ECG Week 5 test 2 Flashcards
Ventricular filling
mid to late ventricular diastole (includes atrial systole)
P-Q interval
Ventricular systole
isovolumetric contraction and ejection phase
Q-T interval
Quiescent phase
isovolumetric relaxation in early ventricular diastole until atrial contraction (end of T wave to beginning of next p wave)
S1 or LUB
closure of AV valves at the beginning of ventricular systole
S2 or DUB
closure of the SL valves and the beginning of ventricular diastole
Specialized pacemaker cells
responsible for the initiation and conduction of electrical signals (APs) through the heart.
SA, AV, His bundle, bundle branches, and Purkinje Fiber
Working myocardial cells
responsible for contraction and relaxation, these make up the majority of the mass of the heart muscle
Normal activation sequence
SA->atria->AV node->His bundle->bundle branches->Purkinje fibers->ventrilces
AV node
contains slowly conducting cells that normally function to create a slight delay between atrial contraction and ventricular contraction
Purkinje Fibers
specialized for rapid conduction and ensure that all ventricular cells contract at nearly the same instant
What is heart normally controlled by?
The SA node
Most cardiac cells have what type of response to action potentials?
Fast
Specialized cells have what type of response to action potentials?
slow.
in phase 4 do the cardiac cells depolarize?
No, they rely on the pacemaker cells stimulus to quickly depolarize.
What causes the plateau in the working myocardial cells
and influx of calcium ions into the cell, which stop the repolarization by efflux of potassium.
steps in working cell (cardiomyocyte) AP
phase 0=rapid depolarization due to Na influx and stim by pacemaker cells
phase 1= K and Cl out to repolarize
phase 2=plateau due to Ca in and K out
phase 3=Ca influx stops and K efflux cont.
phase 4= K out at resting potential
Specialized (pacemaker cell) AP
phase 4 Na and Ca influx (slow)
phase 0= Ca in at threshold
phase 3= K out to repolarize
AP opens the L-type slow Ca channels causing what?
a 1000-fold rise in intracellular free Ca hence the quick depolarization of cardiac muscle.
Ca induced Ca release
what is cardiac output (CO)
Stroke volume x Heart rate
The volume of blood being pumped by the heart per unit of time
what is stroke volume
the end diastolic volume - end systolic volume
or how much blood is pumped out each pump
what is total peripheral resistance (TPR)
sum of the resistance of all peripheral vasculature in the circulatory system
How to calculate blood pressure
Cardiac out put x TPR
thus BP can be maintained by altering either CO and or TPR
Barorecptor reflex
can correct for a change in arterial pressure by
- increasing or decreasing heart rate as needed.
- *Detects changes in heart rate, due to a change in the arterial pressure
Bainbridge relfex
responds to changes in blood volume.
-increases HR when there is an increased in atrial pressure.
What is a normal sinus rhythm, tachycardia, and bradycardia?
HR: 60-100 beats/ min
Tach: greater than 100 beats/min
Brady: less than 60 beats/min
What is lead?
electrical potential difference between two electrodes
P wave
atrial depolarization in response to SA node firing
-precedes atrial contraction
PR interval
time for electrical wave front to move from atria to ventricles( slight delay in AV node to allow filling of ventricles.
**normally PR interval should be isoelectric
QRS complex
ventricular depolarization; triggers main pumping contraction
-atrial repolarization hidden in QRS
ST segment
approximate index of ventricular AP plateau (ventricles contract): normally should be isoelectric
T-wave
ventricular repolarization
QT interval
ventricular AP
What is the only link between the atria and ventricles?
the AV node
R-R interval
interval between ventricular beats; varies with heart rate. The faster the HR the shorter the distance between the interval. opposite is true for slow HR
ECG abnormalities ST elevation
occurs in leads directly over the area of acute infarction
ECG abnormalities T wave inversion
indicates ischemia
ECG abnormalities Exaggerated Q waves
a marker of infarction that develops with time
ECG abnormalities ST depression
seen in leads opposite to or away from the area of ST elevation.
may also indicate ischemia
If the + end of the dipole approaches the + electrode, the deflection will be?
postive or upward
in other words; if the positive recording electrode faces a wave of depolarization, it will be an upward signal.
**arrow or dipole is pointing towards the positive elcetrode
if the + end of the dipole approaches the - electrode what will the deflection be?
negative or downward
**arrow or dipole is pointing towards the negative electrode
If the dipole is perpendicular to the axis of the dipole what happens?
there will be an isoelectric point and no wave will show.
ECG paper
little boxes=
big boxes=
HR
little=0.04 sec, and 0.1 mV
big= 0.2 sec and 0.5 mV
5 little boxes/ large box.
HR = 60 / R-R
3 Bipolar Lead ECG
Lead I: (-) electrode on right arm(RA) and (+) on left arm(LA)
Lead II: neg on RA and pos on left leg (LL)
Lead III: neg on LA and pos on LL
Einthoven’s Law
Lead I + Lead III = Lead II
Normal Sinus ECG 6 things to know
- frequency of QRS complexes is apporx. 1 per sec
- QRS complex is upright and lead II with a duration of 120 ms
- QRS complex is preceded by one P wave
- PR interval is less than 0.2 sec
- QT interval is less than half of the R-R interval
- no extra p waves
What does long QT syndrome lead to?
leads to spontaneous ventricular tachyarrhythmias such as tachycardia.
-can be congenital or acquired due to new meds.
what is Torsade de Pointes
means twisting of the spike and is a stereotypical arrhythmia associated with patients with long QT syndrome and leads to V fib and possibly death if not treated.
describe a supraventricular tachycardia event
atria are abnormally excited and drive the ventricles at a very rapid rate
-QRS complexes may or may not appear normal because the P and T waves may be superimposed at a high HR
-
describe A fib with common ECG signs
- irregular heart rhythm
- No clear P waves
- absence of isoelectric baseline
- irregular ventricular rate (R wave)
- QRS complexes may be prolonged but don’t have to be
what is a first degree AV block and what are the signs on a ECG
P and R waves both present but have irregular pattern
PR interval is greater than 0.2 sec
**key here is a prolonged PR segment hence the AV block
Second degree AV block or Mobitz type I
P waves present but not regular
R waves present but not regular
PR interval is greater than 0.2 sec and progressively increases until a QRS complex is droped
second degree AV block or Mobitz type II
p wave present and regular
R wave present and not regular (same as type I)
PR interval can be normal, but doesn’t have to be before QRS is dropped
*requires pacemaker
third degree or complete AV block
P waves present and regular R waves present but no regular dropped QRS are high PR interval irregular ventricles and atria contracting at own rates leading to ventricular escape
ventricular escape can have two fates
syncope(self terminating) or sudden cardiac death
