Electrophysiology Lecture 4 -- Clinical Arrhythmia 2 Flashcards Preview

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Flashcards in Electrophysiology Lecture 4 -- Clinical Arrhythmia 2 Deck (55):
1

Prevalence trend of atrial fibrillation

Prevalence directly related to age (older = more)

2

What determines the APD in fast channel tisue?

Na+ channel recovery

3

What determines the APD in slow channel tissue?

Ca++ channel recovery

4

Atrial fibrillation exhibits mostly what kidn of reentry?

Irregularly irregular reentry

5

Describe the rate of firing in atrial fibrillation

Rapid and irregular firings at 400 - 600 bpm

6

Maximum beat rate that the AV node can conduct. What effect does this have on atrial fibrillation?

150 bpm

AV node filtering since the 400 - 600 bpm firing in the atria cannot pass into the ventricles

7

Typical untreated ventricular response to atrial fibrillation

130 - 150 bpm

8

Ventrical response to atrial fibrillation involving a fast channel tissue bypass

Firing > 150 bpm = increased response

9

3 potential negative consequences of atrial fibrillation

  • Impaired cardiac performance
  • Symptoms (palpitations, chest discomfort, dyspnea)
  • Stroke

10

Potential consequence of maintaining beat rate over 100 bpm due to atrial fib

Congestive heart failure

11

Potential concentration of maintaining beat rate over 120 bpm due to atrial fib

Tachycardiomyopathy

12

Cause of stroke due to atrial fibrillation

Stasis of blood in left atrial appendage leads to clot formation. Dislodgment of thrombus --> brain = stroke

NOTE: single most important cause of stroke in elderly

13

What is the method to predict stroke risk for atrial fib patients?

CHADS2 score

14

Explain CHADS2

Note that age 65 may also be a good cutoff

15

If CHADS = 1 or higher, what kind of treatment is recommended?

Anticoagulation

16

Classic proposed mechanism for atrial fib

Multiple simultaneous functional reentrant circuits

17

2 mechanisms proposed for atrial fib apart from the classic mechanism

  1. Rapidly firing single ectopic focus, driving atria so fast that different regions respond at different rates according to max frequency they can support, producing fibrillatory response
  2. Single very rapid local reentry circuit, producing fib response as in 1

18

2 treatment approaches for atrial fibrillation

Rate control

Rhythm control

19

How to control rate in atrial fib

Leave patient in AF, but control ventricular response (i.e. slow conduction in AV node, for example)

20

How to control rhythm in atrial fib

Stop AF if needed (usually by electrical cardioversion)

If needed to prevent recurrence (often is), give antiarrhythmetic drugs, or if they fail, perform atrial tissue ablation targeted to arrhythmogenic regions

21

3 types of drugs for rhythm control (i.e. in atrial fib)

  • Class I (propafenone, flecainide)
  • Class II/ beta-blocker (sotalol)
  • Amiodarone

22

3 types of drugs frp rate control (i.e. in atrial fib)

  • Beta-adrenoceptor blockers
  • Calcium channel blockers (diltiazem, verapamil)
  • Digitalis

23

Purpose of electrica cardioversion

Synchronise cardiac electrical activity and "resetting it" = effective for terminating >99% of sustained tachyarrythmias, including atrial fib

24

How to deliver electrical cardioversion for supraventricular arrhythmias (such as atrial fib)

Shock should be synchronized with the QRS to avoid delivery during T wave (when some ventricular muscle is repolarized and some not)

25

Potential consequence of delivering electrical cardioversoin during T wave

Can induce chaotic ventricular reentry and ventricular fibrillation

26

How to prevent recurrance of atrial fibrillation

Increase refractory period

27

Describe the firing in atrial flutter

A single atrial macroreentrant circuit in atrium (most commonly right), typically at 250 - 300 bpm

28

Atrial flutter exhibits mostly what kind of reentry and why?

Rate is slower than in atrial fib, so atria cn respond 1:1 (rapid and regular)

29

Atrial fibrillation ECG

30

Atrial flutter ecg

31

Which type of control approach is more used in treating atrial flutter?

Rate control is harder for AFL, so rhythm control more commonly used (best response to class I and class III antiarrhythmics)

32

Most successful and curative method for atrial flutter

Ablation

33

Why is ablation most often the first choice for prevention of recurrance over antiarrhythmic drugs for atrial flutter?

Single circuit usually allows critical anatomical component to be identified so easy to ablate

34

Stroke risk for atrial flutter

Comparable to atrial fib (same principles apply, i.e. CHAS2 > 1 = anticoagulants)

35

Define ventricular tachycardia

Rapid rhythm arising from a region in the ventricles, most typically 150 - 180 bpm

36

Causes of ventricular tachycardia

  • Enhanced automaticity
  • DADs
  • EADs
  • Reentry

37

VT due to enhanced automaticity is seen most likely in what condition?

Acute MI

38

What does VT due to enhanced automaticity repond well to?

Class I antiarrhythmetics (i.e. intravenous lidocaine)

39

VT due to DADs is most likely seen in which conditions?

Conditions of cardiac hypertrophy and failure (i.e. hypertrophic cardiomypathies, CHF), which cause abnormal Ca++ handling

40

Give an example of a specific genetic context in which DAD-induced VT is seen

Ryanodine receptor mutation in catecholaminergic polymorphic VT (CPVT)

41

DAD-induced VT responds to what kind of antiarrhythmic drug?

Class I

42

Class I effect (i.e. relevant to DAD-induced VT)

Prevents DAD from reaching threshold and may also prevent abnormal RyR2 Ca++ release

43

Conditions associated with EAD-induced VT

  • Conditions that prolong APD/QT interval (i.e. Long QT Syndrome); can be congenital or acquired

44

Example of acquired EAD-VT

Drugs that prolong APD, especially class III drugs

45

Examples of congenital EAD-VT

Genetic conditions that enhance plateau Na+ current (LQT3) or reduce phase 3 K+ current (LQT1, LQT2)

46

What exacerbates the risk of EAD-induced VT?

Concomitant factors tending to prolong QT (slow heart rate, hypokalemia, hypomagnesemia)

47

How to treat EAD-induced VT

Focus on underlying conditions:

  • Beta-blockers useful in LQT1 and 2
  • Increasing HR rate induces QT and may help (i.e. temp. pacemaker in emergency situation)

48

When does reetrant VT tend to occur?

In presence of reentry substrate like a myocardial scar, most commonly post-MI

49

Drugs that reetrant VT is most likely to respond to

Class III

50

Drugs that reetrant VT is unlikely to respond to

Class I

51

When can direct-current cardioversion be used for VT?

Terminate VT when severe hemodynamic compromise is life-threatening

52

Define ventricular fibrillation

Chatoci ventricular rhythm with no effective cardiac pumping

53

Lethality of ventricular fibrillation

Lethal within minutes in the absence of cardiac massage/ CPR (requires emergency cardioversion)

54

How does ventricular fibrillation occur?

  • De novo as a result of a predisposing condition (acute MI, congenital ion-channel mutation)
  • A result of degeneration of VT

 

55

How to prevent recurrence of ventricular fibrillation

Resuscitated individuals from VF generally require implantation of a defibrillator (drug therapy not reliable enough)