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Biomedical subjects

T Simmons

Publications and source records attributed to T Simmons.

At least 19 recordsLinked to original sources
PubMed1992

Effect of atrioventricular synchrony on stroke volume during ventricular tachycardia in man.

The hemodynamic consequences of atrioventricular (AV) synchrony during ventricular tachycardia were evaluated during cardiac electrophysiologic testing. The relationship between stroke volume and the AV interval was investigated on a beat-by-beat basis in six patients during induced monomorphic ventricular tachycardia. Stroke volume was calculated either (1) in the right ventricle using impedance catheter method (four patients) or (2) in the left ventricle using Doppler measurement of aortic blood velocity (two patients). The impedance catheter method underestimated stroke volume by a factor of 4.2 +/- 2.4 compared with the thermodilution cardiac output method. However, there was a highly linear relationship between both methods for computing stroke volume (r greater than 0.9). Five patients had complete AV dissociation during ventricular tachycardia, and different AV intervals spanned the entire tachycardia cycle lengths. Largest stroke volumes were associated with optimal AV intervals within 120 and 230 msec, resulting in a 97 +/- 59% increase in stroke volume over ventricular tachycardia cycles not associated with atrial activity. Customized atrial pacing during ventricular tachycardia may provide a valuable means for artificially establishing the hemodynamically optimal AV interval and eliminating the ventricular tachycardia cycles not preceded by atrial activity.

Atrioventricular Node↗
PubMed1992

Pacing lead survival: performance of different models.

UNLABELLED: Recent reports have shown poor survival of some leads currently in use. Long-term survival analysis of 2,444 leads (1,059 atrial and 1,385 ventricular) implanted in this institution since January 1980, and having at least 1 month of follow-up was performed. The survival of 123 different models was compared with the average survival of all the leads implanted in the corresponding chamber. Failure was defined as inactivation of the lead (electrical abandonment, explant, or cap) due to insulator and/or conductor fracture. RESULTS: The mean follow-up was 33 +/- 32 months. The cumulative survival for different atrial lead models was consistent with the average performance in the atrium. No atrial lead showed better or worse survival compared to the others. In the ventricular group, the Medtronic 4012 lead showed statistically significant poorer survival (P = 0.01) compared with the average survival of the ventricular leads. The Cardiac Pacemakers, Inc. (CPI) 4010 lead showed a nonsignificant (P = 0.12) worse performance than the average for ventricular leads. CONCLUSIONS: (1) The Medtronic 4012 had a significantly poorer performance than the rest of the leads. A trend in similar direction was found for the CPI 4010, also in the ventricular group; (2) Atrial lead models showed a stable survival; and (3) Frequent follow-up is required for some leads, especially in pacemaker dependent patients.

Actuarial Analysis↗
PubMed1991

Automatic implantable cardioverter-defibrillator implantation without thoracotomy using an endocardial and submuscular patch system.

The automatic cardioverter-defibrillator lead system is implanted by a thoracotomy procedure that may result in atelectasis, pleural effusion, cardiac tamponade and lengthy convalescence. A new defibrillator lead system that allows selection of different defibrillating current pathways is implanted without a thoracotomy. Ten patients requiring a cardioverter-defibrillator for recurrent sustained ventricular tachycardia (five patients) or aborted sudden cardiac death (five patients) were evaluated for implantation of this lead system. A lead configuration with a bidirectional defibrillating current pathway was implanted in nine patients. The defibrillation threshold with this lead configuration was 15 J in five patients, 20 J in three and 30 to 35 J in one patient. In the remaining patient the lead system had a 40 J defibrillation threshold and was not implanted. No perioperative complications occurred. Induced ventricular fibrillation was successfully terminated at the predischarge and intermediate follow-up (8 to 12 weeks) electrophysiologic studies. During the follow-up period, there were three deaths (one sudden, two due to heart failure) and two lead system failures (oversensing with inappropriate shocks in one patient and patch lead fracture in another). Implantation of the cardioverter-defibrillator lead system by a nonthoracotomy approach is feasible, has no significant perioperative complications and is well tolerated by patients. Effective defibrillation was demonstrated immediately as well as at intermediate follow-up study. The occurrence of patch lead fracture and oversensing requires improvement in the present (nonthoracotomy) lead system technology.

Cardiac Pacing, Artificial↗
PubMed1991

Clinical performance of the implantable cardioverter defibrillator: electrocardiographic documentation of 101 spontaneous discharges.

Records of 105 patients, who received an automatic implantable cardioverter defibrillator (AICD), were studied to investigate the causes of spontaneous AICD discharges and to correlate the symptoms with the arrhythmias triggering AICD discharges. During a follow-up period of 13 +/- 8 months, 46/105 (44%) patients had 566 spontaneous AICD discharges. A total of 101 discharges were documented with Holter monitoring in 23 patients. In this study group, there were 8 (8%) AICD discharges for 5 episodes of ventricular fibrillation, and 68 (67%) discharges for 63 episodes of sustained ventricular tachycardia. Patients lost consciousness in all episodes of ventricular fibrillation, but were symptomatic prior to only 36 (53%) discharges in ventricular tachycardia. Nonsustained ventricular tachycardia persisting for a period of 7.5 +/- 2 seconds resulted in 20 AICD discharges; patients were symptomatic prior to 13 (65%) discharges. Supraventricular tachycardias triggered three discharges. One patient had two spurious discharges during sinus rhythm. In conclusion, most of the spontaneous AICD discharges were appropriate for the detected rhythms, but only clinically appropriate for the management of arrhythmias in 75% of the cases. A significant portion of the patients with sustained or nonsustained ventricular tachycardias triggering AICD discharges were asymptomatic prior to discharge, which requires further assessment of the physiology of the arrhythmia as a component of the detection algorithm.

Electric Countershock↗
PubMed1990

The effects of percutaneous catheter ablation on preexisting permanent pacemakers.

STUDY OBJECTIVE: Determine the effect of percutaneous catheter ablation (CA) on permanent pacemakers. MEASUREMENTS AND RESULTS: Twenty-three patients who underwent CA at The Cleveland Clinic Foundation from September 1983 to January 1990, and had a previously implanted pacemaker were studied. Electrocardiographic data during the CA procedure and clinic data including pacemaker evaluations were analyzed. Fifty-two percent (12/23) of the pacemakers malfunctioned: five developed transient ventricular loss of capture; two undersensing; one oversensing; three could not be interrogated or programmed, and one did not respond to the magnet test. Four patients developed syncopal episodes and two severe dizziness after the procedure. All had their pacemakers replaced. In total, seven were explanted. Destructive analysis by the individual manufacturer identified pacemaker circuitry failure in five. Unipolar pacemakers and anodal ablation procedures had more frequent and severe malfunctions, but the difference was not statistically significant. CONCLUSIONS: Pacemaker malfunction is frequent during CA. It may be prevented by programming the pacemaker, when possible, to the nonfunctioning mode (000 mode). Temporarily disconnecting the pacemaker during ablation requires further evaluation as an alternative approach. Close follow-up can detect pacemaker malfunction and prevent complications.

Adult↗
PubMed1990

Stature estimation from fragmentary femora: a revision of the Steele method.

The skeletal remains presented to forensic anthropologists are often fragmentary. Previously described methods of estimating stature from segments of long bones have not proved satisfactory because of the difficulty involved in identifying the precise anatomical landmarks by which they are defined. This study represents an assessment of the feasibility of stature estimation from fragmentary femora. A sample of 200 males and females, blacks and whites (total sample = 800), was obtained from the Terry Collection. New regression equations for the estimation of maximum femur length and stature from three well-defined and easy-to-measure segments of the femur are presented. This technique represents an improvement over methods currently in use for estimating stature from femur fragments; the location of the anatomical landmarks and the accuracy of the prediction are enhanced. The applicability of these formulae to a modern forensic sample is addressed with regard to secular trends in stature increase and changes in body segment proportions.

Anthropology, Physical↗
PubMed1989

Continuous right ventricular volume assessment by catheter measurement of impedance for antitachycardia system control.

Current implantable defibrillators are unable to differentiate between hemodynamically stable and unstable arrhythmias. This may result in unnecessary high energy shocks during arrhythmias that are better managed with other interventions. This study assessed the efficacy of the impedance catheter in sensing relative volumetric changes in the right ventricle as a measure of the hemodynamic status during an arrhythmia. During electrophysiological testing, 37 arrhythmias were induced in 12 patients aged 28-74 years. Rhythms recorded were: (A) hemodynamically stable tachyarrhythmias (supraventricular tachycardia and sustained monomorphic ventricular tachycardia)--21 episodes; and (B) hemodynamically unstable ventricular arrhythmias causing syncope (hypotensive ventricular tachycardia and ventricular fibrillation)--16 episodes. During unstable arrhythmias, stroke impedance (32 +/- 17%), arterial systolic pressure (40 +/- 11%), and right ventricular pulse pressure (15 +/- 20%), expressed as percentages of corresponding sinus rhythm values, were significantly lower than in stable arrhythmias (84 +/- 26%, 72 +/- 8%, and 111 +/- 37%, respectively); P less than 0.001. There was a good correlation between stroke impedance and mean arterial pressure during arrhythmia (r = 0.84). Impedance sensing is a practical method for distinguishing between hemodynamically stable and unstable arrhythmias. Implementation of hemodynamic sensing into the algorithm of future antitachycardia systems may improve the management of arrhythmias by adding options for selective pace termination or cardioversion.

Adult↗
PubMed1988

Effects of extracorporeal shock wave lithotripsy on cardiac pacemakers and its safety in patients with implanted cardiac pacemakers.

UNLABELLED: Effects of extracorporeal shock wave lithotripsy (ESWL) were studied on 15 pacemakers (standard single chamber n = 5, dual chamber n = 6, rate responsive single chamber [Activitrax] n = 4). In-vitro testing involved suspending the pacemakers in a bath of degassified, deionized water firmly taped to a platform at the point of maximal pressure, i.e., second focal point (F2), where they received pressure shocks (means = 1300) from the HM3 Dornier lithotriptor. The pacemakers, programmed to their most sensitive setting, were continuously pacing at nominal outputs (atrial and ventricular pacing in the DDD mode). All units were assessed by a pacing system analyzer before and after the study, then underwent destructive analysis. During standard single chamber pacing (VVI) the pacing stimulus triggered ESWL. For dual chamber devices, ESWL was triggered by the atrial paced event which induced inhibition of the ventricular output in two pacemaker. This was eliminated by reprogramming to a less sensitive setting. The pacemaker can, hermetic seal and internal circuitry were undamaged in all units. Two rate responsive single chamber pacemakers had their activity sensing piezoelectric elements shattered when placed at F2. Two other units placed 5 cm from F2 were stimulated to their maximum upper programmed pacing rate with ESWL therapy, but were otherwise unaffected. Subsequent to this study, six patients with pacemakers programmed to the VVI (five), DDD (one) modes implanted in the thorax underwent successful ESWL without pacemaker or arrhythmic event. CONCLUSIONS: (A) It is generally safe for patients implanted with standard single chamber devices in a ventricular application to undergo ESWL without modifying the pacing/sensing parameters. (B) Patients implanted with dual chamber devices who pace in the atrium should be reprogrammed to the VVI mode during ESWL. (C) Patients with piezoelectric activity sensing rate responsive single chamber pacemakers should have this feature programmed off during ESWL and, if implanted in the abdomen, probably should not undergo ESWL.

Aged↗
PubMed1988

Genetic analysis of small nuclear RNAs in Saccharomyces cerevisiae: viable sextuple mutant.

Saccharomyces cerevisiae contains at least 24 distinct small nuclear RNAs (snRNAs), several of which are known to be essential for viability and to participate in the splicing of pre-mRNAs; the RNAs in this subset contain binding sites for the Sm antigen, a hallmark of metazoan snRNAs involved in mRNA processing. In contrast, we showed previously that the single-copy genes for three other snRNAs (snR3, snR4, and snR10) are not required for viability, although cells lacking snR10 are growth impaired at low temperature. None of these RNAs associates with the Sm antigen. To assess this apparent correlation, we cloned and sequenced the genes encoding three additional non-Sm snRNAs. Comparison of these genes with nine additional yeast snRNA genes revealed a highly conserved TATA box located 92 +/- 8 nucleotides 5' of the transcriptional start site. By using the technique of gene replacement with null alleles, each of these three single copy genes was shown to be completely dispensable. We constructed multiple mutants to test the hypothesis that, individually, each of these snRNAs is nonessential because the snRNAs play functionally overlapping roles. A mutant lacking five snRNAs (snR3, snR4, snR5, snR8, snR9) was indistinguishable from the wild type, and growth of the sextuple mutant was no more impaired than that in strains lacking only snR10. This widespread dispensability of snRNAs was completely unexpected and forces us to reconsider the possible roles of these ubiquitous RNAs.

Base Sequence↗
PubMed1987

Right lower quadrant pain in the immunocompromised patient: CT findings in 10 cases.

Ten immunosuppressed patients with right lower quadrant pain were examined by CT. Underlying conditions responsible for immunosuppression included acute myelogenous leukemia (n = 2), acute lymphocytic leukemia (n = 2), aplastic anemia (n = 2), AIDS (n = 3), and cystic fibrosis combined with prolonged steroid therapy for bronchospasm (n = 1). CT suggested the diagnosis of typhlitis (n = 7), intramural hemorrhage (n = 1), ileal perforation (n = 1), and appendiceal abscess (n = 1). The diagnosis of typhlitis was established by clinical evaluation in five patients, by colonoscopy in one patient, and by autopsy in another patient. The single cases of intestinal hemorrhage, ileal perforation, and appendiceal abscess were confirmed by exploratory laparotomy. It is difficult to make an accurate diagnosis of acute abdominal conditions in the immunosuppressed patient. Symptoms and physical findings are often suppressed as a result of steroid or immunosuppressive therapy. CT, being noninvasive, is useful in the evaluation of persistent right lower quadrant pain in the immunocompromised patient.

Adolescent↗
PubMed1986

Electrode configurations for a respiratory impedance measurement suitable for rate responsive pacing.

A rate responsive cardiac pacemaker will benefit the patient only if the input parameter is a reliable indicator of exercise. Part of the reliability is dependent upon selection of the best physiological parameter and part is dependent upon the measurement technique. Twenty-six patients have been studied in order to ascertain the best measurement configuration for an intravascular impedance respiratory monitor. Four electrode configurations have been examined at rest and during exercise. The results have been compared using measures of sensitivity and specificity. The ideal configuration requires that a current field be established between the right ventricular blood and the pacemaker case. And, that voltage sensing be done between an electrode in the SVC and the pacemaker case.

Electrodes↗
PubMed1978

Uptake and early fate of metaphase chromosomes ingested by the Wi-L2 human lymphoid cell line.

Aspects of the ingestion and early intracellular fate of homologous. [3H]-thymidine-labeled chromosomes (donor) were studied in recipient Wi-L2 cells in the absence of reutilized radioactivity. As much as 67% of the cell-associated radioactivity was resistant to hydrolysis by DNase I after 4 h of incubation. Cell fractionation and electron microscope autoradiography indicated that chromosome uptake was rapid, into both cytoplasmic and nuclear fractions and was facilitator and dose dependent. Sedimentation analysis demonstrated that at 4 h donor DNA of approximate single-strand mol wt of 1--6 X 10(6), as compared to 6--12 X 10(6) for chromosomal DNA, was recoverable in cell fractions. By 6 h, a significant portion of the nucleus-associated donor DNA was converted into material of higher mol wt, although no evidence was found for integration into recipient DNA. Cytoplasmic donor DNA continued to be degraded. An average number of chromosome equivalents of nucleus-associated donor DNA to recipient cell nuclei of 1--4 was obtained and its relationship to the lower frequency of chromosome-mediated gene transfer is discussed.

Cells, Cultured↗
PubMed1975

Rectal diverticula.

Eight cases of rectal diverticula are discussed with reference to the etiological, clinical and radiological findings. Males predominated 3:1 and the average number of diverticula in each patient was 2. Diverticulosis of the remaining colon, especially the sigmoid segment, always accompanied rectal diverticula. The average diameter of rectal diverticula was larger than that of the colonic: 2.5 cm vs. 0.5-1.0 cm. Rectal diverticula may be confused with a carcinoma at endoscopy. Surgical treatment becomes necessary if the diverticulum progresses to abscess formation and perforation.

Aged↗
PubMed1973

Nuclear envelope-associated resumption of RNA synthesis in late mitosis of HeLa cells.

The restitution of RNA synthesis in cultures progressing from metaphase into interphase (G(1)) has been investigated in synchronized HeLa S(3) cells by using inhibitors of macro-molecular synthesis and the technique of electron microscope autoradiography. The rate of incorporation of radioactive uridine into RNA approached interphase levels in the absence of renewed protein synthesis. In contrast, maintenance of this rate in G(1) was dependent upon renewed protein synthesis. Restoration of synthesis of heterogeneous nuclear RNA occurred under conditions that inhibited production of ribosomal precursor RNA. In autoradiographs of individual cells exposed to radioactive uridine, silver grains were first detected after nuclear envelope reformation at the periphery of the chromosome mass but before chromosomal decondensation. These data are consistent with the following interpretation. Multiple RNA polymerase activities persist through mitosis and are involved in the initiation of RNA synthesis in early telophase at sites on the nuclear envelope.

Autoradiography↗