Arrhythmia

Question 1

Normal Conduction

Answer 1

• Normally begins at SA-node in right atria
• SA node depolarizes atrial muscles
• AV-node between atria and ventricles is activated and (after a delay) initiates the conduction impulse through ventricles
• Purkinje fibers carry signal through septum to the apex and the rest of the ventricular mass

Question 2

PR Interval

Answer 2

• 100-200 ms normally
• Long: heart block (drugs, electrolytes)
• Represents AV-node conduction
• Drugs and disease states may increase time interval/conduction that may cause blockage of impulse
• Monitor PR with certain drugs

Question 3

QRS Interval

Answer 3

• 80-120 ms normally

- Long: conduction abnormalities (bundle branch block)

Question 4

QT Interval

Answer 4

• Normal range varies with HR
• > 450 ms leads to ventricular tachycardia
• Long: repolarization abnormalities, ion channelopathies (long QT syndrome)
• Represents time for ventricular polar/repolarization
• Rate dependent on HR (QT/ sqrt(R-R))
• *NEED TO MONITOR FOR DRUGS THAT PROLONG QT INTERVAL**

Question 5

Phase 0

Answer 5

• Na+ Dependent: Atrium, ventricles

- Ca++ Dependent: SA and AV node

Question 6

Impulse Generation “Leak”

Answer 6

• During Phase 4, gradual slope in potentials leads to activation of voltage-gated Na channels (THRESHOLD POTENTIAL and Phase 0!!!)
• Electrical energy and start of one heartbeat
• Altering characteristics of this slope or sensitivities of channels can alter cardiac pacing

Question 7

Phase 4 Slope

Answer 7

• Increasing => increases automaticity (HR)
• Sympathetic activity increases slope
• Cholinergic activity decreases slope/HR
• Some antiarrhythmics change slope and HR

Question 8

Impulse Generation

Answer 8

• SA node: 60-100 beats/min (most leaky ion channels thus is primary pacemaker)
• AV node: 30-50 beats/min
• Ventricles: <30 beats/min

Question 9

Tachycardias

Answer 9

• Sinus tachycardia (SA)
• Atrial tachycardia
• Atrial fibrillation/flutter (fib: HR = 500, flutter: HR = 350)
• AV-nodal re-entry tachycardia (HR = 150-250)
• Wolff-Parkinson White Syndrome (WPW: HR = 150-250)
• Ventricular tachycardia
• Ventricular fibrillation (fib: HR = 500, flutter: HR = 350)

Question 10

Bradycardia

Answer 10

-Sinus bradycardia (SA)
-AV node block (1st, 2nd, or 3rd degree)
-Asystole
(Mild-Mod: HR = 40, Severe: HR = 20)

Question 11

Etiology Classifications

Answer 11

Metabolic Abnormalities

• Ectopic conduction (early after depolarization)
• Ischemic tissue
• Genetic abnormalities (QT-prolongation)
• Electrolyte abnormalities
• Drug Toxicity

Structural Abnormalities

• Scarring/fibrotic area of no conduction
• Hypertrophy and cardiomyopathy
• Accessory pathways/block/congenital malformations

Question 12

Mechanisms of Arrhythmia Formation

Answer 12

Disorder of Impulse Generation

• Abnormal automaticity
• Triggered activity, early or delayed after depolarizations (EAD or DAD)

Abnormal Impulse Conduction

• Block
• Reentry

Question 13

EAD vs DAD

Answer 13

• EAD: altered opening of Ca++ or Na+ channels, also K+ channels
• DAD: elevated systolic [Ca++]

Question 14

Heart Blocks

Answer 14

• Area of tissue that does not conduct electrical impulse (action potential)
• Most important areas: SA node, AV node, or His-purkinje system (bundle brunch)
• 3rd degree: atria and ventricles are depolarizing independently, no association between the two

Question 15

Reentry Abnormality

Answer 15

• Unidirectional block caused by myocardial injury or a prolonged refractory period resulting in abnormal conduction pathway
• Reentry is most common cause of arrhythmias, and it can occur at any level of conduction system
• Impulses travel in retrograde direction and cause extra or irregular heart beats
• AV-nodal reentry arrhythmia is common, premature beat can set it up (node has embedded slow and fast pathways)
• Terminate by increase refractoriness (two-way block) or slow conduction (abnormal impulse hit refractory tissue out of damaged area)

Question 16

Proarrhythmia

Answer 16

• Torsades de Pointes
• Rapid form of polymorphic ventricular tachycardia
• Often preceded by prolonged QT interval
• Can be often caused by drugs and some conditions (hypokalemia or magnesemia) or congenital diseases/syndromes
• *Reason to monitor QTc intervals**
• Highest Risk Drugs: Class IA/IC agents, ibutilide, dofetilide, sotalol
• Highest Risk Factors: Structural heart disease, CAD, baseline prolonged QTc, electrolyte imbalances (K+)