Mechanism of Arrhythmia

Question 1

What are the clinical consequences of arrhythmia?

Answer 1

inadequate pump function, leading to low cardiac output and symptoms

Question 2

Describe the APs generated by SA and AV nodes

Answer 2

slow potential, mediated by Ca ions

Question 3

Describe the APs generated by atria, ventricles, and His-Purkinje system

Answer 3

fast potential, mediated by Na ions

Question 4

Describe the manifestations of K channel blockade in the heart

Answer 4

• increase in AP duration, increase in QT interval

Question 5

What are the two general mechanisms of arrhythmia?

Answer 5

• disturbance of impulse formation (initiated somewhere besides the SA node)
• disturbance of impulse conduction (too slow, too fast, or blocked)

Question 6

What are some conditions that can cause a brady arrhythmia? What about a tachyarrhythmia?

Answer 6

Brady bunch: sinus bradycardia, SA exit block, sick sinus syndrome, sinus arrest, type I, II, or III degree heart block
Tricky tachy: supraventricular tachycardia or ventricular tachycardia

Question 7

How does each type of heart block appear on EKG?

Answer 7

1st degree: increased P-R interval
2nd degree, type I (Wenckebach): gradual increase in P-R interval until a beat is skipped
2nd degree, type II: constant P-R interval with intermittent skipped beats
3rd degree: no conduction present from atria to ventricles, no relationship between P wave and R-S waves… why can’t we all just get along?

Question 8

What are the three specific potential mechanisms of tachyarrhythmia?

Answer 8

• increased automaticity (impulse from somewhere besides SA node - atrial, junctional, ventricular)
• triggered automaticity (impulse starts too early)
• reentry (impulse through different tissues)

Question 9

What is the most common mechanism of ventricular arrhythmia?

Answer 9

• reentry: 3 or more consecutive beats at the rate of 100+ bpm, wide but regular QRS

Question 10

What are two examples of triggered automaticity?

Answer 10

• Early Afterdepolarization: interrupts phase 3

- Delayed Afterdepolarization: interrupts phase 4

Question 11

A new patient comes in that has been on digoxin for the past few years. What type of arrhythmia are they most at risk for?

Answer 11

• delayed afterdepolarization

Question 12

In about 10% of the population, there are two pathways that lead into the AV node. What does this put them at risk for?

Answer 12

• reentry
• there is a fast and slow conduction pathway
• requires a unidirectional block
• there must be a final common destination of the two paths
• usually this is harmless, but a premature beat can disrupt the homeostasis

Question 13

You’re looking at an EKG and you see delta waves. What could this indicate?

Answer 13

• Wolff Parkinson White Syndrome
• cells with conduction properties are abherrently around mital and tricuspid annulus to create an accessory pathway for conduction
• conduction down this tissue is faster than AV node conduction
• can also cause reentry
• in the context of A fib, this can really mess a person up and progress to v fib

Question 14

You look at an EKG and see no organized atrial activities! What is going on?!

Answer 14

• atrial fibrillation
• QRS is irregularly irregular
• thankfully, there is a safety mechanism in the AV node to peak at 200 bpm

Question 15

I say saw tooth, you say…

Answer 15

• atrial flutter
• rate can be 240-340 bpm
• QRS is regular