Week 10: Cardiac Rhythm Disorders Flashcards
What are the 2 major phases of the cardiac cycle
- Contraciton (Depolarization)
2. Relaxation (repolarization)
Chronotrophy
Heart Rate
Ionotrophy
Contraction Force
Dromotrophy
Conduction Speed
Path of Cardiac Conduction
SA Node –> AV Node –> Bundle of His –> Right and Left Bundle Branch –> Purkinje Fibers
Depolarization
when Na moves into a cell and K moves out
activity causes electrical activity which causes cardiac muscle movement
as one cell depolarizes it makes the next do so as well and causes a chain reaction
Repolarization
occurs when the cell returns to its resting or baseline state
SA Node
Sinus Node / Sinoatrial Node
Main pacemaker of the heart
Stimulates 60-100 BPM through depolarization
Located high in the right atrium
What part of the heart conduction pathway can a right sided MI destroy
the SA node –> this leads to bradycardia and hypotension
Tx when a Right Sided MI occurs
IV fluids!!!
Nitroglycerin
Patient to cath lab
AV Node
atrioventricular Node
Gatekeeper of the heart
fires if the SA node rate is too low at an intrinsic rate of 40-60 BPM
What does the AV node allow for
it allows the atria to contaract and empty by slowing impulses from the SA node
Where is the AV node located
small group of cells in the lower right atrium
Bundle of HIS
short bundle of fibers at the bottom of teh AV node
they are specialized electrical cells that travel in the septum and spread to both sides of the heart in both ventricles
leads into the bundle branches
The Bundle Branches
Left and Right
Rapidly conduct impulses to the left and right ventricles after the Bundle of HIS
The Purkinje Fibers
Terminal point in the conduction system in the ventricles
they are hair like fibers spreading out from the bundle branches along the endocardial surface of the ventricles
rapidly conduct the impulse to the ventricular cells
The Purkinje Fibers are capable of causing impulses at ___-___ BPM
20-40
P Wave
a normally small smooth and rounded bump at the start of the impulse
indicated atrial contraction / atrial depolarization
PR Interval
Conduction from the atrium to Purkinje fibers depolarizing
Measured from start of P wave to the tip of the R
How long is the PRI usually
normally less than 1 large (or 5 small) blocks so less than 0.2 seconds
So usually 0.12-.20 seconds
Each small box on the EKG is ___ s
0.04 seconds
Each large box on the EKG is ___ s
0.2 seconds
5 of the large boxes (25 small boxes) on the EKG is ___ s
1 second
QRS Complex
Occurs with ventricular contraction/depolarization
Q is the first down, R is the first up, and S is the negative deflection after r
Usually less than 2.5 small boxes (0.1 s) –> 0.06-0.1 s
T Wave
Follows the QRS
Indicated ventricular repolarization
heart resting period
What wave indicates a vulnerable period of the heart where if there is an issue something lethal can occur
T Wave
Different deflections from baseline of the PQRS complex indicates..
different views or LEADS of hearts conduction patterns (lead 2-3 may look different)
When Assessing EKGs it is important to look at what 2 things
- Rhythm - regular/irregular - the origin of beat
2. Rate - number of ventricular contractions per minute
We should check the EKG first to see if there is a…
P wave
We can check rhythm by
measuring distance between P-P2 R-R2 waves and comparing peaks
What are the 3 methods of calculating rate off an EKG
- # Small boxes Between QRS Complexes / 1500
- # Large boxes between QRS complexes / 300
- 6 Second Method - number of peaks x 10
What are the things to ask when evaluating the P wave and PR Interval
Does the rhythm originate in the atrium
Are P waves regular
Are P waves followed by QRS
Is the Pr normal .12-.2 in length or is it longer than .2
What are the things to ask when evaluating QRS complex
Is it normal duration of .06-.1 or is it higher
Do the QRS complexes look the same - wide ones can indicate ventricular arrhythmias
What are the thigns to ask when evaluating ST Segments
Is T Wave height less than 1/2 the QRS height
Is ST elevation above or depression below isometric line - indicates ischemic changes or MI
Raised ST increases threshold which can…
cause a heart attack
What are some other unusual findings on EKGs to see
ST Depression
Q Waves - scar from MI
Ectopic Beats - originate from abnormal pathways
Abnormal Herat Rhythms
Sinus rhythm
normal rhythm
Premature Rhythm
complex earlier than expected
Compensatory rhythm
pause in the beat occurring after a premature beat
Junctional rhythm
at or below AV node, above ventricle
Normal Sinus Rhythm
Rate 60-100 BPM
Regular R to R Interval
Normal PR Interval
Sinus Bradycardia
Rate < 60 BPM
Regular R to R interval
Normal PR Interval
P Wave
Beats are initiated in SA node
Sinus Tachycardia
Rate >100 BPM
Regular R to R Interval
P Wave Present
Normal PR Interval
Beat Initiated in SA Node
Sinus Arrhythmia on EKG
Rate 60-100 BPM
IRREGULAR R-R INTEVAL
P wave present and Normal PRI
Beat initiated in SA Node
BPM increases with inhalation and decreases with exhalation!!!
Dysrhythmias
disorders of formation or conduction (or both) of electrical impulses within heart
potentially alters blood flow, causes hemodynamic changes
Dysrhythmias can cause disturbances of…
rate
rhythm
both rate and rhythm
Dysrhythmias are diagnosed by …
analysis of electrographic waveform
Dysrhythmias can be ___ or ___ in origin
supraventricular (above - SA/AV node)
Ventricular (bundle branches/perkinje)
What are the 3 most common Supraventricular Rhythms
Junctional Rhythms
A Fib
A Flutter
What are the 3 most common Ventricular Rhythms
PVC
VT
VF
What is more deadly supraventricular or ventricular rhythms?
Ventricular Rhythms
Premature Atrial Contraction (PAC)
Abnormal P Wave that comes early and fuses with T wave
There is then a pause after it occurs
Lots of people have this occur
What can cause PAC
caffeine
Nicotine
stress
ischemia (big problem)(
Atrial Fibrillation
Rate: 400-600 BPM atrial; Ventricular rate varies but can be high as 110-160
R to R is irregular
No P WAVES!!!
QRS appears normal usually
What is the most common rhythm seen next to normal sinus rhythm (NSR)
A fib
If A Fib has a rapid ventricular rate as well…
this may cause reduced cardiac output
A Fib may lead to …
Mural Thrombi
In A Fib what is lost and can lead to heart failure
atrial kick
Tx for A Fib
Watch for CO (BP, UO, LOC, Color)
Meds - variety used to control rate or restore normal rhythm (digozin, verapamil, beta blockers)
ASA - anticoagulants
Watchman
Cardioversion or pacemaker may be necessary if unstable