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Biomedical subjects

David G Benditt

Publications and source records attributed to David G Benditt.

At least 37 records · Page 2Linked to original sources
PubMed2005

Unconscious confusion--a literature search for definitions of syncope and related disorders.

BACKGROUND: Imprecise definitions of syncope and related conditions appear common in the medical literature. To investigate the scope of the problem we systematically searched for definitions in high-ranking medical journals. METHODS: Literature review of articles on 'syncope', 'neurocardiogenic syncope', 'neurally mediated syncope', 'orthostatic intolerance', and 'orthostatic hypotension' with these keywords in the title, mainly published in the ten journals with the highest impact in the fields of cardiology, internal medicine, and neurology. RESULTS: Syncope, neurocardiogenic syncope, neurally mediated syncope, orthostatic intolerance, and orthostatic hypotension were defined in only 41%, 34%, 26%, 38%, and 48% of papers respectively. Definitions, when given, differed considerably among papers. Orthostatic hypotension was most frequently defined, with an increase in number and consistency of definitions after publication of a consensus in 1996. CONCLUSIONS: Syncope and related conditions proved to be infrequently and inconsistently defined in current medical literature. The lack of consistent terminology is likely to harm medical education, research, and patient care. There is a strong need for a systematic terminology for syncope and related conditions.

Autonomic Nervous System↗
PubMed2005

Effect of cough on heart rate and blood pressure in patients with "cough syncope".

BACKGROUND: "Cough syncope" is uncommon, and its mechanism remains controversial. OBJECTIVES: This study evaluated susceptibility to cough-triggered neural reflex hypotension-bradycardia among cough syncope patients. We hypothesized that individuals with cough syncope would manifest not only more profound cough-triggered hypotension than do other fainters but also an inappropriate chronotropic response accompanying cough-induced hypotension, thereby supporting the notion that a neural reflex hypotension-bradycardia contributes to the condition. METHODS/RESULTS: Three patient groups were studied. Group 1 patients (n = 9) had "cough syncope." The remaining patients had recurrent faints of other causes: group 2 (n = 13) had a positive head-up tilt test, and group 3 (n = 18) had a negative tilt test. With cough, group 1 patients exhibited a greater drop in systolic pressure (-51 +/- 19.3 mmHg) than did either group 2 (-23 +/- 11.1 mmHg, P < .04) or group 3 patients (-28 +/- 12.4 mmHg, P < .05). Recovery time to normalization of systolic pressure was greater in group 1 (25 +/- 9.1 seconds) than in group 2 or 3 (8 +/- 2.7 seconds and 9 +/- 6.1 seconds, respectively, both P < .01 vs group 1). The expected positive chronotropic response accompanying cough-induced hypotension was diminished in group 1 patients (0.16 +/- 0.21 bpm/mmHg) compared with that in either group 2 (0.74 +/- 0.60 bpm/mmHg, P < .05 vs group 1) or group 3 (0.33 +/- 0.15 bpm/mmHg, P = .06 vs group 1). CONCLUSION: Cough syncope patients not only exhibit more pronounced hypotension in response to cough than other fainters, but they also manifest an inappropriate cough-triggered blood pressure-heart rate relationship. These findings argue in favor of the importance of a neurally mediated reflex contribution to symptomatic hypotension in cough syncope.

Aged↗
PubMed2005

Assessment of percutaneous coronary intervention on regional and global left ventricular function in patients with chronic total occlusions.

BACKGROUND: The improvement of regional and global ventricular function following percutaneous coronary intervention (PCI) with reperfusion of the artery supplying the infarct area in acute myocardial infarction is well-described. However, little is known of the potential effects of late recanalization of chronic coronary artery occlusion on left ventricular function. OBJECTIVE: To determine whether PCI improves regional and global left ventricular function in patients with chronic coronary artery occlusions. PATIENTS AND METHODS: Thirty-five patients having at least one coronary artery occluded for six weeks or longer were included in the present prospective study. Exercise thallium-201 myocardial perfusion scintigraphy, multiple-gated acquisition ventriculography and two-dimensional echocardiography were performed in 19 patients (16 men; mean age of 58+/-5 years) who underwent a successful PCI to assess both regional and global left ventricular function before and six weeks following the procedure. RESULTS: The mean ejection fractions before and after reperfusion were 51+/-7% and 58+/-6% using Simpson's method (P<0.001) by echocardiography, and 45+/-1% and 53+/-1% (P=0.01) by multiple-gated acquisition ventriculography, respectively. The echocardiographic wall motion score was 24+/-9 before and 15+/-6 after PCI (P<0.001). The exercise perfusion score (21+/-1 and 14+/-1 [P=0.01]), rest perfusion score (15+/-1 and 12+/-1 [P=0.02]) and reinjection perfusion score (14+/-1 and 11.1+/-1 [P=0.07]) also improved after PCI. The presence of angina was strongly associated with an improvement in left ventricular function and wall motion score (P<0.01). CONCLUSIONS: PCI significantly improved the regional and global left ventricular function in patients with chronic total coronary occlusion. This procedure may provide symptom benefits in selected patients.

Angina Pectoris↗
PubMed2004

Comparison of catecholamine response during tilt-table-induced vasovagal syncope in patients <35 to those >65 years of age.

This study compared alterations in arterial catecholamine concentrations associated with tilt-induced vasovagal syncope that differed in older (>65 years) and younger patients (<35 years). Older patients with tilt-positive tests tended to exhibit higher baseline epinephrine (E) concentrations and lesser E surge before development of syncope than younger patients (<35 years), whereas both groups manifested comparable norepinephrine (NE) responsiveness.

Adult↗
PubMed2004

New approaches to the treatment and prevention of neurally mediated reflex (neurocardiogenic) syncope.

Neurally mediated reflex syncope (sometimes referred to as neurocardiogenic syncope), encompasses a group of disorders of which the best known and most frequently occurring forms are the vasovagal (or common) faint, and carotid sinus syndrome. Postmicturition syncope, defecation syncope, cough syncope, and other situational reflex faints are also included among these conditions. With the exception of carotid sinus syndrome in which cardiac pacing is effective, treatment of most neurally mediated reflex faints is shifting from reliance on various drugs to greater emphasis on education and nonpharmacologic therapy. Initial management should include counseling of patients regarding recognition of early warning symptoms, and avoidance of precipitating factors. Volume expansion with salt tablets or electrolyte-containing beverages and patient education on how to perform isometric arm contractions and/or leg crossing in order to abort impending syncope are also important. Thereafter, tilt-training has demonstrated benefit in several clinical studies. When symptoms remain despite the above-noted interventions, pharmacologic therapy with midodrine or a nonselective b-blocker can be considered. In the case of most neurally mediated reflex faints, permanent cardiac pacing should be reserved only for those older patients with significant bradycardia or asystole at time of syncope when all other interventions have failed.

Cardiac Pacing, Artificial↗
PubMed2004

Syncope.

Syncope is a syndrome consisting of a relatively short period of temporary and self-limited loss of consciousness caused by transient diminution of blood flow to the brain (most often the result of systemic hypotension). Syncope comprises part of a subset of clinical conditions in which loss of consciousness is transient. Other conditions in this group, which are not syncope and should be clearly distinguished from syncope, include, for example, seizure disorders, posttraumatic loss of consciousness, and cataplexy. Recent surveys indicate that syncope accounts for approximately 1% of emergency department visits in Europe, although older reports from the United States placed this number closer to 3%. The reported prevalence of syncope in the population varies: 15% of children before the age of 18 years; 25% of a military population aged 17 to 26 years; 16% and 19%, respectively, in men and women aged 40 to 59 years; and up to 23% in a nursing home population older than 70 years. The highest frequency of syncope occurs in patients with cardiovascular comorbidity and older patients in institutional care settings. The causes of syncope are numerous and, not infrequently, multiple factors may contribute. The diagnostic evaluation is benefited by availability of a detailed medical history and reports of eyewitnesses. In this context, the physician must consider the classification of the causes of syncope, and address the most likely causes first. The principal groups of causes may be summarized as: (1) neurally mediated reflex syncope (eg, vasovagal faint, carotid sinus syndrome); (2) orthostatic (postural) syncope; (3) cardiac arrhythmias; (4) structural cardiac and pulmonary causes; and (5) cerebrovascular disorders (rare). In addition, conditions that may mimic syncope but are not true syncope (eg, psychogenic pseudosyncope) must be considered. Only after a definitive cause is established can appropriate treatment be initiated. In this regard, the syncope evaluation is facilitated by maintaining an organized diagnostic approach. The practitioner should avoid wasteful use of short-term ambulatory electrocardiographic recordings (eg, Holter monitors) and rarely positive neurologic tests (eg, electroencephelography, head magnetic resonance imaging/computed tomography) in the absence of head trauma or evident neurologic signs. In many medical centers the evaluation of patients with syncope is haphazard, and may be substantially enhanced by establishment of a multidisciplinary syncope evaluation unit or team.

Diagnosis, Differential↗
PubMed2004

Transient modification of baroreceptor response during tilt-induced vasovagal syncope.

AIMS: Normally, arterial baroreceptors attempt to minimize systemic hypotension by initiating reflex vasoconstriction and tachycardia. However, in the setting of vasovagal syncope (VVS), these usual compensatory mechanisms either fail to be triggered or the response is inadequate. We hypothesized that in VVS prone individuals, arterial baroreceptor response (BRR) is normal under most conditions, but that a transient functional BRR disturbance occurs during an evolving vasovagal faint and may in part account for failure of the usual compensatory response. METHODS AND RESULTS: This study assessed BRR in the baseline state and again in association with either VVS induced head-up tilt (HUT) or after a prolonged period of upright posture without VVS. To minimize impact on HUT outcome, BRR was estimated non-pharmacologically by measuring blood pressure and heart rate changes, induced when subjects were returned to the supine position after undergoing diagnostic 70 degrees HUT evaluation. Beat to beat heart rate and arterial blood pressure changes were recorded in 13 patients with syncope and another 16 individuals with negative HUT (control group). Baseline BRR was initially evaluated at the end of a 3 min symptom free HUT (HUT#1), and the measurement was repeated after a 45 min duration HUT in the control group or in conjunction with syncope in VVS prone individuals (HUT#2). Baseline BRR did not differ significantly in controls and VVS prone individuals (controls: 3.37+/-1.56, VVS prone: 6.0+/-2.02 ms/mmHg, p=0.27). Further, at the end of 45 min HUT#2, BRR was unaltered from baseline in control subjects (4.92+/-1.36 ms/mmHg, p=0.48), but was markedly reduced from baseline value in individuals who experienced a faint, -3.30+/-0.81 ms/mmHg (p<0.0003 vs baseline). CONCLUSION: Compared with individuals who do not manifest VVS during HUT, VVS prone individuals appear to demonstrate functional diminution of baroreceptor responsiveness. This altered response may undermine the normal expected compensatory response to evolving systemic hypotension. The basis for this transient disturbance in baroreceptor responsiveness is currently unknown.

Aged↗
PubMed2004

Carotid sinus massage during evaluation for transient loss of consciousness: just a positive test?

An electrocardiographic recording obtained during diagnostic evaluation of recurrent transient loss of consciousness in a 53-year-old man is presented. Carotid sinus massage (CSM), having elicited a ventricular asystole of >5s duration was deemed to have provided a possible diagnostic basis for syncope. However, apart from the pause and somewhat unexpectedly, CSM also suppressed preexisting frequent ventricular ectopy. Explanations for this unexpected finding can only be considered speculative, but include direct CSM-induced parasympathetic suppression of ectopic activity at intra-ventricular pacemaker sites, concomitant diminution of sympathetic neural activity at ectopic sites, or interruption of 'linking' of normal ventricular activation to initiation of premature ventricular contractions.

Carotid Sinus↗
PubMed2004

Impact of age and blood pressure on the lower arterial pressure limit for maintenance of consciousness during passive upright posture in healthy vasovagal fainters: preliminary observations.

Maintenance of consciousness importantly depends on systemic arterial blood pressure (BP) remaining above the lower pressure limit for cerebrovascular autoregulation. This study evaluated the impact of age and baseline arterial blood pressure (BP) on the BP recorded at onset of syncope in otherwise healthy individuals undergoing passive head-up tilt (HUT) testing for suspected vasovagal syncope. Since hypertension is thought to shift the lower autoregulation point to higher values, and since older healthy patients tend to have higher BP than younger individuals, we hypothesized that even among healthy individuals HUT-induced syncope would occur at higher BP in older compared with younger subjects. Three groups of otherwise healthy individuals who had positive HUT were identified: Group 1: <25 years, n=17; Group 2: 25-59 years, n=18; and Group 3: > or =60 years, n=7. As expected, baseline arterial systolic blood pressure of patients > or =60 years (162+/-37 mmHg) was significantly higher than in the other two groups (Group 1: <25 years, 116+/-15 mmHg; Group 2: 25-59 years, 128+/-12 mmHg). Further, the > or =60 age group tolerated upright posture for a longer period before syncope than did younger patients. However, despite a trend for BP at syncope to increase with age, differences were small (Group 3: > or =60 years, 61+/-15 mmHg, Group 2: 25-59 years, 58+/-6 mmHg, and Group 1: 54+/-16 mmHg) and were not statistically significant. Thus, in generally healthy individuals, age and baseline BP has only a minor effect on the lower limit of BP necessary for maintenance of consciousness. On the other hand, higher baseline BP provides older individuals a greater blood pressure 'reserve' for maintenance of consciousness compared with younger subjects.

Adolescent↗
PubMed2004

Biventricular implantable cardioverter defibrillators improve survival compared with biventricular pacing alone in patients with severe left ventricular dysfunction.

INTRODUCTION: Biventricular cardiac pacemakers provide important hemodynamic benefit in selected patients with heart failure and severe left ventricular (LV) dysfunction. Nevertheless, these patients remain at high mortality risk. To address this issue, we examined mortality outcome in patients with heart failure treated with biventricular pacemakers alone and those treated with biventricular implantable cardioverter defibrillators (ICDs). METHODS AND RESULTS: The study population consisted of 126 consecutive patients with LV dysfunction and heart failure who received either a biventricular ICD (n = 62) or a biventricular pacemaker (n = 64) between January 1998 and December 2002. A minimum 12 months of follow-up was obtained in all survivors. ICD indications were conventional in all patients. Kaplan-Meier actuarial method and log rank statistics were used to calculate and compare survival rates in both groups. Comparison of mortality rates utilized Chi-square test. The two groups had similar clinical and demographic features, LV ejection fraction, and medication use. Average follow-up times were 13 +/- 11.8 months (range 4-60) and 18 +/- 13.2 months (range 0.5-53) for biventricular ICD and pacemaker groups, respectively. Overall mortality rate was significantly lower in the biventricular ICD group (13%, 8 deaths) compared to the pacemaker group (41%, 26 deaths) (P = 0.01). Further, the predominant survival benefit for ICD-treated patients becomes evident after the first 12 months of follow-up. CONCLUSION: The findings in this study, although necessarily limited in their interpretation by the absence of treatment randomization, suggest that biventricular ICDs offer a survival benefit compared to biventricular pacing alone. Furthermore, this benefit may be most apparent if other clinical factors do not preclude patient survival >1 year postimplant.

Aged↗
PubMed2004

Treatment of hypotension in pigs with an inspiratory impedance threshold device: a feasibility study.

OBJECTIVE: An inspiratory impedance threshold device was evaluated in spontaneously breathing animals with hypotension to determine whether it could help improve systemic arterial pressures when fluid replacement was not immediately available. DESIGN: Prospective, randomized. SETTING: Animal laboratory. SUBJECTS: Thirty-nine female farm pigs (weight, 28-33 kg). INTERVENTIONS: A total of 39 anesthetized spontaneously breathing pigs were treated with an impedance threshold device, with cracking pressures from 0 to -20 cm H2O. Four separate experimental protocols were performed: protocol A, in which the hemodynamics of seven pigs were examined during application of an impedance threshold device at various levels of inspiratory impedance (-5, -10, -15, and -20 cm H(2)O), both before and after a severe, controlled hemorrhage to a systolic blood pressure of 50 - 55 mm Hg; protocol B, in which nine pigs bled to systolic blood pressure of 50 -55 mm Hg were treated with an impedance threshold device set at -12 cm H2O and were compared with nine others treated with a sham device; protocol C, in which the effects of the impedance threshold device on mixed venous gases were measured in seven hemorrhaged pigs; and protocol D, in which the effects of the impedance threshold device on cardiac output in seven hemorrhaged pigs were measured. METHODS AND MAIN RESULTS: During initial studies with both normovolemic and hypovolemic pigs, sequential increases in inspiratory impedance resulted in a significant increase in systolic blood pressure, whereas diastolic left ventricular and right atrial pressures decreased significantly and proportionally to the level of impedance. When comparing the sham vs. active impedance threshold device (-12 cm H(2)O) in hypotensive pigs, systolic blood pressure (mean +/- sem) with active impedance threshold device treatment increased from 70 +/- 2 mm Hg to 105 +/- 4 mm Hg (p <.01). Pressures in the control group remained at 70 +/- 4 mm Hg (p <.01). Cardiac output increased by nearly 25% (p <.01) with the active impedance threshold device when calculated using the mixed gas equation and when determined by thermodilution. CONCLUSIONS: These studies demonstrate that it is feasible to use a device that creates inspiratory impedance in spontaneously breathing normotensive and hypotensive pigs to increase blood pressure and enhance cardiopulmonary circulation in the absence of immediate fluid resuscitation. Further studies are needed to evaluate the potential long-term effects and limitations of this new approach to treat hypovolemic hypotension.

Animals↗
PubMed2004

An epicardial subxiphoid implantable defibrillator lead: superior effectiveness after failure of standard implants.

A single epicardial implantable lead using the subxiphoid approach is described in this article. It consists of a single halo-shaped coil that is implanted under the inferior surface of the heart, including the right and left inferior ventricular surfaces. It has been implanted in four patients who could not be defibrillated with a transvenous system, even with the adjunct use of subcutaneous leads or left chest wall patch. Three of the patients had progressive heart failure due to ischemic myocardiopathy; the fourth patient had a dilated idiopathic myocardiopathy. The approach is simple and appears to be effective due to its ability to encompass the left and right ventricles. This vector seems to significantly lower the threshold for defibrillation, and may offer substantial benefit in the setting of high defibrillation thresholds with conventional leads, or when conventional systems are inadequate to achieve consistent defibrillation.

Adult↗