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Biomedical subjects

D G Benditt

Publications and source records attributed to D G Benditt.

At least 55 records · Page 3Linked to original sources
PubMed1997

Neurally mediated syncopal syndromes: pathophysiological concepts and clinical evaluation.

The neurally mediated syncopal syndromes encompass a number of apparently related disturbances of reflex cardiovascular control characterized by transient inappropriate bradycardia and/or vasodilation of various arterial and venous beds. Certain of these syndromes (e.g., carotid sinus syndrome, postmicturition syncope) are encountered occasionally in clinical practice, whereas others are quite rare (e.g., swallow syncope). On the other hand, vasovagal syncope occurs so frequently, that as a group, the neurally mediated syncopal syndromes are among the most important causes of syncope. The pathophysiology of the neurally mediated syncopal syndromes is incompletely understood, but can be considered in terms of four basic elements: (1) the afferent limb; (2) central nervous system (CNS) processing; (3) the efferent limb; (4) feedback loops. The afferent limb consists of several peripheral and CNS trigger sites and the associated connections to medullary cardiovascular centers. CNS processing and efferent signals result in both bradycardia, which may be marked or relative, and vasodilatation. Failure of baroreceptor feedback controls to prevent hypotension is important in facilitating development of symptomatic hypotension. Head-up tilt table testing has become the diagnostic technique of choice for clinically assessing susceptibility to neurally mediated syncope, particularly of the vasovagal type. Most studies suggest that such testing discriminates relatively well between symptomatic patients and asymptomatic control subjects, of whom 10%-15% have a false-positive test results. Sensitivity of tilt table testing is more difficult to evaluate because there is no accepted diagnostic gold standard. However, sensitivity (measured against a classic presentation) has been estimated to range from 32%-85%, with most reports favoring the higher end of this range. Treatment strategies for neurally mediated syncope remain controversial. Many single episodes do not warrant treatment unless physical injury has occurred, or a high risk occupation or avocation is involved. Tilt test exposure alone may prove beneficial in educating patients with recurrent syncope to recognize warning signs of an imminent faint. Large controlled clinical studies have not been performed to test the efficacy of pharmacological therapy (e.g., beta-adrenergic blockers, disopyramide, serotonin reuptake blockers, vasoconstrictors) or pacing therapy. Such studies may be difficult to undertake due to the variable frequency of spontaneous symptoms and apparent long periods of remission. Nonetheless, many investigators and clinicians have come to rely on these agents, and on tilt testing to guide treatment decisions. Studies employing careful correlation of long-term clinical follow-up with results of early and perhaps later repeat tilt studies are still needed.

Afferent Pathways↗
PubMed1997

Nonpharmacologic treatment of atrial fibrillation: current and evolving strategies.

Atrial fibrillation is the most common cardiac arrhythmia requiring treatment. Limitations of medical treatment have prompted development of nonpharmacologic therapies for this arrhythmia. These are aimed at ventricular rate control during atrial fibrillation, termination of the arrhythmia, and/or prevention of recurrences. Ventricular rate control can be achieved with transcatheter ablation or modification of the atrioventricular node. The MAZE operation is effective in preventing arrhythmia recurrence, but because it requires cardiac surgery, its appeal is limited. Development of the technique for direct transcatheter ablation of atrial fibrillation is eagerly anticipated and may represent the standard curative treatment of the future. In appropriately selected patients, implantable device therapy may play an important role in the treatment of paroxysmal atrial fibrillation.

Anti-Arrhythmia Agents↗
PubMed1996

Electromagnetic interference from welding and motors on implantable cardioverter-defibrillators as tested in the electrically hostile work site.

OBJECTIVES: This study was designed to determine the susceptibility of an implanted cardioverter-defibrillator to electromagnetic interference in an electrically hostile work site environment, with the ultimate goal of allowing the patient to return to work. BACKGROUND: Normal operation of an implanted cardioverter-defibrillator depends on reliable sensing of the heart's electrical activity. Consequently, there is concern that external electromagnetic interference from external sources in the work place, especially welding equipment or motor-generator systems, may be sensed and produce inappropriate shocks or abnormal reed switch operation, temporarily suspending detection of ventricular tachycardia or ventricular fibrillation. METHODS: The effects of electromagnetic interference on the operation of one type of implantable cardioverter-defibrillator (Medtronic models 7217 and 7219) was measured by using internal event counter monitoring in 10 patients operating arc welders at up to 900 A or working near 200-hp motors and 1 patient close to a locomotive starter drawing up to 400 A. RESULTS: The electromagnetic interference produced two sources of potential interference on the sensing circuit or reed switch operation, respectively: 1) electrical fields with measured frequencies up to 50 MHz produced by the high currents during welding electrode activation, and 2) magnetic fields produced by the current in the welding electrode and cable. The defibrillator sensitivity was programmed to the highest (most sensitive) value: 0.15 mV (model 7219) or 0.3 mV (model 7217). The ventricular tachycardia and ventricular fibrillation therapies were temporarily turned off but the detection circuits left on. CONCLUSIONS: None of the implanted defibrillators tested were affected by oversensing of the electric field as verified by telemetry from the detection circuits. The magnetic field from 225-A welding current produced a flux density of 1.2 G; this density was not adequate to close the reed switch, which requires approximately 10 G. Our testing at the work site revealed no electrical interference with this type of defibrillator. Patients were allowed to return to work. The following precautions should be observed by the patient: 1) maintain a minimal distance of 2 ft (61 cm) from the welding arc and cables or large motors, 2) do not exceed tested currents with the welding equipment, 3) wear insulated gloves while operating electrical equipment, 4) verify that electrical equipment is properly grounded, and 5) stop welding and leave the work area immediately if a therapy is delivered or a feeling of lightheadedness is experienced.

Defibrillators, Implantable↗
PubMed1996

Effect of parenteral d-sotalol on transvenous atrial defibrillation threshold in a canine model of atrial fibrillation.

In an effort to reduce energy requirements for atrial defibrillation to a level low enough to perform painless electrical cardioversion with an implantable atrial defibrillator, we tested the hypothesis that drug therapy with the class III agent d-sotalol, when used concurrently with a low-energy shock, reduces atrial defibrillation threshold. In a nonthoracotomy canine model of atrial fibrillation, intracardiac shocks were delivered between the distal coronary sinus and the mid-right atrium. Based on a step-up energy delivery protocol the atrial defibrillation threshold was defined as the least amount of energy that resulted in a >10% and <90% rate of successful defibrillation. At a dose associated with class III antiarrhythmic effects (5 mg/kg), d-sotalol significantly reduced atrial defibrillation threshold from 1.72 +/- 1.12 J to 0.59 +/- 0.60 J (p < 0.01). These results support the feasibility of using antiarrhythmic drug therapy with d-sotalol to minimize energy requirements for intracardiac electrical cardioversion of atrial fibrillation.

Animals↗
PubMed1995

Syncope associated with exercise, a manifestation of neurally mediated syncope.

A retrospective review of patients evaluated at a university-based referral hospital was performed to assess the basis for syncope associated with exercise in young patients. Over an 8-year period, 54 consecutive young patients (aged 12 to 30 years) were referred for evaluation of frank syncope. Twelve patients had syncope associated with exercise (group I) and 42 patients had syncope not associated with exercise (group II). Patients underwent physical examination, chest x-ray, 2-dimensional echocardiography, and in selected cases, cardiac catheterization. Head-up tilt-table testing was performed in 11 of 12 group I patients. Ten group I patients had no evidence of structural heart disease: 9 of these 10 (90%) developed syncope with tilt-table testing. Head-up tilt-table testing was performed in 41 of 42 group II patients: 34 (83%) developed syncope with tilt-table testing. Standard cardiac electrophysiologic study was performed in 9 of 12 group I and in 30 of 42 group II patients, and identified a basis for syncope in only 2 group I and 1 group II patients. Among 9 group I patients with a positive result on head-up tilt-table testing and no evidence of structural heart disease (mean follow-up 4.3 years), 7 are without further episodes of syncope; 3 have discontinued medication and 5 have resumed at least limited exercise. In conclusion, susceptibility to tilt-induced syncope was the most frequent finding in young patients without structural heart disease referred for evaluation of exercise-associated syncope. Tilt-table testing may be an important diagnostic tool for the evaluation of these patients.

Adolescent↗
PubMed1995

Cardiac pacing for prevention of recurrent vasovagal syncope.

PURPOSE: To review the status of cardiac pacing for the treatment of patients with recurrent vasovagal syncope. DATA SOURCES: A MEDLINE search for English- and French-language articles published between 1980 and 1994 about cardiac pacing for prevention or treatment of vasovagal syncope. The term cardiac pacing was used in conjunction with the terms vasovagal, neurally mediated, or neurocardiogenic syncope, but not with the term carotid sinus hypersensitivity. STUDY SELECTION: Case reports and series from peer-reviewed journals were selected if they documented the presence of vasovagal syncope and assessed pacing effectiveness using tilt-table testing, clinical follow-up, or both. Four case reports and four series met these criteria. DATA EXTRACTION: Findings were summarized individually. Statistical analysis of combined data was inappropriate given differences among studies in patient selection, testing, and follow-up. RESULTS: Pacing may be useful in selected patients with predominantly cardioinhibitory vasovagal responses. Pacing alone may eliminate symptoms in 25% of these patients and may prevent abrupt cardiovascular collapse in others (such as those in whom syncope occurs with minimal or no premonitory sensation). However, interpretation of most available reports has been limited both by the uncertainty associated with using the tilt-table technique to assess pacing effectiveness and by relatively short-term follow-up. CONCLUSIONS: The usefulness of cardiac pacing for patients with recurrent vasovagal syncope remains only partly understood. Randomized controlled trials are needed for this and other aspects of the treatment of this condition. Additionally, substantial room remains for innovation both in earlier recognition of imminent vasovagal syncope by implantable devices and in specifically designing cardiac pacing algorithms for treatment of this condition.

Algorithms↗
PubMed1995

Characterization of subcutaneous microvascular blood flow during tilt table-induced neurally mediated syncope.

OBJECTIVES: This study aimed to characterize subcutaneous blood flow changes during neurally mediated syncope and to determine whether microvasculature oscillation (vasomotion) is characteristically altered in conjunction with syncopal events. BACKGROUND: Marked pallor is commonly associated with neurally mediated syncope. However, little attention has been paid to the evaluation of subcutaneous blood flow and vasomotion in this setting. METHODS: This study utilized laser Doppler flowmetry to assess changes in subcutaneous microvascular blood flow during head-up tilt table testing in 13 patients with syncope and 6 control subjects. Blood flow and vasomotion frequency were measured continuously before, during and after completion of 80 degrees head-up tilt testing (< or = 25-min duration). RESULTS: Among the 13 patients with syncope, tilt testing reproduced syncopal symptoms in 9 (tilt-positive group) but not in 4 (tilt-negative group). None of the six control subjects developed symptoms during testing. Baseline mean subcutaneous blood flow did not differ significantly among the three groups. However, during upright tilt, blood flow gradually diminished in the tilt-positive group, reaching a nadir of 0.8 +/- 0.33 ml/min per 100 g of tissue (mean +/- SD), but remained relatively constant in the tilt-negative group and control subjects. The difference in mean blood flow response to tilt was statistically significant when the tilt-positive group was compared with either the tilt-negative group or control subjects (p < 0.001). Similarly, baseline blood flow oscillation frequency did not differ significantly in the three subgroups (tilt-positive group 0.2 +/- 0.11 Hz; tilt-negative group 0.2 +/- 0.02 Hz; control subjects 0.2 +/- 0.11 Hz). Subsequently, during tilt testing only the tilt-positive group exhibited increased oscillation frequency; oscillation frequency remained essentially constant throughout the tilt test in the tilt-negative group and control subjects (p < 0.001, tilt-positive group vs. either the tilt-negative group or control subjects). CONCLUSIONS: These findings document an expected diminution of subcutaneous blood flow in association with neurally mediated syncope and indicate that characteristic changes in microvasculature oscillation frequency occur in conjunction with syncopal symptoms. To the extent that microvasculature vasomotion is influenced by neural control, the changes in vasomotion frequency are consistent with relative diminution of peripheral sympathetic neural influence during neurally mediated syncopal episodes.

Adolescent↗
PubMed1995

Clinical investigation of antiarrhythmic devices. A statement for healthcare professionals from a joint task force of the North American Society of Pacing and Electrophysiology, the American College of Cardiology, the American Heart Association, and the Working Groups on Arrhythmias and Cardiac Pacing of the European Society of Cardiology.

The goal of radiofrequency catheter ablation and the criterion for efficacy is the elimination of arrhythmogenic myocardium. The application of radiofrequency current in the heart clearly results in lower morbidity and mortality rates than thoracic and cardiac surgical procedures in general, and comparisons of therapy with radiofrequency catheter ablation and therapy with thoracic and cardiac surgical procedures in randomized clinical trials is unwarranted. Trials of radiofrequency catheter ablation versus medical or implantable cardioverter-defibrillator therapy may be indicated in certain conditions, such as ventricular tachycardia associated with coronary artery disease. Randomized trials are recommended for new and radical departures in technology that aim to accomplish the same goals as radiofrequency catheter ablation. Surveillance using registries and/or databases is necessary in the assessment of long-term safety and efficacy.

American Heart Association↗
PubMed1995

Crinkling of epicardial defibrillator patches. A common and serious problem.

The durability and reliability of the implantable cardioverter-defibrillator epicardial patch systems have not been reported. In 128 consecutive patients such systems manufactured by Cardiac Pacemakers, Inc. (St. Paul, Minn.) or Medtronic, Inc. (Minneapolis, Minn.) were implanted with 100% follow-up to investigate the rate of patch crinkling and its consequences. A total of 122 patients survived the operation (operative mortality, 6 patients: 4.7%). Ninety-four patients received Cardiac Pacemakers, Inc. AICD patches and 28 received Medtronic PCD patches. Patients had chest x-ray studies every 3 to 6 months and function of the defibrillator was checked every 3 months. Late mortality occurred in 17 patients (13%) leaving a total of 105 long-term survivors (82%) to the present. Among 122 survivors, severe crinkling of the patches occurred in 48 patients--33 in the Cardiac Pacemakers, Inc. AICD group (36%) and 15 in the PCD group (54%)--within 2 years of the implant. Crinkling of patches caused not only malfunction of the system, but also cardiac pain in three patients. Crinkling occurred as early as 2 months after implant and progressed throughout the period of observation. Fourteen patients later required implant of an additional transvenous defibrillator because of failure of the epicardial system. The percentage of transvenous implantable cardioverter-defibrillator systems needed was higher for the Medtronic group (28%) than for the Cardiac Pacemakers, Inc. AICD group (6.3%). Both systems have shown an unacceptably high rate of patch crinkling that occurs in a relatively short time. There is no difference whether a thoracotomy or midline sternotomy is used or whether the patches are implanted intrapericardially or extrapericardially. The quest should continue for a better patch system design.

Adult↗
PubMed1995

NASPE/ACC/AHA/ESC medical/scientific statement special report--clinical investigation of antiarrhythmic devices: a statement for healthcare professionals from a Joint Task Force of the North American Society of Pacing and Electrophysiology, the American College of Cardiology, the American Heart Association, and the Working Groups on Arrhythmias and Cardiac Pacing of the European Society of Cardiology.

The goal of radiofrequency catheter ablation and the criterion for efficacy is the elimination of arrhythmogenic myocardium. The application of radiofrequency current in the heart clearly results in lower morbidity and mortality rates than thoracic and cardiac surgical procedures in general, and comparisons of therapy with radiofrequency catheter ablation and therapy with thoracic and cardiac surgical procedures in randomized clinical trials are unwarranted. Trials of radiofrequency catheter ablation versus medical or implantable cardioverter defibrillator therapy may be indicated in certain conditions, such as ventricular tachycardia associated with coronary artery disease. Randomized trials are recommended for new and radical departures in technology that aim to accomplish the same goals as radiofrequency catheter ablation. Surveillance using registries and/or databases is necessary in the assessment of long-term safety and efficacy.

Arrhythmias, Cardiac↗
PubMed1995

Transtelephonic monitoring and transmission of stored arrhythmia detection and therapy data from an implantable cardioverter defibrillator.

A new transtelephonic monitoring device designed for use with implantable cardioverter defibrillators (ICDs) was evaluated. It is capable of interrogating ICDs and transmitting the following data via telephone: programmed parameters (e.g., ventricular tachycardia [VT] and ventricular fibrillation [VF] detection, therapies), number of VT and VF episodes, identification of successful therapies, the 20 cycle lengths preceding the last episode detected, the 10 cycle lengths after the last delivered therapy, battery voltage, and real-time transmission of the patient's rhythm. Eighteen patients (mean age 64 +/- 17 years; 15 males) were implanted with an ICD and epicardial lead system. The patients who did not live near the primary hospital were provided with this transmitter and instructed to transmit monthly and whenever presyncope, syncope, or a shock were experienced. Five hundred ten episodes of spontaneous arrhythmia (495 VT, 15 VF) were detected in 14 of 18 patients in a 24-month period and the success of each therapy (antitachycardia pacing, cardioversion 0.4-34 J, defibrillation 34 J) was analyzed. The number of therapies delivered and their success (%) in terminating the arrhythmia were: 380 ramp/86%, 116 burst/84%, 119 cardioversion/57%, and 15 defibrillations/100%. Sixty-three (42%) of the 152 transmissions indicated an arrhythmia. Twenty-five (16%) of the 152 were transmitted because of symptoms. Sixteen (9.7%) of 165 VT episodes could not be terminated by the full set of programmed VT therapies. Analysis of the pre- and post-episode intervals along with the patient's transmitted rhythm indicated that sinus tachycardia or atrial fibrillation were likely responsible for these episodes.(ABSTRACT TRUNCATED AT 250 WORDS)

Atrial Fibrillation↗
PubMed1994

Multiple-sensor systems for physiologic cardiac pacing.

PURPOSE: To review the status of artificial sensors in cardiac pacemakers and the rationale for developing pacing systems that use multiple sensors. DATA SOURCES: Journal articles published between 1982 and 1993 indexed in MEDLINE using the keywords pacemakers, sensors, and rate-adaptive, as well as abstracts and articles in the authors' personal files. STUDY SELECTION: Articles describing clinical experience with or clinical evaluation of cardiac pacing systems using multiple artificial sensors. DATA SYNTHESIS: Artificial sensors were created to adjust pacing rate reliably in response to changes in levels of physical exertion for patients with sinoatrial disease in whom exercise heart rate response is inadequate (for example, chronotropic incompetence in sinoatrial disease). To achieve this, various artificial sensors were developed and many reports confirm improved exertional tolerance. More recently, sensors have assumed a greater role in cardiac pacemakers. For example, sensors are used to permit automatic adjustment of certain programmable pacemaker settings, such as the atrioventricular interval. In the future, they may also be used to maximize pacemaker longevity by automatically optimizing energy output (voltage, pulse width). No single sensor is ideal for all potential applications, and investigators have advocated using two or more sensors. Several pacemakers that use multiple sensors with different but complementary operating characteristics are already commercially available outside the United States. Although preliminary findings are encouraging, additional clinical experience with these pacemakers is needed to determine their ultimate role in clinical practice. CONCLUSION: Simultaneous use of multiple complementary artificial sensors may permit development of cardiac pacemakers that operate more physiologically yet require less specialized medical follow-up.

Clinical Trials as Topic↗