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Biomedical subjects

R W Peters

Publications and source records attributed to R W Peters.

At least 19 recordsLinked to original sources
PubMed1995

Smoking cessation and arrhythmic death: the CAST experience. The Cardiac Arrhythmia Suppression Trial (CAST) Investigators.

OBJECTIVES: This study was performed to assess the effect of cigarette smoking cessation on overall mortality and the incidence of arrhythmic death in the population of the Cardiac Arrhythmia Suppression Trial (CAST). BACKGROUND: Cigarette smoking is a known risk factor for sudden cardiac death. Some of the adverse effects of smoking have been shown to dissipate with smoking cessation, but the time frame over which these changes occur and the population that stands to benefit have not been well delineated. CAST was a multicenter double-blind placebo-controlled study to determine whether suppression of ventricular ectopic activity by means of antiarrhythmic drugs in patients with left ventricular dysfunction after acute myocardial infarction would reduce the incidence of arrhythmic death. METHODS: Of 2,752 patients randomized to blinded therapy, 1,026 were smoking at the time of their baseline examination and completed a 4-month follow-up visit. Of these, 517 stopped smoking by the time of this visit ("quitters") and 509 continued to smoke ("smokers"). RESULTS: Over a mean follow-up period of slightly < 16 months, there were 17 arrhythmic deaths and 32 total deaths among the quitters versus 30 and 45, respectively, among the smokers; these differences were of marginal statistical significance. Most of the fatal events occurred in a group at high risk of ongoing ischemia: the 558 patients who did not have thrombolysis or undergo revascularization after their qualifying myocardial infarction. In this high risk cohort, smoking cessation greatly reduced the incidence of arrhythmic death and was associated with a statistically significant benefit in survival. CONCLUSIONS: Smoking cessation was accompanied by a marked reduction in arrhythmic death and overall mortality that achieved statistical significance in a high risk cohort. These data imply that smoking cessation is important in risk factor reduction in patients with advanced ischemic heart disease.

Aged↗
PubMed1995

Acute electrophysiologic effects of amiodarone in patients with congestive heart failure.

Patients with severe congestive heart failure (CHF) are at increased risk for atrial and ventricular arrhythmias and sudden cardiac death. Amiodarone is generally well tolerated by this population and has a low proarrhythmic potential. Because of its peculiar kinetics, amiodarone requires a prolonged loading period, necessitating lengthy hospitalizations in a monitored setting. This study was planned prospectively to assess the electrophysiologic effects of an abbreviated high-dose oral load of amiodarone in patients with severe CHF and known or suspected life-threatening ventricular arrhythmias. Fifteen patients with stable CHF and known or suspected life-threatening ventricular arrhythmias underwent baseline electrophysiologic study. The study was repeated after administration of oral amiodarone, 50 mg/kg/day for 2 days in 8 divided doses (mean dose 6.9 +/- 0.4 g). After amiodarone administration, there was prolongation in virtually all conduction times and refractory periods. The prolongation of refractoriness was most pronounced in the atrium. Ventricular effective refractory periods demonstrated reverse frequency dependence. We conclude that a brief high-dose oral load of amiodarone is well tolerated by patients with CHF. It has marked and diffuse electrophysiologic actions suggestive of class I and III effects in addition to antiadrenergic and calcium blocking action. These effects are especially pronounced in the atrium.

Administration, Oral↗
PubMed1995

Spurious discharges due to late insulation break in endocardial sensing leads for cardioverter defibrillators.

Despite their similarity to permanent pacemaker leads, endocardial sensing leads for cardioverter defibrillators have a relatively high failure rate. We describe four patients with endocardial rate sensing leads who developed inappropriate discharges 10-30 months after implantation due to small breaks in the lead insulation. This problem may become increasingly common as the number of cardioverter defibrillator implants with transvenous leads continues to grow and should be considered in the differential diagnosis of late sensing failure or inappropriate device discharges.

Aged↗
PubMed1995

Effects of level and frequency on the detection of decrements and increments in sinusoids.

Thresholds for the detection of decrements in level of sinusoidal signals were measured as a function of decrement duration, level (25, 40, 55, and 70 dB SPL) and frequency (250, 1000, and 4000 Hz) in eleven normally hearing subjects. Thresholds for detecting a brief increment in level were also measured. The sinusoids were presented in a background noise intended to mask spectral splatter associated with the decrement or increment. Performance tended to worsen with decreasing frequency, for all decrement durations and for increment detection. Performance also worsened with decreasing level. The results were analyzed using a model consisting of a compressive nonlinearity, a sliding temporal integrator, and a decision device. The analysis indicated that the worsening in performance with decreasing frequency and decreasing level can be attributed partly to increases in the equivalent rectangular duration (ERD) of the temporal integrator, but mainly to changes in the efficiency of the detection process following the temporal integrator; at lower frequencies and levels a larger change is required at the output of the integrator for threshold to be reached. At each frequency, the ERD was relatively invariant with level for levels more than about 20 dB above the absolute threshold.

Adult↗
PubMed1994

Overdrive pacing for atrial flutter.

To determine the incidence and predictors of conversion to normal sinus rhythm, a total of 124 procedures using a standard pacing protocol were performed in 101 consecutive inpatients referred for pace termination of atrial flutter. Normal sinus rhythm was achieved in 75 pace termination procedures (60%), including 10 in which atrial fibrillation occurred initially and later converted spontaneously. Sustained atrial fibrillation was provoked in 39 procedures, and atrial flutter persisted in 10. Clinical and laboratory parameters, including use of antiarrhythmic drugs, were not helpful in predicting the outcome of pacing. Of 17 patients undergoing repeat pacing for recurrent flutter, concordant results were obtained in only 4. It is concluded that: (1) overdrive pacing is only a moderately effective means of restoring sinus rhythm in patients with atrial flutter, although some change in rhythm occurs in the vast majority; (2) pacing-induced atrial fibrillation may be unstable and spontaneously converts to sinus rhythm in > 20% of cases; (3) there are no clinically useful predictors of success; (4) antiarrhythmic drugs do not facilitate pacing-induced conversion to sinus rhythm; and (5) failure to convert to sinus rhythm with 1 episode of flutter does not preclude success on subsequent occasions.

Aged↗
PubMed1994

High dose oral amiodarone loading exerts important hemodynamic actions in patients with congestive heart failure.

OBJECTIVES: The purpose of this study was to use invasive monitoring to analyze the hemodynamic effects of both a large single dose and a 48-h loading regimen of amiodarone in patients with severe heart failure. BACKGROUND: Amiodarone is frequently used as an antiarrhythmic agent in patients with congestive heart failure, but the impact of this agent on cardiac function remains controversial. Recent successful experience with a rapid oral load of amiodarone makes invasive testing of the hemodynamic effects of oral amiodarone in such patients now feasible. METHODS: After baseline hemodynamic assessment (using balloon-tipped pulmonary artery catheters) and electrocardiographic measurements, 16 patients received 12.5 mg/kg body weight of amiodarone orally. Hemodynamic measurements were obtained hourly for 4 h. Patients then received this dose an additional seven times over the next 2 days. Hemodynamic variables and QRS, QT and PR intervals were measured after 48 h of treatment. RESULTS: Vasodilation was seen between 1 and 3 h after drug administration. Systemic vascular resistance decreased 326 +/- 135 dynes.s.cm-5, cardiac index increased 0.24 +/- 0.08 liters/min per m2 and mean arterial pressure decreased 6 +/- 3 mm Hg (mean +/- SEM, all p < 0.05). After 48 h of amiodarone administration, heart rate decreased 23 +/- 3 beats/min (p < 0.005), stroke volume increased 9 +/- 3 ml (p < 0.005), cardiac index decreased 0.23 +/- 0.09 ml/min per m2 (p < 0.05), pulmonary capillary wedge pressure increased 4 +/- 1 mm Hg (p < 0.01), right atrial pressure increased 3 +/- 1 mm Hg (p < 0.005) and QT and PR intervals were markedly prolonged (p < 0.01). CONCLUSIONS: Although the first dose caused vasodilation, a complete loading regimen of amiodarone produced a decreased heart rate with elevated filling pressures and decreased cardiac index.

Administration, Oral↗
PubMed1994

Masking level differences for tones and speech in elderly listeners with relatively normal audiograms.

This study measured the masking level difference (MLD) for both 500-Hz tone detection and spondee word recognition in two groups of listeners. One group consisted of 9 elderly listeners with normal audiometric sensitivity bilaterally, up to at least 2000 Hz. The other group was a control group of 10 young listeners with normal hearing. The intent was to determine whether the elderly listeners exhibited a reduction in binaural performance that might contribute to the difficulties many such listeners have in understanding speech in noisy situations. By measuring MLDs in elderly listeners in the absence of marked peripheral hearing loss, it was hoped that any observed changes in MLD could be more strongly attributed to central effects. For both tone detection and speech recognition, it was found that the elderly performed more poorly than the young listeners, primarily on the NoS pi condition.

Acoustic Stimulation↗
PubMed1994

Comodulation masking release for elderly listeners with relatively normal audiograms.

Thresholds for the detection of a 1.0-kHz pure tone were measured in modulated and unmodulated noise for a group of nine elderly listeners, aged 62-83, with normal or near-normal audiograms, and a reference group of seven younger normal-hearing listeners. The masker was either a band of noise 128 Hz wide [approximately one equivalent rectangular bandwidth (ERB) centered at 1.0 kHz], or a band of noise 1505 Hz wide (approximately five ERBs above and five ERBs below 1.0 kHz). The noise was either unmodulated or was square-wave modulated at rates of 10, 20, 30, 40, and 50 Hz. A measure of comodulation masking release (CMR) was derived from the masking data. Because wider filters have been found to be associated with reduced CMR, auditory filter shapes were also estimated for the elderly listeners. The filters were found to be normal at the center frequencies of 800, 1000, and 2000 Hz ruling out possible confounding effects of impaired auditory filters on CMR. Masked detection thresholds were generally significantly higher for the elderly as compared to the younger listeners for both unmodulated and modulated noise. Thresholds were lower in modulated as compared to unmodulated noise masking for both elderly and young listeners. For both groups of listeners and for both narrow- and wideband masking, detection thresholds continued to increase as modulation rates were increased. CMR was not different for the elderly and young listeners and it was similarly decreased, for both groups, at higher rates of modulation.

Adult↗
PubMed1993

Ischemically mediated sustained monomorphic ventricular tachycardia. Resolution with anti-ischemic therapy.

We describe a patient with ischemically mediated sustained monomorphic ventricular tachycardia occurring at rest and resistant to treatment with intravenously administered procainamide. Percutaneous transluminal coronary angioplasty was initially successful, but rest angina and ventricular tachycardia, resistant to procainamide therapy, recurred 2 weeks later and responded to aggressive anti-ischemic medical therapy. We suggest that anti-ischemic medication may be of benefit in patients with malignant ventricular arrhythmias precipitated by spontaneous myocardial ischemia.

Coronary Angiography↗
PubMed1992

Effects of left ventricular dysfunction on the circadian variation of ventricular premature complexes in healed myocardial infarction.

Circadian variation in the onset of cardiovascular events including sudden cardiac death, myocardial infarction and ventricular arrhythmias has been described. The effect of left ventricular (LV) dysfunction on the circadian variation of ventricular premature complex (VPC) frequency was evaluated in 132 patients with frequent VPCs and reduced LV function after myocardial infarction. Patients were prospectively divided in 2 groups based on LV ejection fraction (EF) (those with LVEF less than or equal to 0.30, and those with LVEF between 0.30 and 0.45). Median hourly VPC frequencies and heart rates were compared between the 2 groups. Subgroup analyses based on treatment with beta-adrenoceptor blocking agents and on New York Heart Association functional class were also performed. In patients with LVEF greater than 0.30, a distinct circadian variation of VPCs, and the expected morning increase in VPC frequency were present. In contrast, a distinct circadian variation of VPCs was absent in patients with LVEF less than or equal to 0.30. A circadian variation of VPC frequency was also absent in patients with severe symptomatic congestive heart failure (New York Heart Association class III-IV). Treatment with beta-adrenoceptor blocking agents was associated with a loss of the circadian variation of VPC frequency. The circadian variation of heart rate was also blunted in the group treated with beta-adrenoceptor blocking agents. The proportion of subjects manifesting a positive correlation between heart rate and VPC frequency was lower in subjects with LVEF less than or equal to 0.30 (26%) than in those with LVEF greater than 0.30 (46%) (p less than 0.05). Thus, circadian variation of VPC frequency is absent in patients with severe LV dysfunction.

Adrenergic beta-Antagonists↗
PubMed1992

Auditory filter shapes at low center frequencies in young and elderly hearing-impaired subjects.

Auditory filter shapes were measured for two groups of hearing-impaired subjects, young and elderly, matched for audiometric loss, for center frequencies (fc) of 100, 200, 400, and 800 Hz using a modified notched-noise method [B. R. Glasberg and B. C. J. Moore, Hear. Res. 47, 103-138 (1990)]. Two noise bands, each 0.4fc wide, were used; they were placed both symmetrically and asymmetrically about the signal frequency to allow the measurement of filter asymmetry. The overall noise level was either 77 or 87 dB SPL. Stimuli were delivered monaurally using Sennheiser HD424 earphones. Although auditory filters for the hearing-impaired subjects were generally broader than for normally hearing subjects [Moore et al., J. Acoust. Soc. Am. 87, 132-140 (1990)], some hearing-impaired subjects with mild losses had normal filters. The filters tended to broaden with increasing hearing loss. There were not any clear differences in filter characteristics between young and elderly hearing-impaired subjects. The signal-to-noise ratios at the outputs of the auditory filters required for threshold (K) tended to be lower than normal for the young hearing-impaired subjects, but were not significantly different from normal for the elderly hearing-impaired subjects. The lower K values for the young hearing-impaired subjects may occur because broadened auditory filters reduce the deleterious effects on signal detection of fluctuations in the noise.

Adult↗
PubMed1992

Pitch discrimination and phase sensitivity in young and elderly subjects and its relationship to frequency selectivity.

Frequency difference limens for pure tones (DLFs) and for complex tones (DLCs) were measured for four groups of subjects: young normal hearing, young hearing impaired, elderly with near-normal hearing, and elderly hearing impaired. The auditory filters of the subjects had been measured in earlier experiments using the notched-noise method, for center frequencies (fc) of 100, 200, 400, and 800 Hz. The DLFs for both impaired groups were higher than for the young normal group at all fc's (50-4000 Hz). The DLFs at a given fc were generally only weakly correlated with the sharpness of the auditory filter at that fc, and some subjects with broad filters had near-normal DLFs at low frequencies. Some subjects in the elderly normal group had very large DLFs at low frequencies in spite of near-normal auditory filters. These results suggest a partial dissociation of frequency selectivity and frequency discrimination of pure tones. The DLCs for the two impaired groups were higher than those for the young normal group at all fundamental frequencies (fo) tested (50, 100, 200, and 400 Hz); the DLCs for the elderly normal group were intermediate. At fo = 50 Hz, DLCs for a complex tone containing only low harmonics (1-5) were markedly higher than for complex tones containing higher harmonics, for all subject groups, suggesting that pitch was conveyed largely by the higher, unresolved harmonics. For the elderly impaired group, and some subjects in the elderly normal group, DLCs were larger for a complex tone with lower harmonics (1-12) than for tones without lower harmonics (4-12 and 6-12) for fo's up to 200 Hz. Some elderly normal subjects had markedly larger-than-normal DLCs in spite of near-normal auditory filters. The DLCs tended to be larger for complexes with components added in alternating sine/cosine phase than for complexes with components added in cosine phase. Phase effects were significant for all groups, but were small for the young normal group. The results are not consistent with place-based models of the pitch perception of complex tones; rather, they suggest that pitch is at least partly determined by temporal mechanisms.

Adult↗
PubMed1992

Detection of temporal gaps in sinusoids by elderly subjects with and without hearing loss.

Thresholds for the detection of temporal gaps in sinusoidal signals were measured as a function of frequency (100-2000 Hz) and level in 15 elderly hearing-impaired subjects and 11 elderly subjects with near-normal hearing at frequencies below 2000 Hz. The sinusoids were presented in a background noise intended to mask spectral splatter associated with the gap. In a separate experiment, auditory filter shapes and detection efficiency were estimated for the same subjects using the notched-noise method, at center frequencies of 100, 200, 400, and 800 Hz. The gap thresholds at higher signal levels were similar for the two groups of subjects at all center frequencies tested. The mean gap thresholds were slightly higher than those obtained previously from young normally hearing subjects, but this was mainly due to the results of a few subjects with large gap thresholds; the majority of the elderly subjects had gap thresholds within the normal range. Thus reduced temporal resolution does not seem to be an inevitable consequence of aging. Gap thresholds at low center frequencies tended to be positively correlated with the equivalent rectangular bandwidth (ERB) of the auditory filter, the opposite of what would be expected if the auditory filter played a role in limiting gap detection. Detection efficiency, as estimated from the notched-noise experiment, was poorer for both groups of elderly subjects than for young normal listeners, but detection efficiency was not significantly correlated with gap thresholds.

Aged↗
PubMed1991

Mortality and morbidity in patients receiving encainide, flecainide, or placebo. The Cardiac Arrhythmia Suppression Trial.

BACKGROUND AND METHODS: In the Cardiac Arrhythmia Suppression Trial, designed to test the hypothesis that suppression of ventricular ectopy after a myocardial infarction reduces the incidence of sudden death, patients in whom ventricular ectopy could be suppressed with encainide, flecainide, or moricizine were randomly assigned to receive either active drug or placebo. The use of encainide and flecainide was discontinued because of excess mortality. We examined the mortality and morbidity after randomization to encainide or flecainide or their respective placebo. RESULTS: Of 1498 patients, 857 were assigned to receive encainide or its placebo (432 to active drug and 425 to placebo) and 641 were assigned to receive flecainide or its placebo (323 to active drug and 318 to placebo). After a mean follow-up of 10 months, 89 patients had died: 59 of arrhythmia (43 receiving drug vs. 16 receiving placebo; P = 0.0004), 22 of nonarrhythmic cardiac causes (17 receiving drug vs. 5 receiving placebo; P = 0.01), and 8 of noncardiac causes (3 receiving drug vs. 5 receiving placebo). Almost all cardiac deaths not due to arrhythmia were attributed to acute myocardial infarction with shock (11 patients receiving drug and 3 receiving placebo) or to chronic congestive heart failure (4 receiving drug and 2 receiving placebo). There were no differences between the patients receiving active drug and those receiving placebo in the incidence of nonlethal disqualifying ventricular tachycardia, proarrhythmia, syncope, need for a permanent pacemaker, congestive heart failure, recurrent myocardial infarction, angina, or need for coronary-artery bypass grafting or angioplasty. CONCLUSIONS: There was an excess of deaths due to arrhythmia and deaths due to shock after acute recurrent myocardial infarction in patients treated with encainide or flecainide. Nonlethal events, however, were equally distributed between the active-drug and placebo groups. The mechanisms underlying the excess mortality during treatment with encainide or flecainide remain unknown.

Actuarial Analysis↗
PubMed1991

A recombinant fowlpox virus that expresses the VP2 antigen of infectious bursal disease virus induces protection against mortality caused by the virus.

The coding sequences of VP2 from a virulent strain, 52/70, of infectious bursal disease virus (IBDV) were excised from a cDNA clone and inserted into a fowlpox plasmid insertion vector. The resulting plasmid, pIBD 1, was used to construct a recombinant fowlpox virus, fpIBD 1, which expressed VP 2 as a beta-galactosidase fusion protein. Chickens vaccinated with fpIBD 1 at 1 and 14 days of age, were challenged at 28 days with either IBDV strain 52/70 or the highly virulent strain CS 89. These chickens were protected against mortality, but not against damage to the bursa of Fabricius. The protection achieved by the use of fpIBD 1 shows that VP 2 is a host protective antigen.

Amino Acid Sequence↗
PubMed1990

Propranolol and the morning increase in sudden cardiac death: (the beta-blocker heart attack trial experience).

To provide insight into the protective effect of propranolol on mortality after myocardial infarction observed in the beta-Blocker Heart Attack Trial, the time of occurrence of sudden cardiac death was examined in this population. Between 5 A.M. and 11 A.M., 25 of the 56 total deaths (38%) occurred in the placebo patients compared with 11 of 45 (24%) in the propranolol patients. Excluding this period, there were nearly equal numbers of sudden cardiac deaths in the propranolol and placebo groups. This retrospective analysis suggests that beta blockade is protective during the morning hours when a surge of sympathetic activity may increase the risk of sudden cardiac death.

Adult↗
PubMed1990

A recombinant fowlpox virus expressing the hemagglutinin-neuraminidase gene of Newcastle disease virus (NDV) protects chickens against challenge by NDV.

The hemagglutinin-neuraminidase (HN) gene from the Beaudette C strain of Newcastle disease virus (NDV) has been expressed in a recombinant fowlpox virus vector. The HN gene, under the control of the vaccinia p7.5 promoter, was inserted into a nonessential gene in the terminal inverted repeats of fowlpox virus. Expression was demonstrated in tissue culture, a protein of the correct size for fully glycosylated HN protein being recognized by an HN-specific monoclonal antibody on Western blots. When the recombinant fowlpox virus was inoculated into chickens by intravenous or wing-web routes, antibody which recognizes HN from purified NDV virions was produced. Protective immunity to NDV was generated in the chickens; at the highest dose of vaccine 100% of the chickens tested were protected against challenge with a virulent strain of NDV.

Animals↗