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W D Toff

Publications and source records attributed to W D Toff.

8 recordsLinked to original sources
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↗
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↗