DDD and single-lead VDD pacing: evaluation of atrial signal dynamic changes.

BACKGROUND: Single-lead VDD pacing systems are an alternative to conventional DDD pacemakers in patients with atrioventricular (AV) block and normal sinus function. HYPOTHESIS: The aim of this study was to assess changes of P-wave amplitude occurring in dynamic conditions in two groups of patients with a single-lead VDD and with a DDD pacing system, respectively. METHODS: Twenty-eight patients with second- or third-degree AV block and normal sinus function were enrolled prospectively into the study. Seventeen patients were implanted with a single-lead VDD pacing system and 11 with a DDD pacemaker. Patients were evaluated at 3 months (all patients) and at 6 months (26 patients) at supine and in dynamic conditions (postural changes, hyperventilation, and during exercise). RESULTS: Mean P-wave values at supine were 1.92 +/- 1.10 mV at 3 months and 1.76 +/- 1.01 mV at 6 months for VDD systems, and 4.63 +/- 2.18 mV at 3 months and 4.58 +/- 2.80 mV at 6 months for DDD pacemakers. In dynamic conditions, P-wave amplitude changes compared with supine condition ranged between -74 and +226% in VDD, and between -53 and +138% in DDD; however P-wave amplitudes showed no significant changes compared with baseline. Moreover, changes in atrial signal amplitudes did not occur randomly, and in both systems P-wave amplitudes remained significantly correlated with supine values. CONCLUSIONS: A wide range of P-wave amplitude variations occurs in different postural conditions or during exercise, both with single-lead VDD and DDD pacing systems. However, with appropriate programming of atrial sensitivity based on supine values, constant atrial tracking can be maintained.

Benefits in projected pacemaker longevity and in pacing related costs conferred by automatic threshold tracking.

The aim of this study was to calculate the battery current drain of different VVI-VVIR pulse generators, with and without automatic adjustment of stimulation output, from the same manufacturer, and obtain projections on pacemaker longevity and pacing related costs. Twenty-five patients who had received a VVIR pacemaker (Microny SR+ 2425T) with Autocapture function, an algorithm able to provide automatic adaptation of device output coupled with continuously monitored capture threshold, were analyzed. Calculations of current drain and projections of device longevity were based on diagnostic data retrieved from device memory and on comparisons of multiple programmed settings of the same device (Microny SR+ 2425T with Autocapture, Low Output [output = 2 x Autocapture threshold, but not less than 2.4 V] versus Standard Output [5 V]). In addition, devices with Autocapture but with different battery capacities (0.35 Ah and 0.79 Ah, Microny and Regency, respectively) were compared to a standard device (battery capacity = 0.78 Ah) at 2.5-V and 5-V output settings. According to a series of assumptions, Autocapture increased device longevity by 53% (Microny) and by 245% (Regency) over a 15-year follow-up with a consequent reduction in pacing related costs of 25% (Microny) and of 57% (Regency) compared to the standard settings of a VVIR device from the same manufacturer. In conclusion, pacing with constant adaptation of generator output coupled with continuous monitoring of stimulation threshold has the potential to increase generator longevity and to reduce pacing related costs as compared to a standard device from the same manufacturer.

The "SPEM" (Studio Policentrico Elettrocateteri Membrane): a multicenter study on membrane leads.

SPEM is a multicenter randomized double-blind study performed to test the acute and chronic electrophysiological behavior of three different ventricular leads: (1) an ion exchange membrane with 30-microgram dexamethasone elution in a contoured activated carbon tip lead (Membrane 1400T, 30 patients); (2) the same lead design without steroid (Membrane 1401T, 24 patients); and (3) the same lead design without steroid or membrane (control group, 27 patients). Twenty-three of the 81 patients were women; the mean age for all patients was 74 +/- 10 years. Parameters are calculated both in uni- and bipolar configuration at implant and at follow-up after 1, 5, 15, 30, 90, 180, and 360 days. Implant threshold (chronaxie = 0.413 +/- 0.280 ms, rheobase = 0.264 +/- 0.099 V), signal amplitude (13.45 +/- 5.87 mV), and slew rate (2.05 +/- 1.38 V/s) reveal no significant differences. Pacing impedance values both at implant (unipolar 571 +/- 165 omega; bipolar 605 +/- 123 omega) and at follow-ups (unipolar 480 +/- 72 omega; bipolar 518 +/- 75 omega) are slightly lower in the unipolar configuration. At 15 and 30-day follow-ups, control group and nonsteroid leads show a higher threshold value growth (in unipolar from 0.16 +/- 0.11 to 1.19 +/- 0.85 microJ; in bipolar from 0.18 +/- 0.13 to 1.24 +/- 0.88 microJ) than the membrane steroid leads (in unipolar from 0.13 +/- 0.11 to 0.70 +/- 0.39 microJ; in bipolar from 0.23 +/- 0.32 to 0.76 +/- 0.36 microJ); the threshold of nonsteroid leads decreases after 1-3 months and it settles at the same threshold level of the leads with membrane and steroid (in unipolar 0.60 +/- 0.33 microJ; in bipolar 0.55 +/- 0.26 microJ), which has been stable since the first month. The ion exchange membrane is effective in reducing the chronic pacing threshold like acute steroid elution at low doses, but membrane alone does not prevent an acute pacing threshold increase through the first month postimplant.

Clinical reliability of single-lead VDD pacing from evaluation of P-wave sensing under dynamic conditions.

In a group of 20 patients implanted with a single-lead VDD pacing system, a wide interindividual variability was found in P-wave amplitude changes occurring under dynamic conditions, even though they were of minor clinical relevance because constant atrial tracking was maintained.

Italian experience with AutoCapture in conjunction with a membrane lead. Pacesetter Automatic Control of Energy and Membrane Automatic Threshold Evaluation (Pacemate) Study Group.

AutoCapture is a programmable feature of the Pacesetter Microny SR + 2425T VVIR pacemaker, which provides for the automatic capture verification, increase in output in the presence of noncapture and threshold searching, with adjustment of output settings. The effectiveness of this unit in conjunction with the Membrane models 1400T and 1401T bipolar endocardial leads was studied in 54 patients followed at 19 Italian Centers. The patients were randomized at the time of implantation to receive either the model 1400T or the 1401T lead. The electrodes in these leads are covered by a Nafion membrane, which was either impregnated (model 1400T) or not-impregnated (model 1401T) with steroid. This paper reports the data collected over the first six weeks postimplantation. The results of the automatic capture function was compared to the capture threshold measured using the Vario technique at the time of predischarge evaluations, and weeks 1,2, and 6 of postimplant follow-up. The reliability and effectiveness of the pulse generator-lead system allowed for consistent pacing at very low outputs and safety preserved at a programmed output only 0.3 V above the capture threshold.