Chapter 13 Cardiac Arrythmias And Their ECG Interpretation

Question 1

How does fever increase heart rate?

Answer 1

Fever increases the metabolism of the sinus node, increasing its excitability and rate of rhythm.

Question 2

Why does a patient with a weakened heart show tachycardia in the early stages of a cardiac disease process?

Answer 2

The weakened heart pumps les blood into the arterial tree, causing reductions in blood pressure and eliciting sympathetic responses to increase heart rate.

Question 3

Why do more athletic patients tend to have bradycardia?

Answer 3

Athletic patients have bigger and stronger hearts, resulting in an increased stroke volume. This larger amount of blood flow to the arterial tree initiates feedback circulatory reflexes or other effects to cause bradycardia.

Question 4

Which of the following finding is found in a sinoatrial block?

A) QRS interval shortened
B) P waves cessation
C) PR interval decreased
D) QRS complex narrowed

Answer 4

B) P waves cessation

A sinoatrial block - impulse from the sinus node is blocked before it enters the atrial muscle; sudden cessation of P waves, but the ventricles are able to pick up their own rhythm, with the impulse originating generally in the AV node; QRS complex is slowed, but generally not altered

Question 5

List 4 reasons causing an AV block.

Answer 5

1) Ischemia of the AV node or AV bundle fibers
2) Compression of the AV bundle
3) Inflammation of the AV node or AV bundle
4) Extreme stimulation of the AV node by the vagus nerve (carotid sinus syndrome)

Question 6

Decide which arrhythmia is described by the following description:

• Increased PR interval
• Slower heartbeat
• Delay of conduction from atria to the ventricle

A) Stokes-Adams Syndrome Ventricular Escape
B) Type II second degree AV block
C) Type I second degree AV block
D) First degree AV block

Answer 6

D) First degree AV block

Question 7

Decide which arrhythmia is described by the following description:

• Almost always caused by abnormality of the AV node
• Irregular loss of the QRS complex compared to the P wave
• Progressive increased length of the PR interval

A) Stokes-Adams Syndrome Ventricular Escape
B) Type II second degree AV block
C) Type I second degree AV block
D) First degree AV block

Answer 7

C) Type I second degree AV block

If conduction through the AV node is slow enough, the action potential’s strength to get through, may not be enough. This results in dropped beats of the ventricles. Type I is also known as the Wenkebach periodicity. This is typically benign and does not require treatment.

Question 8

Decide which arrhythmia is described by the following description:

• Dropped beat of the ventricle
• Generally caused by abnormality of the Purkinje fibers
• Often requires implantation of a pacemaker
• Ratio of QRS complex loss to P waves, i.e. 2:1 implies 2 P waves for every 1 QRS complex

A) Stokes-Adams Syndrome Ventricular Escape
B) Type II second degree AV block
C) Type I second degree AV block
D) First degree AV block

Answer 8

B) Type II second degree AV block

Question 9

Decide which arrhythmia is described by the following description:

• Impulse from the atria does not reach the ventricle at all
• The ventricles spontaneously establish their own signal
• No relation between the rhythm of the P waves and the QRS-T complex

A) Stokes-Adams Syndrome Ventricular Escape
B) Third degree AV block
C) Wenckebach AV block
D) First degree AV block

Answer 9

B) Third degree AV block

Also known as complete AV block, the ventricles are able to establish their own signal, often originating in the AV node or AV bundle distal to the block.

Question 10

What does blockage of impulse conduction in the peripheral ventricular Purkinje system cause?

A) Premature contractions
B) Ventricular paroxysmal tachycardia
C) Electrical alternans
D) Ventricular fibrillation

Answer 10

C) Electrical alternans

This results from partial intraventricular block every other heartbeat. The ECG will also show tachycardia. Parts of the Purkinje system will not be able to recover from the previous refractory period quickly enough to respond during every succeeding heartbeat. Other conditions that depress the heart can result in electrical alternans, such as ischemia, myocarditis, digitalis toxicity, etc.

Question 11

What are 3 causes of ectopic foci, that premature contractions, of the heart?

Answer 11

1) Areas of ischemia
2) Calcified plaques that can press against adjacent cardiac muscle and cause irritation
3) Toxic irritation of the AV node

Question 12

What are some ECG changes in a premature atrial contraction?

2

Answer 12

1) P-R interval shortened

2) Interval between premature contraction and next succeeding contraction is prolonged (compensatory pause)

Question 13

What is the cause of compensatory pause in the ECG reading of a premature atrial contraction?

Answer 13

Since the ectopic foci is some distance away from the sinus node, the impulse has to travel through a considerable amount of atrial muscle. The sinus node discharges late in the premature cycle, making succeeding sinus node discharge also late in appearing.

Question 14

What are the ECG findings in AV nodal or AV branch premature contractions?

Answer 14

1) P wave is missing

2) QRS-T complex is altered, due to the P wave being superimposed

Question 15

Why is the P wave superimposed on the QRS-T complex during an AV nodal or AV premature contraction?

Answer 15

The premature contraction originates in the AV node or AV bundle and the cardiac impulse travels both backward into the atria and forward into the ventricles.

Question 16

In an ECG recording of premature ventricular contraction, what interval is lengthened?

A) PR interval
B) QRS interval
C) PT interval
D) ST interval

Answer 16

B) QRS interval

This is lengthened in the ECG of a premature ventricular contraction due to the impulse being conducted through the slow conducting muscle of the ventricles instead of the fast Purkinje fibers.

Question 17

In a normal heart vs a heart that has experienced a premature ventricular contraction, explain the QRS voltage discrepancy. I.e. in which is the voltage higher? Why?

Answer 17

The voltage of the QRS complex in a heart experiencing a premature ventricular contraction is higher. This is due to the impulse being conducted through one ventricle; the depolarization is occurring ahead of the the other. In a normal heart, the depolarization of both ventricles is occurring at the same time, and this partially neutralizes each other in the ECG.

Question 18

How does the T wave change in a premature ventricular contraction?

Answer 18

The T wave has an electrical potential polarity exactly opposite to that of the QRS complex. This is due to the slow conduction of the impulse through the cardiac muscle causes the muscle fibers that depolarize first also repolarize first.

Question 19

What’s the cause of rapid rhythmical discharge of impulses that spread in all directions throughout the heart? What condition of the heart is this called? How can this be stopped through nervous innervation?

Answer 19

Re-entrant “circus movement” feedback that set up local repeated self-re-excitation. This rapid rhythm in this irritable focus causes this location to become the pacemaker of the heart.

This is the premise behind paroxysmal tachycardia. The heart rate becomes rapid, beginning suddenly and lasting for a few seconds.

This can be stopped with vagal nerve stimulation.

Question 20

Which cardiac drug, when overdosed, can cause ventricular tachycardia?

A) Lidocaine
B) Amiodarone
C) Digitalis
D) Quinodine

Answer 20

C)) Digitalis can cause ventricular tachycardia, due to creating an irritable foci

Question 21

Which 2 drugs can be used to treat ventricular tachycardia? What MOA helps treat?

Answer 21

Lidocaine - depresses the increase in sodium permeability of the cardiac muscle membrane, during the generation of the action potential, blocking the rhythmical discharge of the focal point causing the paroxysmal attack

Amiodarone - prolongs the action potential and the refractory period, thus slowing the AV conduction

Question 22

What are three conditions that can cause an impulse to continue to travel around the heart, and cause the phenomenon of re-entry as the basis for ventricular fibrillation?

Answer 22

1) Pathway is much longer than normal, which occurs in dilated hearts; the originally stimulated muscle will no longer be refractory and the impulse will continue
2) Velocity of conduction becomes decreased enough, that the originally stimulated muscle might be out of refractory state; this occurs due to decreased conduction rate from blockage of Purkinje system, ischemia of the muscle, high blood potassium levels
3) The refractory period of the muscle might be shortened; this can occur in response to epinephrine or after repetitive electrical stimulation

Question 23

Why is it lethal if ventricular fibrillation is allowed to continue for longer than a few seconds?

Answer 23

During ventricular fibrillation, there are sporadic locations of contraction in the ventricle. The large quantity of blood that is needed to be pumped out to the body stays within the ventricle, bc there is no singular large contraction.

Question 24

What is the treatment for ventricular fibrillation?

Answer 24

A strong high-voltage electrical current passed through the ventricles for a fraction of a second can stop fibrillation by throwing all the ventricular muscle into refractoriness simultaneously.

Question 25

A patient is placed under anesthesia for an emergency procedure. Prior to GA, the patient was tachycardia. Once an ECG was placed, the following findings were noted:

• Tachycardia
• No P waves
• Normal QRS-T complexes

Which of the following is the best answer to explain these?

A) Sinoatrial
B) Atrial paroxysmal tachycardia
C) AV nodal premature contraction
D) Atrial fibrillation

Answer 25

D) Atrial fibrillation

This occurs similar to v fib, but in the atria.The most common cause for this is dilated atria, stemming from heart valve lesions preventing adequate emptying of the atria into the ventricles. Ventricular failure can also cause damming of the blood in the atria.

Question 26

How much efficiency of ventricular pumping is lost due to atrial fibrillation?

A) 10-20%
B) 20-30%
C) 30-40%
D) None

Answer 26

B) 20-30% of ventricular pumping efficiency is lost during atrial fibrillation.

This is due to the atria being lost as primer pumps for the ventricles, but passive blood flow from the atria to the ventricles continues. Patients can live with this condition.