Thomas A. Preston

Clinical applications of the threshold tracking pacemaker

The concept of automatic threshold tracking is the most recent adaptation of artificial cardiac pacemakers to physiologic needs. Earlier pacemaker innovations were primarily in the area of timing of impulse delivery, whereas more recent changes have focused on alteration of the amplitude and duration of the pacemaker stimulus. Matching of this stimulus to the cardiac excitation threshold is important because a stimulus greater than necessary is wasteful of battery energy and may produce arrhythmias, whereas a stimulus of less than threshold intensity fails to pace the heart. Because of the wide range of clinically encountered threshold levels it is impossible to design a fixed output pacer that is efficient and safe for all patients at all times. The threshold tracking pacemaker searches for and finds the threshold level, and adjusts its stimulus to just above this level. The device ensures an adequate safety margin of stimulation, but reduces the stimulus level to the lowest safe level possible. It is fully automatic, adjusts immediately to any threshold changes and is not dependent on manual alteration.

A Medical Ethics Assessment of the Case of Terri Schiavo

ABSTRACT The social, legal, and political discussion about the decision to stop feeding and hydration for Terri Schiavo lacked a medical ethics assessment. The authors used the principles of medical indications, quality of life, patient preference, and contextual features as a guide to medical decision-making in this case. Their conclusions include the following: (a) the use of a feeding tube inserted directly in to the stomach constituted artificial treatment; (b) the treatment prolonged biological life but did not lead to a cure and did not restore health; (c) quality of life was absent for the patient, with no sensation and no motor or cognitive functioning; and (d) by preponderance of medical opinion, she would have chosen not to live in a persistent vegetative state. The authors find the withdrawal of treatment was permissible and correct. It was not a choice between living and dying, but a decision of when to allow dying consistent with the patients choice.

A new temporary pacing catheter with improved sensing and safety characteristics

Temporary artificial cardiac pacing is a fully accepted procedure with widespread application. The indications for temporary pacing are numerous,‘, 2 but most temporary pacing is done for acutely ill patients who have bradyarrhythmias or tachyarrhythmias. Two serious manifestations of pacing failure are: (1) inadequate demand (standby) pacer sensing of spontaneous beats leading to competitive pacing35 4 and (21 stimulation during the vulnerable period of the preceding beat, leading to pacer-induced ventricular tachycardia or fibrillation.5*6 It is the acutely ill patient, with myocardial infarction, hypoxia, or metabolic imbalance, who is in jeopardy of improper pacing. Because of the recurrent problem of inadequate sensing in temporary pacing systems33 4* 7 and the infrequent but potentially fatal complication of competitive pacing (pacemaker-induced ventricular arrhythmia),5s 6 there is a need for a safer pacing electrode system that can avoid these complications. This report describes a unipolar pacing catheter that is designed to give improved sensing, and a decreased likelihood of pacer-induced arrhythmia even in the presence of competitive pacing. One electrode (cathode) is at the distal tip of the catheter, and the other electrode (anode) is 23 cm. proximal to the distal tip. The improved sensing derives from widely spaced electrodes, and the decreased risk of arrhythmia is a result of placing the anode outside of the heart.

Professional Norms and Physician Attitudes Toward Euthanasia

he chair of the ethics committee of a major medical center agonized over how he, as a physician, T and his organization should deal with Initiative 119, which, if passed, would legalize physician involvement in active, voluntary euthanasia in Washington State.’ In the end, he said, he could not vote for aid-in-dying because, “However much I want to reduce suffering, I myself just couldn’t do it to one of my patients.” He spoke of a personal distaste for the potential act, of a profound desire not to have to do it. It was not an ethical argument, but an honest and compelling expression of feelings. Why can’t this sincere man do it, even for patients who requcst such aid? In a 1991 poll, taken in Washington State prior to the vote on Initiative 119,49 percent of the physicians surveyed supported the initiative, but 75 percent did not want to participate in aid-in-dying? In response to a post-election questionnaire, sent to a select group of physicians in the Seattle area, 45 percent of respondents opposed euthanasia as a medical practice despite the fact that 65 percent supported the concept; 70 percent said that they would like to use it as a treatment option in case they themselves were the patient.J These findings suggest that physicians have the capacity to substitute both professional standards and rules of conduct for personal beliefs when deciding what they ought or ought not to do for their patients? but many are not willing to do unto their patients as they would have done unto themselves? In debates leading up to the vote, physicians who spoke against Initiative 119 did so most frequently on the grounds that there were insufficient safeguards and issues of potential abuse by physicians; often dissenters incorporated these concerns into “slippery slope” arguments. However, when voicing their opposition to euthanasia as physicians, three major objections emerged: a revulsion to the act, a taboo against killing, and a perceived violation of the proper role of the physician. I have chosen these three objections in order to examine the influence of professional norms on the reactions of clinicians to forms of euthanasia.

Permanent rapid atrial pacing to control supraventricular tachycardia.

A case is reported of a patient who had continuous supraventricular tachycardia with a ventricular rate of about 170. The arrhythmia was refractory to drugs and DC countershock, and did not convert with atrial pacing. Rapid atrial stimulation controlled the ventricular rate by simulating atrial fibrillation (pacing at 300‐400/min), or by simulating a faster atrial tachycardia with 2:1 conduction (pacing at 205‐210/min), This form of therapy was used on a permanent basis for more than five months. (PACE, Vol. 2, May‐June, 1979)

The automatic rate adjustment pacemaker. The possibilities of rate hysteresis.

Since the first use of pacemakers there have been attempts to regulate the fixed, or basic rate of implanted pulse generators: Earlier models employed the use of magnets or percutaneous needles to change the pacemaker rate after implantation. A recent development is the programmable pacemaker, which utilizes external electromagnetic signals to alter the basic rate.

Characteristics of persons approving of physician-assisted death.

ABSTRACT The present study describes the characteristics and attitudes of non-terminally ill persons who support physician-assisted death (PAD) along with their expectations and preferences for care in the future. Participants (N = 101) completed a survey assessing current affect and attitudes and those expected if terminally ill. Participants’ responses indicated they were a well-adjusted group with little evidence of depressive symptoms or past suicidal ideation. Current attitudes were differentially related to future care preferences. Findings suggest a need for longitudinal research on the stability of current attitudes and how they relate to PAD among non-terminally ill supporters of assisted death.

The Patent System and Cardiac Pacing: Is the System Serving Its Users?

Patents have been utilized to protect technical innovations in pacemakers virtually since their inception and are becoming increasingly important to the industry. In the U.S. alone, about 100 patents are granted each year covering pacer‐related technology and reflecting the main areas of technical development. The increase in the number of outstanding patents has been accompanied by a significant increase in patent litigation among pacer companies. The rate and cost of pacer‐related patent litigation raises a question of whether the system is being used to its best advantage. A recommendation is made for an industry‐sponsored board to aid in voluntary settlement of patent disputes.