DESIGN AND DEVELOPMENT OF MEDICAL ELECTRONIC ...

VENTRICULAR TACHYARRHYTHMIAS 411ImpedanceSensorPacemaker LeadDelivered TransvenouslySuperiorVenaCavaRightVentricleLeftVentricleProximal (“ring”)ElectrodeDistal (“tip”) Electrode(b)Figure 8.30 (Continued)antiarrhythmic drugs to implanted devices. Ventricular tachycardia, a condition thatoccurs in approximately 2 out of 10,000 people, is a potentially lethal arrhythmia thatoften causes the heart to become inefficient at pumping blood through the body.Ventricular rates of 160 to 240 beats/minute are usually considered to be the result of anonphysiologic tachycardia (i.e., a high rate that is not the result of the body’s metabolicdemand).Ventricular tachycardia can occur spontaneously. It can also develop as a complicationof a heart attack, cardiomyopathy, mitral valve prolapse, or myocarditis, and afterheart surgery. It may be a result of scar tissue formed after an earlier heart attack or asan undesired effect of antiarrhythmic drugs. It may be triggered by disrupted bloodchemistries (such as a low potassium level), pH (acid–base) changes, or insufficient oxygenation.AV nodal reentry tachycardia (AVNRT) is the most common form of paroxysmalsupraventricular tachycardia (PSVT, a tachycardia not directly of ventricular origin whichcomes in sudden attacks). Patients with this arrhythmia do not usually have other structuralproblems with their heart. PSVT originates in tissues near the AV node, which as we discussedearlier, is the electrical structure that transmits impulses between the atria and theventricles. Susceptible persons have two pathways that can conduct impulses to and from