Two-chamber pacemaker

Details Two-chamber pacemaker Two-chamber pacemaker

1999-06-16

2001-02-20

Kamm, William E. (Department: 3762)

Surgery: light, thermal, and electrical application

Light, thermal, and electrical application

Electrical therapeutic systems

Reexamination Certificate

active

06192274

ABSTRACT:

The invention relates to a two-chamber pacemaker according to the preamble to claim
1
.
Two-chamber pacemakers have long been known and have proven themselves in the treatment of multiple cases of arrhythmia. However, despite the meanwhile extensive experience gained in the use of these devices, the clinical use of these pacemakers still poses certain problems.
One of the best known and most important problems is the danger of pacemaker-induced tachycardias:
An increase in the ventriculoatrial conduction must be expected following the occurrence of ventricular extrasystoles in the clinical sense (in the following called “clinical VES”) because the chamber depolarization was not preceded by an atrial depolarization and the ventriculoatrial conduction path (here in particular of the AV nodes) is therefore not refractory. If this physiological condition is not considered when designing the pacemaker timing, a pacemaker-induced tachycardia (PMT) can result following a clinical VES. Such a tachycardia develops in that following the clinical VES, a p-wave formed by retrograde conduction is detected outside of a post-ventricular atrial refractory period (post-ventricular ARP or also “PVARP”) that is adjusted on the pacemaker, which then triggers a chamber pulse. As a result, the retrograde p-wave following this chamber pulse is detected and triggers a chamber pulse and so forth.
To prevent the triggering of a pacemaker-induced tachycardia following a clinical VES after a ventricular sensory event, identified by the pacemaker as VES, a PVARP must be started that is longer than the (assumed) VA conduction time following the clinical VES and thus also lasts longer than the normal PVARP following a ventricular sensory event that is not identified as VES. Compare also the EP-B-0 077 808 in this connection.
All pacemaker manufacturers use the missing AV synchronicity of the ventricular sensory event as recognition criterion for a clinical VES. It means that any ventricular-sensed event, which was not preceded by an atrial event (atrial sensory event outside of the ARP or atrial pace event), is considered a ventricular extrasystole by the pacemaker. Such an extrasystole—quasi defined via the perception capacity of the pacemaker—is also referred to as a “pacemaker VES.” This previously mentioned VES recognition criterion has a high sensitivity. That is to say, with intact ventricular perception without interference signals, all occurring clinical VES also manifest themselves as pacemaker VES. However, the specificity of the recognition criterion is lower, meaning not all pacemaker VES are also actually clinical VES.
In the case of an atrium depolarization, which is conducted into the chamber and is perceived therein, an incorrect evaluation can occur, for example, if the atrium depolarization did not start an AV time because it was either not perceived in the atrium at all or it was perceived within the ARP and therefore did not become effective for the pacemaker control. Such an atrium depolarization is also called a “refractory A-sensory event.” If such an A-sensory event is conducted into the heart chamber, the ventricular sensory event is rated as pacemaker VES and triggers a prolonged PVARP. With respect to this, compare also the EP-A-0 308 535.
If the inherent atrial frequency in addition is sufficiently high and/or the PR interval is relatively long, the subsequent p-wave falls within the extended PVARP and is not detected or at the very least is not used for the pacemaker control. It means that not every atrial action is followed by an atrium-synchronous chamber stimulation. This mode of operation of the pacemaker is referred to in the following as “pacemaker VES behavior.” A special case is the function of the 2:1 blockage, where a chamber stimulus follows only after each second atrial action. This mode of operation continues until the RP interval is shorter than the extended PVARP, started by the pacemaker VES. However, as soon as a p-wave arrives outside of the extended PVARP, an AV time is started and the chamber is again atrium-synchronous stimulated.
An atrium-synchronous stimulation of the chamber at a ratio of 1:1 occurs, for example, if a patient with a known two-chamber pacemaker and a PR interval of 200 ms for a PVARP of 200 ms and an AV time<200 ms has an inherent atrial frequency (rate)<150/min, meaning a chamber pulse follows each p-wave. If the atrial rate exceeds a threshold value (in the following also called an “entrance threshold”) of 150/min at the onset of an atrial tachycardia, the aforementioned pacemaker VES behavior occurs and the PVARP is extended to 400 ms. However, if the atrial rate falls once more below the entrance threshold, the pacemaker does not immediately return to the atrium-synchronous operation, but returns to it only if the RP interval reaches>400 ms. In the example, this is the case only for an atrial rate of<100/min, meaning if the rate falls below a second threshold value (in the following also referred to as “exit threshold”). Only then does the p-wave respectively arrive outside of the extended PVARP, which is started by a pacemaker VES.
Thus, the return from the pacemaker VES behavior to the atrium-synchronous operation during the disappearance of an atrial tachycardia is delayed longer, meaning the exit threshold is lower, the longer the time interval for which the extended PVARP was adjusted and/or the longer the PR interval. A comparable problem occurs with two-chamber pacemakers where the AV time can be adjusted to match the currently valid stimulation rate and for which a longer AV time is valid in the region of the 2:1 blockage behavior than outside of this operational mode. For this, compare also the EP-A-0 726 082. An equally comparable problem occurs with pacemakers having a so-called total atrial refractory period (TARP), which normally starts with the A-sensory event or, if such an event does not occur, with the following V-sensory event (pacemaker VES).
This pacemaker behavior can lead to ECG interpretation problems because an atrium-synchronous chamber stimulation does not (yet) occur at atrial rate values, for which such a stimulation is expected. A longer-lasting pacemaker VES behavior is physiologically a disadvantage for the patient, specifically in the case of a hypertrophic, obstructive cardiomyopathy or a symptomatic AV blockage
1
.
Thus, it is the object of the invention to create a two-chamber pacemaker with improved response behavior during the dying out of an atrial tachycardia, which pacemaker does not require a considerable increase in expenditure for the realization.
This object is solved with a two-chamber pacemaker having the features as stated in claim
1
.
The invention incorporates the idea of making it possible to return to the atrium-synchronous chamber stimulation while the p-waves are still detected as refractory A sensory event. If a predetermined number of event sequences are detected, involving a ventricular sensory event, followed by a refractory A sensory event, followed by a ventricular sensory event, followed by a refractory A sensory event, etc., the ARP is clearly shortened as a test for at least one operating cycle. This is designed to allow the pacemaker to return to the 1:1 atrium-synchronous chamber stimulation, specifically if the actual atrial rate is below the aforementioned entrance threshold, but still above the exit threshold.
For this, a predetermined succession of signal sequence patterns that mirror the heart activities—namely based on the above pattern (Vs-Asref)
n
in a predetermined number n of repeat actions—is stored (programmed) in a signal pattern memory, while the actual sequence of output signals of the atrial and the ventricular sensory means is recorded during the 1:1 non-synchronous operation in a signal sequence memory, and a comparison is made in a comparator to compare the sequence of output signals with the stored signal sequence pattern. Finally, if the result of the comparison is positive, refractory time changeover means serve to adjust a shortened

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