The Effect of 50 Hz External Electrical Interference on Implanted Cardiac Pacemakers

The effects of injected 50 Hz alternating current on the function of cardiac pacemakers has been observed in 18 patients with implanted unipolar VVI units. Current, in the range 0-600 microA was applied via electrodes attached to the patients' upper body and feet and fed from a specially designed current injection unit at the bedside. Most implanted pacemakers reverted to interference mode in the current range 29-250 microA. At current levels just below the reversion current all units developed irregular and inappropriate pacing. This current level was pacemaker dependent and varied in the range 27-246 microA. The total reversion current depended on the location of the injecting electrodes and on the patients' posture. The sensitivity of the units to injected interference was increased by deep inspiration. Temporary pacing catheters fitted to an additional ten patients were used to monitor the interference voltage which would be sensed by an implanted unit. This voltage was similarly dependent on patient posture and on deep respiration. Current injection has proved to be a safe, controllable and reproducible method of testing the sensitivity of implanted pacemakers to 50 Hz external interference.     

MALABSORPTION CAUSED BY COELIAC DISEASE IN PATIENTS WHO HAVE SCLERODERMA

Coeliac disease may account for malabsorption in sclerodermapatients even when tests suggest bacterial overgrowth. A smallbowel biopsy is essential. KEY WORDS: Coeliac disease, Scleroderma, Malabsorption, Hydrogen breath test     

Clinical Use of Intracardiac Impedance: Current Applications and Future Perspectives

ARTHUR, W., et al. : Clinical Use of Intracardiac Impedance: Current Applications and Future Perspectives. For over 40 years the measurement of intracardiac impedance has been proposed as a method of assessing the contractile state of the heart muscle. This technique requires the positioning of one or more intracavitary electrodes and the generation of an electric field from an alternating current source. Variations in the calculated impedance signal reflect changes in the ventricular blood pool volume adjacent to the electrodes. Intracardiac impedance measurement has been successfully developed as a research tool to assess myocardial contractility, and from this, clinical uses have evolved. Commercial rate responsive pacing systems use intracardiac impedance to assess the inotropic state of the heart. Further development of this technology might allow hemodynamic discrimination of cardiac arrhythmias.     

Failure of Plasma Atrial Natriuretic Peptide Levels to Increase During Exercise in Patients with Chronic Atrial Fibrillation

It is generally accepted that plasma atrial natriuretic peptide release occurs secondary to atrial stretch. The influence of coordinated atrial contraction (AC) upon this process is not fully appreciated. The aim of the study was to determine the importance of coordinated AC upon peripheral atrial natriuretic peptide levels (α-hANP) during exercise. Peripheral α-hANP levels were measured at rest and during exercise in 12 patients with complete heart block (CHB) and permanent rate responsive pacemakers. Seven patients had coordinated AC and five had chronic atrial fibrillation (AE). Each patient performed three treadmill exercise tests. Maximal inspired oxygen volume (VO₂ max) was determined during test 1. Tests 2 and 3 were performed to 70% VO₂ max, the pacemaker being programmed to either VVI or VVIR mode. Plasma α-hANP was measured using a two-site immunoradiometric assay. At rest there was a small but significant difference between the two patient groups: AF 60.2 pg/mL versus AC 97.6 pg/mL; P = 0.03. During exercise in the AC patients, there was a significant increase in α-hANP levels, in VVIR mode, to 238.4 pg/mL, and in VVI mode, to 207.9 pg/mL, P = 0.002 and 0.003, respectively. In those patients with chronic AF, there was no significant rise or fall in α-hANP levels in either pacing mode, VVIR 65.2 pg/mL, VVI 46.6 pg/mL. Previous workers have suggested that α-hANP release by nonfunctioning atria is normal. We have shown that the presence of coordinated AC is required for the release of α-hANP during exercise in patients with CHB, and that this appears to be independent of ventricular rate.