Cardiac Exam Lecture 3

Question 1

All cardiac dysrhthmias result from disturbances in __________ or _________ or __________

Answer 1

All cardiac dysrhytmias result from disturbances in IMPULSE FORMATION or IMPULSE CONDUCTION or from a combination of BOTH.

Question 2

What are the three general mechamisms of cardiac dysrhytmias?

Answer 2

General Mechanisms of Cardiac Dysrhytmia’s:

1. Altered Automaticity
2. Re-entry of Excitation
3. Triggered Activity

Question 3

Explain what Altered Automaticity is

Answer 3

Altered Automaticity is essentially problems with the pacemaker… there are alterations in the pacemaker rate that are mediated through changes in the pacemaker mechanisms that normally exist in pacemaker cells (located within the special conduction system)

Question 4

What HR is defined as Tacycardia?

What HR is defined as Bradycardia?

Answer 4

Tachycardia is any HR > 100 bpm

Bradycardia is defined as any HR < 60 bpm

Question 5

List the possible causes of TACY-dysrhythmias

Answer 5

Possible Causes of Tacy-Dysrhythmias:

1. NE (sympathetic nervous activity)
2. Stimulants - amphetamines
3. Stretching- ventricular aneurysm
4. Electrolytes - hypokelemia
5. Sick Sinus Syndrome (where the location of the pacemaker is changing)
6. Fever
7. Hypothyroidism (symptoms of high sympathetic NS activity, you increase the expression of adrenergic receptors)

Question 6

What are the possible EKG manifestations of enhanced automaticity? (increase pacemaker rate)

Answer 6

Some EKG manifestations of enhanced automaticity:

1. sinus tachycardia
2. premature atrial contraction (PAC)
3. Premature Ventricular Contraction (PVC)
4. Atrial or Ventricular Tachycardia (AT, VT)
5. Supraventricular Tachycardia (SVT)

Question 7

What are the possible causes of BRADY-dysrhytmia’s? What are the possible EKG manifestations of brady dysrhthymia’s?

Answer 7

Brady-dysrhytmia causes:

1. Drugs - anti arrhythmics, Beta blockers, Ca antagonists, Digatalis, Barbiturates, Anethesia
2. Ischemia or Infart
3. Sick Sinus Syndrome
4. Aging - fibrosis

Some EKG Manifestations:

a) sinus bradycardia
b) atrial or ventricular premature beats - these occur due to the loss of overdrive suppresion

Question 8

Where can Re-entry of Excitation occur in the heart?

What are the three general requirements for re-entry of excitation?

Answer 8

Re-entry of Excitation can occur anywhere in the heart!

Most common cause of dysrhytmias seen clinically.

Three general requirements for re-entry of excitation:

1. Geometry for a Conduction Loop
2. Slow or delayed conduction
3. Unidirectional Concuction Block

Question 9

What are some of the causes of Re-entry of Excitation?

Answer 9

Causes of Re-entry of Excitation:

a) ischemia
b) infarction
c) congenital bypass tracts (example Wolf Parkinson White aka “WPW” where there are little connections between atria and ventricles)

Question 10

What are the manifestations of Re-entry of Excitation on an EKG?

Answer 10

EKG Manifestations of Re-entry:

1. Premature atrial or ventricular beats
2. Atrial or Ventricular Tachycardia
3. SVT
4. Atrial Flutter
5. Atrial or Ventricular Fibrillation

Question 11

Where can Triggered Activity occur in the heart?

Answer 11

Triggered Activity can occur in atrial or ventricular tissues

Question 12

Explain the mechanism of a DAD.

Answer 12

Elevated calcium is taken up by the SR. When the SR becomes overloaded with calcium, and AP can trigger an abnormal release of Ca AFTER an action potential had ended. This released Ca is extruded from the cell via Na/Ca exchanger, causing depolarization and thus causing a Delayed Afterdepolarization.

Question 13

What is a DAD due to essentially?

What are the possible causes for DAD?

What are the possible EKG manifestations of a DAD?

Answer 13

DAD is due to abnormally high intracellular calcium

Clinically documented in dysrhythmias resulting from digitalis toxicity

Possible Causes:

a) digatalis toxicity
b) elevated catecholamines
c) rapid HR
d) all of those combined

Possible EKG manifestations: premature atrial or ventricular contractions (PAC or PVC)

Question 14

Explain DADs and PVCs

Answer 14

DAD can result in PAC or PVCs. For Premature Ventricular Contractions, they might occur spontaneously and then not recur, or they may lead to ventricular tachycardia and VF.

Question 15

Explain what an EAD is.

What are the possible causes

Possible EKG manifestations?

Answer 15

EAD: (more dangerous than DAD)

a) related to prolongation of action potential duration
b) mechanism is still not certain but believed to be due to abnormal reactivation of slow inward L type Ca channel
c) also may contribute to prolonged Q-T syndrome by extending duration of the action potential

Possible causes: acidosis (as in ischemia), hypokalemia, quinidine, slow heart rates (ALL OF THESE CAUSE LENGTHENED AP DURATION, leads to triggered activity)

Possible EKG manifestations: PAC or PVC, atrial or ventricular tachycarida (torsades)

Question 16

EADs are manifested at faster/slower HR’s because______?

So the next AP comes in during the _________.

What would this look like on an EKG?

Answer 16

EADs are manifested at slower heart rates because slow HR lengthens the action potential (leads to coupled beats aka regular irregularity)

So the next AP comes in during the relative refractory period (very dangerous)

This would look like an R on T on an EKG. Spontaneous beat (R wave) on the repolarization wave of the previous beat.

Question 17

Draw what the following EKG strips look like:

Atrial premature beat

Ventricular Premature Beat

VTach

VFib

Answer 17

Question 18

Describe the four anti-arrthymic therapy options

Answer 18

Anti Arrthymic Therapies:

1. Drugs (Na channel blockers, K channel blockers, Ca channel blockers, Beta blockers)
2. Radio Frequency Ablation
3. DC Cardioversion
4. Implantable Cardioverter-Defibrillator (ICD)

Question 19

What is a normal PR interval (in milliseconds)?

What is a normal QRS interval?

Answer 19

PR: 120-200 milliseconds

QRS: 70-100 msec