Automatic Adjustment of Pacemaker Stimulation Output Correlated with Continuously Monitored Capture Thresholds: A Multicenter Study

Pacing threshold is affected by many factors. A pacing system able to confirm capture at each beat and automatically adjust its output close to the actual pacing threshold is highly desirable. This study evaluates the safety and efficacy of the Autocapture function of the Pacesetter Microny SR+. One hundred thirteen patients were recruited from 16 centers in 7 European countries and followed up for 1 year. All pacemakers were implanted with Pacesetter's low polarization, bipolar leads. The key feature of Autocapture is the immediate delivery of a 4.5 V safety backup pulse 62.5 ms after any ineffective ongoing low output pulse. Holter recordings confirmed total reliability of this feature without any exit block. The measured evoked response (ER) signal was stable over time. Acute and chronic pacing thresholds measured by VARIO and Autocapture tests correlated (r > 0.79) over the period of the study. The incidence of backup pulses was 1.1% during pacing. With Autocapture programmed ON, the overall total current consumption was 4.1 μA for VVI and 5.0 μA for VVIR pacing. Tbis study proved that the Autocapture safely and reliably regulates the pacemaker's output according to the prevailing threshold thus providing maximum patient safety and prolonging service life.     

Comparison of Continuously Recorded Sensor and Sinus Rates During Daily Life Activities and Standardized Exercise Testing: Efficacy of Automatically Optimized Rate Adaptive Dual Sensor Pacing to Simulate Sinus Rhythm

The normal sinus rhythm remains the gold standard to compare the rate response of a rate adaptive pacemaker. The aim of this study was to assess an automatically optimized dual sensor system by continuous comparison of the normal sinus (SR) and sensor indicated rates (SIR). Twelve patients with complete heart block (mean age 60 ± 9 years) with normal sinus rhythm received a dual sensor pacemaker driven by combined, automatically adaptive activity and QT sensors. After I month of automatic adaptation, patients performed a treadmill exercise in the VDD mode with simultaneous collection of SR and combined SIR. Thereafter the difference between SR and SIR was recorded over a 1-month period using a software downloaded into the pacemakers, with the patients ambulatory during this period. During exercise testing, the SR and SIR were significantly correlated (r =0.96 ± 0.02, P < 0.001), and the mean difference between SR and SIR was 4.01 ± 4.47 beats/mm. The percentages of paced beats, over the 1 month ambulatory period, that exhibited a difference between SR and SIR of 8 beats/mm were 98%± 2%, 90%± 4% and 67%± 8% for low, medium, and high workloads, respectively (P < 0.05, ANOVA). whereas > 95% of SIR were within 15 beats/min of SR independent of the level of activities. Thus, an automatically programmed dual sensor gives an accurate reflection of SR during exercise. SIR was less accurate for more vigorous daily life activities, but most of the SIR were within the normal SR variation of 15 beats/min.     

Clinical Evaluation of a Thin Bipolar Pacing Lead

The main disadvantages of bipolar pacing leads have traditionally been related to their relative thickness and stiffness compared to unipolar leads. In a new "drawn filled tube" plus "coated wire" technology, each conductor strand is composed of MP35N tubing filled with silver core and coated with a thin ETFE polymer insulation material. This and parallel winding of single anode and cathode conductors into a single bifilar coil resulted in a bipolar lead (ThinLine, Intermedics) with a body diameter and flexibility similar to unipolar leads. The lead is tined. polyurethane. with the cathode and the anode made of iridium-oxide-coated titanium (IROX). The slotted 8-mm² cathode tip is coated with polyethylene glycol. a blood soluble material. We present the clinical evaluation results from four pacemaker clinics, where 47 leads (23 atrial-J model 432–04 and 24 ventricular model 430–10) were implanted in 25 patients and followed for up to 2 years. The lead handling characteristics were found to be very satisfactory. Electrical parameters of the leads were measured at implant and noninvasively on postoperative days 1, 2, 21, 42. and months 3, 6, 12, and 24. Mean chronic pulse width thresholds at 2.5 V were 0.14 ± 0.05 ms in the atrium and 0.10 ± 0.02 ms in the ventricle, pacing impedances 443 ± 104 Ω and 520 ± 241 Ω. while median electrogram amplitudes were ≥ 3.5 mV and ≥ 7 m V, respectively. Pacing impedances and thresholds were found to be slightly but statistically significantly higher in unipolar than in bipolar configuration—the findings are explainable bv the lead construction. One of 47 leads failed 3 weeks after implant; the conductors were short circuited due to an error during the manufacturing process. We conclude that the new lead thus far has demonstrated appropriate mechanical and electrical characteristics.     

Effect of Chronic Alcohol Feeding on Adrenergic and Cholinergic Neurotransmission Mechanism

Experimental data is presented indicating that chronic alcohol consumption in rats has a direct CNS effect resulting in increased activity of the autonomic nervous outflow. Changes in neurohormonal transmitters have been demonstrated in four organs: salivary glands, spleen, adrenals and heart. These changes may account for the alterations in end organ sensitivity and secretory patterns which occur in alcoholic animals and man. They may, moreover, represent an initial pathogenetic mechanism whereby alcohol induces its various clinical syndromes.