Use of Telemetered Electrograms in the Assessment of Normal Pacemaker Function

The facility of direct real-time endocardial electrogram recording offered by newer pacemaker models can be helpful in the assessment of normal pacemaker function. Confirmation of the main hallmarks of sensing (amplitude, slew rate, and timing of the electrogram) can be achieved. Assessment of pacing capture also can be made; techniques for further analysis using external signal averaging can enhance this. The measurement of atrial and ventricular electrograms by telemetry has led to alterations in the protocol used at implantation to allow for the input impedance of the sensing circuit of the pacemaker. Accurate measurements of retrograde VA conduction times and confirmation of normal upper rate limit behavior of ODD pacemakers can be achieved simply and reliably using telemetered electrograms from the permanent pacemaker system.     

微处理器控制的植入式心脏起搏器专用电路研制

介绍了一种基于微处理器的植入式心脏起搏器专用电路设计。该设计采用的技术路线和国外现有技术方案不同，它采用通用微处理器设计，降低了投资风险，缩短了开发周期．特别适合于我国这样的发展中国家。     

Telemetry of Programmed and Measured Data in Pacing System Evaluation and Follow-up

Telemetry of programmed and measured data is an important feature of many pacemakers currently used in clinical practice. The ability to receive non-invasive data from the implanted device constitutes a major advantage for the long-term follow-up of the patients and of device performance. There are numerous types of data retrievable via telemetry: parameters of device characteristics (output, battery longevity, impedance, etc), event recorders or counters, event markers, and endocardial electrograms. Ideally, this information should be beneficial in the longitudinal surveilance of modern pacemakers.     

Direct and Telemetered Lead Impedance

Objectives: We undertook this study to determine whether telemetered lead impedance measurements (LIM) can be correlated with direct LIM and to determine the stability of LIM over time when measured directly and via telemetry. Methods: Direct LIM and telemetered LIM were measured in 91 patients; 101 leads during initial implantation and 40 leads during pulse generator replacement. Differences in direct LIM measured during initial implant and pulse generator replacement (direct-direct) were compared in 41 patients (28 atrial leads and 37 ventricular leads). The stability of telemetered LIM obtained immediately postoperatively, at 1 month and 1 year, postimplantation was assessed in 50 patients (23 atrial and 49 ventricular leads). Results: In atrial leads acute direct LIM was 633.9 ± 18.4 Ω versus 575.8 ± 18.5 Ω for telemetered LIM (r = 0.58), and chronic direct LIM was 670.9 ± 49.3 Ω versus 607.0 ± 36.3 Ω for telemetered LIM (r = 0.87). In ventricular leads acute direct LIM was 747.3 ± 16.9 Ω and 684.7 ± 16.4 Ω for telemetered LIM (r = 0.69), and chronic direct LIM was 674.8 ± 29.9 Ω and 625.2 ± 28.5 Ω for telemetered LIM (r = 0.68). The mean direct–direct UM rose 124 Ω (P < 0.001) in atrial leads and 10 Ω (P = NS) in ventricular leads. Telemetered LIM for atrial leads was 581.0 ± 27.6 Ω immediately postimplantation compared to 625.7 ± 34.8 Ω at 1 month and 754.1 ± 43.0 Ω at 1 year. Telemetered LIM for ventricular leads was 661.3 ± 17.5 Ω at implant, 684.6 ± 20.7 Ω at 1 month and 724.7 ± 22.7 Ω at 1 year. Conclusions: There is a good but limited correlation between direct and telemetered LIM. Mean direct LIM obtained at initial implantation is similar to that measured at pulse generator replacement. The telemetered LIM is stable over the first month postimplantation but tends to rise during the first year of follow-up and substantial changes in impedance are not uncommon in individuals with normal function. There is a tendency for LIM to rise with lead maturation. If telemetered LIM is to be followed over time, a baseline telemetered value should be obtained immediately postoperatively.     

Requirement for cardiac telemetry during intravenous phenytoin infusion: guideline fact or guideline fiction?

Guidelines recommend the use of cardiac telemetry when phenytoin is administered intravenously. Clinical areas where telemetry is available may not always be the most suitable place to monitor and treat these sick patients. We sought to clarify the evidence regarding the need for cardiac telemetry during intravenous infusion of phenytoin.     

Neonatal exposure to low-dose domoic acid lowers seizure threshold in adult rats

Exposing Sprague–Dawley rat pups to very low, sub-convulsant doses of domoic acid (DOM) during perinatal development has been previously shown to result in seizure-like activity in adulthood similar to partial complex epilepsy in humans, and to produce cellular and molecular changes in the dentate gyrus and area CA-3 of the hippocampus. To further these investigations we recorded electroencephalographical and behavioural activity in DOM and control rats following a normally sub-convulsant dose (25 mg/kg) of pentylenetetrazol. During this exposure, 50% of DOM-treated rats experienced a Stage V (tonic-clonic) seizure (X²₍₁₎=5.33, P=0.021), indicating a lowering of generalized seizure threshold in these animals. In a separate experiment we explored focal seizure (afterdischarge) threshold as well as seizure propagation rates in treated rats, using a 25 consecutive day standard amygdala kindling paradigm. We report that the afterdischarge threshold for DOM-treated rats was significantly lower than controls (F_(1,27)=7.117, P=0.013). No difference between groups was found in seizure progression as measured by afterdischarge duration, latency to first Stage V seizure, or latency to reach a fully kindled state (defined as five consecutive Stage V seizures). Timm staining to assess mossy fibre sprouting (MFS) in the hippocampus revealed a significant MFS increase relative to sham at the ventral level in both left and right inner molecular layer of the dentate gyrus for all DOM-treated animals, as well as in the dorsal stratum oriens of CA3 contralateral to electrode placement, and these increases were further enhanced by the kindling procedure. We conclude that perinatal exposure to subconvulsive doses of DOM results in permanent changes in neuronal excitability in the adult rat, as demonstrated by a lowering of both generalized seizure and focal afterdischarge threshold, and produces increased MFS following kindling.     

Renoprotective effects of vasopeptidase inhibition in an experimental model of diabetic nephropathy

Aims Although ACE inhibitors slow progression of diabetic renal disease, the mortality and morbidity is still high. As other hormonal factors are involved, inhibition of vasopeptidases could further reduce progression. We studied dual inhibition of angiotensin converting enzyme and neutral endopeptidase in a model of progressive diabetic renal injury. The major endpoints were reductions in systemic blood pressure, albuminuria and renal structural injury.Methods Diabetic spontaneously hypertensive rats were treated with the ACE inhibitor perindopril (mg·kg^–1·day^–1) or the vasopeptidase inhibitor omapatrilat at doses of 10 (oma10) and 40 (oma40) mg·kg^–1·day^–1 for 32 weeks. In vivo ACE and NEP inhibition was quantitated by in vitro autoradiography. Renal structural injury was assessed by measurement of the glomerulosclerotic (GS) index and tubulointerstitial area (TI). The expression of transforming growth factor , -inducible gene-h3 and nephrin were also quantitated.Results Despite a similar reduction in blood pressure by perindopril and oma10, greater attenuation of albuminuria was afforded by oma10, with a complete amelioration observed with oma40. Oma40 lead to a 33% reduction in renal NEP binding and this was associated with less albuminuria and prevention of GS, TI area and overexpression of TGF and ig-h3. Diabetes-associated reduction in nephrin expression was restored by both drugs.Conclusion/Interpretation These findings suggest that other vasoactive mechanisms in addition to angiotensin II are important in the prevention of diabetic nephropathy, and that vasopeptidase inhibition might confer an advantage over blockade of the RAS alone in the treatment of diabetic renal disease.Abbreviations ACEi angiotensin converting enzyme inhibitor - AII angiotensin II - ig-h3 -inducible gene-h3 - GSI glomerulosclerotic index - NEP neutral endopeptidase - Oma omapatrilat - Per perindopril - PRA plasma renin activity - RAS renin-angiotensin system - SBP systolic blood pressure - TIA tubulointerstitial area - VPI vasopeptidase inhibitor     

Thieving rodents as substitute dispersers of megafaunal seeds

The Neotropics have many plant species that seem to be adapted for seed dispersal by megafauna that went extinct in the late Pleistocene. Given the crucial importance of seed dispersal for plant persistence, it remains a mystery how these plants have survived more than 10,000 y without their mutualist dispersers. Here we present support for the hypothesis that secondary seed dispersal by scatter-hoarding rodents has facilitated the persistence of these large-seeded species. We used miniature radio transmitters to track the dispersal of reputedly megafaunal seeds by Central American agoutis, which scatter-hoard seeds in shallow caches in the soil throughout the forest. We found that seeds were initially cached at mostly short distances and then quickly dug up again. However, rather than eating the recovered seeds, agoutis continued to move and recache the seeds, up to 36 times. Agoutis dispersed an estimated 35% of seeds for >100 m. An estimated 14% of the cached seeds survived to the next year, when a new fruit crop became available to the rodents. Serial video-monitoring of cached seeds revealed that the stepwise dispersal was caused by agoutis repeatedly stealing and recaching each other's buried seeds. Although previous studies suggest that rodents are poor dispersers, we demonstrate that communities of rodents can in fact provide highly effective long-distance seed dispersal. Our findings suggest that thieving scatter-hoarding rodents could substitute for extinct megafaunal seed dispersers of tropical large-seeded trees.