1.5 Cardiac electrophysiology 59-68 Flashcards
an arrhythmia due to blockage in electrical conduction system of the heart (not a flow problem)
A-V heart block
first degree A-V heart block is what degree of interruption to the heart?
mild interruption (slowdown)
second degree A-V heart block is what degree of interruption to the heart?
moderate interruption
third degree A-V heart block is what degree of interruption to the heart?
severe interruption/disruption
what is a relatively common and essentially symptom-free AV heart block?
first degree
what AV heart block is a complete disruption and results in CO problems such as syncope (lightheadedness)?
3rd degree
lab findings for A-V heart block
abnormal ECG: lengthened P-R interval
wiring system of the heart is called
conduction system
the SA node is the fastest to recycle, it leads the pack and its therefore called the:
pacemaker
the SA node produces what kind of rhythm
sinus
when the SA node is stretched, it fires faster/slower/stays the same
faster. so increased venous return, increased atrial pressure, increased heart rate
impulse propagation is held up at the AV node for how long
1/10th second
knowledge of the electrical behavior of the heart lept forward with advances in cardiology sub-field of:
electrocardiography
a display from a super sensitive voltmeter called an electrocardiograph is called
electrocardiogram
the ECG represents electrical activity of the heart during its cycle. voltage recordings produce “___” on a graphical printout
waves
atrial depolarization is what on the ECG
P wave
ventricular depolarization is what on the ECG
QRS complex
ventricular repolarization is what on the ECG
T wave
Where are all the waves on the ECG/EKG? sketch it out
check yo’self
… before you wreck yo’self …
corresponds to rapid reversal of the impulse direction at the apex and now toward the base (atria)
S wave
rapid depolarization of the rest of the ventricles (initially toward apex)
R wave
described as septal activation
Q wave
the ___ wave corresponds to atrial muscle cells.
the ___ corresponds to steep phase of ventricular action potentials
the ___ corresponds roughly to the relative refractory periods
P wave; QRS complex; T wave
a flat spot or baseline on the ECG is termed
segment
combination of waves or waves/segments on the ECG is termed
interval
Note: ST segment during the ____
absolute refractory period
Note: PR segment due to ___
AV nodal slowdown
an important stretch often examined in ventricles that are in trouble. Serious problem in the muscle cells of the pumping chambers when this segment is “elevated” (injury, infarct) or “depressed” (non-specific)
ST segment
represents the delay at the AV node. long segments here indicate some sort of electrical system blockage between atria and ventricles
PR segment
What could cause a shift in the mean QRS vector (AKA electrical axis of the ventricles)?
inhalation/exhalation or tall/thin or short/stocky body type
How would inhalation or tall/thin body type shift the mean QRS vector (AKA electrical axis of the ventricles)?
right shift
How would exhalation or short/stocky body type shift the mean QRS vector (AKA electrical axis of the ventricles)?
left shift
what causes heart to shift right on axis?
inhalation or tall/thin body type
what causes heart to shift left on axis?
exhalation or short/stocky body type
a (heart) shift out of normal range
axis deviation
asynchronous contractions
arrhythmia
tachycardia can happen because:
high body temp, sympathetic stimulation to the heart
bradycardia can happen because
athletic conditioning (normal), and abnormal when parasympathetic stimulation is excessive ie when baroreceptors in the neck become compressed by arteriosclerosis
sinus arrhythmia usually due to
ventilation … causes changes in sympathetic and parasympathetic signals. ie. inhalation = increased heart rate and exhalation = decreased heart rate
ischemia of the AV node or bundle or bundle branches
atrioventricular block
a heart block that results in minor lengthening of the PR interval or segment
1st degree AV block
heart block that is serious lengthening of the PR interval with occasional missing, “dropped” beats in ventricles though atria still regular
2nd degree AV block
heart block that is ventricular “escape” as atria beat at ~ 75bpm and ventricles at ~30 bpm
3rd degree AV block (complete)
the “AV block” in the Purkinje system is called
intraventricular block
usually produces a very abnormal QRS interval
intraventricular block
an electrical event out of proper location (from the normal sequence)
Ectopi Foci
atria prematurely beats
premature contration (usually harmless)
premature ventricular contractions (“PVS”s)
premature contraction, can be deadly
why premature contraction?
hyper-excitability of myocardial tissue such that it depolarizes at the wrong time
what can cause hyper-excitability of myocardial tissue
over use of stimulants (caffeine, nicotine)
lack of sleep
local ischemia (atherosclerosis and low O2 availability)
most common cause of fibrillation
myocardial ischemia due to atherosclerosis
impulse re-entry (AKA circus movement)
positive feedback
- Start at “12 o’clock” and proceed clockwise around a loop of cardiac muscle
- Normally, impulse ends when it reaches absolutely refracted tissue (at the starting point)
- However, imagine that the starting tissue is ready to go again! Due to: slow impulse conduction, long impulse paths
- Impulse “reentry” occurs (and continues) with no coordinated contractions
- Nearly zero ejection fraction so no cardiac output = no coronary blood flow = weakening heart
technique to interrupt ventricular fibrillation by the application of a large electrical shock
defibrillation
a technique used to get the SA node back on rhythm by timing a mild shock during an R-S wave
cardioversion
a disease/condition of slowing or blockage of normal electrical impulse propagation through cardiac conducting system
A-V heart block
