A Simple Method for Preoperative Assessment of the Best Fitting Electrode Length in Single Lead VDD Pacing

For single lead VDD pacing, electrodes with various distances between the lead tip and the floating atrial dipole (AV distance) are available. Using different AV distances allows positioning of the atrial dipole in the mid- to high right atrium, regardless of the size of the right heart. In this position, reliable atrial sensing and rejection of ventricular far-field potentials can be expected. A simple test for the preoperative assessment of the best fitting AV distance in the individual patient was tested. We studied 24 consecutive patients prior to implantation of AVDD pacemaker. With the patient in supine position, a test electrode with an AV distance of 13 cm was taped onto the thorax. Under fluoroscopic control, it was moved until its course and projection onto the heart was equal to that of a ventricular lead. If fluoroscopy then showed a projection of the atrial dipole onto the mid- to high right atrium, a lead with a similar AV distance of 13 or 13.5 cm was used for implantation. If the atrial dipole projected itself too high or too low, a shorter or longer lead had to be implanted. The maximum time for the test was 2 minutes, and the maximum fluoroscopy time was 15 seconds. According to the test, a lead with an AV distance of 13 or 13.5 cm was implanted in 18 of 24 patients, and a lead with an AV distance of 15.5 or 16 cm was implanted in 6 of 24 patients. The atrial dipole could easily be positioned in the mid- to high right atrium in all patients, demonstrating a correct preoperative assessment of the best fitting AV distance. Intraoperatively, a P wave amplitude of 3.5 ± 3.0 mV was measured. The described test allows a fast and reliable assessment of the best fitting electrode length in single lead VDD pacing.     

Clinical significance of ventricular late potentials in patients with obstructive sleep apnoea

SUMMARY  Patients with obstructive sleep apnoea (OSA) have an increased cardiovascular mortality and probably also an increased incidence of sudden cardiac death. Thus the question arises whether ventricular late potentials can constitute markers for an increased electric vulnerability in these patients. Signal-averaged electrocardiograms were recorded in 64 patients (6 female, 58 male; mean age 53.2 y) with OSA (mean apnoea-hypopnoea index (AHI) 41.7 h^-1 ± 24.3 h^-1). Furthermore, a continuous ambulatory electrocardiogram and gated radionuclide ventriculography were performed. Ventricular late potentials were recorded in 5 men out of 64 patients. Two of them had coronary artery disease (1 patient post-myocardial infarction), 2 hypertension, and 1 nocturnal hypertension. No correlation could be traced between left ventricular ejection fraction, severity and extent of ventricular premature beats, or severity of OSA and occurrence of ventricular late potentials. It was noticeable, however, that the patients with ventricular late potentials had severe OSA (mean AHI 50.2/h vs. 40.9/h). Although OSA may lead to structural myocardial changes that could be the basis for re-entrant circuits, ventricular late potentials were found in only 7.8% of these patients. The results of this study demonstrate that at present ventricular late potentials and signal-averaged electrocardiograms do not prove useful as screening methods for risk stratification of patients with OSA.     

SERUM PROLACTIN LEVELS IN RENAL INSUFFICIENCY IN CHILDREN

Abstract. Ijaiya, K., Roth, B. and Schwenk, A. (The University Children's Hospital, University of Cologne, Cologne, Federal Republic of Germany). Serum porlactin levels in renal insufficiency in children. Acta Paediatr Scand, 69: 299, 1980.—Basal prolactin concentrations in forty-eight children with acute or chronic renal disease have been compared with those in thirty-four healthy control subjects. Elevated basal prolactin levels and an abnormal prolactin response to intravenous thyrotropin-releasing hormone were found in children with chronic renal failure on maintenance intermittent haemodialysis. No significant change in plasma prolactin concentrations and osmolality was observed before and after haemodialysis, despite a fall in plasma creatinine concentrations. The elevated prolactin levels fell to normal in three patients after successful renal transplantation. It is suggested that the kidney has an important role to play in prolactin metabolism.     

A Case of Hidden Receptacle-Adapter Incompatibility

Connection of a universal VS-1 adapter to a VS-1 receptacle resulted in intermittent loss of pacing and of sensing in a pacemaker dependent patient. This was caused by the use of an adapter that only provides stable electric contact if the adapter pin is deformed by the set screw. Since we had implanted a pulse generator with a "side-lock" connector without screws, only a loose connection was achieved. The manufacturers should provide information on such hidden incompatibilities.     

Performance Evaluation of a Right Atrial Automatic Capture Verification Algorithm using Two Different Sensing Configurations

Background: This acute data collection study evaluated the performance of a right atrial (RA) automatic capture verification (ACV) algorithm based on evoked response sensing from two electrode configurations during independent unipolar pacing. Methods: RA automatic threshold tests were conducted. Evoked response signals were simultaneously recorded between the RA_Ring electrode and an empty pacemaker housing electrode (RA_Ring→Can) and the electrically isolated Indifferent header electrode (RA_Ring→Ind). The atrial evoked response (AER) and the performance of the ACV algorithm were evaluated off‐line using each sensing configuration. An accurate threshold measurement was defined as within 0.2 V of the unipolar threshold measured manually. Threshold tests were designed to fail for small AER (< 0.35 mV) or insufficient signal‐to‐artifact ratio (SAR < 2). Manual threshold measurements were obtained during RA unipolar and bipolar pacing and compared across device indications. Results: Data were collected from 38 patients with RA bipolar leads from four manufacturers. AER signals were analyzed from 34 patients who were indicated for a pacemaker (five), implantable cardioverter‐defibrillator (11), or cardiac resynchronization therapy pacemaker (six) or defibrillator (12). The minimum AER amplitude was larger (P < 0.0001) when recorded from RA_Ring→Can (1.6±0.9 mV) than from RA_Ring→Ind (1.3±0.8 mV). The algorithm successfully measured the pacing threshold in 96.8% and 91.0% of tests for RA_Ring→Can and RA_Ring→Ind, respectively. No statistical difference between the unipolar and bipolar pacing threshold was observed. Conclusions: The RA_Ring→Can AER sensing configuration may provide a means of implementing an independent pacing/sensing method for ACV in the RA. RA bipolar pacing therapy based on measured RA unipolar pacing thresholds may be feasible.     

Implantable Cardioverter Defibrillator: Possible Hazards of Electromagnetic Interference

We report on three patients with an automatic, implantable cardioverter defibrillator (AICD, CPI) in whom the device had been deactivated due to electromagnetic interference. In all cases, the source of the electromagnetic disturbances could be identified.     

Metabolism of Roxithromycin in the Isolated Perfused Rat Liver

Roxithromycin is a macrolide antibiotic with high clinical potency. N-Demethylation is considered to be one of the main pathways of roxithromycin metabolism in rats. We have studied the hepatic metabolism of roxithromycin in the isolated perfused rat liver. After addition of roxithromycin (30 μM) to the perfusion medium the parent compound and one major metabolite were detected in bile by high-performance liquid chromatography. The metabolite was identified as monodesmethylated roxithromycin by mass spectrometric analysis. Onset of biliary excretion of native roxithromycin was fast, reaching a maximum (130.52 ±43.88 pmol g^?1 min^?1) after only 10 min, whereas excretion of the metabolite was delayed (maximum 75.83 ± 11.92 pmol g^?1 min^?1 at 30 min). The cumulative excretion of roxithromycin and its metabolite into bile during the 60 min of application amounted to only 1.09 ± 0.30 and 0.64 ± 0.22% of the roxithromycin cleared from the perfusate during the same time. The liver content was 0.48 μmol (g liver)^?1, indicating high retention within the organ. No release of the metabolite into the perfusate was detected. In conclusion, this study has demonstrated the importance of phase-I metabolism for the biliary excretion of roxithromycin in rat liver. These findings might be predictive of roxithromycin biotransformation and biliary excretion in man.