Dysrhythmias and Conduction Disorders Flashcards
What is electrocardiology?
ability to generate spontaneous action potentials, aka “pacemaker ability”
In the resting state, cardiac cells are _______.
electrically polarized (insides are neg charged with respect to their outsides)
Membrane ion channels open and close using _____ to transfer ions between the intracellular and extracellular compartment.
pumps (ex: Na+, K+, Ca2+)
What can spontaneously depolarize and are the electrical power source of the heart?
pacemaker cells
What are contractile cells?
they carry out the actual contraction but are also capable of transmitting the action potential (automaticity), at a much lower speed than the conduction cells
What are conduction cells?
form the fiber networks inside the myocardium and disseminate the action potential, they have no contractile function
What acts as the normal pacemaker of the heart?
SA node
What is the SA node?
oval structure located near the entrance of the SVC in the right atrium, pacemaker cell that spontaneously and repeatedly generates electrical impulses and does not have a resting phase
SAN action potential is mediated by
calcium ion currents (node= slow response tissue)
Parasympathetic innervation (vagus nerve) _____ conduction.
slows
Sympathetic innervation (spinal cord) ____ conduction.
speeds
How is the rate of spontaneous depolarization in the SAN modified?
by altering electrolyte exchange or input from the autonomic nervous system
What are cardiac agents for the SA node?
calcium channel blockers, digoxin, beta blockers
What are noncardiac agents for the SA node?
parasympathomimetic agents, sympatholytic drugs
Tell me about calcium channel blockers.
block influx of calcium, reduces upstroke of AP
Tell me about digoxin.
increase parasympathetic effects
Tell me about beta blockers.
offsets sympathetic inputs
What are examples of parasympathomimetic agents?
Betachol, Pilocarpine, Acetylcholinesterase inhibitors
What are examples of sympatholytic drugs?
Methyldopa clonidine, Lithium, Ivabradine
What modulates the response between the atrium and the ventricle by impeding impulse conduction?
AV node
What is the AV node?
conducting cell located at boundary between atria and ventricles, has no automaticity, excited only by pulses that propagate through it
In a normal heart, the AVN is the only ________ from the atria to the ventricles.
conducting path
The AV node modulates ventricular response by _____ impulse conduction. It generates a slow action potential that is mediated by ___ currents (node= slow response tissue).
impeding, calcium
The ____ node DOES NOT have automaticity while the ____ cells surrounding it do possess it.
AV, pacemaker
What are the cardiac agents of the AV node?
calcium channel blockers, digoxin, Beta blockers, adenosine
Tell me about adenosine.
transiently inc potassium conduction and dec calcium influx
What are the noncardiac agents of the AV node?
carotid sinus massage, valsalva maneuver
What is the carotid sinus massage?
5 secs of firm manual pressure applied on carotid sinus area, left side is more likely to act on AV node whereas right side acts on SAN
What is the Valsalva maneuver?
bearing down, coughing, applied abdominal pressure (forcefully exhaling against a closed airway)
The SAN is supplied by the ______ in 60% of individuals and by the _________ in the remainder.
right coronary artery, left circumflex artery
The AVN and proximal Bundle of His is supplied by the ____ in 90% (
right dom system) of individuals whereas the remaining 10% vines from the ____ (left dom system).
RCA, LCA
Inferior MI due to RCA occlusion compromises supply to AV nodal artery affecting ______, ____, and ______ which can lead to ____ and ____.
SAN, AVN, and proximal His bundle, bradycardia, high-grade AV block
What is an action potential?
a rapid sequence of changes in the voltage across a membrane
After a cardiac cell has depolarized, there is a period of time in which it ______ to any other stimuli.
won’t respond
What is the absolute refractory period?
phase 0-3 where absolutely no other stimulus will excite the cell
What is the relative refractory period?
Phase 3 where a strong enough stimulus could potentially excite the cell and produce another action potential. The T wave corresponds with relative refractory period.
What are causes of arrhythmia?
abnormal impulse formation (enhanced automaticity- or triggered activity) and abnormal impulse transmission (re-entry phenomena or conduction disturbance)
What is enhanced automaticity?
inc firing of cells with pacemaker ability, abnormal firing of cells without automaticity (ex: sinus tachycardia, ischemic ventricular tachycardia)
What is triggered activity?
depolarization of a cell triggered by a preceding action potential, defined as early (phase 2 or 3) or late (phase 4) afterdepolarizations (early afterdepolarization- PVCs, delayed- digoxin related)
What is Re-Entry (Circus Movement)?
a depolarizing impulse encounters a blocked area that can only be passed on one side, impulse gets around the block on one side, circulates around it and travels back to repetitively excite a region of the heart
The Re-entry/Circus Movement may arise because of a …
fixed anatomic structure (Wolff-Parkinson-White syndrome) but more commonly due to abnormal physiologic states (ischemic VT).
What are the sinus dysrhythmias?
sinus bradycardia, sinus tachycardia, sinus arrhythmia, sinus node dysfunction, sinus arrest, sinus exit block
Tell me about sinus bradycardia.
Rate: less than 60 bpm
Rhythm: regular
Conduction: 1:1
normal sinus P waves and PR intervals
What causes sinus bradycardia?
Physiologic: inc vagal tone
Pharm: CCB, BB, digitalis
Patho: inferior infarct, inc ICP, carotid hypersensitivity, SSS, hypothyroidism
Tell me about sinus tachycardia.
Rate: greater than 100 bpm
Rhythm: regular
Conduction: 1:1
normal sinus P waves and PR intervals
What causes sinus tachycardia?
Physiologic: pain, exertion
Pharm: sympathomimetics, caffeine, bronchodilators
Patho: fever, hypoxia, anemia, hypovolemia, PE, hyperthyroidism
Tell me about sinus arrhythmia.
Rate: variable
Rhythm: irregular
Conduction: 1:1
results from changes in autonomic tone during respiratory cycle
inspiration- lowers vagal tone, inc sinus rate
expiration- raises vagal tone to previous state, sinus rate decline
rhythm becomes completely regular if person holds their breath
What causes sinus arrhythmia?
Physiologic: respiration in young healthy individuals
Pharm: Morphine, digitalis (drugs that inc vagal tone)
Patho: loosely associated with myocardial ischemia, obesity, DM, hypertension, herald sign of sinus node dysfunction
Tell me about sick sinus (“tachy-brady”) syndrome.
Rate: variable
Rhythm: irregular
Conduction: 1:1 or 0:1 (sinus arrest w ventricular escape)
Associated with sinus bradycardia, chronotropic incompetence, sinus arrest/pause, sinoatrial block
What causes sinus node dysfunction?
sinus bradycardia- purest form of SND, diminished automaticity
chronotropic incompetence- inability of SAN to adequately inc its automaticity during physical activity
sinus arrest/pause- intermittent failures to discharge impulses
sinoatrial block- delayed or blocked impulse conduction between the sinoatrial node and the atrium
sinus arrhythmia in elderly
Sick sinus syndrome includes sinus node dysfunction and these symptoms:
fatigue, dizziness, dyspnea, presyncope/syncope, diminished exercise tolerance
What causes sick sinus syndrome?
Physiologic: N/A
Pharm: BB, CCB, digitalis
Patho: idiopathic degenerative fibrosis (commonest), ischemia, cardiomyopathies, congenital abnormalities, hypothyroidism, electrolyte abnormalities (hyperkalemia)
What are the atrial dysrhythmias?
premature atrial contractions, atrial flutter, atrial fibrillation
Tell me about premature atrial contraction.
Rate: variable, depending on underlying rhythm
Rhythm: irregular
Conduction: 1:1 (or 0:1 if premature beat not conducted)
occurs earlier than the next expected sinus beat, may be single or repetitive events, unifocal or multifocal (rare) in morphology
PRI is normal or prolonged b/c AV junction is often partially refractory when the premature impulse enters
What causes premature atrial contraction (PAC)?
Physiologic: stress, fatigue
Pharm: digitalis toxicity, alcohol
Patho: CAD, valvular heart disease, electrolyte abnormality, hypoxia
Normally conducted PAC
uninhibited conduction through AVN, looks similar to other QRS complexes in the EKG
Non-conducted “blocked” PAC
not conducted b/c AVN is refractory
Conducted with aberrancy PAC
premature beat conducted past the AVN but one or more of conducting fascicles or bundle branches are refractory, resulting QRS is usually wide, sometimes called Ashman beat or Ashman phenomenon
