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Biomedical subjects

W D Toff

Publications and source records attributed to W D Toff.

17 recordsLinked to original sources
PubMed2004

Dual chamber versus single chamber ventricular pacemakers for sick sinus syndrome and atrioventricular block.

BACKGROUND: Dual chamber pacing or single chamber atrial pacing ('physiologic' pacing) is believed to have an advantage over single chamber ventricular pacing in that it resembles cardiac physiology more closely by maintaining atrioventricular (AV) synchrony and dominance of the sinus node, which in turn may reduce cardiovascular morbidity and mortality thus contributing to patient survival and quality of life. However, a significant proportion of pacemakers currently implanted are single chamber ventricular pacemakers. OBJECTIVES: The objective of this review was to assess the short- and long-term clinical effectiveness of dual chamber pacemakers compared to single chamber ventricular pacemakers in adults with AV block, sick sinus syndrome or both. An additional objective was to assess separately any potential differences in effectiveness between dual chamber pacing and single chamber atrial pacing. The clinical effectiveness of single chamber atrial pacing versus single chamber ventricular pacing was not examined. SEARCH STRATEGY: The Cochrane Controlled Trials Register (The Cochrane Library Issue 3, 2002), MEDLINE (1966 to 2002), EMBASE (1980 to 2002) and the Science Citation Index (1980 to 2002) were searched on 19th August 2002. Citation lists and web sites were checked and researchers in the field contacted. SELECTION CRITERIA: Parallel group or crossover randomised controlled trials of at least 48 hours duration comparing dual chamber pacing and single chamber ventricular pacing, and investigating cardiovascular morbidity, mortality, patient related quality of life, exercise capacity and complication rates. DATA COLLECTION AND ANALYSIS: Data was extracted onto pre-piloted data extraction forms. Quality assessment was undertaken using a checklist, with a sub-sample of quality data independently extracted by a second reviewer. Where appropriate data was available, meta-analysis was performed. Where meta-analysis was not possible, the number of studies showing a positive, neutral or negative direction of effect and statistical significance were simply counted. MAIN RESULTS: Five parallel and 26 crossover randomised controlled trials were identified. The quality of reporting was found to be poor. Pooled data from parallel studies shows a statistically non-significant preference for physiologic pacing (primarily dual chamber pacing) for the prevention of stroke, heart failure and mortality, and a statistically significant beneficial effect regarding the prevention of atrial fibrillation (odds ratio (OR) 0.79, 95% CI 0.68 to 0.93). Both parallel and crossover studies favour dual chamber pacing with regard to pacemaker syndrome (parallel: Peto OR 0.11, 95% CI 0.08 to 0.14; crossover: standardised mean difference (SMD) -0.74, 95% CI - 0.95 to -0.52). Pooled data from crossover studies shows a statistically significant trend towards dual chamber pacing being more favourable in terms of exercise capacity (SMD -0.24, 95% CI -0.03 to -0.45). No individual studies reported a significantly more favourable outcome with single chamber ventricular pacing. REVIEWERS' CONCLUSIONS: This review shows a trend towards greater effectiveness with dual chamber pacing compared to single chamber ventricular pacing, which supports the current British Pacing and Electrophysiology Group's Guidelines regarding atrioventricular block. Additional randomised controlled trial evidence from ongoing trials in this area will further inform the debate.

Cardiac Pacing, Artificial↗
PubMed2004

Individualised quality of life after pacing. Does mode matter?

AIMS: To examine the hypothesis that atrial based pacing improves Quality of Life (QoL) after pacing by undertaking a detailed QoL evaluation that includes an individualised assessment as well as disease specific evaluation. METHODS: Prospective study of patients randomised to VVI(R) or atrial based pacing modes using the Schedule for the Evaluation of Individual QoL (SEIQoL), the 36-item Medical Outcomes Study Short-Form General Health Survey (SF36), and a modified version of the Karolinska Cardiovascular Symptomatology Questionnaire (KCSQ). RESULTS: Seventy-three patients completed the two-year follow up of the study. Pacing improved SEIQoL scores, cardiovascular symptoms and the physical role limitation, social limitation and mental health domains of SF36 from baseline to one month. Pacing mode had no effect on QoL the major determinants of which were baseline QoL and a history of coronary artery disease. CONCLUSION: Atrial based pacing does not improve QoL in the two years after pacing when compared with VVI(R) pacing.

Aged↗
PubMed2003

Left ventricular dysfunction resulting from frequent unifocal ventricular ectopics with resolution following radiofrequency ablation.

A case is presented, in which asymptomatic but persistent right ventricular outflow tract (RVOT) ectopics resulted in left ventricular (LV) dilatation and systolic dysfunction. The patient underwent extensive investigation with no other cause for the cardiomyopathy being found. Successful ablation of the RVOT ectopic focus resulted in normalization of LV size and function. This case suggests that frequent ventricular ectopy should be considered as a potentially remediable cause of LV dysfunction.

Adult↗
PubMed1992

Cardiac pacing and aviation.

Certain applicants with stable disturbances of rhythm or conduction requiring cardiac pacing, in whom no other disqualifying condition is present, may be considered fit for medical certification restricted to multi-crew operations. The reliability of modern pacing systems appears adequate to permit restricted certification even in pacemaker dependent subjects except for certain models of pacemakers and leads known to be at increased risk of failure. These are to be avoided. There is little evidence to suggest that newer devices are any more reliable than their predecessors. Single and dual chamber systems appear to have similar reliability up to 4 years, after which time significant attrition of dual chamber devices occurs, principally due to battery depletion. All devices require increased scrutiny as they approach their end of life as predicted from longevity data and pacing characteristics. Unipolar and bipolar leads are of similar reliability, apart from a number of specific bipolar polyurethane leads which have been identified. Atrial leads, particularly those without active fixation, are less secure than ventricular leads and applicants who are dependent on atrial sensing or pacing should be denied certification. Bipolar leads are to be preferred due to the lower risk of myopotential and exogenous EMI. Sensor-driven adaptive-rate pacing systems using active sensors may have reduced longevity and require close scrutiny. Activity-sensing devices using piezoelectric crystal sensors may be subject to significant rate rises in rotary wing aircraft. The impracticality of restricted certification in helicopters will, in any event, preclude certification. Such devices would best be avoided in hovercraft (air cushioned vehicle) pilots. Only minor rate rises are likely in fixed-wing aircraft which are unlikely to be of significance. Anti-tachycardia devices and implanted defibrillators are inconsistent with any form of certification to fly.

Aerospace Medicine↗
PubMed1988

Selective vibration sensing: a new concept for activity-sensing rate-responsive pacing.

A clinically available model of an activity-sensing, rate-responsive pacemaker (Activitrax, Medtronic) utilizes body vibration during exercise as an indicator of the need for a rate increase. Although having the advantage of rapid onset of rate response, this system lacks specificity and the rate response does not closely correlate with the level of exertion. In addition, this pacemaker is susceptible to the effects of extraneous vibration. In this study involving 20 normal subjects fitted with an external Activitrax pacemaker, the rate responses to a variety of exercises were studied and were compared with the corresponding sinus rates. The vibration generated at the level of the pacemaker was also measured by accelerometers in three axes. Only a fair correlation (r = 0.51) was achieved between the pacemaker rate and the sinus rate. The total root mean square value of acceleration in either the anteroposterior or the vertical axes was found to have a better correlation (r = 0.8). As the main accelerations during physical activities were in the lower frequency range (0.1-4 Hz), a low-pass filter was used to reduce the influence of extraneous vibration. Selective sensing of the acceleration level may be usefully implemented in an algorithm for activity pacing.

Adult↗
PubMed1988

Limitations of rate response of an activity-sensing rate-responsive pacemaker to different forms of activity.

The responses of an activity-sensing rate-responsive system (Activitrax) to various forms of physiological activity were assessed in 15 individuals who had this pacemaker. Nine were patients with complete heart block and atrial arrhythmias; their mean age was 60 years (range, 41-85 years). Six were age-matched healthy volunteers who were exercised with an external Activitrax system attached firmly to the chest wall. The pacemaker was programmed to achieve a pacing rate of about 100 bpm at the end of the first stage of the Bruce protocol (pacemaker settings: rate = 70-150 bpm; threshold = low to medium; response = 6-9). In the activity-sensing ventricular pacing mode, all patients achieved a significant increase in treadmill time compared to constant-rate ventricular pacing (mean +/- SD, 8.0 +/- 3.3 vs 5.4 +/- 2.3 minutes; p less than 0.01), with a mean maximum pacing rate of 123 +/- 18 bpm. Jogging in place produced a prompt increase in pacing rate, with the maximum achieved at the end of the exercise. However, physiological activities such as hand-grip, the Valsalva maneuver and standing resulted in only minimal rate response. Pacing rate after ascending 4 flights of stairs was the same as that achieved after descending the same stairs (100 +/- 8 vs 105 +/- 4 bpm; p = 0.1). All 15 subjects were exercised from resting heart rate for 3 minutes on a treadmill at 1.2 mph and 2.5 mph with four gradients at each speed. Although the pacing rate increased with a faster treadmill speed (p less than 0.005), it did not respond appropriately to a change in gradient compared to the sinus rate. We conclude that although activity-sensing rate-responsive pacing gives a prompt increase in pacing rate and improves maximum exercise tolerance, further refinement is necessary because: (1) physiological activities not associated with significant movement are not detected by this pacing system; (2) detection of vibrations as an indicator of activities does not correlate well with the level of exertion.

Adult↗
PubMed1982

The effect of surgical procedures on blood vessel innervation. A fluorescence histochemical study of degeneration and regrowth of perivascular adrenergic nerves.

Four commonly used surgical procedures have been shown to cause extensive damage to the sympathetic nerves which supply and accompany blood vessels. One of these procedures, which produced a localised crush lesion, was shown by fluorescence microscopy to cause extensive degeneration of adrenergic nerves in two densely innervated blood vessels of different character in the guinea pig: the elastic carotid artery and the muscular mesenteric artery. The extent of denervation was different in the two vessels: in the carotid artery the crush lesion destroyed all the nerves near the lesion, but left undamaged sparse nerves which reached the vessel wall along its length with the vasa vasorum; in the mesenteric artery all the nerves ran with the artery, consequently denervation could be extensive (at least 2 cm distal to the crush), although the largest nerve bundles were resistant to crush injury. The regrowth rate of nerves in the mesenteric artery was faster than that found in the carotid artery. A plexus of normal density and appearance was re-established between 3 and 8 weeks, and hyperinnervation was observed in some specimens. In the carotid artery this process was usually not complete by 8 weeks and involved both the regrowth of injured fibres and collateral sprouting distal to the lesion of the sympathetic nerve fibres that had not been injured. Axon sprouting was observed in both vessels near the lesion site. Explanations for these differences are discussed.

Adrenergic Fibers↗
PubMed1981

The opioid control of LH and FSH release: effects of a met-enkephalin analogue and naloxone.

The effect of long-acting analogue of met-enkephalin (DAMME) and naloxone on gonadotrophin secretion has been investigated in man. In menopausal women DAMME induced a progressive fall in LH to approximately 60% of basal levels at 3 h, which was blocked by naloxone; there was a smaller fall in FSH that did not attain statistical significance. However, the LHRH-induced rise in LH and FSH in young male volunteers was unaffected by pretreatment with a high-dose DAMME infusion. Naloxone infusion in young male and female normal subjects produced a significant rise in both LH and FSH. Long-term infusion of naloxone appeared to increase the rate, and possibly the amplitude, of LH pulsatility. These results suggest that met-enkephalin-like opioid peptides exert a tonic inhibitory control of LH release in both menopausal and young subjects of both sexes. This control is most likely to be at the level of the hypothalamus, and involves modulation of pulsatile LHRH release.

Adolescent↗
PubMedDate not supplied

The development of a system for the evaluation of electromagnetic interference with pacemaker function: hazards in the aircraft environment.

It has been recognized for many years that the electromagnetic (EM) environment within aircraft presents a potential hazard to the subject with a pacemaker. Most of the information currently available is, however, several years old and may not be strictly relevant to modern pacemakers and the electromagnetic environment found in today's civil aircraft. In mid 1986 it was therefore decided to investigate the effect on a number of currently available unipolar pacemakers of typical levels of electromagnetic interference encountered in civil aircraft.

Aircraft↗