Myocardial action potential-Pacemaker action potential-ΗΚΓ

Question 1

During what phase of the cardiac myocyte action potential does extracellular calcium enter the cell? What is the effect of this calcium?

Answer 1

The plateau phase; causes calcium release from sarcoplasmic reticulum (calcium-induced calcium release) and then muscle myocyte contraction

Question 2

During what phase of the cardiac myocyte action potential does extracellular calcium enter the cell? What is the effect of this calcium?

Answer 2

The plateau phase; causes calcium release from sarcoplasmic reticulum (calcium-induced calcium release) and then muscle myocyte contraction

Question 3

What do the cardiac nodal cells do during diastole?

Answer 3

They spontaneously depolarize, as this automaticity is due to the If (funny current) channels that create slow, mixed Na+/K+ inward current

Question 4

What cellular adaptation allows cardiac myocytes to be electrically coupled?

Answer 4

Gap junctions

Question 5

What is the voltage value of the resting potential of a ventricular myocyte? How is that resting potential maintained?

Answer 5

-85 mV; the value is maintained by high K+ permeability through K+ channels

Question 6

Name the phases of the myocardial action potential, in order.

Answer 6

Rapid upstroke/depolarization, initial repolarization, plateau, rapid repolarization, resting potential

Question 7

At each phase of the myocardial action potential, list the ions that enter and exit cells through the cellular membranes.

Answer 7

Phase 0 = Na+ in, 1 = Na+ in (tapering off), K+ out, 2 = Ca2+ in, K+ out, 3 = Ca2+ in (tapering off), K+ out, 4 = K+ out

Question 8

What are some key features that distinguish cardiac muscle action potentials from skeletal muscle action potentials?

Answer 8

Ca2+/K+-mediated plateau, Ca2+-induced Ca2+ release from sarcoplasmic reticulum, If (funny current) channels, gap junctions for coupling

Question 9

Cardiac myocytes in which locations have pacemaker action potentials?

Answer 9

The sinoatrial and atrioventricular nodes

Question 10

What effect does the resting voltage of the pacemaker cell have on the speed of conduction?

Answer 10

Permanent inactivation of voltage-gated Na+ channels slows conduction (how the AV node prolongs transmission from atria to ventricles)

Question 11

• Compared with the myocardial action potential, which phases are absent from the pacemaker potential?

Answer 11

Phases 1 and 2 (initial repolarization and plateau phases)

Question 12

The slope of which phase in the sinoatrial node determines the heart rate? What neurotransmitters increase and decrease the heart rate?

Answer 12

Phase 4; catecholamines increase heart rate by increasing the rate of depolarization; ACh/adenosine decrease depolarization and heart rate

Question 13

What phase of the cardiac action potential accounts for the automaticity of the pacemaker nodes? How?

Answer 13

Phase 4; the If (funny current) channels conduct Na+ and K+, which causes spontaneous depolarization

Question 14

Sympathetic stimulation ____ (decreases/increases) the possibility that If (“funny current”) channels are open.

Answer 14

Increases (as a result, the pacemaker cell depolarizes more frequently and the heart rate increases)

Question 15

During which phase are K+ channels open?

Answer 15

Phase 3 (leading to K+ efflux and repolarization)

Question 16

Name the phases of the pacemaker action potential, in order.

Answer 16

Phase 0 = upstroke, phase 3 = inactivation of Ca2+ channels/activation of K+ channels, phase 4 = slow spontaneous diastolic depolarization

Question 17

What part of the electrocardiogram represents atrial repolarization?

Answer 17

Atrial repolarization is masked within the QRS complex

Question 18

A 67-year-old man has U waves on his electrocardiogram in the ED. He has a normal heart rate. What is the treatment?

Answer 18

Replenish potassium (U waves are caused by hypokalemia or bradycardia, the latter of which this patient does not have)

Question 19

What is the physiologic benefit of the atrioventricular delay? How long is it?

Answer 19

It allows time for ventricular filling; 100 msec

Question 20

Order the following pacemakers from fastest to slowest heart rate: His-Purkinje system/ventricles, SA node, AV node

Answer 20

SA node, AV node, His-Purkinje system/ventricles

Question 21

Order the following structures from fastest to slowest conduction: AV node, atria, Purkinje, ventricles

Answer 21

Purkinje, atria, ventricles, AV node

Question 22

Outline the conduction pathway starting from the SA node and ending with the ventricles.

Answer 22

SA node, atria, AV node, common bundle, bundle branches, fascicles, Purkinje fibers, ventricles

Question 23

How long is a normal PR interval? QRS complex?

Question 24

A patient has a prolonged QT interval. What does this interval on the electrocardiogram measure?

Answer 24

Ventricular depolarization, mechanical contraction of the ventricles, ventricular repolarization

Question 25

A man had chest pain recently. Inverted T waves are seen on his electrocardiogram. What happened? What does this wave usually represent?

Answer 25

He likely had a recent MI; inverted T waves (ventricular repolarization) are a common finding in such patients

Question 26

A man is given a drug that slows AV nodal conduction. Which segment of the electrocardiogram do you expect to change as a result?

Answer 26

The PR interval, which represents the time from start of atrial depolarization to start of ventricular depolarization (AV node conduction)

Question 27

On a patient's electrocardiogram, you note oddly enlarged P waves. This may indicate pathology in which part of the heart?

Answer 27

The atrium (P waves represent atrial depolarization)

Question 28

A patient has an MI and loses the SA node pacemaker. The heart, however, still beats. What is happening?

Answer 28

The AV node (located in the posteroinferior part of the interatrial septum) can take over if the SA node (inherent dominance) is knocked out

Question 29

On a man's ECG, at the end of the QRS complex, before the ST segment begins, you note a small sharp point. Are you worried about pathology?

Answer 29

No, as this is likely the J point, which is a normal finding

Question 30

What do the cardiac nodal cells do during diastole?

Answer 30

They spontaneously depolarize, as this automaticity is due to the If (funny current) channels that create slow, mixed Na+/K+ inward current

Question 31

What cellular adaptation allows cardiac myocytes to be electrically coupled?

Answer 31

Gap junctions

Question 32

What is the voltage value of the resting potential of a ventricular myocyte? How is that resting potential maintained?

Answer 32

-85 mV; the value is maintained by high K+ permeability through K+ channels

Question 33

Name the phases of the myocardial action potential, in order.

Answer 33

Rapid upstroke/depolarization, initial repolarization, plateau, rapid repolarization, resting potential

Question 34

At each phase of the myocardial action potential, list the ions that enter and exit cells through the cellular membranes.

Answer 34

Phase 0 = Na+ in, 1 = Na+ in (tapering off), K+ out, 2 = Ca2+ in, K+ out, 3 = Ca2+ in (tapering off), K+ out, 4 = K+ out

Question 35

What are some key features that distinguish cardiac muscle action potentials from skeletal muscle action potentials?

Answer 35

Ca2+/K+-mediated plateau, Ca2+-induced Ca2+ release from sarcoplasmic reticulum, If (funny current) channels, gap junctions for coupling

Question 36

Cardiac myocytes in which locations have pacemaker action potentials?

Answer 36

The sinoatrial and atrioventricular nodes

Question 37

What effect does the resting voltage of the pacemaker cell have on the speed of conduction?

Answer 37

Permanent inactivation of voltage-gated Na+ channels slows conduction (how the AV node prolongs transmission from atria to ventricles)

Question 38

• Compared with the myocardial action potential, which phases are absent from the pacemaker potential?

Answer 38

Phases 1 and 2 (initial repolarization and plateau phases)

Question 39

The slope of which phase in the sinoatrial node determines the heart rate? What neurotransmitters increase and decrease the heart rate?

Answer 39

Phase 4; catecholamines increase heart rate by increasing the rate of depolarization; ACh/adenosine decrease depolarization and heart rate

Question 40

What phase of the cardiac action potential accounts for the automaticity of the pacemaker nodes? How?

Answer 40

Phase 4; the If (funny current) channels conduct Na+ and K+, which causes spontaneous depolarization

Question 41

Sympathetic stimulation ____ (decreases/increases) the possibility that If ("funny current") channels are open.

Answer 41

Increases (as a result, the pacemaker cell depolarizes more frequently and the heart rate increases)

Question 42

During which phase are K+ channels open?

Answer 42

Phase 3 (leading to K+ efflux and repolarization)

Question 43

Name the phases of the pacemaker action potential, in order.

Answer 43

Phase 0 = upstroke, phase 3 = inactivation of Ca2+ channels/activation of K+ channels, phase 4 = slow spontaneous diastolic depolarization

Question 44

What part of the electrocardiogram represents atrial repolarization?

Answer 44

Atrial repolarization is masked within the QRS complex

Question 45

A 67-year-old man has U waves on his electrocardiogram in the ED. He has a normal heart rate. What is the treatment?

Answer 45

Replenish potassium (U waves are caused by hypokalemia or bradycardia, the latter of which this patient does not have)

Question 46

What is the physiologic benefit of the atrioventricular delay? How long is it?

Answer 46

It allows time for ventricular filling; 100 msec

Question 47

Order the following pacemakers from fastest to slowest heart rate: His-Purkinje system/ventricles, SA node, AV node

Answer 47

SA node, AV node, His-Purkinje system/ventricles

Question 48

Order the following structures from fastest to slowest conduction: AV node, atria, Purkinje, ventricles

Answer 48

Purkinje, atria, ventricles, AV node

Question 49

Outline the conduction pathway starting from the SA node and ending with the ventricles.

Answer 49

SA node, atria, AV node, common bundle, bundle branches, fascicles, Purkinje fibers, ventricles

Question 50

How long is a normal PR interval? QRS complex?

Question 51

A patient has a prolonged QT interval. What does this interval on the electrocardiogram measure?

Answer 51

Ventricular depolarization, mechanical contraction of the ventricles, ventricular repolarization

Question 52

A man had chest pain recently. Inverted T waves are seen on his electrocardiogram. What happened? What does this wave usually represent?

Answer 52

He likely had a recent MI; inverted T waves (ventricular repolarization) are a common finding in such patients

Question 53

A man is given a drug that slows AV nodal conduction. Which segment of the electrocardiogram do you expect to change as a result?

Answer 53

The PR interval, which represents the time from start of atrial depolarization to start of ventricular depolarization (AV node conduction)

Question 54

On a patient's electrocardiogram, you note oddly enlarged P waves. This may indicate pathology in which part of the heart?

Answer 54

The atrium (P waves represent atrial depolarization)

Question 55

A patient has an MI and loses the SA node pacemaker. The heart, however, still beats. What is happening?

Answer 55

The AV node (located in the posteroinferior part of the interatrial septum) can take over if the SA node (inherent dominance) is knocked out

Question 56

On a man's ECG, at the end of the QRS complex, before the ST segment begins, you note a small sharp point. Are you worried about pathology?

Answer 56

No, as this is likely the J point, which is a normal finding

Question 57

Define torsades de pointes.

Answer 57

Ventricular tachycardia, characterized by a polymorphic sinusoidal pattern on electrocardiogram

Question 58

What are the most dangerous sequelae of torsades de pointes?

Answer 58

Ventricular fibrillation and death

Question 59

A 25-year-old man has a congenital long QT syndrome. What is the most likely cause of the condition? What is he at risk for?

Answer 59

Typically due to ion channel defects that disrupt myocardial repolarization; ↑ risk of torsades de pointes & sudden cardiac death

Question 60

Congenital long QT syndromes can be associated with what other pathology?

Answer 60

Sensorineural deafness (Jervell and Lange-Nielsen syndrome, autosomal recessive) (Romano-Ward syndrome [autosomal dominant] is pure cardiac)

Question 61

Name five classes of medications that can prolong the QT interval.

Answer 61

Antiarrhythmics (IA,III), antibiotics (macrolides), anticychotics (haloperidol), antidepressants (TCAs), antiemetics (ondansetron) (ABCDE)

Question 62

An Asian man's ECG shows a pseudo&8211;right bundle branch block and ST elevations in V1-V3. You suspect which inherited disorder?

Answer 62

Brugada syndrome, which is an autosomal dominant disorder most common in Asian male subjects.

Question 63

An Asian male has Brugada syndrome. What is he at risk for? What preventive measure should you take to help this patient?

Answer 63

He is at ↑risk for ventricular tachyarrhythmias and sudden cardiac death; prevent with implantable cardioverter-defibrillator

Question 64

What is Wolff-Parkinson-White syndrome?

Answer 64

A disorder with an abnormal fast accessory conduction pathway from the atria to the ventricles, leading to early ventricular depolarization

Question 65

In the lab, you study the heart of a patient with Wolff-Parkinson-White syndrome.

Answer 65

You note a pathway bypassing the AV node. What is it? | This is likely the accessory pathway (bundle of Kent) giving rise to the disorder

Question 66

Why are patients with atrial fibrillation at increased risk for stroke? How is it treated?

Answer 66

It causes atrial stasis, which can lead to cardioembolic events; treat with rate/rhythm control, antithrombotics, and/or cardioversion

Question 67

A patient has electrocardiogram findings consistent with third-degree heart block. What are they? What is the treatment?

Answer 67

P waves and QRS complexes are present but have no relation with one another, because the atria and ventricles beat independently; pacemaker

Question 68

An 18-year-old woman presents with a targetoid rash after hiking in the woods. Without treatment, she is at risk for what heart condition?

Answer 68

Third-degree (complete) atrioventricular block from Lyme disease

Question 69

Why does atrial flutter present with sawtooth waves on electrocardiogram? How is it treated?

Answer 69

Rapid sequence of identical back-to-back atrial depolarization waves; rate control, anticoagulation, cardioversion, or ablation (definitive)

Question 70

A patient has a PR interval of 250 msec. What type of atrioventricular block is this?

Answer 70

First degree (patients will generally be asymptomatic) (benign and no treatment required)

Question 71

Does progressive lengthening of the PR interval occur in Mobitz type I, type II, or both? Which is more likely to progress to third degree?

Answer 71

Mobitz type I only; Mobitz type II

Question 72

One can use rate or rhythm control for the treatment of atrial fibrillation. What drug classes are commonly used for each approach?

Answer 72

Rate control = β-blockers, non-dihydropyridine Ca2+ channel blockers, digoxin, rhythm control = class IC or III antiarrhythmics

Question 73

During a stroke work-up, it is common to perform both ECG and an echocardiogram. Certain findings may prompt treatment with warfarin. Why?

Answer 73

Atrial fibrillation can predispose a patient to cardioembolic events, which can be prevented with antithrombotics such as warfarin