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PHYSL 404 - Cardiovascular Physiology > 15 - LQT Syndromes > Flashcards

15 - LQT Syndromes Flashcards

1
Q

What are top 7 causes of sudden cardiac death in young people?

A
  1. Hypertrophic Cardiomyopathy (#1 in NA)
  2. RV Dysplasia (ARVC) (#1 in italy) (arrhythmogenic Right Ventricular Cardiomyopathy)
  3. Brugada Syndrome (#1 in Southeast asia)
  4. CPVT (catecholaminergic polymorphic ventricular tachycardia)
  5. Coronary Anomalies/Premature CAD (coronary artery disease)
  6. Long QT syndromes
  7. Short QT syndromes
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2
Q

Label the heart:

A

A) SA Node

B) Atria

C) AV Node

D) Purkinje

E) Ventricle

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3
Q

Where is the action potential seen in the image?

Label 0-4

A

Atria

0 - upstroke

1 - initial repolarization

2 - plateau

3 - Late repolarization

4 - rest (diastole)

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4
Q

The action potential in the image is seen in which area of the heart?

Label 0, 3, 4

What is important about phase 4?

A

SA Node

0 - Upstroke

3 - late repolarization

4 - depolarization in SA nodal cells

Phase 4 depolarization in SA nodal cells = pacemaker activity

SA node >> Atrial > Ventricle

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5
Q

Which area of the heart would create the action potential in the image?

Label 0-4

What is the arrow representing?

A

Ventricle

0 - upstroke

1 - Initial repolarization

2 - plateau

3 - late repolarization

4 - rest (diastole)

Arrow - transient outward K+ current through Ito channels = repolarizing - contributes to initial repolarization phase 1

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6
Q

Which ion channels contribute to depolarization?

A
  • Ca++
  • Na+
  • Move into the cell
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7
Q

Nernst potential of:

  • Ca++
  • Na+
  • Cl-
  • K+
A

Nernst potential of:

  • Ca++
    • +150mV
  • Na+
    • +70mV
  • Cl-
    • -30 to -65mV
  • K+
    • -98mV (Resting Em)
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8
Q

Movement of ____ out of the cell causes ______

A

Movement of K+ out of the cell causes repolarization

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9
Q

There is constant recycling of ___ channels with every heart beat

A

There is constant recycling of Ca++ channels with every heart beat

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10
Q

Why does hyperkalemia cause QRS widening and asystole (eg lethal KCl injection)?

A

As serum potassium levels increase to greater than 6.5mM, the rate of phase 0 (upstroke/depolarization) of the action potential decreases leading to a longer action potential and, in turn, a widened QRS complex and prolonged PR interval

  • delayed intraventricular and atrioventricular conduction
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11
Q

PR interval of ECG is related to ______ (ion moving)

A

PR interval of ECG is related to Na+ moving into cell - depolarization

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12
Q

The QRS interval of the ECG is related to which phase of the AP

ion moving in/out

A

The QRS interval of the ECG is related to action potential depolarization

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13
Q

The T wave of the ECG is associated with ________

ion moving in/out

A

The T wave of the ECG is associated with ventricular repolarization

K+ moving out of cell

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14
Q

What does the QT interval represent?

A

The time for both ventricular depolarization and repolarization to occur - estimates the duration of an average ventricular AP

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15
Q

Complete the table

A
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16
Q

K+ currents move _____ and cause _____. They are present in which phases of the ventricular AP?

A

K+ currents move outward and cause repolarization. They are present in which phases of the ventricular AP?

  • Phase 1 - Ito
  • Phase 2/phase 3 - IKr , hERG
  • Phase 3 - IKs
  • Phase 4 - IK1

Ito - transient outward K+ current

IKr , hERG - Rapidly activating delayed rectifying K+ current

IKs - Slowly activating delayed rectifying K+ current

IK1 - Inward rectifying K+ channels

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17
Q

What are the following channels and when are they active during ventricular AP?

  • Ito
  • IKr , hERG
  • IKs
  • IK1
A

Ito - transient outward K+ current

IKr , hERG - Rapidly activating delayed rectifying K+ current

IKs - Slowly activating delayed rectifying K+ current

IK1 - Inward rectifying K+ channels

  • Phase 1 - Ito
  • Phase 2/phase 3 - IKr , hERG
  • Phase 3 - IKs
  • Phase 4 - IK1
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18
Q

Na+ currents move _____ and cause _____. They are present in which phases of the ventricular AP?

A

Na+ currents move inward and cause depolarization. They are present in which phases of the ventricular AP?

Phase 0

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19
Q

Ca++ currents move _____ and cause _____. They are present in which phases of the ventricular AP?

A

Ca++ currents move inward and cause depolarization. They are present in which phases of the ventricular AP?

Phase 2 (phase 1 according to slide 11) (plateau phase)

L-type Ca++ channel (ICa,L)

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20
Q

Na+ current is a ______ current (phase _\_ of AP) Cardiac Sodium current is important for: (2)

A

Na+ current is a depolarizing current (phase 0 of AP) Cardiac Sodium current is important for: (2)

  1. AP duration (and QTc interval)
  2. Rapid Conduction eg. Purkinje fibres
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21
Q

Ca2+ current is a _____ current (phase __ of AP)

Cardiac Calcium current is important for: (2)

A

Ca2+ current is a depolarizing current (phase 1 of AP) (also phase 2 - plateau phase - very important for excitation contraction-coupling)

Cardiac Calcium current is important for:

  1. AP duration (and QTc interval)
  2. Triggers excitation-contraction coupling
22
Q

K+ current is a _____ current (phase ___ of AP) Cardiac Potassium current is important for: (2)

A

K+ current is a repolarizing current (phase 2/3 of AP) Cardiac Potassium current is important for: (2)

  1. AP duration (and QTc interval)
  2. Repolarization
23
Q

In 1957, Jervell and Lange-Nielsen reported a syndrome of congenital sensory deafness with a prolonged QT interval in four children: ______________

A

In 1957, Jervell and Lange-Nielsen reported a syndrome of congenital sensory deafness with a prolonged QT interval in four children: autosomal recessive…..LQT1 (and 5)

24
Q

Romano–Ward syndrome is an ________ form of the long-QT syndrome NOT associated with deafness …higher incidence than JLN (jervell and Lange-Nielsen) syndrome, but affected persons generally have milder symptoms…….due to _______

A

Romano–Ward syndrome is an autosomal dominant form of the long-QT syndrome NOT associated with deafness …higher incidence than JLN (jervell and Lange-Nielsen) syndrome, but affected persons generally have milder symptoms…….due to LQT2, LQT3 and LQT4

25
Q

What drugs case acquired LQT syndrome?

A
  • Blockers of K+ channels (eg Quinidine)
    • Decrease surface expression
26
Q

How is LQT syndrome diagnosed?

27
Q

LQT1,2 results from a (__∆ _____)

A

LQT1,2 results from a (-∆ repolarizing currents) (K+ current, Ik)

28
Q

What causes LQT3 in AP?

A

+∆ depolarizing currents (Na+, current, INa)

29
Q

What is torsade de pointes? What causes it?

A

TdP = polymorphic ventricular tachycardia with a twisting QRS morphology associated with a prolonged QT (LQT) interval

  • triggered by reactivation of Ca++ channels, reactivation of a delayed sodium current, or a decreased outward potassium current that results in early afterdepolarization (EAD)
30
Q

Label the image

31
Q

Electrophysiological basis for LQT3 syndrome

32
Q

Which ion channels are associated with LQT syndromes? (gene and protein)

  • LQT1
  • LQT2
  • LQT3
  • LQT4
  • LQT5
  • LQT6
  • LQT7
  • LQT8 (+LQT9, 10)
A

Which ion channels are associated with LQT syndromes?

  • LQT1
    • gene: KCNQ1 (KVLQT1)
    • Protein: IKsK+ channel alpha subunit
  • LQT2
    • gene: KCNH2 (HERG)
    • protein: IKrK+ channel alpha subunit
  • LQT3
    • gene: SCN5A
    • protein: INaNa+ channel alpha subunit
  • LQT4
    • gene: ANKB
    • protein: Ankyrin-B
  • LQT5
    • gene: KCNE1 (minK)
    • protein: IKsK+ channel beta subunit
  • LQT6
    • gene: KCNE2 (MiRP1)
    • protein: IKrK+ channel beta subunit
  • LQT7
    • gene: KCNJ2
    • protein: IKr2.1K+ channel alpha subunit
  • LQT8 (+LQT9, 10)
    • gene: CACNA1
    • protein: Cav1.2 Ca++ channel alpha subunit
33
Q

Genotype-specific ECG changes:

Which chromosome is involved in the following LQT syndromes? Which LQT type are shown?

A
  • Chromosome 3
    • LQT3
    • Flat ST segment with normal T-waves
  • Chromosome 2
    • LQT2
      • bifib T waves
  • Chromosome 11
    • LQT1
    • peak and broad T waves
34
Q

How would you recognize LQT2 caused by chromosome 7?

A

Bifib T-waves

35
Q

How would you recognize LQT1 in Chromosome 11?

A

Peak and broad T-waves

36
Q

How would you recognize a LQT3 in chromosome 3?

A

Flat ST segment with Normal T-waves

37
Q

Gain of function mutation in I<u>Na</u> causes _____

A

Gain of function mutation in I<u>Na</u> causes LQT3

38
Q

Loss of function mutation in IKr and IKs causes ________

A

Loss of function mutation in IKr and IKs causes LQT2 and 1

39
Q

The image shows?

A

LQT3 syndrome

  • QT interval longer than in LQT1 and LQT2
  • HR increases
  • QT inverval shortens more in LQT3
  • Late appearance of T wave
40
Q
A

fill in the table

41
Q

3 methods to manage LQT1 and 2 syndromes

A
  1. K+ and MG++ supplementation
  2. Beta-blocker
  3. ICD (implantable cardioverter-defibrillator)- if symptomatic and/or aborted SCD (sudden cardiac death)
42
Q

Management of LQT3 Syndrome (3)

A
  1. Bradycardia dependent i.e. unlike LQT1 and 2; avoid beta-blockers
  2. ICD (implantable cardioverter-debrillator)
  3. Class I anti-arrhythmic eg. mexilitine (Sodium Channel Blockers)
43
Q

How to recognize LQT7 on ECG?

A
  • A triad of K+-sensitive periodic paralysis, ventricular dysrhythmias, and dysmorphic features
  • T and U form a continuum - resultant of one and the same process: Repolarization of the Ventricular Myocardium
44
Q

The image shows:

A

Short QT1 syndrome

45
Q

SQTS1,2,3 caused by __∆ repolarizing current

A

SQTS1,2,3 caused by +∆ repolarizing current

46
Q

SQTS4,5 caused by __∆ depolarizing current

A

SQTS4,5 caused by -∆ depolarizing current

47
Q

What are the 3 gain of function mutations in K+ channels associated with?

IKr

IKs

IK1

A
  1. IKr = SQT1 (LQT2)
  2. IKs = SQT2 (LQT1)
  3. IK1 = SQT3 (LQT7)
48
Q

What are the 3 gain of function mutations in K+ channels associated with?

IKr

IKs

IK1

A
  1. IKr = SQT1 (LQT2)
  2. IKs = SQT2 (LQT1)
  3. IK1 = SQT3 (LQT7)
49
Q

Management of Short QT syndromes

_____ is the therapy of choice in patients with syncope and a positive family history of SCD

A

ICD is the therapy of choice in patients with syncope and a positive family history of SCD

50
Q

ICD therapy in patients with a short QT syndrome has an increased risk for inappropriate shock therapies due to _______

A

ICD therapy in patients with a short QT syndrome has an increased risk for inappropriate shock therapies due to possible T wave oversensing

51
Q

How is Quinidine used for Short QT syndromes?

A

Quinidine (IKr blocker) causes QT prolongation

QTc increased from 263 +/- 12ms to 362+/- 25ms

52
Q

Management of Short QT syndromes

_______ is particularly important because SQT1 patients are at risk of sudden death from birth, and ICD implant is not feasible in very young children

A

Quinidine is particularly important because SQT1 patients are at risk of sudden death from birth, and ICD implant is not feasible in very young children

PHYSL 404 - Cardiovascular Physiology (17 decks)

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