II. COMPLETE HEART BLOCK A. Pathophysiology
Normally an electrical current originates in the sinus node (the natural pacemaker) and is conducted through the AV node (Fig. 1). It then traverses the right and left bundle branches to reach the ventricular muscle and endocardium. The electrical current stimulates cardiac contraction that causes ejection of blood from the left ventricle into the aorta which results in an adequate supply of blood, oxygen, and other nutrients to the brain and vital organs. The electrical current may be halted by diseases that destroy the specialized conducting tissue in the AV node or lower in the bundle of His; the current fails to reach the ventricle and no cardiac contraction occurs (asystole). The brain
is deprived of blood and the individual loses consciousness. The block in the electrical conduction may be temporary and last several seconds to a minute. With return of elec¬trical conduction, blood supply to the brain is restored and the patient recovers. If blood fails to reach the brain and head, the facial skin becomes blanched and when the heart begins to contract again blood is pushed quickly and rapidly into the facial arteries causing intense flushing of the face. Loss of consciousness accompanied by facial pallor and during recovery followed flushed facies is a characteristic of complete heart block (Stokes-Adams attacks).