Unexplored Territory: AV Block

Question 1

Physiologic and Pathophysiologic causes of AV block:

Answer 1

1. Increased vagal tone
2. Fibrosis and sclerosis of conduction system
3. IHD
4. Cardiomyopathy and myocarditis
5. Congenital heart disease
6. Familial AV Block

Other causes- hyperkalemia,infiltrative malignancies,neonatal Lupus, severe hypo or hyperthyroidism, trauma,degenerative neuromuscular disease

Question 2

AV Block Iatrogenic

Answer 2

Drugs: Digitalis, calcium channel blockers, beta blockers, amiodarone, adenosine
Cardiac Surgery
Catheter ablation of arrhythmias
Transcatheter VSD closure
Alcohol Septal ablation for HOCM
TAVr (Transcatheter AV replacement)

Question 3

AV Block-Definition

Answer 3

AV Block is defined as a delay or interruption in the transmission of an impulse from the atria to the ventricles due to an anatomic or functional impairment in the conduction system.

Question 4

What accounts for half of AV block?

Answer 4

Fibrosis and sclerosis of the conduction system accounts for about 50% of cases of AV block and may be induced by several different conditions that often cannot be distinguished clinically. These are frequently progressive to complete heart block.

IHD (Ischemic Heart Disease) accounts for 40% of cases. Conduction distrubances range from first degree AVB to complete with either chronic IHD or an Acute MI.

Question 5

Familial AV Block

Answer 5

may be transmitted as an autosomal dominant trait.

Question 6

drugs that can cause AV Block

Answer 6

Drugs, including digitalis, calcium channel antagonists (verapamil and diltiazem), amiodarone, adenosine, and beta blockers can impair AV conduction, occasionally resulting in AV block.
Most are atleast partially reversible following drug withdrawel.

Question 7

heart procedures –> AV Block

Answer 7

A variety of procedures performed on the heart may result in AV block.These include valve replacement, catheter ablations, closure of VSD’s, alcohol septal ablations and TAVr.

Question 8

Types of AV Block

Answer 8

First Degree AVB
Second Degree AVB:
Mobitz Type I, progressive PR interval prolongation precedes a nonconducted P wave
Mobitz Type II, PR interval remains unchanged prior to a P wave that suddenly fails to conduct to the ventricles

Third Degree AVB (complete heart block)
No atrial impulses reach the ventricle in 3rd Degree AVB. The block can exist in the AV node or in the infranodal specialized conduction system.