| 摘要 |
A mode switching bradycardia pacemaker especially adapted for incorporation in an antitachyarrhythmia pacing and/or cardioversion/defibrillation system, provides AAI pacing in the absence of an intrinsic atrial rate exceeding the pacing lower rate and as long as the patient's heart is capable of normal AV conduction. The pacemaker switches to VVI mode any time that the patient's ventricular rate falls below a predetermined value. The mode switching may be implemented in a DDD pacing system or in a pacing system employing an atrial and ventricular sense amplifier and a single pacing output circuit and switching circuitry for switching its output between atrial and ventricular leads. This bimodal operation allows use of AAI pacing for the antiarrhythmic and hemodynamic benefits of maintaining atrial function in patients with sinus node disease, by obviates the risk of ventricular asystole should the AAI mode become ineffective due to transiant or newly evolving permanent impairment of AV conduction in those patients where atrial synchronous tracking is considered undesirable. In the AAI/VVI bimodal operation, only a single chamber of the patient's heart is paced at any given time, AAI pacing occurs in the presence of spontaneous or conducted ventricular depolarization, and VVI pacing is resorted to in AV dissociation or in the absence of a ventricular rhythm exceeding the lower pacing rate.
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