PPT 14: Cardiac Arrhythmias Flashcards
Exam 2
How prevalent are cardiac arrhythmias in anesthetized patients?
50%
What are the types of cardiac arrhythmias?
- Bradycardia - Slowing (<60 bpm)
- Block
- Tachycardia
- Supraventricular (SVT, atrial)
- Sinus (regular)
- Ventricular Tachycardia (Vtach) - Fibrillation (Atrial or Ventricular)
What are the components of the intrinsic conduction system of the heart?
Sinoatrial node/pacemaker
Atrioventricular node
Atrioventricular bundle/bundle of His
Purkinje fibers
Which part of the intrinsic conduction system is the pacemaker of the heart? What is the contraction rate?
SA node - 75 beats/min
The _______ is the crescent shaped node in right atrium of the intrinsic conduction system
Sinoatrial node/pacemaker
The _______ is the junction of atria and ventricles of the intrinsic conduction system
Atrioventricular node
How fast does the AV node contract?
40-50 beats/min - slow
The _______ is in the interventricular septum of the intrinsic conduction system
Atrioventricular bundle/bundle of His
The _______ is spread within the muscle of the ventricle walls of the intrinsic conduction system
Purkinje fibers
Discuss the changes of the electrocardiogram throughout the intrinsic conduction system
Impulses that deviate from the normal electrical pathway are _______
Arrhythmias
What are the different types of abnormalities of arrhythmias?
- Site of origin
- Rate
- Regularity
- Conduction
What are the 3 main ions that determine cardiac action potential?
- Sodium
- Potassium
- Calcium
Discuss the phases of ion channel currents in cardiac action potential
Discuss the three states of sodium channels
- Resting
- slowly approaching threshold
- m gates closed - Activated
- threshold reached; m gates open
- massive sodium influx - Inactivated - h gates close
The ________ is the time between the inactivation and resting states of sodium channels
Refractory period
K+ channels are open at rest are called ______
Inward rectifier channels - Very little flow (electrical gradient)
______ establish the membrane potential of resting cardiac cell
K+ current
Ca++ channels open _____ and at more ______ potentials
slowly and positive
What are the 2 main classes of arrhythmias?
- Disturbances in Impulse Formation
- Disturbances in Impulse Conduction
What are the types of disturbances in impulse formation that result in arrhythmias?
- Early or late afterdepolarizations
- SA/AV nodal abnormalities
- Ion changes
- SNS stimulation
What are the types of disturbances in impulse conduction that result in arrhythmias?
- Block
- Reentry
Abnormal depolarizations that occur during phase 2, 3, or 4
Afterdepolarizations (AD)
Differentiate between Early (EAD) and Delayed Afterdepolarizations (DAD)
Early Afterdepolarizations (EAD)
- Phase 2 or 3
- Sodium or calcium channels
Delayed Afterpolarizations (DAD)
- Occur before a normal action potential
- Elevated intercellular calcium
Severe depression of conduction may result in ______
block
Discuss the ECG changes of the various degrees of heart block
________ inhibits conduction of depolarization
Heart block
What is considered “blocked” in heart block?
- AV nodal block
- Bundle branch block
- Block – allows one-way conduction
Describe the reentry block and “circus movement”
One impulse “circles around” and re-excites areas more than once
What must happen in order for reentry to occur?
- There must be an obstacle (scar tissue)
- Block must be unidirectional
- Conduction time must be long enough to reenter same areas after refractory period
How is heart block treated?
- Type II/III: Transcutaneous pacing, pacemaker
- Pharmacology (reentry):
a. Slow down circular current – sync with next action potential
- Drugs – block sodium or calcium current
b. Lengthen or shorten refractory period
What are the 4 classes of antiarrhythmic agents?
Vaughan-Williams classification:
- Class I – sodium channel blockade
- Class II – sympatholytic (beta blockers)
- Class III – prolong action potential duration (other mechanisms besides sodium channels – K+)
- Class IV – block cardiac calcium channel currents
What are the 3 subclasses of Class I antiarrhythmic agents?
IA, IB, IC
What meds are included in Class IA antiarrhythmic agents? What are the effects on APD and ERP? What are the cardiac effects?
Quinidine (Procainimide, Disopyramide)
- Prolong the action potential duration (APD)
- ↑ Effective Refractory Period (ERP)
- Cardiac effects: Depresses pacemaker rate, Lengthens QT interval, Depresses conduction and excitability
What meds are included in Class IB antiarrhythmic agents? What are the effects on APD and ERP?
Lidocaine
- Shorten the APD
- ↓ ERP
What meds are included in Class IC antiarrhythmic agents? What are the effects on APD and ERP?
Flecainide
- Minimal effects on APD
- Slow dissociation
- No effect on ERP (But Na+ channels are still blocked)
What meds are included in Class II antiarrhythmic agents? How do these agents work as antiarrhythmics?
Beta blockers - propanolol and esmolol (short acting)
- Antiarrhythmic properties associated with direct membrane effects - Exact antiarrhythmic action unknown
- Suppress ventricular ectopic depolarization
- Prevent infarction and sudden death in patients recovering from acute MI
What meds are included in Class III antiarrhythmic agents? How do these agents work as antiarrhythmics?
Amiodarone (VT) and dronedarone (A-fib)
Prolong AP usually by:
- Blocking cardiac K+ channels
- Enhancing inward current (Na+ or Ca2+ channels)
What meds are included in Class IV antiarrhythmic agents? How do these agents work as antiarrhythmics?
Calcium channel blockers - verapamil
- Prolongs AV node conduction
- Slows SA node
- Hypotensive action
- Useful for supraventricular arrhythmias
- Can reduce ventricular rate in atrial fibrillation and flutter
What are the antiarrhythmic agents that do not fit into the conventional classes?
- Digoxin
- Adenosine - SVT, Enhanced K+ conductance, Inhibition of cAMP induced calcium influx
- Magnesium - digitalis induced arrhythmias
- Potassium - normalizing levels
What are the non-pharmacologic interventions used to treat arrhythmias?
- Vagal maneuvers
- Pacemakers
- Cardioversion
- Catheter ablation
- Surgery
What is the treatment for symptomatic bradycardia?
1st - atropine
2nd - epi, dopamine
What is the treatment for chronic bradycardia?
pacemaker
What is the treatment for symptomatic heart block?
atropine and transcutaneous pacing
What is the treatment for chronic heart block?
pacemaker
What is the treatment for symptomatic SVT?
adenosine
What is the treatment for chronic SVT?
CCBs, beta blockers
What is the treatment for symptomatic sinus tachycardia?
Adenosine, CCBs, cardioversion
What is the treatment for chronic sinus tachycardia?
catheter ablation
What is the treatment for symptomatic Vtach?
amiodarone
What is the treatment for chronic Vtach?
amiodarone, satolol
What is the treatment for symptomatic Afib?
diltiazem, verapamil
What is the treatment for chronic Afib?
beta-blockers, amiodarone
What is the treatment for symptomatic Vfib?
CPR, defirillation
What is the treatment for chronic Vfib?
amiodarone, lidocaine
