CARDIAC PACING AND DEFIBRILLATION - Design and Development of Medical Electronic Instrumentation - page 411

Impedance
Sensor

Pacemaker Lead
Delivered Transvenously

Superior
Vena
Cava

Left
Ventricle

Right
Ventricle

Proximal (“ring”)
Electrode

Distal (“tip”) Electrode

(b)

Figure 8.30 ( Continued )

antiarrhythmic drugs to implanted devices. Ventricular tachycardia, a condition that
occurs in approximately 2 out of 10,000 people, is a potentially lethal arrhythmia that
often causes the heart to become ine cient at pumping blood through the body.

Ventricular rates of 160 to 240 beats/minute are usually considered to be the result of a
nonphysiologic tachycardia (i.e., a high rate that is not the result of the body's metabolic
demand).
Ventricular tachycardia can occur spontaneously. It can also develop as a complica-
tion of a heart attack, cardiomyopathy, mitral valve prolapse, or myocarditis, and after
heart surgery. It may be a result of scar tissue formed after an earlier heart attack or as
an undesired e

ect of antiarrhythmic drugs. It may be triggered by disrupted blood
chemistries (such as a low potassium level), pH (acid-base) changes, or insu

ff

cient oxy-

genation.
AV nodal reentry tachycardia (AVNRT) is the most common form of paroxysmal
supraventricular tachycardia (PSVT, a tachycardia not directly of ventricular origin which
comes in sudden attacks). Patients with this arrhythmia do not usually have other structural
problems with their heart. PSVT originates in tissues near the AV node, which as we dis-
cussed earlier, is the electrical structure that transmits impulses between the atria and the
ventricles. Susceptible persons have two pathways that can conduct impulses to and from