Impaired rapid eye movement sleep in the Tg2576 APP murine model of Alzheimer's disease with injury to pedunculopontine cholinergic neurons

Impaired rapid eye movement sleep (REMS) is commonly observed in Alzheimer's disease, suggesting injury to mesopontine cholinergic neurons. We sought to determine whether abnormal beta-amyloid peptides impair REMS and injure mesopontine cholinergic neurons in transgenic (hAPP695.SWE) mice (Tg2576) that model brain amyloid pathologies. Tg2576 mice and wild-type littermates were studied at 2, 6, and 12 months by using sleep recordings, contextual fear conditioning, and immunohistochemistry. At 2 months of age, REMS was indistinguishable by genotype but was reduced in Tg2576 mice at 6 and 12 months. Choline acetyltransferase-positive neurons in the pedunculopontine tegmentum of Tg2576 mice at 2 months evidenced activated caspase-3 immunoreactivity, and at 6 and 12 months the numbers of pedunculopontine tegmentum choline acetyltransferase-positive neurons were reduced in the Tg2576 mice. Other cholinergic groups involved in REMS were unperturbed. At 12 months, Tg2576 mice demonstrated increased 3-nitrotyrosine immunoreactivity in cholinergic projection sites but not in cholinergic soma. We have identified a population of selectively compromised cholinergic neurons in young Tg2576 mice that manifest early onset REMS impairment. The differential vulnerability of these cholinergic neurons to Abeta injury provides an invaluable tool with which to understand mechanisms of sleep/wake perturbations in Alzheimer's disease.

Torsade de pointes in a patient with complex medical and psychiatric conditions receiving low-dose quetiapine

OBJECTIVE

Describe potential cardiac complications of low-dose quetiapine and other atypical antipsychotic drugs.

METHOD

We present a case report of a 45-year-old Black woman with multiple medical and psychiatric problems taking low-dose quetiapine.

RESULTS

Coincident with a generalized seizure, the patient developed 'ventricular fibrillation'. She was countershocked with restoration of normal sinus rhythm. The initial electrocardiogram showed QT interval prolongation. Shortly thereafter, classical torsade de pointes appeared, lasted 10 min, and resolved spontaneously. Hypomagnesemia was present. A cardiac electrophysiologist was concerned that the very slow shortening of the prolonged QTc interval after magnesium replacement implicated quetiapine as a risk factor for QTc interval prolongation and torsade de pointes. A psychosomatic medicine consultant asserted that the fragmented medical and psychiatric care almost certainly contributed to the patient's medical problems. We discuss other cases of QT interval prolongation by newer antipsychotic drugs and previous reports by our group concerning the association of psychotropic drugs, QT interval prolongation, and torsade de pointes.

CONCLUSION

Atypical antipsychotic drug administration, when accompanied by risk factors, may contribute to cardiac arrhythmias including torsade de pointes.

Transgenic mice expressing a truncated form of CREB-binding protein (CBP) exhibit deficits in hippocampal synaptic plasticity and memory storage

Deletions, translocations, or point mutations in the CREB-binding protein (CBP) gene have been associated with Rubinstein-Taybi Syndrome; a human developmental disorder characterized by retarded growth and reduced mental function. To examine the role of CBP in memory, transgenic mice were generated in which the CaMKII alpha promoter drives expression of an inhibitory truncated CBP protein in forebrain neurons. Examination of hippocampal long-term potentiation (LTP), a form of synaptic plasticity thought to underlie memory storage, revealed significantly reduced late-phase LTP induced by dopamine-regulated potentiation in hippocampal slices from CBP transgenic mice. However, four-train induced late-phase LTP is normal. Behaviorally, CBP transgenic mice exhibited memory deficits in spatial learning in the Morris water maze and deficits in long-term memory for contextual fear conditioning, two hippocampus-dependent tasks. Together, these results demonstrate that CBP is involved in specific forms of hippocampal synaptic plasticity and hippocampus-dependent long-term memory formation.

Ubiquitin C-terminal hydrolase L3 (Uchl3) is involved in working memory

Regulated proteolysis by the ubiquitin pathway has been implicated in control of the cell cycle, transcriptional activation, cell fate and growth, and synaptogenesis. The ubiquitin-proteasome system is involved in synaptic plasticity and is proposed to be part of a molecular switch that converts short-term synaptic potentiation to long-term changes in synaptic strength. In Aplysia, a component of the ubiquitin system termed ubiquitin C-terminal hydrolase (Ap-Uch) has been shown to be essential for long-term facilitation. To examine whether Uch plays a role in learning, memory, and synaptic plasticity in mammals, we have analyzed mice homozygous for a targeted mutation in ubiquitin C-terminal hydrolase L3 (Uchl3), an orthologue of Ap-Uch. Mice homozygous for the mutation in Uchl3 are viable, with no obvious developmental, histological, or fertility abnormalities. We demonstrate that Uchl3-/- mice have a significant learning deficit relative to wild type littermates in the spatial version of the Morris water maze and the 8-arm radial maze. Further, the impaired performance in the 8-arm radial maze of Uchl3-/- mice is due to significantly increased working memory errors. Examination of hippocampal long-term potentiation (LTP), a form of synaptic plasticity thought to underlie memory storage, revealed no significant differences in LTP in hippocampal slices from Uchl3-/- mice. Our results suggest a novel role for ubiquitin C-terminal hydrolase enzymes in mammals in spatial learning and working memory.

TIP49, but not TRRAP, modulates c-Myc and E2F1 dependent apoptosis

We previously described two nuclear cofactors, TRRAP and TIP49, that have functional roles in Myc-mediated oncogenesis. We have now expanded the analysis of these Myc-associated cofactors to investigate their roles in apoptosis and cell proliferation. Although TRRAP and TIP49 are both essential for transformation, TIP49 modulates c-Myc-mediated apoptosis whereas disruption of TRRAP activity has no apparent effect on apoptosis. We extended our analysis of TIP49 to show that it also binds to the E2F1 transactivation domain and modulates both transforming and apoptotic activities. These results indicate that individual cofactors differentially potentiate c-Myc and E2F1 functions.

BAF53 forms distinct nuclear complexes and functions as a critical c-Myc-interacting nuclear cofactor for oncogenic transformation

The c-Myc oncoprotein functions as a transcription factor that can transform normal cells into tumor cells, as well as playing a direct role in normal cell proliferation. The c-Myc protein transactivates cellular promoters by recruiting nuclear cofactors to chromosomal sites through an N-terminal transactivation domain. We have previously reported the identification and functional characterization of four different c-Myc cofactors: TRRAP, hGCN5, TIP49, and TIP48. Here we present the identification and characterization of the actin-related protein BAF53 as a c-Myc-interacting nuclear cofactor that forms distinct nuclear complexes. In addition to the human SWI/SNF-related BAF complex, BAF53 forms a complex with TIP49 and TIP48 and a separate biochemically distinct complex containing TRRAP and a histone acetyltransferase which does not contain TIP60. Using deletion mutants of BAF53, we show that BAF53 is critical for c-Myc oncogenic activity. Our results indicate that BAF53 plays a functional role in c-Myc-interacting nuclear complexes.

Substratum nanotopography and the adhesion of biological cells. Are symmetry or regularity of nanotopography important?

Animal cells live in environments where many of the features that surround them are on the nanoscale, for example detail on collagen molecules. Do cells react to objects of this size and if so, what features of the molecules are they responding to? Here we show, by fabricating nanometric features in silica and by casting reverse features in polycaprolactone and culturing vertebrate cells in culture upon them, that cells react in their adhesion to the features. With cliffs, adhesion is enhanced at the cliff edge, while pits or pillars in ordered arrays diminish adhesion. The results implicate ordered topography and possibly symmetry effects in the adhesion of cells. Parallel results were obtained in the adhesion of carboxylate-surfaced 2-microm-diameter particles to these surfaces. These results are in agreement with recent predictions from non-biological nanometric systems.

Implantable cardioverter defibrillator T wave oversensing caused by hyperglycemia

This case report highlights a previously unreported cause of T wave oversensing in a patient with an ICD and recent onset diabetes. Consistent T wave oversensing was observed at elevated serum glucose levels and this finding was reproduced with a glucose challenge. No T wave oversensing was seen during treatment of hyperglycemia. Alterations in serum chemistry may account for intermittent T wave oversensing in patients with ICDs.

Effects of sodium channel blockade on ibutilide induced prolongation of repolarization in the isolated rabbit ventricle

INTRODUCTION

Ibutilide fumarate is indicated for the termination of atrial fibrillation and atrial flutter. It's mechanism of action is unclear but may involve activation of a late inward Na(+) current.

METHODS AND RESULTS

Twenty seven experiments were performed using an isolated perfused rabbit right ventricle preparation. In each experiment effective refractory periods (ERP) and transmembrane 90% action potential durations (APD) were measured. In 8 experiments ERP and APD were measured at baseline, in the presence of ibutilide (0. 1[emsp4 ]uM), and in the presence of both ibutilide and tetrodotoxin (TTX, 2[emsp4 ]uM). In 8 experiments lidocaine (10[emsp4 ]uM) was used in place of TTX. Measures were made at 200, 400, and 800[emsp4 ]msec paced cycle lengths under each condition. The baseline values for APD at 200, 400 and 800[emsp4 ]msec cycle lengths for the experiments treated with ibutilide and TTX were 111+/-8, 140+/-14 and 159+/-22[emsp4 ]msec, respectively. In the presence of ibutilide, APD increased to 130+/-19, 192+/-26 and 217+/-35[emsp4 ]msec at 200, 400 and 800[emsp4 ]msec cycle lengths, respectively (all p< or =0.03). After the addition of TTX there was no shortening of APD or ERP compared to treatment with ibutilide alone at any cycle length (all p> or =0.062). Similarly, in the presence of ibutilide and lidocaine there were no changes in APD or ERP compared to treatment with ibutilide alone (all p > or =0.41). In 11 control experiments, there were no changes in APD or ERP on serial measures after placebo and TTX or lidocaine.

CONCLUSION

Ibutilide induced prolongation of ventricular repolarization is not affected by Na(+) channel blockade with lidocaine or TTX in the isolated rabbit heart. These findings suggest that the effects of ibutilide are not mediated by a Na(+) channel dependent late current or that this mechanism contributes minimally to its action in this model.

Influence of autothreshold sensing and sinus rate on mode switching algorithm behavior

Mode switching is beneficial to pacemaker patients with paroxysmal atrial tachyarrhythmias. However, the optimal mode switching algorithm is still in evolution. Mode switching algorithms and atrial sensing circuitry can influence mode switching behavior. This study compared the mode switching behavior of four Medtronic, Inc. implantable devices: Thera DR model 7960 pacemaker, Kappa 700 model KDR701 pacemaker, Gem DR model 7271 dual chamber pacing defibrillator, and Jewel AF model 7250 dual chamber pacemaker atrial and ventricular defibrillator. The Thera and Gem DR use the same mean atrial rate mode switch algorithm. The Kappa and Jewel AF use four of seven short atrial intervals and an atrial fibrillation evidence counter algorithm, respectively. The Thera and Kappa devices use fixed gain sensing and the Gem DR and Jewel AF use autothreshold atrial sensing. Digitally recorded atrial electrograms from 52 episodes of human atrial fibrillation were fed into each device with differing simulated sinus rates before and after the atrial fibrillation. The percent of appropriate mode switching was highest for the Kappa 700 (94%) and lowest for the Thera (85%) (P = 0.046). The time to mode switching was significantly longer for the Thera and Gem DR compared to the Kappa 700 or Jewel AF (all P < 0.05). The time to mode switching was shorter for the Gem DR (9.0 +/- 1.6 s) using autothreshold atrial sensing than for the fixed gain Thera (11.1 +/- 2.1 s, P < 0.05). The mean atrial electrogram amplitude and cycle length were not correlated with the time to mode switching for any device. Faster sinus rates shortened the time to mode switching and prolonged the time to resynchronization in the two devices using the mean atrial interval algorithm. In conclusion, (1) mode switching function among these devices is influenced by algorithms and sensing circuitry, (2) the time to mode switching among these devices is influenced by the algorithm and use of autothreshold atrial sensing, and (3) the sinus rate before and after episodes of atrial fibrillation greatly influences the times to mode switching and resynchronization in devices using the mean atrial interval algorithm.

A prospective randomized-controlled trial of ventricular fibrillation detection time in a DDDR ventricular defibrillator. Ventak AV II DR Study Investigators

Implantable cardioverter defibrillators (ICDs) with dual chamber and dual chamber rate responsive pacing may offer hemodynamic advantages for some ICD patients. Separate ICDs and DDDR pacemakers can result in device to device interactions, inappropriate shocks, and underdetection of ventricular fibrillation (VF). The objectives of this study were to compare the VF detection times between the Ventak AV II DR and the Ventak AV during high rate DDDR and DDD pacing and to test the safety of dynamic ventricular refractory period shortening. Patients receiving an ICD were randomized in a paired comparison to pacing at 150 beats/min (DDD pacing) or 175 beats/min (DDDR pacing) during ICD threshold testing to create a "worst case scenario" for VF detection. The VF detection rate was set to 180 beats/min, and VF was induced during high rate pacing with alternating current. The device was then allowed to detect and treat VF. The induction was repeated for each patient at each programmed setting so that all patients were tested at both programmed settings. Paired analysis was performed. Patient characteristics were a mean age of 69 +/- 11 years, 78% were men, coronary artery disease was present in 85%, and a mean left ventricular ejection fraction of 0.34 +/- 0.11. Fifty-two episodes of VF were induced in 26 patients. Despite the high pacing rate, all VF episodes were appropriately detected. The mean VF detection time was 2.4 +/- 1.0 seconds during DDD pacing and 2.9 +/- 1.9 seconds during DDDR pacing (P = NS). DDD and DDDR programming resulted in appropriate detection of all episodes of VF with similar detection times despite the "worst case scenario" tested. Delays in detection may be seen with long programmed ventricular refractory periods which shorten the VF sensing window and may be avoided with dynamic ventricular refractory period shortening.

Clinical characteristics of patients intolerant to VVIR pacing

The incidence and clinical predictors of the development of intolerance to VVIR pacing have not been extensively studied in prospective long-term randomized trials comparing different pacing modes. The frequency and clinical factors predicting intolerance to ventricular pacing are controversial. The Pacemaker Selection in the Elderly (PASE) Trial enrolled 407 patients aged >/=65 years in a 30-month, single-blind, randomized, controlled comparison of quality of life and clinical outcomes with ventricular pacing and dual-chamber pacing in patients undergoing dual-chamber pacemaker implantation for standard clinically accepted indications. We reviewed the clinical, hemodynamic, and electrophysiologic variables at the time of pacemaker implantation in 204 patients enrolled in the PASE trial and randomized to the VVIR mode, some of whom subsequently required crossover (reprogramming) to DDDR pacing. During a median follow-up of 555 days, 53 patients (26%) crossed over from VVIR to DDDR pacing. A decrease in systolic blood pressure during ventricular pacing at the time of pacemaker implantation (p = 0.001), use of beta blockers at the time of randomization (p = 0.01), and nonischemic cardiomyopathy (p = 0.04) were the only variables that predicted crossover in the Cox multivariate regression model. After reprogramming to the dual-chamber mode, patients showed improvement in all aspects of quality of life, with significant improvements in physical and emotional role. The high incidence of crossover from VVIR to DDDR pacing along with significant improvements in quality of life after crossover to DDDR pacing strongly favors dual-chamber pacing compared with single-chamber ventricular pacing in elderly patients requiring permanent pacing.

The acute effects of biatrial pacing on atrial depolarization and repolarization

Permanent biatrial and/or multisite atrial pacing may prevent atrial fibrillation (AF), but the effects on atrial electrophysiology remain incompletely understood. Acute biatrial pacing was studied in 20 patients with and 28 without (controls) a history of atrial fibrillation and/or flutter. Twelve-lead electrocardiograms were recorded during pacing from the high right atrium (RA), from the distal coronary sinus (LA), and biatrial pacing. P wave duration was measured in each lead and the difference between maximum and minimum P duration was termed P wave dispersion. Effective refractory periods (ERPs) were measured during each pacing mode. The dispersion of P wave duration was 35 +/- 14 ms in controls and 40 +/- 29 ms in AF patients (P = 0.17). Compared to RA pacing, LA pacing shortened P duration in controls (127 +/- 18 to 107 +/- 16 ms, P < 0.05) and biatrial pacing markedly shortened P duration in controls (127 +/- 18 to 93 +/- 14 ms, P < 0.05) and AF patients (114 +/- 43 to 97 +/- 21 ms, P < 0.05). P wave dispersion was unaffected. In controls, the LA ERP was longer than the RA ERP. This phenomenon was not present in AF patients, whose LA ERP was shorter than that of controls. Biatrial pacing had no effect on atrial ERPs or the dispersion of atrial refractoriness. In conclusion, acute biatrial pacing does not affect atrial repolarization but it does cause a marked shortening of global biatrial depolarization. Distal coronary sinus pacing produces a shorter P wave than RA pacing. There is substantial dispersion in the surface P wave of the electrocardiogram, the significance of which awaits further study.

Left ventricular tachycardia originating near the left main coronary artery

Eight patients with idiopathic ventricular tachycardia (VT) underwent mapping and radiofrequency ablation. Mapping showed VT originating in the high posterolateral left ventricular outflow tract in proximity to the left main and proximal circumflex coronary arteries. Ablation was not attempted due to this proximity to the left main and proximal circumflex coronary arteries. Ablation was not attempted due to this proximity in 2 patients and limited in 1 patient. It was successful in VT suppression in 5 of 6 patients.

Smoothed Particle Hydrodynamics Simulations of Apsidal and Nodal Superhumps

In recent years, a handful of systems have been observed to show "negative" (nodal) superhumps, with periods slightly shorter than the orbital period. It has been suggested that these modes are a consequence of the slow retrograde precession of the line of nodes in a disk tilted with respect to the orbital plane. Our simulations confirm and refine this model: they suggest a roughly axisymmetric, retrogradely precessing, tilted disk that is driven at a period slightly less than half the orbital period as the tidal field of the orbiting secondary encounters, in turn, the two halves of the disk above and below the midplane. Each of these passings leads to viscous dissipation on one face of an optically thick disk-observers on opposite sides of the disk would each observe one brightening per orbit, but 180 degrees out of phase with each other.

Clinical outcomes after ablation and pacing therapy for atrial fibrillation : a meta-analysis

BACKGROUND

Radiofrequency ablation of the atrioventricular node and permanent pacing are used for symptomatic relief in patients with medically refractory atrial fibrillation. In this study, meta-analysis was used to clarify clinical outcomes and survival after ablation and pacing therapy using data from the published literature.

METHODS AND RESULTS

We used 21 studies with a total of 1181 patients in the meta-analysis. All patients had medically refractory atrial tachyarrhythmias, primarily atrial fibrillation (97%). Nineteen measures of clinical outcome, encompassing quality of life, ventricular function, exercise duration, and healthcare use, were derived from the studies. The meta-analysis demonstrated significant improvement after ablation and pacing therapy in all outcome measures except fractional shortening, which demonstrated a trend toward improvement (P=0.08). Ejection fraction did show significant improvement (P<0.001). The calculated 1-year total and sudden death mortality rates after ablation and pacing therapy were 6.3% and 2.0%, respectively.

CONCLUSIONS

Ablation and pacing therapy improves a broad range of clinical outcomes for patients with medically refractory atrial fibrillation. The calculated 1-year mortality rates after this therapy are low and comparable with medical therapy.

An ATPase/helicase complex is an essential cofactor for oncogenic transformation by c-Myc

The c-Myc transactivation domain was used to affinity purify tightly associated nuclear proteins. Two of these proteins were identified as TIP49 and a novel related protein called TIP48, both of which are highly conserved in evolution and contain ATPase/helicase motifs. TIP49 and TIP48 are complexed with c-Myc in vivo, and binding is dependent on a c-Myc domain essential for oncogenic activity. A missense mutation in the TIP49 ATPase motif acts as a dominant inhibitor of c-Myc oncogenic activity but does not inhibit normal cell growth, indicating that functional TIP49 protein is an essential mediator of c-Myc oncogenic transformation. The TIP49 and TIP48 ATPase/helicase proteins represent a novel class of cofactors recruited by transcriptional activation domains that function in diverse pathways.

Automated pacemaker function

Pacemakers have used automated functions since the introduction of the inhibited mode more than 30 years ago. Currently, virtually all aspects of pacemaker function are subject to automated control, including automated threshold tracking and sensitivity adjustment. These features are designed to enhance patient safety and quality of life, extend battery life, and simplify pacemaker programming and follow-up for health care providers. Many of these automated algorithms are still in evolution and the clinical benefits are not clearly demonstrated for all functions. Although pacemaker function will become increasingly automated, these features should not be accepted uncritically and without demonstrating benefit to the pacemaker patient.

The essential cofactor TRRAP recruits the histone acetyltransferase hGCN5 to c-Myc

The c-Myc protein functions as a transcription factor to facilitate oncogenic transformation; however, the biochemical and genetic pathways leading to transformation remain undefined. We demonstrate here that the recently described c-Myc cofactor TRRAP recruits histone acetylase activity, which is catalyzed by the human GCN5 protein. Since c-Myc function is inhibited by recruitment of histone deacetylase activity through Mad family proteins, these opposing biochemical activities are likely to be responsible for the antagonistic biological effects of c-Myc and Mad on target genes and ultimately on cellular transformation.

Induction of ventricular fibrillation by T wave shocks: observations from monophasic action potential recordings

INTRODUCTION

Shocks given during the vulnerable period of cardiac repolarization may induce ventricular fibrillation (VF). However, the relationship of the vulnerable period and the monophasic action potential (MAP) has not yet been reported in humans. The purpose of this study was, therefore, to determine how the monophasic action potential recorded from the right ventricle correlates with inducibility of VF using T wave shocks during ventricular pacing.

METHODS

Eleven patients undergoing implantable cardioverter defibrillator (ICD) implantation had a MAP catheter positioned in the right ventricle (RV). The local monophasic action potential duration at 90% repolarization (MAP90) duration was measured during pacing at 400 ms. VF induction was attempted by pacing at 400 ms for 10 cycles and then giving a 1.0 joule monophasic T wave shock at varying coupling intervals (CI) to the last paced stimulus. The maximum and minimum CI that induced VF were determined and mapped in relation to the MAP90 recording.

RESULTS

The average paced MAP duration was 275 +/- 20 ms. The minimum and maximum CI to induce VF were 255 +/- 24 ms and 325 +/- 36 ms respectively. This ranged from 93% to 118% of the MAP90 duration but because of delay in conduction time to the MAP catheter, shocks that induced ventricular fibrillation occurred between 74% and 99% of local repolarization time.

CONCLUSION

VF is inducible with low energy T wave shocks falling during the last 25% of the right ventricular MAP90 recording. This corresponds with VF initiation during phase III repolarization.

Variation of spectral power immediately prior to spontaneous onset of ventricular tachycardia/ventricular fibrillation in implantable cardioverter defibrillator patients

INTRODUCTION

Short-term heart rate variability (HRV) may change immediately before onset of a ventricular arrhythmia (ONSET).

METHODS AND RESULTS

Power spectrum analysis was performed on instantaneous heart rate (IHR; including all beats) and normal heart rate (NHR; excluding ectopics) curves obtained at equally spaced 0.5-second intervals using a cubic spline. The database consisted of 135 sets of 1,024 RR intervals leading to ventricular arrhythmia (VA) and controls from 78 patients. Total periodogram and time course of spectral power were obtained. Ten spectral bands of 0.1-Hz bandwidth (0 to 1 Hz) were analyzed. A simple threshold technique was retrospectively used to predict the onset of a VA. RR intervals that led to VA ONSET had significantly higher total spectral power than controls (P < 0.001 for both NHR and IHR for every band). Spectral power remained constant until 100 seconds before ONSET and then increased significantly in the time window immediately preceding ONSET (P < 0.02 compared with others). Using a simple threshold method, a predictive accuracy of 68%+/-1.4% was obtained with different window sizes. Using specific spectral bands, the predictive accuracy of VA ONSET could be improved to 76% for IHR and 71% for NHR (0.8- to 0.9-Hz band).

CONCLUSION

Our results suggest that a sustained higher power increase in NHR and IHR occurs during the course of 12.11+/-.57 minutes, followed by a sudden elevation in spectral power within 100 seconds of ONSET, and may be a precursor to ventricular tachycardia/ventricular fibrillation episodes.

Diagnostic utility of mechanical, pharmacological and orthostatic stimulation of the carotid sinus in patients with unexplained syncope

OBJECTIVES

The purpose of the present study was to systematically evaluate the diagnostic utility of mechanical, pharmacological and orthostatic stimulation of the carotid sinus in a consecutive series of patients with recurrent unexplained syncope.

BACKGROUND

Carotid sinus hypersensitivity (CSH) is an infrequently recognized cause of recurrent unexplained syncope usually diagnosed by carotid sinus massage (CSM) in the supine position. The diagnostic utility of systematic assessment of mechanical, pharmacological and orthostatic stimulation of the carotid sinus has not been clearly established.

METHODS

Eighty consecutive patients (63 +/- 12 years) with a history of recurrent unexplained syncope (mean episodes: 6 +/- 3); 30 age-matched controls (65 +/- 14 years) and 16 patients (59 +/- 12 years) with syncope not related to CSH were studied. Pharmacological stimulation of the carotid sinus was achieved by randomly administering bolus injections of nitroprusside and phenylephrine. Mechanical stimulation of the carotid sinus was performed by CSM applied for 5 s in the supine position and after 2 min at 60 degrees. A 60 degree low-dose isoproterenol head-up tilt test (HUTT) was also performed for a total duration of 30 min.

RESULTS

Carotid sinus hypersensitivity was elicited by CSM in the supine position in seven (8.7%) patients, two (6.6%) controls and one (6.3%) patient with syncope unrelated to CSH, compared with 48 (60%) patients, two (6.6%) controls and one (6.3%) syncope unrelated to CSH patient after 60 degree HUTT, increasing the diagnostic yield by 51%. Baroreceptor gain was significantly reduced in the CSH group. Head-up tilt test was positive in 12 (25%) patients with CSH, two (6.6%) controls and two (12%) with documented syncope but not positive in any of the patients in which syncope remained unexplained. Diagnostic accuracy was enhanced by 38% (31% supine vs. 69% upright) when CSM was performed at 60 degrees.

CONCLUSIONS

CSH was documented in 68% of patients, 8.7% in the supine position and 60% in the upright position. Sensitivity was increased by 51%, and diagnostic accuracy was enhanced by 38% by performing CSM in the upright position. Decreased baroreceptor gain was documented and may play a role in the pathophysiology of CSH.