Examination of Explanted Polyurethane Pacemaker Leads Using the Scanning Electron Microscope

Since 1978, 2,365 polyurethane (PU) insulated cardiac pacing leads were implanted transvenously at our institution. To date, there have been no insulation failures in those leads. Thirty-seven PU leads were explanted, mainly for exit block, and 28 of these were investigated using the scanning electron microscope. We found a homogeneous distribution of surface changes in all lead segments in 56% of the 28 examined. These changes were more pronounced at the ligature site; severe surface cracking was noticed in 21%, with the deepest crack being 40 micron (average range of 10-15 micron). There appeared to be no time-dependency of the surface changes as indicated by regression analysis (r = 0.32, p greater than 0.05). The ultimate severity and outcome of this degradation process in the leads reported in this study will only be known in the future after longer use. We conclude that excess stress must be avoided during the implantation procedure and that careful surveillance is necessary.     

Endothelium-dependent and endothelium-independent vasomotion in large coronary arteries and in the microcirculation after cardiac transplantation

Endothelium-dependent and endothelium-independent vasodilationof the epicardial conduit vessels and the microcircu-latorycoronary vessels was investigated with cumulative doses of acetylcholine(ACh 50µg and 100µg i.e.), nitroglycerin (0.3 mgi.e.) and dipyridamole (0.56mg. kg^–1 i.v.) in 17 patients(3 female114 male; age: 47±3.6 years) with angiographicallynormal coronary arteries 40 ± 51 months after cardiactransplantation. The effect of ACh on large conduit arterieswas evaluated angiographically. Coronary blood flow velocitychanges were measured utilizing an 8F Judkins style 20 MHz Dopplercatheter positioned in the left main coronary artery. A coronaryflow index was calculated from the mean Doppler flow velocityand the computed cross-sectional vascular area. After 50 µgof ACh the diameter of proximal, middle and distal segmentsof the left anterior descending coronary artery decreased significantlyby 7.6±2.06% (P<0.05), 10.6 ±3.5% (P<001)and 12.6±3.29% (P<0.01) and after 100 µg AChby 10.5 ±2.4% (P<0.05), 13.0 ±3.7% (P<001)and 15.3 ±3.9% (P<001). The endothelium-independentvasodilator nitroglycerin (0.3 mg i. e.) induced an increasein vascular diameter of 14.4±31% (P<001), 18.6±4.1%(P<001) and 20.8 ± 2.9% (P<0.01) in proximal, midand distal segments of the left anterior descending coronaryartery. In the circumflex branch the diameter of proximal, middleand distal vascular segments decreased after 50 µg ofACh by 5.1 ±2.7% (P<005), 9.5 ±2.6% (P<001)and 8.8 ±3.27% (P<005) and after 100µg by 9.9±2.5% (P<001), 11.1 ±3.7% (P<001) and 10.8±3.8% (P<0.01). An increase of 17.4 ±3.5% (P<001),20.7 ±3.4% (P<001) and 26.2 ± 3.4% (P<001)was noted after nitroglycerin. Coronary flow index increased after 50 µg of ACh by 133±23% (P<0.01) and after 100 µg by 106.8± 29.8%(P<0.05). The endothelium-independent microcirculatory vasodilator,dipyridamole, caused an increase of coronary flow index of 165.2±36.1%(P<0.01). In conclusion, the ACh-induced decrease in conduit coronaryartery diameter suggests that endothelial dysfunction couldresult long-term after cardiac transplantation, whereas endothelium-independentvasodilation after nitroglycerin is preserved Additionally,the vasodilatory response of the microcirculation to stimulationby ACh is reduced in the long-term after cardiac transplantation,as is endothelium-independent vasodilation after dipyridamole.     

Adrenergic regulation of fat-cell lipolysis in multiple symmetric lipomatosis

The responsiveness towards catecholamines of normal and lipomatous fat cells of two male subjects suffering from multiple symmetric lipomatosis has been studied by means of a newly developed bioluminescent method for microdetermination of glycerol. In contrast to previous findings, lipomatous fat cells displayed normal alpha 2-and beta-adrenergic responsiveness in both subjects studied. The apparent discrepancies between the results of the present study and those reported by others therefore support the contention that multiple symmetric lipomatosis is a symptom with various underlying causes rather than a nosological entity.     

STUDIES ON THE COSUBSTRATE SITE OF PROTEASE SOLUBILIZED NADPH-CYTOCHROME P450 REDUCTASE

Modification of the protease solubilized NADPH-cytochrome P450 reductase (= NADPH-cytochrome c reductase) at the critical SH group in the cosubstrate binding site affects K^NADPH_m but not V for the cytochrome c reduction. The increase of K^NADPH_m is dependent on the size and the charge of the substituent introduced. Substitution of the cosubstrate site SH by the CN-, S₂ O₃- and the (N-ethyl) succinimido group effects a 3-, 7- and 23-fold increase of K^NADPH_m respectively. The critical SH group in the NADPH binding region can be specifically radiolabeled by N-ethyl (2,3-¹⁴C) maleimide after preincubation of the reductase with unlabeled NEM in the presence of 1 mM NADP+. The selective reaction at the essential cysteine in the cosubstrate site is demonstrated by peptide mapping of the thermolytic digest and urea SDS gel electrophoresis of the cyanogen bromide fragments of the reductase. Protease solubilized NADPH-cytochrome P450 reductase is inactivated by reagents directed to histidine, orginine and lysine residues. NADP (H) (1 mM) and 2′-AMP (1 mM) give effective protection only for the reaction of 1, 2-cyclohexanedione (12 mM). The functional role of the basic amino acid residues for the cosubstrate binding by the NADPH-cytochrome P450 reductase cannot be established therefore by the modification experiments described. The number of NADPH binding sites in the NADPH-cytochrome P450 reductase is determined to one site/mol reductase by titration of the enzyme with NADP+ monitored by CD-spectroscopy.     

Studies of the Tissue Reaction Induced by Transvenous Pacemaker Electrodes. I. Microscopic Examination of the Extent of Connective Tissue Around the Electrode Tip in the Human Right Ventricle

The purpose of this study was to investigate the extent of connective tissue of the human right ventricle induced by cardiac pacing electrodes. Between January 1984 and July 1987, 34 consecutive patients with VVI-pacing systems were autopsied in the Department of Pathology at the University of Frankfurt/M. The surrounding tissue of these 34 electrodes (17 Siemens Elema 412 S, five Medtronic 6957, one Medtronic 6959, one Medtronic 4011, three Biotronik D2K, three Biotronik K10, two Osypka FY 62, one Biotronik N, and one Siemens Elema 588) in the right ventricle were investigated histologically. The tissue was stained with Giemsa and the thickness of the connective tissue layer was measured. Stimulation threshold data at various times were known in four of eight screw-in electrodes, in seven of 17 vitreous carbon electrodes and in two of seven smooth surface electrodes. Electrode surface area, implantation time, age of the patient and cause of death were comparable for all three electrode groups. However, a significant difference was found in the extent of connective tissue between the porous surface and screw-in electrodes (128 ± 55 VS 397 ± 269 μm, P 0.01) and porous surface and smooth surface electrodes (128 ± 55 vs 307 ± 117 μm, P 0.01). No relation (r = 0.106) was found between the duration of implantation and the extent of connective tissue for the vitreous carbon electrodes (Siemens Elema 412 S). The lowest chronic stimulation thresholds were measured in the latter type of electrodes (0.5 ± 0.3 V) as compared to the screw-in (0.75 ± 0.30 V) and smooth surface electrodes. We conclude from this study, that vitreous carbon electrodes induce only a small amount of connective tissue around the insertion site in the human right ventricle, as compared to other smooth surface or screw-in electrodes. Chronic stimulation threshold data parallel those morphological results.     

Rate Responsive Pacemakers: Assessment after Two Years

Rate responsive pacemakers (RRPM) for patients without sufficient response of the heart rate (HR) to exercise represent an alternative to improve cardiac output (CO) and capacity for exercise via an increase of HR. From 1983 until December 1985, we implanted 30 QT-related (TX), 25respiratory dependent (RDP), and 35 body activity directed (ACT) pacemakers. The follow-up examination consisted of Holter-ECG, treadmill and/or bicycle workload, and determination of CO (TX: thermodilution technique, n = 11; 6 months after implantation. RDP: equilibrium radionuclide ventriculography, n = 13; 1 month after implantation). The capacity for exercise of patients with ACT was studied using a climbing step. Adaptation of HR could be achieved with TX. RDP, and ACT. There was a significant increase in CO during exercise TX or RDP versus VVI-mode (TX: δ= 1.7l/min, RDP: δ= 2.1 l/min).Although all systems exhibited weak points, RRPM are reliable devices. We abide by using these pacemakers.     

Advanced Pacemaker Diagnostic Features in the Characterization of Atrial Fibrillation: Impact on Preventive Pacing Algorithms

YANG, A., et al .: Advanced Pacemaker Diagnostic Features in the Characterization of Atrial Fibrillation: Impact on Preventive Pacing Algorithms. Pacing algorithms to prevent PAF are mainly based on the suppression of premature atrial complexes (PACs), which play an important role in its initiation. In contrast to 24-hour ambulatory electrocardiograms, advanced pacemaker (PM) diagnostic features are capable of recording AF episodes during long follow-up periods and of characterizing AF in a detailed fashion. For the specific use of these algorithms, a detailed characterization of AF was performed in 91 dual chamber PM recipients with histories of AF. Fifteen patients with episodes of oversensing due to far-field signals or frequent episodes of "2:1-undersensing" of atrial flutter were excluded. The remaining 76 patients had high recurrence rates of AF (median 0.8 episodes/day), however, the majority of episodes lasted <7 minutes. Despite frequent PACs (median 10.8/hour) during sinus rhythm, a median of 66.4% of the AF episodes were preceded by <2 PACs/min before onset. In conclusion, frequent, short-lived AF episodes seem best suited for AF preventive pacing therapies. However, the small number of PACs preceding many AF episodes may limit the efficacy of PAC suppressing algorithms. (PACE 2003; 26[Pt. II]:310–313)