Autonomic Nervous System-Controlled Cardiac Pacing: A Comparison Between Intracardiac Impedance Signal and Muscle Sympathetic Nerve Activity

BINGGELI, C., et al. : Autonomic Nervous System‐Controlled Cardiac Pacing: A Comparison Between Intracardiac Impedance Signal and and Muscle Sympathetic Nerve Activity. A recently introduced rate responsive cardiac pacing system is based on information derived from the intracardiac impedance signal containing information on the inotropic state of the ventricle. This study compared the inotropic state index (ISI) with muscle sympathetic activity (MSA), both being modulated by the autonomic nervous system. Nine patients (66 ± 3 years, mean ± SEM ) with Inos2DR pacemakers were included. Each patient was studied at rest and during cold pressor test (CPT). Microneurography of the peroneal nerve was performed to measure MSA continuously, which was digitally stored along with continuous surface ECG and blood pressure. The intracardiac impedance signal was transmitted by the pacemaker and stored simultaneously. Linear correlation between ISI and MSA was calculated for the period of the CPT. During CPT, mean systolic blood pressure increased from 122 ± 4 to 149 ± 6 mmHg (P < 0.0001), diastolic blood pressure increased from 74 ± 8 to 86 ± 4 mmHg (P = 0.02 ), and intrinsic heart rate increased from 69 ± 7 to 75 ± 7 beats/mill (P = 0.019 ). ISI increased by 21 ± 7% (P = 0.018 ), MSA by 26 ± 6% (P = 0.004 ). ISI and MSA were positively correlated during the CPT in eight of nine patients (R2 = 0.86–0.99, P < 0.0001 ). Negative correlation was found in one patient (R2 = 0.94 ). This study demonstrates parallel increases of the ISI and MSA during CPT. ISI and MSA showed a close linear relationship during provoked changes of sympathetic activity. These results provide further evidence that the sympathetic nervous system is responsible for the observed ISI changes.     

GLIAL CELL INTERACTIONS WITH TENASCIN-C: ADHESION AND REPULSION TO DIFFERENT TENASCIN-C DOMAINS IS CELL TYPE RELATED

The multimodular glycoprotein tenascin-C is transiently expressed, predominantly by glial cells, during the development of the central and peripheral nervous systems. This extracellular matrix glycoprotein is involved in the control of cell adhesion, neuron migration and neurite outgrowth. Distinct functional properties for neuronal cell types have been attributed to separate tenascin-C domains using antibody perturbation studies and in vitro experiments on tenascin-C fragments. In order to study potential roles of tenascin-C for glial cell biology, a library of recombinant tenascin-C domains was used in a bioassay in vitro. Embryonic day 14 astrocytes, various astroglial-derived cell lines (C6, A7 and Neu7) and oligodendroglial-derived cell types (Oli-neu and G26-20) were examined in an adhesion assay and compared to the neuroblastoma cell line N2A. A binding site for most cell types, except for A7 and N2A, could be assigned to the first three fibronectin type III domains. Repulsive properties could be mapped to three different sites, the epidermal growth factor-like repeats, fibronectin type III repeats 4 and 5 and to the alternatively spliced region of the molecule. The responses to these repulsive sites varied according to the cell type. These data are consistent with the interpretation that different cell types express distinct sets of tenascin-C receptors which might regulate cellular responses via distinct second messenger pathways. Copyright © 1996 ISDN. Published by Elsevier Science Ltd.     

Is Atrial Sensing of Ventricular Far-Field Signals Important in Single-Lead VDD Pacing?

In single-lead VDD pacing the atrial sensitivity frequently is programmed to sensitive values. Atrial sensing of ventricular far-field signals should be reduced by differential atrial sensing. The aim of the study was to evaluate the effectiveness of this approach. Methods: The study included 10 patients with a single-lead VDD pacemaker (Thera 8948, Lead 5032). The atrial sensitivity was set to its most sensitive value of 0.18 mV and the telemetered intraatrial EGM was continuously recorded. After atrial tracked ventricular pacing, VVI pacing was performed with pacing rates from 100 to 160 beats/min in steps of 10 beats/min and up to 165 beats/min. The peak-to-peak amplitudes of P waves (P) and ventricular far-field signals (VFFS) were measured from the recordings. The ratio P/VFFS that defines the atrial signal-to-noise ratio was calculated, and the time from stimulus to maximum of the far-field signals amplitude (Tmax) was measured. Results: P measured 0.98 ± 0.76 mV. A VFFS was visible in the atrial channel in all patients with an amplitude of 0.45 ± 0.25 mV (range 0.01–1.0 mV), independent of the pacing rate. The ratio P/VFFS was 3.9 ± 4.2 (range 0.9–21.0). Tmax measured 99.4 ± 15.2 ms during sinus rhythm. A rate dependent shortening of Tmax to 92.7 ± 11.2 ms at 140 beats/min was observed (P = 0.001). At rates above 140 beats/min no further shortening occurred. Conclusion: Ventricular far-field signals are measurable in the atrial channel of VDD systems and may reach considerable amplitudes, which are not rate dependent. Although differential sensing provides favorable P waves to ventricular far-field signal ratios, refractory periods are needed to avoid far-field sensing. The rate dependent shortening of the ventricular signal can be detected in the atrial channel in VDD pacing.     

Carcinoma of the Breast and Pacemaker Generators

A 90-yearold woman developed intraductol adenocarcinoma (TNM classification pT2, G2) of the left breast 18 years after initial pacemaker implantation deep to the left breast. There was no evidence of local or distant metastasis and she was treated with local excision and tamoxifen.     

Assessing Acute Ventricular Volume Changes by Intracardiac Impedance in a Chronic Heart Failure Animal Model

Background: Implantable device diagnostics may play an essential role in simplifying the care of heart failure patients by providing fundamental insights into their complex clinical patterns. Early recognition of heart failure progression by a continuous hemodynamic monitoring would allow for timely therapeutic interventions to prevent decompensation and hospitalization. In this study, the feasibility of assessing ventricular volume changes by implant-based measurements of intracardiac impedance was tested in a heart failure animal model.
Methods: Heart failure was induced in five minipigs by high-rate pacing over 3 weeks. During a final open-chest examination a graded dobutamine stress test was performed. Stroke volume (SV) was measured by an ultrasonic flow probe at the ascending aorta. End diastolic pressure (EDP) and maximum pressure slope (dP/dt_max) were calculated from a left ventricular microtip catheter signal. Impedance was measured by an implanted pacemaker between biventricular leads. Stroke impedance (SZ) was calculated as the difference between end-systolic and end-diastolic impedance (EDZ).
Results: Administration of dobutamine led to an increase in SV (55 ± 16%), dP/dt_max (107 ± 89%), and SZ (56 ± 30%). EDP changed by 37 ± 21% whereas EDZ changed by 7.4 ± 4%. Significant correlations were found between SZ and SV (r = 0.88), and between EDZ and EDP (r =−0.82).
Conclusion: The strong correlation with SV allows the application of intracardiac impedance measurements for an implant-based continuous monitoring of cardiac function. Impedance may also be used for hemodynamic optimization of cardiac resynchronization therapy.     

Long-Term Sinus Rhythm Stability after Intraoperative Ablation of Permanent Atrial Fibrillation

Introduction: Short‐ and medium‐term sinus rhythm (SR) rates after intraoperative radiofrequency ablation to treat permanent atrial fibrillation (AF) are well documented. Is rhythm success stable during a long‐term follow‐up? Methods and Results: A total of 130 patients who had undergone intraoperative radiofrequency cooled‐tip endocardial ablation (SICTRA) of permanent AF (mean AF duration 6±5 years) concomitant to open heart surgery more than 3 years ago were followed up using electrocardiogram (ECG), Holter‐ECG, and echocardiography and compared with 12‐month follow‐up data. In 55% of patients, only the left atrium and in 45%, both atria were treated using SICTRA. Mitral valve replacement was performed in 21, mitral valve reconstruction in 25, aortic valve replacement in 13, CABG procedures in 51 (including 11 patients with additional mitral valve surgery), and complex procedures in 20 patients. Sixty‐nine percent of patients (90/130) were in stable SR after a median period of 48 months, whereas 28% (36/130) were in AF and 3% (4/130) were in atrial flutter. In between the 12‐month follow‐up and the long‐term follow‐up, seven patients converted to AF after having documented SR, two patients converted to typical right atrial flutter after being in SR, and two patients from AF to left atrial macroreentry. After left and biatrial SICTRA, SR rates were comparable (73% vs 66%, P = 0.45). Echocardiography revealed 73% of patients in SR to have effective left atrial contraction. Conclusions: SICTRA restores long‐term stable SR in 69% of all patients. Nine percent of patients reconverted back to atrial arrhythmia after having documented SR at 12 months.     

A New Temporary Occlusion and Aspiration System for Prevention of Distal Embolization During Percutaneous Transluminal Renal Angioplasty

Cholesterol embolization has been described as a severe complication of percutaneous transluminal renal angioplasty (PTRA) and may lead to renal insufficiency with the need of transient or permanent hemodialysis. We describe a case of successful angioplasty of a renal artery in-stent restenosis utilizing a new temporary balloon occlusion and aspiration system for prevention of distal embolization. Histological examination of blood retrieved from the distally occluded vessel showed lipid-rich macrophages (foam cells) and an amorphic lipoid substance as markers of atherosclerotic plaque debris. Further studies are necessary to evaluate the clinical relevance of atheromatous microembolization and its renal function and clinical course following angioplasty.     

Does Radiofrequency Catheter Ablation Induce a Deterioration in Sympathetic Innervation? A Positron Emission Tomography Study

Radiofrequency catheter ablation (RFCA) is an effective treatment for the interruption of accessory bypass tracts in WPW syndrome or the modification of the Ay-nodal conduction system in patients with A V-nodal tachycardias. However RFCA may also damage cardiac innervation. The purpose of this pilot study was to assess possible changes in sympathetic innervation after RFCA as evaluated by the cathecholamine analog carbons-11- hydoxyephedrine (HED) positron emission tomography (PET) which allows the visualisation of sympathetic nerve terminals. We investigated nine patients with supraventricular tachycardias before and two to six weeks after RFCA. Myocardial perfusion was depicted by n-I3-ammonia-PET. In addition to visual analysis, HED retention was quantified in the myocardial quadrant distal to the location of intervention; these results were compared with values in remote areas. Before RFC A, myocardial perfusion showed homogenous distribution in 8 of 9 patients. One patient showed a perfusion defect in the posterior wall. HED retention matched perfusion distribution in all patients. After RF'CA there was no significant change observed either in ammonia or in HED distribution. Quantitative HED retention data showed no significant change before versus after RFC A. Thus, HED-PET does not demonstrate any abnormalities of tracer uptake indicating integrity of sympathetic nerve terminals after radiofrequency ablation therapy.     

The varying time courses of attentional and affective modulation of the startle eyeblink reflex

In previous research on modulation of the startle eyeblink reflex, emotional effects have been demonstrated only at late probe positions, whereas attentional effects have been found at both early and late positions but only when the prepulses were affectively neutral. In Experiment 1, participants viewed emotionally valenced pictures and were instructed to attend to the duration of half of the slides. Affective modulation of the startle eyeblink occurred at long lead intervals, but attentional modulation also occurred late. In Experiment 2, participants viewed the same slides used in Experiment 1 but were instructed to attend to the duration of only the positive or the negative slides. Affective modulation occurred at both early and late probe positions, whereas attentional effects occurred only following slide offset. Early (250 ms) affective modification of startle eyeblink has not been previously reported. These results suggest that the time courses of emotional and attentional modulation of startle are variable and can occur at both early and late startle probe positions, depending on task requirements.