Potential hazards of fixed gain sensing and arrhythmia reconfirmation for implantable cardioverter defibrillators

Appropriate sensing of ventricular tachycardia (VT) and ventricular fibrillation (VF) is of paramount importance for safety of patients with implanted cardioverter defibrillators (ICDs). Recently, the GuardianR ATP 4210, a new third generation ICD that uses programmable but fixed sensing during sinus rhythm and doubles its sensitivity settings when VF is detected, to a maximum programmable sensitivity of 1 mV, has been tested in phase I and II clinical trials. A reconfirmation algorithm of this ICD confirms the presence of VT or VF prior to therapy. This case report describes undersensing of VF in a patient with the GuardianR ATP 4210 at the maximum programmed sensitivity of 1 mV. Inappropriate episodes of asystole and prolonged bradycardias were also observed in this patient due to shortcomings in the reconfirmation algorithm design. Reoperation was required, with positioning of a new endocardial sensing lead to correct the undersensing of VF. This, however, did not correct asystolic pauses following antitachycardia pacing or spontaneous tachycardia termination prior to therapy. This case report highlights the hazards of fixed gain sensing for implantable ICDs and a potential limitation of a specific tachyarrhythmia reconfirmation algorithm used in this device.

Is defibrillation testing safe?

Determination of defibrillation thresholds (DFTs) and implantable cardioverter defibrillator (ICD) testing requires repeated inductions of ventricular fibrillation (VF) and defibrillation attempts using known energy outputs. Little is known about the individual and cumulative effects of repetitive brief episodes of VF and hypoperfusion on cerebral function. The potential clinical utility of quantitative electroencephalographic (QEEG) monitoring during intraoperative ICD testing, by using processed 19-channel EEG (0.5-35 Hz bandwidth), was examined in ten anesthetized patients, five males and five females (mean age 62 +/- 10 years), who underwent ICD implantation and testing. Ischemic QEEG patterns were defined as those with a 3 standard deviation increase (P less than 0.01) in absolute delta (1.5-3.5 Hz) power persisting for greater than or equal to 2.5 minutes. The majority (80%) of the VF episodes (70) were accompanied by QEEG "slowing" (doubling of the pre-VF low frequency delta waves amplitude). All the patients (5/5) experiencing greater than 6 VF episodes showed a statistically significant increase in the low frequency amplitude. In contrast, this EEG abnormality was apparent in only one of five patients experiencing less than 6 VF episodes. These results suggest a cumulative QEEG depression associated with ICD testing. QEEG may provide an objective means for establishing an individualized upper safe limit of DFT testing and the total number of induced VF episodes.

The initial clinical experience with an implantable cardioverter defibrillator/antitachycardia pacemaker

Guardian antitachycardia pacing (ATP) 4210 is a third generation, multi-programmable cardioverter defibrillator undergoing Phase I clinical trials. The tiered response includes ATP, low energy cardioversion or defibrillation, and bradycardia support. Extensive telemetry is available, including an episode log and details of all episode events. Five patients underwent the implantation of Guardian ATP 4210 as part of a Phase I trial at the University of Louisville. Two of the five patients had multiple VT episodes that were reverted successfully using ATP pacing (slow VT) and defibrillation (fast VT) and VF episodes, which resulted in defibrillation therapy over a follow-up period of 6 to 8 months. Four of the five patients required bradycardia support for bradyarrhythmias unassociated with ATP therapy or defibrillation and one patient required bradycardia support postdefibrillation therapy. The device design is microprocessor based and requires continuous interrogation of the microprocessor memory and checks of the validity of programmed parameters to continue its operation. When the safety check fails, the device is designed to shut down its antitachycardia and defibrillator functions. This design feature has a potential for leaving the patient unprotected if the device shuts down. Modification of this feature is required to ensure the device's long-term safety.

The use of lasers in pediatric surgery

This report is a condensation of the Fred McLoed Lecture given at the Annual Meeting of the Canadian Association of Paediatric Surgeons. It briefly cites the basic fundamentals of lasers, the characteristics of those used in surgery, and their delivery systems. The advantages of laser surgery include the sealing of blood vessels, lymphatics, and nerve ends when used for cutting. This results in a relatively dry field of surgery and less postoperative pain. There is reduced opportunity for contaminants in a clean wound, and no spreading of infection in a contaminated one. Surgery can be carried out in confined areas in a drier field of view, and can be brought to small areas by fiberoptic cables. Highly precise and localized microsurgery is possible. The use of lasers is indicated in operations where significant blood loss is expected and in patients with bleeding tendencies. It is useful in surgery for malignant disease and through highly infected tissue. Other general indications are discussed. Specific surgical procedures where lasers have been useful include treatment of hemangiomas, surgery of the tongue, repair of pectus excavatum, partial splenectomy and splenic repair, hepatic lobectomy and hepatic repair, and resection of adrenal tumors. Lasers have also been useful in partial nephrectomy, excision biopsy, revision or closure of ileostomy or colostomy, endorectal mucosectomy, posterior sagittal anorectoplasty, treatment of condyloma acuminata, burn wound debridement, and infected tissue debridement. Anticipated uses include vascular, biliary tract, and intestinal repair and anastomoses, and photodynamic therapy (PDT) of neoplasms.

Records review for (in case of) litigation

This article examined the role of records review in litigation. Ways to benefit from records analysis both before and during litigation were stressed. Use your records to improve documentation and reduce litigation.

Neurotoxicity of intrathecal local anesthetics in rabbits

The authors developed a new method of intrathecal local anesthetic injection in rabbits in order to study the relationship between anesthetic concentration and impaired neurologic function. They found that none of the local anesthetics studied produced persistent neurologic damage in concentrations used clinically. However, lidocaine and tetracaine can be prepared in high concentrations (far exceeding those clinically used) that will produce extensive irreversible neurologic injury and histologic changes. This was also true for sodium bisulfite, an antioxidant used in a number of commercially prepared local anesthetic solutions. Pure solutions of relatively insoluble local anesthetics (bupivacaine and 2-chloroprocaine) failed to produce comparable neurologic or neuropathologic changes when tested at concentrations up to their solubility limits. Extensive neurologic impairment was not necessarily accompanied by equally extensive lesions in the spinal cord and nerve roots.

The prevalence of antibodies to Rickettsia rickettsii in an area endemic for Rocky Mountain spotted fever

A study of Rickettsia rickettsii was conducted in Rowan, Cabarrus, and Granville counties, North Carolina in an attempt to define the prevalence of endemic infection in this area. Serum samples were obtained from 1,976 healthy persons and tested by indirect hemagglutination for detectable antibodies to R. rickettsii. Of this group, 568 (28.7%) had detectable antibody (greater than or equal to 1:8), 80 (4%) had titers greater than or equal to 1:64, and 1,408 (70%) had no detectable antibody (less than or equal 1:8). Indirect immunofluorescence testing for antibody was also performed for 315 (15%) of the serum samples, of which 301 (95%) had undetectable titers and 14 (5%) had detectable titers ranging from 1:8 to greater than or equal to 1:64. Serological reactivity by indirect hemagglutination was detected in persons in the absence of known Rocky Mountain spotted fever. The study failed to show a good correlation of either the height of the geometric mean titer or percentage of seropositive persons with the previously determined age-related rates of acquisition of the disease. These data suggest that the antibodies measured may not be specific for R. rickettsii or that the antibody levels wane with time or both. It is probable that unrecognized infection occurs, but the true incidence or prevalence cannot be determined by available serological tests.

Epidemiology of Rocky Mountain spotted fever as determined by active surveillance

Prospective, active surveillance for Rocky Mountain Spotted fever (RMSF) was undertaken in two North Carolina counties for the years 1979-1981. Appropriate age, sex, and geographically matched controls were compared with the serologically confirmed cases of disease. Patients who were suspected of having infection, but were shown not to have RMSF, were also compared with the serologically proven cases. Ninety-eight cases were identified, and three of these patients died. The mean annual incidence of RMSF in these two counties was 14.59 cases/100,000 population. Identified cases occurred between the months of March and September. The overall mean annual incidence for men was 19.65/100,000 and for women 10.3/100,000. The study suggests that persons contracting RMSF are exposed to the vectors at their residences, which tend to be detached dwellings in woody, brushy areas. Children are more likely than adults both to be seen by physicians early in the illness and to be checked for ticks. Eighty-four percent of patients with serologically confirmed cases developed a rash. The epidemiology of RMSF in these two endemic counties is described.

Hitchcock's birds, or the increased rate of exposure to histoplasma from blackbird roost sites

A statewide survey of populations in proximity to blackbird roost sites to determine exposure to histoplasmosis from such sites has demonstrated that a site harboring Histoplasma capsulatum, even though undisturbed, adds significantly to the exposure rate of proximal populations. Disturbance of such a site increases the exposure rate dramatically with or without concurrent clinical cases of histoplasmosis.

Developmental dissociation of myelin synthesis and "myelin-associated" enzyme activities in the shiverer mouse

Developmental changes in three enzymes associated with myelin lipids were studied in the shiverer mouse, a murine mutant showing a severe deficiency of CNS myelin. Age-related changes in cerebroside sulfotransferase (measured in brain) and arylsulfatase A and cerebroside B-galactosidase (measured in brain and liver) were the same for shiverer and control mice. The shiverer mouse, therefore, demonstrates a dissociation between the genetic mechanisms regulating myelination in the CNS and developmental changes in enzyme activities thought to be closely related to the synthesis of myelin. In addition, we found no defect in the shiverer mouse in the incorporation of glycine-labeled basic protein into CNS myelin, indicating an important metabolic difference between the morphologically similar shiverer and quaking mutants.

Family abuse of the elderly

In 12 cases of family abuse of disabled elderly persons, the majority of the abused were women. Caretakers included spouses, children, siblings or other relatives. Abuse was both physical and verbal/psychologic. Neglect, the most common form of physical abuse, sometimes resulted in decubitus ulcers and vermin infestation. Misuse of medical therapy and nutrition were other areas of physical abuse. Psychologic abuse included derogation, infantilization, and threats of institutionalization, abandonment, and homicide. Possible causes of abuse included alcoholism in the caretaker, financial concerns, and long-term family conflicts. Various recommendations are made for the management of abusive families.

The antepartum diagnosis of conjoined twins

This is a case report in which the diagnosis of conjoined twins was made in a woman by ultrasonography in her eigth month of pregnancy. With this diagnosis, the mother-to-be was transported to a hospital with sophisticated obstetrical, neonatal, and pediatric surgical facilities. The twins were delivered by elective caesarian section and were seen to have anomalies requiring immediate surgery. Following stabilization and basic investigations, surgery was performed on the infants at 3 hr of age. This resulted in a condition that permitted a thorough postoperative work-up and elective separation several months later.

Minilaparoscopy for blunt abdominal trauma

A new technique of minilaparoscopy has been developed for use in patients with blunt abdominal trauma. Fifteen injured patients underwent laparoscopy using this new method. Six patients had normal findings, seven patients had evidence of minor injury, and two patients had what seemed to be major injuries. The patients with normal findings or minor injuries were treated nonoperatively and all did well. The two remaining patients underwent laparotomy where serious injuries were found and repaired accordingly. With this modified instrumentation, emergency laparoscopy is simple and rapid enough to become a practical tool in the management of blunt abdominal trauma.

Identification of anastomotic sites with radiopaque markers

Routine marking of the anastomotic site in gastrointestinal and biliary tract operations by hemoclips is a useful adjunct in the study and interpretation of postoperative roentgenologic studies. The addition of this simple maneuver has been greeted with enthusiasm by our radiologists. We suggest that the use of hemoclips be made routine in gastrointestinal and biliary tract operations.

A model for deposition of stable and unstable aerosols in the human respiratory tract

A model has been developed for deposition of stable and unstable aerosols in the human respiratory tract. This model has the advantages of employing a realistic asymmetric lung model and utilizing actual breath curves. Results from the model are presented for normal and abnormal breath patterns for both stable and unstable particles. Insofar as comparison is possible, agreement between model calculations and experiment appears to be reasonable.

Solitary meningocerebral metastasis from squamous cell carcinoma of the esophagus: a case report

A case of a solitary meningocerebral metastasis from an esophageal carcinoma is described and the rarity of such an occurrence, as compared with cerebral metastases from other organs, is stressed. A possible metastatic pathway from the esophagus to the brain through the vertebral veins is postulated.

Solitary meningocerebral metastasis from squamous cell carcinoma of the esophagus: a case report

A case of a solitary meningocerebral metastasis from an esophageal carcinoma is described and the rarity of such an occurrence, as compared with cerebral metastases from other organs, is stressed. A possible metastatic pathway from the esophagus to the brain through the vertebral veins is postulated.