VII Electric and Magnetic Stimulation of the Heart
VIIElectric and Magnetic Stimulation
of the Heart
Part VII continues the discussion on the second
subdivision of bioelectromagnetism, i.e. electro- and magnetobiology, with
applications to cardiology. The electric stimulation of cardiac tissue has two
very important clinical applications: cardiac pacing and cardiac
defibrillation. The purpose of cardiac pacing is to maintain the heart rate at a
sufficient level even though the activity of the sinus node may not reach the
ventricular muscle because of an interrupt in the conduction system. Too low a
heart rate cannot provide a high enough blood pressure to maintain the body with
sufficient oxygen concentration. The purpose of cardiac defibrillation is to stop continuous and
uncontrolled multiple re-entrant activation circuits causing fibrillating
muscular contractions. Fibrillation of the ventricular muscle causes a total
loss of the blood pumping action and thus leads to a dramatically decreased
blood pressure, lack of oxygen in the brain tissue and death, unless the
fibrillation can be stopped with a defibrillator within a few minutes. In clinical practice, both cardiac pacing and cardiac defibrillation
are achieved solely with electric methods. Some experiments in accomplishing
these with magnetic stimulation have been perfotmed. They are, however, so
limited that a separate chapter on magnetic stimulation of the heart muscle is
not included but these experiments are referred to in the appropriate chapters
on (electric) cardiac pacing and defibrillation.