Biomedical subjects

W Boute

Publications and source records attributed to W Boute.

11 recordsLinked to original sources

PubMed1994

Avoiding atrial undersensing by assessment of P wave amplitude histogram data.

Reliable sensing of the P wave is an essential requirement for the appropriate functioning of any device that uses atrial tracking to provide AV synchrony. However, a single measurement of the P wave amplitude, either at implantation or during follow-up, may not be a reliable reflection of the P wave amplitudes that occur during daily life. The P wave amplitude histogram is a new feature that automatically measures the P wave amplitude at regular intervals and provides the distribution of these measurements. This enables the assessment of the smallest P wave amplitudes that occur. Two populations were studied: 104 patients with a fixed atrial lead and a DDDR pacemaker and 100 patients with a single pass VDD lead and a VDD pacemaker. Both pacemakers incorporate the P wave amplitude histogram feature. Data in the P wave amplitude histogram were compared with a single measurement of the P wave amplitude at each follow-up. Programming of a 100% safety margin based on a single measurement of the P wave amplitude provided reliable atrial sensing in only 72% and 43% of the patients of both populations, respectively. Data continued in the P wave amplitude histogram may be a useful adjunct for the optimal programming of atrial sensitivity.

Adolescent↗

PubMed1991

One-year follow-up of automatic adaptation of the rate response algorithm of the QT sensing, rate adaptive pacemaker.

Optimal functioning of a rate adaptive pacemaker depends upon reliable sensing of the sensor and appropriate programming of the rate of response algorithm. QT sensing pacemakers use data derived from the endocardial electrogram in the programming of the rate response algorithm. In the latest versions of these pacemakers, programming of the rate response algorithm may be performed using either a semiautomatic Fast Learn (FL) procedure or by using the newly developed, fully Automatic Slope Adaptation (ASA) mechanism. We report our experience in a prospective study of 17 patients in the first year postimplantation. ASA was characterized by significant changes only in the values of the slope settings at the lower rate limit (3.7 msec/msec at time 0 to 5.77 msec/msec at 2 weeks, P less than 0.001) during the first 2 weeks after its enablement. Further adaptation between weeks 2 to 4 was observed (5.77 msec/msec to 6.4 msec/msec, P = 0.2) but this was not significant. The slope settings derived using the FL procedure were also checked at 2 and 4 weeks and were reproducible. They were closest in value to the values attained by the automated mechanism at 4 weeks. This suggests that the final value of the slope setting at the lower rate limit using ASA is reached between weeks 2 to 4. Both methods of slope determination result in satisfactory and similar rate response profiles but the time to achieve slope stability will necessarily be slower with ASA.

Algorithms↗

PubMed1990

Analysis of the morphology of the unipolar endocardial paced evoked response.

In a retrospective study we analyzed the unipolar endocardial evoked response signal (ERS) of 103 patients prior to pacemaker implantation. The objective of this study was to give a complete description of the ERS morphology and to evaluate influences on this morphology of both various electrode characteristics and pacing rate. In addition, spontaneous endocardial signals were studied. The results demonstrate that acute leads had both higher R wave and T wave amplitudes and a faster downslope of the T wave. In the acute leads those with porous titanium carbon coated tips showed a more pronounced T wave. Pacing rate influences the R wave amplitude and the stimulus to T wave interval. Both stimulus to maximum and stimulus to minimum T wave interval show an exponential correlation with the stimulus interval. The interval between maximum and minimum of the T wave and the absolute amplitude of T wave are not influenced by rate. Although there were significant correlations of the spontaneous endocardial signal with the ERS, the predictive value of the spontaneous signal for the ERS morphology is low. Prospective studies will be necessary to confirm the findings in this study.

Aged↗

PubMed1989

Improved rate responsive algorithm in QT driven pacemakers--evaluation of initial response to exercise.

The QT pacemaker is a rate modulated pacemaker that uses the evoked QT interval as an indicator to determine its optimal pacing rate. Despite the generally favorable clinical results with this form of pacing, some flaws in the system have been reported, such as the frequently observed rather slow initial response of the pacing rate to physical exercise, and the phenomenon of oscillation of the heart rate. These problems can be attributed to the rate adaptive algorithm used in the current QT pacemaker. Recently, in a reexamination of the relationship between evoked QT interval and pacing rate, a curvilinear relationship between these parameters has been demonstrated. As a result, a new algorithm has been developed for the next generation of the QT pacemaker. Before this new algorithm was implemented in new implantable devices, it was evaluated in a multicenter clinical investigation, with emphasis on the initial response of the pacing rate to exercise. This study was carried out by means of special software in the programmer of the QT pacemaker. By employing real-time bidirectional telemetry, it was possible to submit the study population, consisting of 37 patients with implanted QT pacemakers of the current generation, to identical exercise tests. Comparing these exercise tests, it appears that a considerable gain in speed of response to exercise can be achieved by using the same sensor with a faster reacting, nonlinear rate adaptive algorithm.

Aged↗

PubMed1989

Improved pattern of rate responsiveness with dynamic slope setting for the QT sensing pacemaker.

We have recently described the electrophysiological basis of a new algorithm for the QT (TX) sensing rate responsive pacemaker. By using the new software program running on the standard programmer it has been possible to simulate the new algorithm in ten patients with complete heart block (seven patients had implanted TX units and three were paced with an external TX pacemaker) during routine exercise testing. In this way a single-blind, intra-patient comparison of the pattern of pacing rate change using both the existing and new algorithms was possible. In nine out of the ten cases the time taken to increase the pacing rate from 70 to 80 bpm was reduced significantly when the new algorithm was used (P = 0.037). Additionally, the correlation between the atrial and ventricular rates in those patients with normal sinus node function (seven patients) was determined. In all cases we have observed a significantly improved correlation between the atrial and ventricular paced rates during exercise with the new algorithm (P less than 0.001).

Adult↗

PubMed1988

Nonlinear relationship between pacing and evoked QT intervals.

The paced evoked response is an established biosensor which has been used in the design of a rate responsive pacemaker. The unit is capable of sensing the interval between the delivery of a pacing stimulus and the downslope of the evoked T wave. With fixed rate pacing this interval has been shown to shorten with exercise and the main cause of this effect is thought to be mediated by the increase in the plasma catecholamines which are released on exertion. The detection of a reduction in the stimulus-T interval results in an increase in pacing rate. The rate of change of pacing rate is referred to as the slope setting and this must be determined for each individual patient so that optimal rate responsive pacing can be effected. The algorithm underlying the slope setting is the pacing rate-evoked QT interval relationship. This relationship was implemented as a linear function, but this study, which was conducted to reevaluate it, has demonstrated nonlinearity between the pacing and evoked QT intervals. The degree of QT shortening is least at low heart rates. This finding has resulted in the development of a new algorithm for the pacemaker in the form of a new program for the pacing system. This should result in a more physiological rate of change of heart rate with exercise and less chance of sudden changes in rate. These postulates are the subject of current clinical trials.

Adolescent↗

PubMed1988

Automatic refractory period.

Pacemakers have become more and more complex over the years, whereby technological advances were used to create more and new possibilities in existing pacemaker applications. As a result a demand has grown for more automatic functions to reduce the time to program the pacemakers and eleviate follow-up procedures. One of the parameters which can be adjusted automatically is the refractory period. We measured the pacing threshold as a function of coupling interval between the stimulus and the previous paced complex and related this to the morphology of the paced evoked T-wave. When the stimulus falls far away from the T-wave the pacing threshold is constant. When it approaches the T-wave the threshold reduces slightly (superconductivity) and at the peak of the T-wave there is a sharp increase of the pacing threshold. The refractory period coincides with the period from the stimulus until the top of the T-wave (stim-T interval). This result is used in the Rhythmyx pacemaker where the stim-T interval is used to automatically adjust the pace refractory period. Automatically adjusting the refractory period has the extra advantage of higher allowable pacing rates as the refractory period shortens with increasing heart rates. Future applications will include use antitachycardia pacing where the stim-T interval can be used to prevent pacing in the refractory period or in the vulnerable zone.

Algorithms↗

PubMed1988

Heart rate monitoring in implanted pacemakers.

Increasing pacemaker memory allows integration of heart rate monitoring into the pacemaker. Two main methods can be distinguished. 1. Heart rate monitoring in histograms. 2. Heart rate monitoring in the time domain (heart rate holter). Method 1 is useful in antitachycardia and diagnostic pacemakers when short specific events must be detected (tachycadia, bradycardia). For the analysis of a rate adaptive pacemaker this method is less appropriate as it does not give any information about the dynamics of rate changes or its time relations. For this purpose Method 2 will give more information about the functioning of the pacemaker as it does not only store the heart rate but also the timing of the heart rate so that changes in heart rate can be correlated to the activity of the patient. An algorithm was developed to store the average heart rate over 7.8 minute periods in a pacemaker. On interrogation of the pacemaker the information will always reveal the heart rate over the 24 hours prior to interrogation. This monitor can also be temporarily programmed to store the average heart rate in 20 second intervals to monitor the response to an exercise test for a period of 1 hour. The time needed for a standard follow-up procedure of a rate adaptive pacemaker can be dramatically reduced to a value close to the follow-up time of a standard VVI pacemaker.

Algorithms↗

PubMed1988

Morphology of endocardial T-waves of fusion beats.

Recently developed stimulation techniques are capable of eliminating polarization afterpotentials caused by the emitted stimulus. A well-controlled study method was developed to initiate various degrees of fusion and to monitor changes in the morphology of the endocardial signal. The study was performed on two dogs. The zone during which fusion could be provoked was less than 30 ms in both dogs. In addition, the results show a significant decrease in the endocardial T-wave amplitude as soon as fusion was noticed, while the QT interval then slightly lengthened. Furthermore, the evoked R-wave duration shortened during fusion, while the stimulus to R-wave interval lengthened. These results have consequences for pacemakers that use evoked endocardial signal characteristics for driving a pacemaker function.

Animals↗

PubMed1988

Introduction of an automatic QT interval driven rate responsive pacemaker.

QT driven rate responsive pacemakers have been implanted since 1981. The more than 6 years experience and additional knowledge gained during several clinical studies have culminated in the design of an automatic rate responsive pacemaker. The adjustment of the rate responsive function to each individual patient is carried out automatically by the pacemaker, which therefore performs several measurements both at rest and during exercise. The results of these measurements are used to adapt the rate responsive parameters in order to optimize the rate response, even under changing circumstances.

Algorithms↗

PubMed1986

Reliability of evoked endocardial T-wave sensing in 1,500 pacemaker patients.

Intracardiac measurements of the evoked endocardial T-wave were performed on 1,500 pacemaker patients. The sensed evoked T-wave amplitude was found to be above 0.75 mV in 94.1 percent of all cases. No correlation was found between the amplitude of the spontaneous R-wave and that of the evoked T-wave. Some electrode characteristics proved to be more favorable than others for evoked endocardial wave sensing, i.e., a surface area of less than 12 mm2, porous surface structure (preferably carbon), and atraumatic fixation.

Electrocardiography↗