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Biomedical subjects

C Andrews

Publications and source records attributed to C Andrews.

At least 19 recordsLinked to original sources
PubMed1992

DDD pacing mode survival in patients with a dual-chamber pacemaker.

Dual-chamber (DDD) pacing mode survival was assessed by reviewing 486 consecutive initial transvenous DDD pacemaker implantations between December 1981 and December 1988 inclusive, with a mean follow-up time of 33 months. The patients' mean age was 71.4 years and 55% were male; 38% had dominant sinoatrial and 62% had dominant atrioventricular (AV) node disease. Nineteen patients (4%) underwent secondary operative intervention for lead dislodgement (n = 11), lead or pulse generator malfunction (n = 6) or infection (n = 2). During follow-up, 87 patients (18%) had their device permanently reprogrammed out of the DDD mode and 10 others (2%) required temporary reprogramming out of this mode; 12 patients who required device reprogramming were managed in other dual-chamber or atrial pacing modes. Reasons for reprogramming included atrial fibrillation (n = 48; 10%); loss of atrial sensing (n = 26; 5%); recurrent "endless loop" tachycardia (n = 5; 1%); lead dislodgement without repositioning (n = 4; 1%); pulse generator malfunction (n = 1; 1%) and other (n = 5; 1%). The occurrence of atrial fibrillation was associated with dominant sinoatrial disease and a prior history of atrial fibrillation; 19% of atrial sensing loss was attributable to early or faulty pacemaker technology. The DDD mode survival rate at 1, 2, 3, 4 and 5 years was, respectively, 90%, 88%, 84%, 79% and 78%.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1992

The clinical relevance of electromyopotential oversensing in current unipolar devices.

UNLABELLED: Electromyopotential oversensing of unipolar pacemakers was first appreciated 20 years ago, but its prevalence in present day devices is less well defined. Thirty-four pacemaker patients, only two with symptoms suggestive of oversensing, were evaluated in unipolar settings to assess the frequency of provocation of oversensing in one or, if present, both pacing channels. The sensing threshold of each patient, whenever possible, was recorded as well. RESULTS: Atrial oversensing occurred in 11/18 patients (61%), all at sensitivities in the 0.4-1.0 mV range. Ventricular oversensing was noted in 13/33 patients (39%), with all but one programmed to settings of 1.25 mV or more sensitive (i.e. < 1.25 mV). Twenty six of 26 patients amenable to testing had ventricular sensing thresholds of at least 4.0 mV or more. Of the 15 patients amenable to atrial sensing threshold testing, 4 had a threshold of 1.0 mV or < 1.0 mV, 6 had thresholds between 1.0-2.0 mV, and 5 sensed at settings > 2.0 mV. CONCLUSION: Electromyopotential oversensing remains a relevant issue in current day unipolar pacemakers. Most patients do not describe symptoms related to electromyopotential interference, yet such interference is frequently provoked. Oversensing is common at high sensitivities typically utilized for atrial sensing, but quite unusual at settings necessary for adequate ventricular sensing. Programming unipolar devices to unnecessarily high sensitivities should be avoided or serious consequences may result.

Cardiac Pacing, Artificial↗
PubMed1992

Removal of infected transvenous leads requiring cardiopulmonary bypass or inflow occlusion.

Infection, although uncommon, can be the most lethal of all potential complications after transvenous pacemaker implantation. The infection rate at our institution has been 0.56% (42 implants) during the preceding 17 years for 7435 transvenous pacemakers implanted in 4333 patients. Four of the 42 patients required use of cardiopulmonary bypass or inflow occlusion to remove the infected transvenous leads. Seven patients had their pacemakers implanted elsewhere and were transferred to our medical center for treatment. One patient died postoperatively because of persistent sepsis from a retained lead segment. All other patients survived, and none had recurrent infection. We recommend removal of all hardware if there is infection of the pacemaker system. If traction or other methods fail to remove the transvenous portion of the pacemaker system, open methods of removal, although rarely required, are safe and effective and should be used without delay.

Adolescent↗
PubMed1991

Pacemaker infection with Mycobacterium avium complex.

A 21-year-old. HIV negative, malnourished, homeless woman with congenital heart block had a pacemaker implanted at 7 years of age and multiple procedures thereafter. The most recent of these procedures was replacement of a pulse generator in the right pectoral region. Four months later she had fever, pain, and swelling over the implant site resulting from infection with mixed flora and Mycobacterium avium complex. The pacemaker system was removed by thoracotomy via a median sternotomy and a new DDD pacemaker simultaneously implanted. She was treated with systemic antibiotics--isoniazid, rifampin, ethambutol--for 2 weeks. Six months later she was healthy, pacing well, and apparently free of infection, off all medications.

Adult↗
PubMed1990

Clinical predictors and natural history of atrial fibrillation in patients with DDD pacemakers.

Effective DDD pacing requires that patients remain free of atrial fibrillation (AF). Four hundred eighty-nine consecutive patients undergoing initial transvenous DDD implants were reviewed to determine the incidence of postimplant AF in this population and to assess what factors, known at implant, predicted the later development of AF. The variables analyzed included age, sex, indication for implant (dominant SA or AV node disease), history of AF, atrial electrogram characteristics and pacing threshold, and the status of retrograde conduction. Forty-eight patients (9.8%) developed AF a mean of 23 months postimplant, and 11 of these patients returned to sinus rhythm and were managed once again in DDD for significant periods. A prior history of AF and the presence of dominant sinoatrial disease were far more prevalent in the patients who developed AF (P less than 0.001) though the vast majority of patients with these two independent risk factors remained in sinus rhythm through much or all of their follow-up period. We conclude that the incidence of AF is not of a magnitude to preclude DDD pacing in the vast majority of patients in sinus rhythm at implant.

Aged↗
PubMed1989

Lyme carditis: an important cause of reversible heart block.

Lyme disease is a tick-borne spirochetal infection, characterized by erythema chronicum migrans and an acute systemic illness. The disease is endemic in many parts of the north-eastern United States. Without treatment, late rheumatic, neurologic, and cardiac complications frequently occur. We report four serologically confirmed cases of Lyme carditis in previously healthy young men (mean age, 45 years) from endemic areas. Each presented with severe symptomatic atrioventricular block, three with episodes of prolonged ventricular asystole. Two had permanent pacemakers implanted (one was later removed), and another, very nearly did, before diagnosis. All four patients were treated with antibiotics, and in each case their rhythm returned to sinus, though one patient has Wenckebach second degree block with atrial pacing at 120 beats/min 16 months later. Carditis occurs in 4% to 10% of cases of Lyme disease and usually begins 3 to 6 weeks after the initial illness. It manifests as a transient myocarditis with varying degrees of atrioventricular block. The diagnosis is made primarily on clinical grounds and confirmed by serologic testing. Temporary cardiac pacing is frequently needed by patients who have severe heart block with hemodynamic instability. The evidence suggests that, in most cases, the block is at the level of the atrioventricular node. The block generally resolves completely with antibiotic treatment. Complete heart block rarely persists more than 1 week and the long-term prognosis appears to be excellent. Consideration and prompt recognition of this potentially lethal, but reversible, cause of heart block is crucial in order to avoid inappropriate permanent pacemaker implantation.

Adult↗
PubMed1989

Stage II endometrial carcinoma treated with external-beam radiotherapy, intracavitary application of cesium, and surgery.

From September 1972 to September 1987, thirty-six patients with stage II carcinoma of the endometrium were treated with external-beam radiotherapy to the pelvis, a single intracavitary application of cesium-137, and extrafascial hysterectomy with adnexectomy. Patients were followed for a median of 54.4 months. Overall 2- and 5-year actuarial survival rates were 83 and 58%, respectively. Survival was analyzed in terms of the independent variables surgical stage, presence of a gross cervical lesion, and residual disease within the myometrium or cervix. Factors contributing to patients survival were analyzed by the log-rank method. The 12 patients with a gross cervical lesion had an adverse prognosis, as compared to those without such a lesion (P less than 0.05). Seven of the twelve patients (58%) with a cervical lesion at clinical staging demonstrated persistent or recurrent disease. The presence of extrauterine disease at surgery was a major prognostic factor in patient survival (P less than 0.01). All six patients with extrauterine disease expired 2.3 to 53.0 months after hysterectomy. Two patients with persistence of disease expired 2.3 and 7.5 months after hysterectomy. Eleven patients developed recurrent disease 2.1 to 56.5 months after hysterectomy. All presented with distant metastases. Four of the thirteen patients with persistent or recurrent disease had no residual tumor within the myometrium.

Aged↗
PubMed1989

Assessment of pretreatment laparotomy in patients with cervical carcinoma prior to radiotherapy.

One hundred fifty-five patients with cervical cancer not amenable to radical surgery underwent selective, paraaortic lymphadenectomy and exploratory laparotomy prior to the initiation of radiotherapy. Fifty-one patients underwent transperitoneal lymphadenectomy; the remainder had the procedure performed using the extraperitoneal approach. Twenty-six patients (17%) were found to have metastatic disease to the paraaortic lymph nodes. The incidence of paraaortic metastases increased with advancing clinical stage. Twenty-four of the 26 patients were treated with extended-field radiotherapy which did not exceed 5100 cGy to the paraaortic region. Twenty-three percent of the patients with positive paraaortic nodes had documented intraperitoneal tumor. Two- and five-year actuarial survival rates for patients with paraaortic metastases were 35 and 27%, respectively. Approximately 4.6% of patients undergoing a selective paraaortic lymphadenectomy derived therapeutic benefit from the information supplied by the procedure. Using a Cox model, tumor histology, status of the paraaortic lymph nodes, tumor size, and presence of intraperitoneal disease were statistically significant prognostic factors in patient survival. Tumor size and presence of intraperitoneal disease were major predictors of patient survival.

Adenocarcinoma↗
PubMed1989

Treadmill assessment of an activity-modulated pacemaker: the importance of individual programming.

Maximum benefit from a rate-modulated pacemaker requires individualized programming of rate response settings. We tested an externally strapped activity-sensing pacemaker (Activitrax-Medtronic 8400) in eight healthy volunteers, to assess the pacing responses of the different rate response and activity threshold settings. Five males and three females, aged 20 to 70 years (mean 40), performed a total of 67 treadmill exercise tests, using a specific protocol designed to assess the activity-sensing unit. The external unit was compared to implanted units in four patients, to validate its accuracy. A reproducible sinus response to the treadmill protocol was observed, against which pacing responses were compared. The activity threshold determines the degree of activity required to elicit a pacing rate response, whereas the rate response setting determines the rate attained. Rates of 140 bpm were rarely achieved, despite vigorous exercise. The sensor responds rapidly to activity, not to physiologic demand; to increase in speed, not grade. Four patients performed repeated limited treadmill tests to determine their optimum program setting, with symptomatic status and the healthy volunteer sinus response as guides. These results, and those from the external Activitrax unit, suggest that LOW 6 and MEDIUM 6-10 settings will prove optimum for most patients.

Adult↗
PubMed1989

Clinical determinants of abnormalities in pulmonary functions in survivors of the adult respiratory distress syndrome.

Pulmonary function tests (PFTs) were performed in 39 survivors of the adult respiratory distress syndrome (ARDS) in whom clinical data had been prospectively collected during the acute episode. PFTs stabilized within 6 months of the episode and had returned to normal in most survivors. Persistent abnormalities were found after 6 months in diffusing capacity (14 of 23 patients, 61%), vital capacity (10 of 23 patients, 43%), and total lung capacity (five of 24 patients, 21%). To clarify the mechanisms underlying these persistent abnormalities, we attempted to correlate long-term PFT outcomes with estimates of the severity of initial lung injury as assessed from clinical data and with other features of the patient's course. The severity of lung function impairment during the first 3 days of ARDS was not related to long-term PFT values. However, a lower DLCO was related to a higher AaDO2, higher pulmonary artery pressure, and worse radiographic appearance on Days 4 through 7 and to the occurrence of sepsis. A lower FVC was related to higher pulmonary vascular resistance in Days 4 through 7 of ARDS. Long-term values for FVC and TLC were directly related to increasing levels of PEEP applied from Days 4 through 7 of ARDS in patients with peak airway pressures less than 50 cm H2O. Long-term abnormalities of pulmonary function of survivors of ARDS were not related to initial lung impairment but were directly related to persistence of impaired lung function during the acute episode. Recovery of lung function may also have been directly related to therapeutic modalities such as PEEP and impaired by the occurrence of sepsis.

Adolescent↗
PubMed1989

Efficacy of hyperimmune bovine colostrum for prophylaxis of cryptosporidiosis in neonatal calves.

Twelve neonatal calves were experimentally infected with oocysts of Cryptosporidium parvum. Six calves in group A fed hyperimmune colostrum at birth had significantly less diarrhea and shed oocysts for less time than did 6 calves in group B fed colostrum from cows that were not hyperimmune. Calves in group A had diarrhea for 0-4 days (means = 2.3 days), whereas calves in group B had diarrhea for 4-6 days (means = 5.0 days). Calves in group A shed oocysts for 4-9 days (means = 6.2 days), whereas calves in group B shed oocysts for 7-11 days (means = 8.5 days). These findings indicate that passive lacteal immunity conferred partial protection against cryptosporidiosis. Whether such protection was provided by the immunoglobulins that were highly elevated in the colostrum (greater than 1:200,000 for IgG1, IgM, and IgA) and constituted a large part of the circulating antibody in the calves, or by other biologically active factors, such as cytokines, is undetermined.

Animals↗
PubMed1988

Lysates of Sarcocystis cruzi bradyzoites stimulate RAW 264.7 macrophages to produce tumor necrosis factor (cachectin).

Lysate of Sarcocystis cruzi bradyzoites induced RAW 264.7 macrophages to release a factor that killed L 929 cells. Rabbit antibody to murine tumor necrosis factor (TNF) inhibited this killing effect, indicating that the factor causing cell death was similar to TNF (also called cachectin). Based on the present findings we hypothesize that TNF mediates, at least in part, the disease associated with this parasitic infection.

Animals↗
PubMed1987

Comparison of myopotential interference in unipolar-bipolar programmable DDD pacemakers.

Myopotential interference (MPI) can inhibit or trigger single and dual chamber unipolar pacemakers while bipolar pacemakers are resistant. Twenty units of two different models of dual chamber pacemaker, each capable of being programmed to single chamber or dual chamber and unipolar or bipolar function were tested to provoke myopotential interference. No patient had evidence of myopotential interference at any sensitivity setting in the bipolar configuration either in atrium or in ventricle. All patients (20/20) interfered with pacemaker function at the highest atrial or ventricular sensitivity settings in the unipolar configuration. T wave sensing occurred at the 0.25 mV sensitivity setting in four patients in pacemaker model 925, in both bipolar and unipolar configurations. Twenty-five percent of patients had myopotential interference at the unipolar atrial sensing threshold and did not allow a setting which would reject myopotential interference while providing satisfactory atrial sensing. Twenty percent (2/10) had myopotential caused ventricular inhibition at the least sensitive ventricular channel setting in model 240G so that myopotential interference could not be avoided in that unit no matter how large the electrogram.

Arrhythmias, Cardiac↗