Tachyarrhythmias

Question 1

What are the three major mechanisms of tachyarrhythmia generation and propagation?

Answer 1

• Increased automaticity
• Reentry
• Triggered activity

Question 2

Describe the major ion currents driving the three phases of the cardiac pacemaker cell action potential

Answer 2

• Phase 4: Slow inward Na⁺ current (I_f). Perhaps inward Ca²⁺
• Phase 0: Rapid inward Ca²⁺
• Phase 3: Outward K⁺

Question 3

List 6 basic types of tachyarrhythmias

Answer 3

• Sinus tachycardia
• Atrial fibrillation (with RVR)
• Atrial flutter
• Multifocal atrial tachycardia
• Supraventricular tachycardia
  
  • includes AVRT and AVNRT
• Ventricular tachycardia
  
  • Includes monomorphic and polymorphic

Question 4

What are four conditions under which a tachycardia originating above the ventricles would have a wide QRS complex?

Answer 4

• Underlying BBB
• Preexcitation (as in WPW)
• Drugs that prolong the QRS (Class 1a or 1c antiarrythmics, procainamide/flecainide)
• Profound hyperkalemia

Question 5

Ventricular Tachycardia _______ (always/sometimes/never) has a wide QRS complex

Answer 5

always

Question 6

The usual cause of sinus tachycardia is:

Answer 6

enhanced normal automaticity from sympathetic activation of SA node. (β1-activation by epi and norepi)

Question 7

What are features of sinus tachycardia?

Answer 7

• Regular
• Rate >100bpm
• P-waves clearly precede each QRS with identical morphology to NSR
• Develops over minutes to hours
• Rate is usually variable over time

Question 8

What is the general mechanism of atrial fibrillation?

Answer 8

microreentry causing multiple, simultaneous, chaotic waves of depolarization at rates >500bpm in the atria.

Question 9

What are features of atrial fibrillation?

Answer 9

• The classic irregularly irregular rhythm
• Atrial activity consists of irregular low-amplitude “f”-waves
• Develops abruptly
• Rate may vary dramatically over time

Question 10

What is implied by bradycardic A Fib?

Answer 10

Severe AV node disease or excessive AV nodal blocking dosages

Question 11

Compare and contrast the mechnisms underlying AFib and AFlutter

Answer 11

Both are caused by reentry circuits in the atria. AFib is caused by multiple microreentry circuits throughout the atria, whereas AFlutter is generally caused by a single, well-defined macroreentry circuit, often at the cavotricuspid isthmus.

Question 12

It is ________ (common/rare) for patients to alternate between AFib and AFlutter

Answer 12

common!

Question 13

The risk factors for AFib and AFlutter are _________ (similar/dissimilar)

Answer 13

similar

Question 14

Flutter activity is best viewed in which leads?

Answer 14

II, III, and aVF (the inferior leads)

Question 15

What are features of atrial flutter?

Answer 15

• Rhythm may be regular, regularly irregular, or irregularly irregular
• Atrial rate is generally 240-340, most commonly 300bpm
• Flutter waves (F-waves) best seen in inferior leads
• Usually 50% or more of atrial impulses are blocked by the AV node
• Develops abruptly
• Rate may vary over time in a distinctive pattern of abrupt, discrete, incremental changes in rate with changes in degree of AV block (often switches between factors of 300)