FIRST-DEGREE AV BLOCK

Description:

Long PR interval on ECG (> 200 milliseconds).

Symptoms & Signs:

Asymptomatic

Treatments:

Usually, none.

Risk Factors:

Common in highly-trained athletes, due to enlarged heart muscle; Myocarditis, hypokalemia or hypomagnesium, certain medications (channel blockers or digoxin).

Clinical Concerns:

May increase risk of atrial fibrillation.

SECOND-DEGREE AV BLOCK

Description:

Mobitz Type 1 (aka, Wenckenbach’s Block) = PR interval gets progressively longer until AV node completely fails and ventricular contraction is completely skipped. Morbitz Type 2 = PR interval doesn’t change, but ventricular depolarization is skipped.

Symptoms & Signs:

Type 1 = Dizziness, fainting.
Type 2 = Chest pain, difficulty breathing, tiring easily, hypotension.

Treatments:

Type 1 = No treatment if asymptomatic; consider medications as the source of the issue.
Type 2 = Pacemaker

Risk Factors:

Type 1 may be physiologic in healthy athletes.
Type 2 is pathologic. Cardiac injury (fibrosis, sclerosis, scarring from heart attack), Lyme disease (Type 2), Drugs (beta blockers, calcium channel blockers, digoxin, amiodarone), vavluopathy.

Clinical Correlations:

Type 2 can lead to complete heart block (3rd degree heart block).

THIRD-DEGREE AV BLOCK

Description:

AV dissociation: No electrical communication between atria and ventricles, therefore, no relationship between P waves and QRS complexes.

Symptoms & Signs:

Fatigue/lethargy, dizziness, fainting, slow heart beat.

Treatment:

Pacemaker.

Risk Factors:

Congenital in infants from mothers with autoimmune condition or in infants born with other cardiac conditions.
Acquired as result of complications in heart surgery, radiotherapy, infection (such as diphtheria or rheumatic fever), hypertension, cancer, radiofrequency ablation, medications (digoxin, calcium-channel blockers, beta blockers, tricyclic antidepressants, clonidine).

Clinical Concerns:

Low cardiac output deprives organs of oxygen.