G. Frank O. Tyers

The effects of insulin and anoxia on the metabolism of isolated mature rat cardiac myocytes

Abstract Cardiac myocytes from adult rat ventricles were isolated by perfusion and incubation with buffer containing collagenase and hyaluronidase. This method gave a high yield of viable cells with normal morphology and metabolic properties. The isolated cells can tolerate 2.5 m m extracellular calcium and have physiologic levels of ATP (20 μmol/g protein). The cells metabolized glucose at a linear rate up to 4 h. Glucose utilization was stimulated by insulin and anoxia. Protein synthesis was maintained at a steady rate for 3 h and was significantly stimulated by insulin. A reasonably constant rate of protein degradation was observed for 3 h. Insulin significantly inhibited the rate of protein degradation.

Recent experience with tuberculous pericarditis.

Twelve patients with tuberculous pericarditis were found among 1,194 patients with tuberculosis treated at the University of Texas Medical Branch over a 10-year period, an incidence of 1%. Surgical treatment was undertaken in 4 patients, and the rest were treated medically. The surgically treated patients had no major complications, and none of them died. In the medically treated group, however, 1 patient died, 1 had an anaerobic empyema, and 1 experienced respiratory arrest. In addition, the average hospital stay was 33 days less in the surgically treated group. Early surgical intervention should be carried out in patients with tuberculous pericarditis who do not respond promptly to adequate antituberculosis chemotherapy.

Intrapleural Instillation of Quinacrine for Treatment of Recurrent Spontaneous Pneumothorax

We used intrapleural instillation of quinacrine hydrochloride in 20 patients (Group A) with recurrent spontaneous pneumothorax (one bilateral) and compared their clinical course with 19 patients who underwent thoracotomy and scarification or pleurectomy (Group B) and 63 patients treated by tube thoracostomy alone (Group C). In Group A, there was one complication of treatment, a pneumothorax immediately following tube removal, which necessitated repeat tube thoracostomy, and there was one late ipsilateral recurrence 2 years after treatment. These 20 patients with 21 recurrent spontaneous pneumothoraces treated with intrapleurally administered quinacrine have been followed for from 6 months to more than 4 years with only one late recurrence on the treated side. Eight patients in Group B had postoperative complications: 2 patients who had had pleurectomy required reoperation for postoperative bleeding; lobar pneumonia developed in 3; 1 had lack of total expansion of the lung; an intrathoracic hematoma developed in 1; and an ipsilateral pneumothorax necessitating tube thoracostomy developed in 1. In Group C, the rate of recurrence of pneumothorax was 23% during the first year following treatment. Intrapleural instillation of quinacrine is a simple, low-risk, reliable, and effective treatment for recurrent spontaneous pneumothorax, and is equally as effective as thoracotomy and scarification.

Use of Cold Cardioplegic Solution for Vein Graft Distention and Preservation: A Light and Scanning Electron Microscopic Study

To evaluate the effect of a cardioplegic solution on the endothelium of the saphenous vein, portions of this vein were harvested from each of 5 patients undergoing coronary artery bypass operation. Each sample was divided into five segments. One segment was distended with heparinized saline solution, one with heparinized blood, and one with heparinized cardioplegic solution (25 mEq of potassium per liter). All of the distending solutions were kept at 10 degrees C, and pressure was carefully limited to 200 mm Hg. The fourth segment of vein was distended with heparinized saline solution but no effort was made to limit distending pressure, and the fifth segment was not distended. All samples were then examined with light and scanning electron microscopy. There were no great morphological differences in the endothelium of veins distended to 200 mm Hg with saline solution, blood, or cardioplegic solution. The morphology of these samples compared favorably with the control vein endothelium although scattered areas of endothelial disruption were present in every sample. Veins distended without pressure control showed massive endothelial disruption. The particular solution used to distend the sephenous veins is not as important as limiting the distending pressure.

Myocardial Stimulation Impedance: The Effects of Electrode, Physiological, and Stimulus Variables

With exposed metal at the electrode tissue interface (8 mm2, 28 mm2, 57 mm2), myocardial threshold stimulation impedance increased as pulse duration was lengthened, with left ventricular intramyocardial stimulation, and with the smaller surface area electrode. An 0.5 mm2 differential-current-density electrode, which eliminated direct metal-to-tissue contact at the electrode-myocardial interface, was associated with notably higher impedances than each of the three metal tip electrodes and did not show increasing impedance levels with changes in pulse duration, confirming the minimization of polarization energy losses with this device. The majority of electrode, electrode tissue interface, and myocardial variables that are characterized by high threshold stimulation impedance are associated with low threshold energy requirements for pacing and reduced pacemaker power source drain. No accurate information about sensing impedances can be derived from current knowledge of pacing impedance.

Suppression of a Demand Pacemaker in the Presence of Redundant Transvenous Right Ventricular Leads

A ventricular inhibited demand cardiac pacemaker was inhibited in the presence of intimate contact between the active temporary bipolar electrode ring and a retained inactive permanent bipolar electrode tip. Electromagnetic interference effects, lack of insulation, lead breaks, and loose connections were all ruled out as the cause of pacemaker suppression.

Current status of pacemaker power sources.

After years during which pacers of very similar design and capabilities were provided by a small number of manufactures, many different lithium, halogen, rechargeable, and nuclear power sources are now available. The variety of chemistries, methods of construction, and sealing techniques used in the batteries of the different manufacturers is almost unlimited. This has made it necessary for physicians who implant and follow pacer to acquire a general knowledge of the field if they are to make an informed choice of pacemaker power source for implantation and if they are to manage recalls with a minimum of patient and physician trauma. More experience is required before it can be definitely determined which of the new pacer power sources will prove superior, but when coupled with well-designed, hermetically sealed pulse generators, all are capable of providing continuous pacing for at least 5 years and the 10-year pacemaker is now a probability.