natural electrical activity
seen on ECG as pacer spikes too close behind QRS complex
oversensing
pacer senses extraneous electrical stimuli or artifact for actual atrial or ventricular depolarization
fails to fire
implantable cardioverter-defibrillator
similar in size and placement to pacemaker
constantly monitors HR and rhythm
programmable to deliver pacing, cardioversion, and/or defibrillation
implantable cardioverter-defibrillator indications
pts at risk of sudden cardiac death 2/2 VF
pts who have experienced one or more episodes of VT or VF unrelated to an MI
radiofrequency catheter ablation
treats tachydysrhythmias (SVT, atrial flutter, A-fib)
performed in EP lab under conscious sedation
high frequency electrical current creates small necrotic lesions in the heart by means of thermal injury
MAZE procedure
series of incisions arranged in maze-like pattern in atria
used for pts in chronic A-fib who are scheduled for an open heart procedure for other cardiac problems
largely replaced by RFCA
cardiac/EP mapping
multiple flexible wires are threaded into the heart
catheters have miniature electrodes that act as antennae and receive signals from all around the heart chamber
computer process into 3D image of chamber
