Chronic Stimulation Thresholds Research Articles

Spontaneous daily variability of atrial sensitivity.: A study with an implanted DDD pacemaker

Background: Spontaneous variations in the chronic stimulation threshold were widely investigated in the last few years and formed the basis of the safety margin concept of stimulation energy. The dynamic variability of sensitivity, particularly in the atrium, is less studied and, in the literature, contrasting data are present about the actual entity of these variations. A 2:1 safety margin is still recommended by many authors, although some papers reported that this value was inadequate to guarantee a correct sensing function. Aim of the study: We evaluated daily variability of atrial sensitivity (AS) in patients implanted with the Cosmos 3 DDD cardiac pacemaker, with a special algorithm that continuously measures the minimum–maximum sensitivity values in atrium or in the ventricle during a 12-h sampling period. Materials and methods: 34 patients, 20 males and 14 females, with a mean age of 72±5 years, were implanted with a Cosmos 3 DDD pacemaker (PM). The indication to implant a PM was sick sinus syndrome in 21 patients and a high degree of AV block in 13 patients. Atrial bipolar leads were always employed. At 1, 2, 3 and 6 months after the implant, we analyzed the minimum–maximum values of atrial sensitivity for the last 12-h. This analysis was performed in the late afternoon. Results: The mean AS varied more than threefold, from a mean minimum of 0.68 to a mean maximum value of 2.19 mV at 1 month, from 0.68 to 2.21 mV at 2 months, from 0.69 to 2.19 mV at 3 months and from 0.67 to 2.17 mV at 6 months, without significant differences among the four follow-up controls. In seven patients, there was a fourfold variation, while the variation was fivefold in five patients. Conclusion: In conclusion, from our data, we can confirm that atrial sensitivity may vary widely during the day and, consequently, we recommend that a 3:1 safety margin should be programmed and the recommended 2:1 ratio should be abandoned. Moreover, at implant, particular attention should be paid to obtaining the best atrial signal amplitude, at least threefold higher than the highest sensitivity value available in the implanted PM. To achieve this goal and to obviate to the oversensing phenomena, bipolar leads are preferable to unipolar leads.

The impact of automatic threshold tracking on pulse generator longevity in patients with different chronic stimulation thresholds.

Automatic adjustment of the stimulation output of pacemakers to changing stimulation thresholds using the Autocapture feature increases patient safety and decreases energy consumption. This study examined the impact of Autocapture on pulse generator longevity in patients with different chronic stimulation thresholds. Eighty patients (mean age 79 +/- 9 years; 37 men, 43 women) with Pacesetter Regency SR+ pacemakers were included in the study. Data were collected before discharge of the patients from the hospital, 6-12 weeks postimplant, and then every 6-12 months. Pulse generator longevity was calculated theoretically, assuming 100% stimulation with a stable threshold, at a pacing rate of 65 +/- 6 beats/min and 1% backup pulses. Theoretical pulse generator longevity was calculated for low (< 1 V), intermediate (> or = 1 V and < 2 V), and high (> or = 2 V) stimulation thresholds. Pulse generator longevity was compared among three groups: (A) Autocapture programmed On, (B) Autocapture programmed Off, (C) theoretical calculations using thresholds of patients in group A with the stimulation voltage programmed at twice pacing threshold, or at a minimum of 2.4 V. The mean follow-up time since implantation was 19 +/- 8 months. The calculated longevity benefits for patients in group A were 36%, 59%, and 30% compared to group B, and 19%, 32%, and 49% compared to group C in patients with low, intermediate, and high chronic stimulation thresholds, respectively. Theoretical calculations based on chronic stimulation thresholds in our patient population with Regency SR+ pacemakers suggest that Autocapture may markedly prolong pulse generator longevity in patients with a broad range of long-term pacing thresholds.

Avaliação do sensor de contratilidade cardíaca em sistema DDDR: estudo multicêntrico

Introdução: O tratamento de distúrbios na condução atrioventricular associados a doenças do nó sinusal com o emprego de marcapassos DDDR tem incentivado a procura de um sensor ideal. Objetivo: Avaliar a resposta de freqüência do marcapasso com sensor de contratilidade em situações de esforço físico e mental, tanto em laboratório como em atividades diárias de pacientes com bradicardia e insuficiência cronotrópica. Casuística e Métodos: Do estudo multicêntrico brasileiro "Projeto Inos DR _ Brasil", que emprega um sistema de estimulação DDDR cujo indicador é o estado contrátil do miocárdio, foram selecionados 38 pacientes com insuficiência cronotrópica, sendo 21 do sexo masculino e 17 do sexo feminino, com idades variando de 13 a 83 anos (média de 57 anos). O marcapasso utiliza um parâmetro do próprio controle cardiovascular (contratilidade cardíaca obtida pela medida da impedância cardíaca unipolar) para a adaptação da freqüência cardíaca, num sistema de malha fechada que, teoricamente, possibilita um ajuste a todas as necessidades fisiológicas. A calibração e programação do sistema só foi realizada 30 dias após o implante (tempo de maturação da irterface coração-eletrodo), realizando-se, então, teste de estresse mental (matemático) e teste ergométrico (em esteira), monitorados com histograma de freqüência e com curvas de consumo de oxigênio. Resultados: A média de limiares agudos de estimulação foi de 0,82 Volts e 0,55 Volts, e a média de limiares de sensibilidade foi de 2,37 mV e 10,61 mV, respectivamente, para átrios e ventrículos. A média de limiares crônicos de estimulação foi de 1,44 Volts e 1,18 Volts, e a média de limiares de sensibilidade foi de 2,81 mV e 6,3 mV, respectivamente para átrios e ventrículos. A freqüência cardíaca variou de 5% a 128% nas atividades físicas e de 5% a 80% nas atividades mentais, com elevação logo no início das atividades, permitindo uma curva normal de consumo de oxigênio, comparável à de indivíduos normais de mesma faixa etária, sexo e peso. As médias foram comparadas pelo teste T de Student e as variáveis, pela análise de variância. Conclusão: O sensor de contratilidade cardíaca tem excelente desempenho na adaptação da freqüência cardíaca, com valor semelhante ao produzido pelo sistema nervoso autônomo de indivíduos normais.

Electrophysiological Characteristics of Bipolar Membrane Carbon Leads With and Without Steroid Elution Compared With a Conventional Carbon and a Steroid‐Fluting Platinum Lead

In a controlled study, the following four bipolar leads with passive fixation were implanted in 46 patients with the Siemens-Multilog-VVI or Sensolog-VVIR-pacemakers: membrane covered activated porous carbon with steroid elution (Siemens 1402 T, 11 patients) and without (Siemens 1403 T, 15 patients); activated carbon (Siemens 1010 T, 10 patients); and platinum with steroid elution (Medtronic Cap-Sure 5026, 10 patients). Stimulation threshold (STH) (assessed by a vario-test), impedance (IMP), and the intracardial R wave potential (IRW) (both gauged by a telemetric method) were measured 1, 5, and 10 days as well as 3 and 6 months after implantation during unipolar and bipolar stimulation, chronaxie rheobase product (CRP) and energy consumption (EC) were systematically determined. Differing insignificantly at the first day after implantation, STH is significantly lower for the 1402 T and CapSure 5026 leads at the tenth day. However, the 1402 T lead shows a significant increase of STH in the follow-up, in contrast to the other leads. The lowest chronic STH was found in the CapSure 5026 lead (CRP is significantly lower in all other leads, too). IMP is significantly lower in the CapSure 5026 lead compared to 1010 T lead. EC does not differ significantly during chronic stimulation in spite of the best possible programming of pulse amplitude and duration. No significant changes of IRW were observed. Unipolar versus bipolar stimulation shows significantly lower STH, CRP, and IMP, differences of EC and IRW were insignificant. In conclusion, the addition of steroid in membrane covered carbon leads protracts the increase of STH, but does not prevent it. The CapSure 5026 lead shows advantageous stimulation characteristics, but energy consumption is not significantly reduced because of low impedance and impossibility of programming an appropriate low output in Multilog pacemakers.

Treatment of patients with prior exit block using a novel steroid-eluting active fixation lead. Model 4068 Investigators.

An increased interest has developed in active fixation leads for several reasons. Exit block is an uncommon complication that is seen with both active and passive fixation leads. Exit block has not been a significant problem with passive fixation steroid-eluting leads and has been treated with these leads. A new steroid-eluting active fixation lead was examined for its performance in patients in whom exit block had previously occurred. The lead function was evaluated prospectively in 24 patients with a history of exit block (15 ventricular and 9 atrial). The results in patients with atrial exit block are encouraging with an average chronic stimulation threshold of 0.19 msecs at 2.5 volts. Results in the ventricle are less encouraging with 3 occurrences of recurrent exit block in 15 patients; however, the remaining patients had a good mean threshold of 0.21 +/- 0.11 msecs at 2.5 volts. There were a remarkable number of non-lead related complications suggesting that this is a substantially different group than routine implantations.

Acute and long-term ventricular stimulation thresholds with a new, iridium oxide-coated electrode.

Efforts have been made to design electrodes that significantly reduce not only the acute and chronic stimulation thresholds, but also attenuate the early peaking phenomenon and polarization. At two voltage levels (2.7 V and 5.4 V, respectively), we evaluated the right ventricular stimulation thresholds obtained with a new, iridium oxide-coated electrode in ten patients who received a VVI pacemaker. Measurements were made at implant and at multiple intervals for 1 year. Pulse width stimulation thresholds at implant were as follow: 0.04 +/- 0.008 msec at 2.7 V, 0.03 +/- 0.004 msec at 5.4 V; values at 2 weeks were 0.14 +/- 0.06 msec at 2.7 V, 0.07 +/- 0.025 msec at 5.4 V; values at 3 months were 0.09 +/- 0.03 msec at 2.7 V, 0.05 +/- 0.01 msec at 5.4 V; values at 1 year were 0.08 +/- 0.02 msec at 2.7 V, 0.04 +/- 0.01 msec at 5.4 V. The maximal increase of 0.11 +/- 0.05 msec occurred at 2.7 V, 2 weeks after implant. Our results indicate that this new electrode provides low acute and long-term stimulation thresholds, as well as an attenuated early peaking phenomenon, being able to stimulate safely at 2.7 V even early after implant.

The Influence of Endocardial Electrode Fixation Status on Acute and Chronic Atrial Stimulation Threshold and Atrial Endocardial Electrogram Amplitude

The endocardial atrial electrogram or "P wave amplitude" (PWA) and pacemaker atrial stimulation thresholds are important parameters determining correct pacing system function. Pacemaker lead fixation mechanism and lead age may negatively influence these parameters. Therefore, we compared acute and chronic PWA and atrial stimulation thresholds in 33 patients with permanent transvenous atrial screw-in leads, follow-up 647 days +/- 297 days; and in 31 patients with nonscrew leads, follow-up 855 days +/- 512 days (P = ns). The PWA differed between the two lead types acutely (1.97 mV +/- 0.8 mV for screw-in versus 2.48 mV +/- 1.1 mV for nonscrew-in leads; P less than 0.05), but not chronically (2.21 mV +/- 0.8 mV vs 2.2 mV +/- 1.2 mV; P = ns). Acute and chronic atrial pacing thresholds did not differ between groups. We also analyzed an early interim PWA in a subgroup of patients (mean 31 days after implantation). The nonscrew fixation group interim PWA was 1.76 mV +/- 0.9 mV versus 2.7 mV +/- 1.2 mV at implant (P less than 0.001). The screw-in lead interim PWA was 2.04 mV +/- 0.9 mV versus 1.97 mV +/- 0.7 mV at implant (P = ns). (1) A significantly higher endocardial PWA occurs at the time of lead implantation in nonscrew versus screw-in lead groups, but the chronic PWA does not differ between the two groups. (2) A transient but marked early (mean approximately 31 days) attenuation of the PWA occurs only with nonscrew-in leads. (3) Atrial threshold stimulation energies do not differ between the two lead groups acutely or during follow-up.

Stimulation Characteristics of a Steroid‐Eluting Electrode Compared with Three Conventional Electrodes

Stimulation thresholds of a steroid-eluting electrode (Medtronic CapSure 4003, 9 patients) were compared with three conventional electrodes (carbon-tipped lead, Siemens-Elema 423 S/60, 10 patients; Elgiloy-tipped lead, Cordis Encor, 10 patients; platinum-tipped lead, Telectronix Laserdish 030-276, 9 patients). Voltage thresholds were determined during implantation, 1-3 days, 6 weeks, and 6 months postimplantation. No significant difference among the four electrodes was found in regard to stimulation and sensing behavior during implantation. Compared to intraoperative measurements, mean increase in voltage threshold and absolute voltage thresholds were substantially less for the steroid-eluting electrode than for the other tested electrodes 6 weeks and 6 months after implantation. The rheobasechronaxie product, a parameter of the stimulation performance of electrodes, underlined the superior pacing characteristics of the steroid-eluting electrode. To achieve low chronic stimulation threshold by pharmacological means is an attractive direction for future electrode technology.

Lower Chronic Stimulation Threshold in the Carbon‐Tip than in the Platinum‐Tip Endocardial Electrode: A Randomized Study

Seventy-nine patients admitted for VVI pacemaker treatment were randomly given a Siemens-Elema 412 S endocardial electrode (tip material vitreous carbon, tip area 12 mm2) (41 patients) or a Siemens-Elema 415 S endocardial electrode (tip material platinum, tip area 12 mm2) (38 patients). The groups did not differ in age, sex, magnitude of intracardiac signal or indication for pacemaker treatment. Pacing threshold was measured by the vario technique at 3 and 15 months after the implantation. In the group of carbon-tip electrodes and in the group of platinum-tip electrodes stimulation thresholds at implantation were 0.49 +/- 0.10 V and 0.54 +/- 0.14 V (ns), at months 31.40 +/- 0.45 V and 1.57 +/- 0.53 V (ns), and at months 15 1.12 +/- 0.33 V and 1.37 +/- 0.38 V (P = 0.003), respectively. After 1 year, 88% of the patients in the carbon-tip group and 66% (P = 0.04) in the platinum-tip group fulfilled our criteria for reducing pacemaker output from 5.0 V to 2.5 V. In comparable platinum-tip and carbon-tip pacing electrodes, the chronic stimulation threshold was lower in the carbon-tip than in the platinum-tip electrode.

Active Fixation Atrial Leads: Randomized Comparison of Two Lead Designs

Active fixation leads have reduced the incidence of lead dislodgement in patients with permanent pacemakers. However, theoretic concern that the tissue trauma associated with a myocardial screw-helix may increase the chronic pacing threshold of active compared to passive fixation leads has remained. Whether active fixation leads with a stimulating electrode that is independent of the fixation mechanism are associated with a lower chronic pacing threshold than leads utilizing a screw-helix for both fixation and stimulation is unknown. The present prospective, randomized study compared the acute and chronic atrial pacing and sensing characteristics of two unipolar active fixation leads, one utilizing a screw-helix for both fixation and electrical stimulation, the other with an active porous tip electrode and an electrically inactive helix. Patients were randomized to receive either a Medtronic 6957J lead with an electrically active myocardial screw-helix or a Cordis 329-101P lead with an inactive helix and a porous tip electrode. The baseline characteristics of the groups were comparable. At implantation, the 329-101P lead had a lower mean voltage threshold than the 6957J lead (0.61 +/- 0.16 V vs 1.05 +/- 0.34 V, P = 0.0004). There were no significant differences in atrial electrogram amplitude, slew rate, or lead impedance between the groups. At 6 weeks follow-up, there were no differences in the mean threshold voltage (1.85 +/- 0.36 vs 1.93 +/- 0.69 V), impedance (528 +/- 81 vs 530 +/- 118 ohms), or atrial electrogram amplitude (2.63 +/- 0.50 vs 2.42 +/- 0.95 mV) between the two leads. At long-term follow-up (mean 16.2 +/- 2.8 months, range 13.1-20.0 months) there were no significant differences in voltage threshold (1.65 +/- 0.61 vs 1.97 +/- 0.64 V), impedance (565.5 +/- 81.6 vs 617.7 +/- 146.7 ohms), or atrial electrogram amplitude (2.79 +/- 0.75 vs 3.10 +/- 1.53 mV). Thus, these results suggest that active fixation leads in the atrium with an electrode that is independent of the fixation mechanism do not provide chronic stimulation thresholds or electrogram amplitudes that are superior to those obtained with leads utilizing a myocardial screw-helix as both the active electrode and the fixation device.

The Porous Titanium Steroid Eluting Electrode: A Double Blind Study Assessing the Stimulation Threshold Effects of Steroid

A transvenous pacing lead with a porous electrode which slowly elutes the steroid, dexamethasone sodium phosphate, has been developed. Previous investigations show low and constant stimulation thresholds persisting over at least the first two years post-implantation. As it is not known whether this low threshold results from the steroid or electrode configuration, a double blind study was designed to compare the same electrode configuration with and without steroid over a 2-year follow-up period. There were ten patients in each group with similar age, sex, indications for pacing and implantation data. Regular measurements of postoperative pulse duration thresholds were performed using a customized VVIM pulse generator programmed to 1.5 V output. For the first two days post-implantation, there were no statistical differences in the pulse duration thresholds between the two pacing leads. From 2 weeks to 2 years the pulse duration thresholds for the steroid leads remained almost constant, whereas the leads without steroid showed a typical rise. The difference in pulse duration thresholds between the two groups of leads from two weeks onwards confirmed that it was the steroid rather than the electrode configuration which prevented the rise in chronic stimulation threshold.

Long‐Term Threshold Stability with Porous Tip Electrodes

Experience with 163 unipolar tined porous endocardial electrodes is reported. One patient required repositioning of the electrode because of exit block. There were no other complications in the entire series of patients. All of the patients had low chronic stimulation thresholds. The mean pulse width 24 hours after implantation was 0.0534 +/- 0.0128 ms. Seventy-four patients were restudied six months after implantation. The mean pulse width threshold was then 0.07432 +/- 0.0775 ms. Fifty-four patients were evaluated one year after lead implantation. The mean pulse width threshold was then 0.0611 +/- 0.0230 ms. The pulse generator was reprogrammed to a lower pulse width in all of the patients. This permitted a substantial prolongation of the pulse generator life. The cost effectiveness of the pulse generator was also greatly improved by pacing with reduced pulse widths. In an additional 16 patients, the voltage amplitude was reduced from 5.0 volts to 2.5 volts. This permitted an even greater increase in the pulse generator longevity.

Effect of Transvenous Atrioventricular Nodal Ablation on the Function of Implanted Pacemakers

We report on seven patients with implanted pacemakers who underwent transvenous ablation of the atrioventricular junction using direct current shocks of 200 to 350 joules. Pacemaker impulse duration and rate were unaffected, but one rate responsive (TX) pacemaker was reprogrammed by a 300-joule shock. Transient increases in stimulation threshold did occur in two patients, and exit block for 2-15 seconds developed on four occasions. Chronic stimulation thresholds were unaffected. We conclude that it is preferable to carry out ablation before pacemaker implantation, but it is possible to perform transvenous ablation of the atrioventricular junction without damage to an implanted pacemaker; however, a transient rise in stimulation threshold or even exit block may occur, and pacemaker function should be carefully assessed after the procedure.

Inverse relation between patient age and chronic stimulation threshold in permanent endocardial ventricular pacing

The influence of age of the adult pacemaker patient upon postoperative threshold rise and chronic stimulation threshold was investigated by means of noninvasive threshold measurements in a group of 47 patients (aged 50 to 93 years), all provided with porous endocardial ventricular electrodes (Cardiac Pacemakers, Inc.) and Siemens-Elema Vario pulse generators. The voltage threshold recorded at implantation showed no age dependence; however, the threshold rise within 1 month after implantation, maximal recorded threshold, as well as the chronic threshold were inversely related to age—i.e., in older patients lower values were obtained. These results probably reflect a lesser local tissue reaction at the site of the electrode tip in the elderly. In the individual patient no relation could be found between stimulation threshold at implantation and maximal or chronic threshold.

Experience with 407 transvenous, finned pacing leads with a sintered porous-surfaced electrode.

Experience with 407 transvenous ventricular finned pacing leads with a sintered porous-surfaced electrode is reported. A low complication rate was encountered: 97% of patients were free from lead-related complications. Four patients (1%) required re-operation: two for lead displacement, one for failure to sense spontaneous ventricular activity and one for exit block. A further patient developed exit block which resolved spontaneously. The vast majority of patients had low chronic stimulation thresholds; for example at six months after implantation, the mean threshold for a group of pacemakers with a pulse duration of 0.5 ms was 1.4 +/- 0.7 V and for another group with a pulse duration of 0.8 ms it was 1.9 +/- 0.7 mA. However, six patients developed a transient high stimulation threshold during the month after implantation, and a high threshold developed in another patient at five months and persisted. Mean acute stimulation and sensing thresholds were satisfactory: 0.7 +/- 0.2 V at 0.5 ms pulse duration and 7.6 +/- 2.4 mV, respectively.

An evaluation of long-term stimulation thresholds by measurement of chronic strength duration curve.

Successful long-term cardiac pacemaker therapy requires both reliable generator output and stable, attainable chronic stimulation thresholds. Strength duration curves, which display cardiac stimulation thresholds as a function of impulse duration, provide needed data to evaluate more thoroughly acute and chronic lead thresholds. We measured chronic strength duration curves at the time of generator replacement in 47 patients with three different types of lead systems of variable geometry and surface area and compared these curves with acute strength duration curves measured at the time of initial implantation in 19 patients. We found that strength duration curves has a characteristic shape; however, chronic strength duration curves were shifted upward and to the right of acute strength duration curves, regardless of electrode tip surface area or geometric design. Our data suggest that variable pulse width exceeding 1 ms may not significantly reduce stimulation thresholds.

Screening of Solid and Porous Materials for Pacemaker Electrodes

Several different materials, including one which was porous, were studied to assess their properties as pacemaker electrode tips. Leads were implanted in sheep for periods up to one year. Electrical measurements were made during the implant period and histopathological examination performed after sacrifice. Although titanium vapor-deposited carbon, and silver did not lower the chronic stimulation threshold below that of platinum, their electrical characteristics were within generally acceptable limits. Zinc evoked a severe tissue reactions and a high threshold. Porous titanium alloy electrodes demonstrated reduced dislodgement, more frequent attachment and a lower sensing impedance than other electrodes.

Acute and Chronic Stimulation Thresholds of Intramyocardial Screw-in Pacemaker Electrodes

Two screw-in intramyocardial electrodes were inserted in the left ventricle of each of 6 mongrel dogs, and the electrical characteristics were studied over a six-month period. The unipolar lead configuration had consistently better threshold and sensing values than the bipolar configuration during this period. Peaking between implantation and 3 weeks later, mean lead thresholds increased significantly (unipolar, 0.4 to 8.2 μJ; bipolar, 0.6 to 10.2 μJ) while R wave amplitude decreased (unipolar, 16.6 to 8.5 mv; bipolar, 10.6 to 5.8 mv). Mean chronic values for stimulation thresholds were as follows: unipolar, 2.6 μJ, and bipolar, 3.1 μJ. Mean values for the R wave amplitude were as follows: unipolar, 10.6 mv, and bipolar, 7.2 mv. Analysis of the results indicated that with certain exceptions, the optimum system has 2 intramyocardial electrodes, 1 in unipolar configuration and 1 “reserve.” In general, adequate values at implantation are a stimulation threshold of 1.4 μ) (e.g., 1.1 v at 500 ohms and 0.6 msec pulse width) and an R wave amplitude of 5 mv.

Stimulation threshold of myocardial electrodes in long-term cardiac pacing.

The stimulation threshold behaviour in long-term cardiac pacing is presented for a material of 45 myocardial electrodes. The initial stimulation threshold was measured in 25 cases and the mean value was 1.5 +/- 0.7 mA. The follow-up period was from 17 to 99 months (mean 50 months) and during that time 63 threshold measurements were made. The mean chronic stimulation threshold was 2.2 +/- 0.7 mA. It was not dependent on the aetiology or type of the conduction defect. There was no relationship between the initial and chronic stimulation threshold. In the region of the left ventricular apex, the chronic stimulation threshold was higher than in the anterior wall of the right ventricle. The long-term stimulation threshold was significantly higher in the cases of enlarged heart and in the age group less than or equal to 50 years than in those with a heart of normal size and in the age group greater than or equal to 70 years.