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Welcome to today's module on arrhythmias. My name is Christine LaGrasta. I work at Children's Hospital of Boston as a pediatric nurse practitioner. Disturbances of atrioventricular or AV conduction.

This occurs when there is a disturbance in the conduction between the normal sinus impulse and the ventricular response. There are three main types of AV block. There's first degree AV block, second degree AV block, and then there are two types of second degree AV block. They are Mobitz Type 1 or Wenkebach, and then there's Mobitz Type 2. And the final main type of block is third degree or a complete AV block.

So first degree AV block. The PR interval is prolonged beyond the upper limit of normal for the patient's age and heart rate. PR interval is greater than 0.20 seconds. Sinus rhythm is maintained, and the QRS complex is normal in configuration.

Causes include congenital heart disease, cardiomyopathy, rheumatic heart disease, surgical intervention, as in septal defect repairs, and digitalis toxicity. Treatment: not necessary, except to address the underlying cause.

Second degree AV block or Mobitz type 1 occurs when there is an intermittent failure of conduction between the atrium and ventricle. There's a progressive lengthening of the PR interval until one QRS is dropped completely. The PR interval lengthening occurs over three to six cycles, until the QRS complex is dropped. All the QRS complexes are normal in configuration.

Causes again include congenital heart disease, cardiomyopathy, rheumatic heart disease, myocarditis, surgical interventions such as patients with septal defect repairs, medication such as digitalis or beta blockers. Treatment includes addressing the underlying cause. If the patient is unstable, AV pacing is indicated to restore synchrony between the atria and the ventricles.

Second degree AV block or Mobitz Type 2. AV conduction is all or none. There is either normal AV conduction with normal PR intervals, or the conduction from the atria to the ventricles is completely blocked.

Causes again include the same as the other two blocks. Congenital heart disease, cardiomyopathy, rheumatic heart disease, myocarditis, surgical interventions such as patients with septal defect repairs, and medication such as digitalis or beta blockers. Treatment, again, treat the underlying cause. If the patient is unstable, AV pacing is indicated to restore synchrony between the atria and the ventricles.

Third degree or a complete AV block. There's AV dissociation where the atria and ventricles beat entirely independent of one another. There's no P wave before each QRS complex, or the PR interval is too short for the P wave to be associated with a QRS complex. There are more P waves than QRS complexes.

Causes include cardiac surgical procedures that occur near the cardiac conduction pathway, the block can be congenital complete AV block, or from rheumatic fever, myocarditis, or cardiomyopathy. Treatment includes AV pacing to restore synchrony between the atria and the ventricles.

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