Heart Block

Question 1

First Degree AV Block

Answer 1

Consistent prolongation of the PR interval (>0.2 seconds) where the 1:1 ratio between PR intervals and QRS complexes is preserved.

Usually represents impaired conduction within the AV node itself due to some structural effect, which may or may not be reversible.

Question 2

Reversible causes of first-degree AV block

Answer 2

• Heightened vagal tone (physiologic)
• Transient AV nodal ischemia (AV nodal artery pathology)
• Drugs that effect conduction through AV node:
  
  • beta blockers
  • non-dihydropyridine calcium channel blockers
  • digitalis

Question 3

Structural causes of first-degree AV block

Answer 3

• Myocardial infarction
• Chronic degenerative diseases of conduction system
  
  • Fibrosis
  • Sarcoidosis
  • Amyloidosis

Question 4

What abnormal electrical pattern is represented by this ECG?

Answer 4

First Degree AV Block

Question 5

Second Degree AV Block

Answer 5

Intermittent failure of AV conduction, resulting in some P waves that are not followed by a QRS. Separated into two categories, Möbitz type I and Möbitz type II.

Question 6

Möbitz Type I block

Answer 6

Form of second degree AV block. The degree of AV delay gradually increases with each beat until an impulse is skpped, and then the cycle starts anew.

Almost always results from impaired conduction in the AV node. Usually benign, seen in children, athletes, people with high vagal tone, and people sleeping. Treatment rarely necessary.

Question 7

Treating Möbitz type II block

Answer 7

Not usually necessary, but in rare symptomatic cases IV atropine or isoproterenol usually improves AV conduction transiently. If this does not work, a permanent pacemaker can cure the problem indefinitely.

Question 8

What abnormal electrical pattern is represented by this ECG?

Answer 8

Möbitz type I second-degree AV block

Question 9

Pathologic examples of Möbitz type I block

Answer 9

May occur during an acute MI due to increased vagal tone or ischemia of the AV node. Even here, it is usually temporary.

Question 10

Möbitz type II heart block

Answer 10

Type of second degree AV block. Characterized by sudden intermittent loss of AV conduction without preceding lengthening of PR interval. May persist for two or more beats, in which it is a high grade AV block.

Usually caused by a block beyond the AV node (in bundle of His or Purkinjes).

Indicates more serious disease than a type I block. May progress to third-degree without warning if untreated.

Question 11

Pathologic example of Möbitz type II block

Answer 11

May arise from extensive MI involving the septum or from a chronic degeneration of the His-Purkinje system.

Question 12

Treating a Möbitz type II block

Answer 12

Pacemaker implantation is indicated!!!

Best way to prevent a progression to third-degree.

Question 13

What abnormal electrical pattern is represented by this ECG?

Answer 13

Möbitz type II second-degree AV block

Question 14

Third Degree AV Block

Answer 14

aka complete heart block.

Complete failure of conduction between the atria and ventricles. Thus, there is no relationship between atrial and ventricular depolarization. There will still be QRS (an escape rhythm), it just won’t be in ine with P.

Question 15

Typical escape rhythm

Answer 15

No relationship to P waves

Often with widened QRS width and HR between 40 and 60 bpm

As a result, patients often experience hypotension, light-headedness, and syncopy.

Question 16

Treating third degree AV block

Answer 16

Pacemakers pacemakers pacemakers

This is why they were made

Question 17

What abnormal electrical pattern is represented by this ECG?

Answer 17

Third Degree AV Block

Question 18

Causes of third degree AV block

Answer 18

Myocardial infarction or chronic degradation of conduction pathwyas (age correlated)

Question 19

AV dissociation

Answer 19

General description that refers to any situation where atria and ventricles beat independently.

No relationship between P and QRS.

Third-degree AV block is one example, but not the only case in which this occurs.

Question 20

The __ artery supplies the AV node.

Answer 20

The Right coronary artery supplies the AV node.

Question 21

If a patient presents with likely diagnosis on lung exam, you should order ___.

Answer 21

If a patient presents with likely diagnosis on lung exam, you should order an ECG and an eye exam.

These are the two most important regular screenings for sarcoid patients.

Question 22

Sometimes very healthy individuals will have completely asymptomatic ___.

Answer 22

Sometimes very healthy individuals will have completely asymptomatic Mobitz type I heart block.

This is not pathological. It happens all the times in very fit athletes

Question 23

Mobitz type 2 second degree block is associated with ___.

Answer 23

Mobitz type 2 second degree block is associated with infra-nodal block in the His-Purkinje system.