| 摘要 |
<p>Disclosed is a synchronous artificial cardiac pacemaker having a pulse generator which includes a timing circuit that, in the absence of any heart activity for a predetermined maximum time interval, provides stimulating pulses at a lower base pacing rate to a ventricular electrode to effect contraction of the heart to maintain a minimal cardiac output level when the heart is asystolic. A first sensing circuit is coupled to the ventricular electrode and a reset circuit is coupled to the timing circuit. Natural ectopic heart beats indicative of ventricular activity are picked up by the ventricular electrode, sensed by the sensing means and applied to the reset circuit which resets the operation of the timing circuit, so that if the ventricles are contracting at a rate exceeding the base pacing rate, the operation of the pulse generator is inhibited. A second sensing circuit is coupled to an atrial electrode and, through a memory circuit and a time delay circuit, to the timing circuit. When atrial heart activity is picked up, the sensing circuit produces a signal that sets the memory circuit and after a time delay, triggers the timing circuit into producing a stimulatig pulse for application to the ventricle in synchronism with the natural atrial contraction of the heart. Therefore, when the heart's natural conduction system frm the sino-atrial mode of the atrium to the ventricles is blocked while atrial activity is normal, the pacemaker synchronously paces the heart. If the atrial rate becomes excessive, the pulse generator circuit operates through an upper rate limit circuit coupled to the timing circuit and the operation of the memory circuit to synchronously pace the ventricles at an average rate not exceeding the upper rate of the timing circuit.</p> |
