CLASS 22 - Cardiac Arrhythmias + Exemplars Flashcards
(60 cards)
What does it mean to be chronotropic ?
Affects the heart rate and rhythm by affecting the electrical conduction system of the heart
What does it mean to be inotropic?
Changes the force of the heart’s contractions. Can be +ve or -ve inotropes.
Positive inotropes strengthen the force of the heartbeat, negative inotropes weaken the force of the heartbeat.
What initiates the Cardiac Conduction System?
The SA node.
Why is the SA node considered to be the pacemaker of the heart?
the cells of the SA node spontaneously depolarize FASTER than other cardiac cells and create electrical impulses, therefore setting the normal rhythm and rate of the heart.
once the SA node creates an electrical impulse, where does it travel?
travels through atria and reaches the AV node.
then travels to the ventricles by the bundle of His and the Purkinje fibers
synchronized so that all ventricles contract at the same time
what is overdrive suppression?
SA node depolarizes first and resets all other cells
what is an ectopic rhythm?
occurs if another cardiac cell initates contraction resulting in premature atrial conraction
describe the effects of the SNS and PSNS on the SA Rate
SNS: increases SA rate
PSNS: slows SA rate via vagus nerve
what is the only electrical pathway from the atra to the ventricles?
AV node
what is the PR interval?
AV node conduction
what is a normal sinus rhythm (NSR)?
temr used to decribe a normal ECG rate and rhythm generated in the SA node
what are the effects of potassium balances on the ECG?
potassium has effects on the myocardium’s resting potential and ability to repolarize
potassium imbalances tend to slow impulse conduction through the AV node and myocytes.
what are the effects of hypokalemia on the ECG?
- PR
- ST
- U
- QT
prolonged PR depressed ST low or inverted T appearance of U increased in QT
what are the effects of hyperkalemia on the ECG?
diminished or absent P
widening of QRS
peaked T
unexcitable cells
progresses to VT or VF and cardiac arrest
what are ‘U’ waves thought to represent?
repolarization of purkinje fibers
compare cardiac arrhythmias and dysrhythmias
arrhythmias are alterations in cardiac rhythm, where dysrhythmias imply loss of rhythm
when are cardiac arrhythmias / dysrhythmias harmful?
when the interfere with the heart’s pumping ability.
what do cardiac arrhythmias / dysrhythmias indicate ?
may indicate alterations in automaticity, excitability, conductivity, or refraction due to ischemia and infarction, electrolyte imbalances, drug effects, or defects in condiction.
what is sinus bradycardia?
where is it often seen?
defined as sinus rhythm with a resting rate less than 60 per minute
seen in trained athletes or during sleep, but may occur during myocardial infarction, respiratory depression, hypothyroidism, or drug toxicity.
can also be a compensation for an underlying disorder.
what is sinus tachycardia?
sinus rhythm with a resting rate over 100 per minute
seen with exercise or fever, but may occur with CHF, MI, hyperthyroidims, drug toxicity, and hypovolemia
why are sinus tachy - and bradycardia not often treated directly?
bc they usually occur secondary or as a compensation for another underlying disorder.
describe increased automaticity as a mechanism of arrhythmias.
increase in the natural depolarization rate of nodal cells
occurs commonly in response to SNS activation, can lead to uncontrolled electrical activity
decribe triggered activity as a mechanism of arrhythmias
occurs whn ischemia or fibrosis are present, or during heart failure.
following a normal AP, myocytes can sometimes depolarize spontaneously. These are called early or delayed afterpolarizations. (EAD or DAD) commonly causes ectopic or premature beats.
how does re-entrant activation occur?
in the presence of a one-way block, the stip of muscle is excited at only one location (instead of 2)
impulses spreading from this area meet no impulses coming from the left, and therefore can trael far enough to simulate branch 1 of the Purkinje fiber . This stimulation passes back up the fiber, past the region of one-way block, and then stimulates branch 2, causing reentrant activation.
