I. Historical
II. Complete Heart Block
III. Second Degree AV Block
IV. Sinus Node Dysfunction
V. Permanent Pacemakers
VI. What a Pacemaker will not do
VII. Activities

GLOSSARY
AOO a pacemaker that stimulates the atrium as a fixed rate,
independent of atrial activity. capture effective depolarization of the heart by the artificial
pacemaker. demand or inhibited pacemaker any pacemaker that inhibits
its output upon sensing a natural or paced event and fires at
the preset rate when the sinus rate falls below the pacemaker’s
programmed escape rate. transvenous anything that passes through a vein (catheter or
pacemaker lead)
WHEN THE HEART TEMPORARILY STOPS BEATING for 10–30 seconds, or the heart beat suddenly becomes remarkably slow (< 30 beats per minute) transient loss of consciousness occurs. This may be accompanied by convulsive seizures that resemble an epileptic attack, or the patient may fall without sufficient warning and injuries or death may occur. The invention of the cardiac pacemaker is one of the greatest cardiologic developments of modern medicine. Countless lives have been saved and accidents prevented by this innovative technologic solu¬tion.

• I. HISTORICAL
  In 1719 Gerbezius described a patient with a very slow pulse. The patient often had dizzy spells and from time to time was subjected to slight epileptic attacks. He did not connect the slow pulse as the reason for the seizures. In 1761 Morgani reported two cases with recurrent fainting spells associated with slow pulse rate, but listed the disturbance as neurological, perhaps, because it was associated with convulsive seizures. In 1826 Robert Adams was the first to realize that the loss of consciousness (apoplectic attack or seizures) was related to a very slow pulse rate and that the disorder had a cardiac origin. Later an autopsy revealed fatty degeneration of the myocardium and Adams assigned a cardiac cause for the seizure-like disorder.
• 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
• III. SECOND DEGREE AV BLOCK
  Type II second degree AV block (Mobitz type II block) associated with a bundle branch block pattern is due to conduction defects usually below the bundle of His. Other dropped beats are caused by intermittent block in the
• IV. SINUS NODE DYSFUNCTION
  In this condition, because of coronary heart disease, degenerative disease, or unknown cause the normal sinus node pacemaker may have been destroyed because of lack of blood supply or replaced by fibrous tissue. The heartbeat then becomes erratic and the heart may beat very slowly (28–42 beats per minute) and at other times may beat very quickly (100–150 per minute). Thus the condition is sometimes called bradytachycardia or sick sinus syndrome.
• V. PERMANENT PACEMAKERS
  A. Types of Pacemakers
• VI. WHAT A PACEMAKER WILL NOT DO
  A pacemaker does not cause the heart muscle to contract more forcefully; therefore, it does not help heart failure, except in some cases where a very slow heart rate was contributing to the heart failure. In a special group of patients with heart failure and intraventricular conduc¬tion delay pacing the heart may decrease the recurrence of heart failure (see the chapters Heart Failure and Bundle Branch Block).
• VII. ACTIVITIES
  Patients are allowed to exercise freely to the extent of major advances in electronics, and now virtually all pacemakers are powered by a variety of lithium batteries. The life of the lithium pacemaker varies from 7–10 years. Each patient is given a card that documents the type, model, serial number, date of installation, and approximate life of the pacemaker and should carry the card at all times and wear a pacemaker awareness bracelet.
• BIBLIOGRAPHY
  Acierno, L. J. Electrophysiologic disturbances. In The History of Cardiology. Parthenon Publishing, New York, 1994.