Arrhythmias

Question 1

The two broadest categories of arrhythmogenesis are:

Answer 1

disorders of impulse conduction and disorders of impulse formation.

Question 2

What are the three categories of altered impulse formation that lead to arrhythmias

Answer 2

1. Altered automaticity
2. Abnormal automaticity
3. Triggered activity

Question 3

What are the three forms of enhanced automaticity which may result in arrhythmia?

Answer 3

1. Increased sinus automaticity
2. Increased automaticity of latent pacemakers
3. Abnormal automaticity of non-pacemaker cells

Question 4

What are the two mechanisms by which altered impulse conduction leads to arrhythmia?

Answer 4

1. Unidirectional block and reentry (tachyarrhythmias)
2. Conduction block (bradyarrhythmias)

Question 5

What three factors influence the firing rates of pacemaker cells?

Answer 5

1. threshold potential (higher means a slower rate)
2. maximum diastolic potential (lower means slower)
3. Slope of phase 4 depolarization (slower means slower)

Question 6

Briefly describe the role of overdrive suppression in preventing arrhythmia

Answer 6

pacemaker cells that are forced to depolarize at a higher rate than their intrinsic pacemaker rate become hyperpolarized, reducing the automaticity of latent pacemakers under normal sinus function

Question 7

Describe how electrotonic interactions prevent arrhythmia, and how this process is impeded followin infarction.

Answer 7

pacemaker cells in the AV node and His-Purkinje system are hyperpolarized through gap junctions with surrounding myocardium that is depolarizing. This lowers their automaticity. If the myocardium around these pacemaker cells is unable to depolarize, the result is increased automaticity of latent pacemakers.

Question 8

Early and delayed afterdepolarizations are examples of what form of arrhythmogenesis?

Answer 8

triggered activity

Question 9

What is the most likely cause of polymorphic VT (TdP)?

1. enhanced automaticity
2. unidirectional block and reentry
3. early afterdepolarizations
4. late afterdepolarizations

Answer 9

c. early afterdepolarizations

Question 10

Late afterdepolarizations leading to ventricular tachycardia may be seen in __________ toxicity

Answer 10

digitalis

Question 11

The two conditions that are required for re-entry are:

Answer 11

1. unidirectional block
2. delayed conduction through the reentry path

Question 12

The mechanism of arrhythmogenesis in AVNRT is:

1. Enhanced automaticity
2. Unidirectional block and reentry
3. Triggered activity
4. Abnormal automaticity

Answer 12

b. Unidirectional block and reentry

Question 13

The primary difference between synchronized electrical cardioversion and defibrillation is:

Answer 13

defibrillation is asynchronous, i.e. it is not timed to coincide with the QRS complex.

Question 14

AVNRT is most commonly orthodromic or antidromic?

Answer 14

orthodromic