| 摘要 |
A cardiac pacer has separate digital filter circuits for sensing atrial and ventricular activity. Parameter data stored in memory is used by the digital filters for identifying the various components of cardiac activity, such as the P, R and T waves, as well as for identifying Premature Ventricular Contractions (PVC). A Ventricular Rate Time Out period is established from the last natural beat or stimulating pulse; and if a P wave or natural R wave is not sensed during that period, the system generates a stimulating pulse and, using T wave parameters in the ventricular filter, tests to verify capture. Loss of capture increases stimulating pulse width and amplitude to regain capture. If a P wave is sensed before the Rate Time Out period ends, the system establishes a predetermined P-R interval period to override the Ventricular Rate Time Out period in which the ventricular filter is set to detect a natural R wave in an effort to synchronize the ventricle with the atrium. Prior to the Ventricular Rate Time Out period of each cardiac cycle, the ventricular filter is set to detect Premature Ventricular Contractions. If a predetermined number of PVCs is detected, the system generates a train of stimulating signals at a rate higher than expected tachycardia in an effort to break the tachycardia cycle. Many of the system's functions can be enabled or disabled by action of the physician; and many of the system parameters can be externally programmed, such as ventricular rate, stimulating pulse amplitude and/or duration, atrial and ventricular filter parameters, P-R delay interval and others. |
