The problem of crosstalk in dual chamber pacemakers has been recognized for some time. Crosstalk can occur when an atrial pace pulse (AP) is delivered, and the ventricular sensing electrodes pick up a signal from the atrial pulse before the cardiac conduction system delivers a QRS depolarization wave to the ventricle. When and if this happens, the pacemaker on-demand logic "sees" a ventricular sense, and if it didn't know better the pacemaker would inhibit delivery of a ventricular pace pulse and reset the atrial and ventricular escape intervals. This can have the highly detriment result that the ventricle is not always paced when the atrium is paced.
The pacemaker logic can attempt to distinguish the crosstalk event by recognizing that such a false crosstalk sense occurs before the normal QRS, e.g., a crosstalk sense occurs within about 100 ms after the atrial pace whereas a normal QRS occurs within an AV delay of about 120-200 ms. This distinction could be used by blanking ventricular sensing for about 100 ms, but this has the disadvantage that real ventricular signals, e.g., PVCs or atrial undersensing followed by a true ventricular sense (VS), would not be recognized. Some short blanking interval is necessary following the delivery of an atrial pulse, but in order to detect the maximum amount of information, the shorter the blanking period the better.
Another approach to the problem is that represented by U.S. Pat. No. 4,825,870. In this approach, the pacemaker times out an early interval following an AP, e.g., 64-100 ms. If a "VS" is detected in this interval, the pacemaker times out a shorter AV interval, e.g., 120 ms. If no VS is sensed within this shortened interval, the pacemaker logic does not take a chance, assumes that the sense was crosstalk, and delivers a ventricular safety pulse to be safe. Of course, if a VS does intervene in the shortened AV interval, delivery of a ventricular pulse is inhibited. Various other schemes have been proposed, which establish a crosstalk interval, treat an early sense in the crosstalk interval as noise, and reset the crosstalk interval by a short duration whenever a sense occurs in it, up to a maximum AV interval. In these schemes, generally, a safety pulse will be delivered if consecutive senses are timed at a rate that indicates noise. See, for example, U.S. Pat. No. 5,552,857, assigned to Vitatron Medical B.V., the assignee of this invention.
The above solutions to the crosstalk problem have the disadvantage of not reacting to precise information, and of providing a compromise solution. If a sense is crosstalk, the desireable response is to wait for timeout of the normal AV interval, not to deliver a pulse to the ventricle after timeout of a shortened interval. And if the sense was that of a true R wave, it is better not to deliver a pulse shortly thereafter. It is our observation that generally, if crosstalk is being sensed, the pacemaker can detect a pattern, and treat such early senses as crosstalk, i.e., ignore them; and that if these senses are intrinsic signals, the pacemaker logic should respond appropriately, e.g., by simply re-setting the escape intervals. Accordingly, we base a solution to the crosstalk problem on a technique for obtaining data which, in most cases, establishes the nature of the early senses with a high degree of confidence, so that the pacemaker can respond appropriately.