Identification of Porphyromonas levii isolated from clinical cases of bovine interdigital necrobacillosis by 16S rRNA sequencing

Laboratories use pigmentation, antibiotic susceptibility, and biochemical tests to identify anaerobic organisms that play a role in bovine interdigital necrobacillosis (bovine foot rot). In this study, 16S rRNA gene sequencing was used to identify strains to the species level that were originally classified as Prevotella or Porphyromonas spp by conventional phenotype assessment methods. Of 264 qualified strains from ceftiofur clinical trials, 241 isolates were definitively identified by 16S rRNA sequencing as Porphyromonas levii. Similarly, of 275 qualified strains from tulathromycin clinical trials, 156 isolates were definitively identified by 16S rRNA sequencing as P. levii. The predominance of P. levii in this study supports the role of this organism as an associative agent of bovine foot rot and may have implications for routine laboratory diagnosis.

Characterisation of tone oscillations in placental and myometrial arteries from normal pregnancies and those complicated by pre-eclampsia and growth restriction

Agonist-induced tone oscillations (rhythmic contractions and relaxations) occur in vascular beds to allow acute regulation of volume flow and thus the delivery of oxygen and nutrients to the tissue. Mechanisms responsible for the control of human placental vasomotor tone and blood flow are poorly characterized. This study aimed to characterise thromboxane-induced tone oscillations in human placental and myometrial arteries. Chorionic plate and myometrial arteries obtained from biopsies at term were mounted for isometric tension measurement. Tone oscillations were observed in chorionic arteries only when exposed to sub-maximal (<1 microM) concentrations of U46619. Slow (mean+/-SEM) frequency (2.6+/-0.5 per hour), large amplitude (39+/-7% of peak contraction) tone oscillations were elicited by 0.03 microM U46619 (n=18). In the presence of the nitric oxide synthase (NOS) inhibitor l-NNA (100 microM) the amplitude was significantly reduced (40+/-13% to 18+/-8%, P<0.05, n=6), frequency was unaltered and the bradykinin-dependent vasodilator response was reduced (68+/-13% to 40+/-19%, P<0.05, n=6). Myometrial arteries exposed to 1 microM U46619 developed tone oscillations within 10 min, which increased in amplitude over 30min occurring at relatively constant frequency. The mean amplitude of oscillations at 30 min (31+/-7%, n=16) was similar to that in chorionic arteries but the occurrence more frequent (42.8+/-9.7 per hour, P<0.001). Inhibition of NOS did not alter tone oscillations in myometrial arteries. Tone oscillations in chorionic arteries from pre-eclamptic and growth restricted (FGR) pregnancies were reduced in amplitude whereas those in myometrial arteries had increased frequency. Inhibition of NOS further reduced oscillation amplitude in chorionic arteries from FGR pregnancies. The alterations may contribute to the vasculopathology of these conditions, or, may represent compensatory mechanisms to maintain a matching of materno-placental blood flow.

The oral health of people with intellectual disability participating in the UK Special Olympics

BACKGROUND

Research on the dental health of people with intellectual disability has consistently reported more untreated dental disease, more extractions and fewer fillings than in the general population. This paper describes the oral health of participants at the 2005 Glasgow Special Olympics (SO), relating this to the general population studied in the 1998 UK Adult Dental Health Survey (ADHS) and to participants' age and region of residence.

METHODS

Consenting SO participants were offered oral examinations which followed the standardized SO protocol plus an innovative soft tissue examination. Urgency of any treatment required was noted and reported to participants and carers. Three measures of good dental health--having 21 or more natural teeth, absence of fillings and having no obvious untreated decay--were compared across age groups, regions and with the general population. Logistic regression was used to control for age differences between regions.

RESULTS

In total, 1021 oral examinations were completed. Older SO participants were more likely to have fewer than 21 teeth and to have fillings, untreated decay, gum inflammation and heavy plaque levels. In all, 28% of SO participants had 21 or more teeth, no fillings and no obvious decay. Those from the north, midlands and south regions of England had significantly more chance of good dental health so defined compared with participants from Scotland [ORs 1.67 (1.09, 2.67), 1.69 (1.12, 2.54), 1.99 (1.26, 3.16), respectively]. Compared with the general population surveyed in the 1998 ADHS study, SO participants were more likely to be free from fillings and obvious untreated decay, but fewer had 21 or more natural teeth among older age groups. Nine per cent were found to have soft tissue problems, and one in four of these required follow-up. Gum inflammation was common. Overall, 5% of participants were judged to require urgent treatment for dental or soft tissue problems and 40% to require non-urgent treatment. This rose to 9% and 66% respectively among those aged 35 years and over.

DISCUSSION

The low prevalence of untreated decay and fillings among SO participants compared with the general population may be due to their being well supported by family and carers. The study identifies the vulnerability of the older participants to dental problems, and this may indicate greater difficulty maintaining surveillance as individuals age or informal carers become less able or available. Regional variations are similar to those found in the general population. The implications for the organization of care for this group are discussed.

Phenotypic homogeneity of the Huntington disease-like presentation in a SCA17 family

We describe clinical and genetic analysis of a family with spinocerebellar ataxia 17 (SCA17) presenting with a Huntington disease-like (HDL) syndrome. Clinically diagnosed, HD is genetically heterogeneous. Differential diagnosis includes SCA17. However, SCA17 HDL presentation has been observed only sporadically or in solitary individuals within a family. HDL phenotypic homogeneity in SCA17 has not been described. SCA17 can present with a HDL syndrome in multiple family members.

Familial dopa-responsive cervical dystonia

The authors present four cases from two unrelated families with young-onset predominant cervical dystonia with a dramatic sustained response to levodopa. Onset age was 12 years (range 9 to 15). Additional symptoms included postural hand tremor and laryngeal dystonia. Genetic testing for GTP cyclohydrolase I, tyrosine hydroxylase, and sepiapterin reductase was negative. These cases may represent new forms of dopa-responsive dystonia. Levodopa is advisable in all patients with young-onset cervical dystonia.

Ultrastructural features of smooth muscle and endothelial cells of isolated isobaric human placental and maternal arteries

The ability of a blood vessel to develop tone is dependent upon morphological parameters of the smooth muscle cells (SMC), including density, relationship with the endothelium and subcellular distribution of myofilaments and intracellular organelles. Consequently, wall ultrastructure of isolated human placental chorionic plate arteries (n=12), fixed when pressurised to mimic their in vivo geometry, was examined qualitatively using electron microscopy, and compared with maternal arteries (omental, n=10, myometrial, n=6). Arteries from women with uncomplicated pregnancy were tested for contractile viability before fixing, with some vessels post-fixed in osmium-ferricyanide for sarcoplasmic reticulum (SR) identification. In contrast to maternal arteries, placental arteries had no internal elastic lamina but exhibited considerable extracellular matrix separating circularly orientated SMC. Human SMC contained tightly packed arrays of myofilaments running parallel to the plasma membrane, enveloping cellular organelles. Synthetic SMC, with few myofilaments and much rough SR, were observed in placental arteries only. SR in SMC from maternal arteries was located centrally, often encircling mitochondria, and also near the plasma membrane associated with caveolae. Positive SR staining was rarely observed in SMC of placental arteries. This study highlights ultrastructural differences between placental and maternal arteries that may underlie specialised mechanisms of regulating vascular tone in the placenta.

A double blind, randomised study of sildenafil citrate for erectile dysfunction in men with multiple sclerosis

OBJECTIVE

Identifying and effectively treating erectile dysfunction (ED) can result in an improvement of the quality of life (QoL) in men with multiple sclerosis (MS).

METHODS

This randomised, double blind (DB), placebo controlled, flexible dose study with an open label extension (OLE) assessed efficacy, QoL, and safety of sildenafil citrate in men with MS and ED. Overall, 217 men received sildenafil (25-100 mg; n = 104) or placebo (n = 113) for 12 weeks. Efficacy was assessed by the International Index of Erectile Function (IIEF) questionnaire that includes questions on achieving (Q3) and maintaining (Q4) an erection as well as a global efficacy question (GEQ). QoL was also assessed.

RESULTS

After 12 weeks, patients receiving sildenafil had higher mean scores for IIEF Q3 and Q4 compared with those receiving placebo (p<0.0001), and 89% (92/103) reported improved erections compared with 24% (27/112) of patients receiving placebo (p<0.0001). At the end of the OLE phase, 95% of men reported improved erections. Patients receiving placebo during the DB phase showed a nearly fourfold increase in improved erections (97% v 26%). Men receiving sildenafil also showed improvements in five of the eight general QoL questions compared with men receiving placebo (p<0.05). The total mean score for the QoL questionnaire improved by 43% for the sildenafil group versus 13% for the placebo group (p<0.0001). Treatment related AEs were predominantly mild in nature, and no patient discontinued due to an AE.

CONCLUSION

Sildenafil treatment for ED in men with MS was effective and well tolerated, and resulted in significant improvements in both general and disease specific QoL variables.

Increased DMT1 but not IREG1 or HFE mRNA following iron depletion therapy in hereditary haemochromatosis

BACKGROUND AND AIMS

While upregulation of divalent metal transporter 1 (DMT1) and iron regulated gene 1 (IREG1) within duodenal enterocytes is reported in patients with hereditary haemochromatosis (HH), these findings are controversial. Furthermore, the effect of HFE, the gene mutated in HH, on expression of these molecules is unclear. This study examines duodenal expression of these three molecules in HH patients (prior to and following phlebotomy), in patients with iron deficiency (ID), and in controls.

METHODS

DMT1, IREG1, and HFE mRNA were measured in duodenal tissue of C282Y homozygous HH patients, in ID patients negative for the C282Y mutation with a serum ferritin concentration less than 20 microg/l, and in controls negative for C282Y and H63D mutations with normal iron indices, using real time polymerase chain reaction.

RESULTS

DMT1 and IREG1 mRNA levels were not significantly different in non-phlebotomised (untreated) HH patients compared with controls. DMT1 expression was significantly increased in HH patients who had undergone phlebotomy therapy (treated) and in patients with ID compared with controls. IREG1 was significantly increased in ID patients relative to controls, and while IREG1 expression was 1.8-fold greater in treated HH patients, this was not statistically significant. HFE mRNA expression was not significantly different in any of the groups investigated relative to controls.

CONCLUSIONS

These findings demonstrate that untreated HH patients do not have increased duodenal DMT1 and IREG mRNA, but rather phlebotomy increases expression of these molecules, reflecting the effect of phlebotomy induced erythropoiesis. Finally, HFE appears to play a minor role in the regulation of iron absorption by the duodenal enterocyte.

Treatment satisfaction in patients with erectile dysfunction switching from prostaglandin E1 intracavernosal injection therapy to oral sildenafil citrate

Treatment satisfaction, subanalysed by demographic variables, was evaluated in patients switching from successful intracavernosal prostaglandin E(1) (PGE(1)) therapy to oral sildenafil citrate. The validated Erectile Dysfunction Inventory of Treatment Satisfaction questionnaire was administered at the end of PGE(1) therapy and after 12 weeks of sildenafil treatment in a multicentre, open-label study. Men with erectile dysfunction (n=176) who were switched from stable PGE(1) therapy to sildenafil (25-100 mg) were equally satisfied with onset of action, duration of action, and confidence in ability to engage in sexual activity, but expressed greater overall treatment satisfaction with sildenafil (P<0.01), better ease of use (P<0.001), naturalness of erectile process (P<0.001), and intention to continue treatment (P<0.001). Partners (n=32) were overall more satisfied with sildenafil (P<0.05), and their responses correlated with patient satisfaction (r=0.68). Compared with PGE(1) injection, these data suggest that patients may be less likely to discontinue taking sildenafil treatment for their erectile dysfunction.

Minimal time to successful intercourse after sildenafil citrate: results of a randomized, double-blind, placebo-controlled trial

OBJECTIVES

To determine the minimal time to successful intercourse after taking sildenafil citrate for erectile dysfunction (ED).

METHODS

Male patients with ED (mean age 60 years; mean ED duration 7.0 years) who were successfully treated with sildenafil (100 mg) for 2 months or longer were randomized to sildenafil (n = 115) or placebo (n = 113) for 4 weeks of double-blind treatment. Using a stopwatch, patients recorded the time needed to obtain an erection hard enough for sexual intercourse after taking the study drug at least 2 hours after eating.

RESULTS

Within 14 and 20 minutes of sildenafil dosing, 35% and 51% of sildenafil-treated patients, respectively, versus 22% and 30% of placebo-treated patients, respectively, had an erection that led to successful intercourse (P <0.05 for both). The median time to erection leading to successful intercourse after sildenafil dosing was 36 minutes compared with 141 minutes for placebo.

CONCLUSIONS

In this study, slightly more than one half of a population of prior sildenafil responders achieved an erection that led to successful sexual intercourse within 20 minutes of sildenafil administration, suggesting that the onset of action of sildenafil can be less than 30 minutes in men with ED.

The release of mercury from dental amalgam and potential neurotoxicological effects

OBJECTIVES

The aim of this study was to estimate the amount of mercury released into both air and saliva from fresh and aged, abraded amalgam discs and then investigate neurotoxic effects of inorganic mercury upon sensory neuronal cultures.

METHODS

An air-tight chamber was constructed to allow the combined estimation of mercury species released from amalgam pellets. The level released into air and saliva from both freshly packed and aged-abraded amalgam pellets was assessed. Dorsal root ganglia cultures from male CBA mice were exposed to 1 and 10 microM mercuric chloride concentrations. The effects of this were assessed by means of morphology, adhesion, size and immunocytochemistry.

RESULTS

The mercury released into air from dry fresh amalgam was low and less than the recommended industrial exposure limit for mercury. However, covering the discs with saliva reduced air-mercury levels by 46-56% and there was a statistically significant difference in the air-mercury levels recorded (p=0.013-0.048). The mercury released into air from dry abraded amalgam was shown to be above the recommended industrial limit. Coating the abraded amalgam discs with saliva reduced the mercury by 66-72% with the levels recorded being significantly lower (p<0.001). The level of total mercury within the saliva was found to be highly variable. Little change was noted in the neuronal cultures treated with 1 microM mercuric chloride. However, the cultures exposed to high level (10 microM) mercuric chloride showed cells that became rounded and clumped together indicating pathological change.

CONCLUSIONS

Amalgam placement appears to present minimal mercury exposure risk. To reduce the amount of mercury released into air, however, amalgam should be polished in a moist atmosphere with high volume aspiration. The neurotoxic effect of mercury appears to be related to concentration, as only in the cultures treated with 10 microM mercuric chloride showed striking qualitative and quantitative cellular changes.

Anorexic effect of K+ channel blockade in mesenteric arterial smooth muscle and intestinal epithelial cells

Activity of voltage-gated K+ (Kv) channels controls membrane potential (E(m)). Membrane depolarization due to blockade of K+ channels in mesenteric artery smooth muscle cells (MASMC) should increase cytoplasmic free Ca2+ concentration ([Ca2+]cyt) and cause vasoconstriction, which may subsequently reduce the mesenteric blood flow and inhibit the transportation of absorbed nutrients to the liver and adipose tissue. In this study, we characterized and compared the electrophysiological properties and molecular identities of Kv channels and examined the role of Kv channel function in regulating E(m) in MASMC and intestinal epithelial cells (IEC). MASMC and IEC functionally expressed multiple Kv channel alpha- and beta-subunits (Kv1.1, Kv1.2, Kv1.3, Kv1.4, Kv1.5, Kv2.1, Kv4.3, and Kv9.3, as well as Kvbeta1.1, Kvbeta2.1, and Kvbeta3), but only MASMC expressed voltage-dependent Ca2+ channels. The current density and the activation and inactivation kinetics of whole cell Kv currents were similar in MASMC and IEC. Extracellular application of 4-aminopyridine (4-AP), a Kv-channel blocker, reduced whole cell Kv currents and caused E(m) depolarization in both MASMC and IEC. The 4-AP-induced E(m) depolarization increased [Ca2+]cyt in MASMC and caused mesenteric vasoconstriction. Furthermore, ingestion of 4-AP significantly reduced the weight gain in rats. These results suggest that MASMC and IEC express multiple Kv channel alpha- and beta-subunits. The function of these Kv channels plays an important role in controlling E(m). The membrane depolarization-mediated increase in [Ca2+]cyt in MASMC and mesenteric vasoconstriction may inhibit transportation of absorbed nutrients via mesenteric circulation and limit weight gain.

Sildenafil citrate for the treatment of erectile dysfunction in men with Type II diabetes mellitus

AIMS/HYPOTHESIS

Ninety percent of all men with diabetes have Type II (non-insulin-dependent) diabetes mellitus, and erectile dysfunction (ED) is common in this patient group. This study evaluated the effects of sildenafil on men with erectile dysfunction and Type II diabetes and compared the results with glycated haemoglobin concentrations and chronic diabetic complications.

METHODS

Patients (mean age, 59 years) in this double-blind, placebo-controlled trial were randomised to sildenafil (25-100 mg; n = 110) or matching placebo (n = 109) for 12 weeks. Primary criteria for efficacy included questions 3 (achieving an erection) and 4 (maintaining an erection) from the International Index of Erectile Function (IIEF, score range, 0-5). Secondary outcome measures included a global efficacy question (GEQ), patient event logs, a life satisfaction checklist, and the remaining IIEF questions.

RESULTS

After 12 weeks, the mean scores for questions 3 and 4 had improved significantly in patients receiving sildenafil (3.42 +/- 0.23 and 3.35 +/- 0.24) compared with placebo (1.86 +/- 0.22 and 1.84 +/- 0.23; p < 0.0001). Similarly, the GEQ score was higher in the sildenafil (64.6 %) than the placebo group (10.5 %). Even when correlating efficacy with glycated haemoglobin concentrations ( < or = 8.3 % or > 8.3 %, the median concentration found in this study) or the number of diabetic complications (0 or > or = 1), the mean scores for the GEQ and questions 3 and 4 from the IIEF remained higher for all the sildenafil groups compared with the placebo groups (p < 0.0001).

CONCLUSION/INTERPRETATION

Sildenafil was well-tolerated and effective in improving erectile dysfunction in men with Type II diabetes, even in patients with poor glycaemic control and chronic complications.

Efficacy of paroxetine in the treatment of adolescent major depression: a randomized, controlled trial

OBJECTIVE

To compare paroxetine with placebo and imipramine with placebo for the treatment of adolescent depression.

METHOD

After a 7- to 14-day screening period, 275 adolescents with major depression began 8 weeks of double-blind paroxetine (20-40 mg), imipramine (gradual upward titration to 200-300 mg), or placebo. The two primary outcome measures were endpoint response (Hamilton Rating Scale for Depression [HAM-D] score < or = 8 or > or = 50% reduction in baseline HAM-D) and change from baseline HAM-D score. Other depression-related variables were (1) HAM-D depressed mood item; (2) depression item of the Schedule for Affective Disorders and Schizophrenia for Adolescents-Lifetime version (K-SADS-L); (3) Clinical Global Impression (CGI) improvement scores of 1 or 2; (4) nine-item depression subscale of K-SADS-L; and (5) mean CGI improvement scores.

RESULTS

Paroxetine demonstrated significantly greater improvement compared with placebo in HAM-D total score < or = 8, HAM-D depressed mood item, K-SADS-L depressed mood item, and CGI score of 1 or 2. The response to imipramine was not significantly different from placebo for any measure. Neither paroxetine nor imipramine differed significantly from placebo on parent- or self-rating measures. Withdrawal rates for adverse effects were 9.7% and 6.9% for paroxetine and placebo, respectively. Of 31.5% of subjects stopping imipramine therapy because of adverse effects, nearly one third did so because of adverse cardiovascular effects.

CONCLUSIONS

Paroxetine is generally well tolerated and effective for major depression in adolescents.

Capacitative Ca(2+) entry in agonist-induced pulmonary vasoconstriction

Agonist-induced increases in cytosolic Ca(2+) concentration ([Ca(2+)](cyt)) in pulmonary artery (PA) smooth muscle cells (SMCs) consist of a transient Ca(2+) release from intracellular stores followed by a sustained Ca(2+) influx. Depletion of intracellular Ca(2+) stores triggers capacitative Ca(2+) entry (CCE), which contributes to the sustained increase in [Ca(2+)](cyt) and the refilling of Ca(2+) into the stores. In isolated PAs superfused with Ca(2+)-free solution, phenylephrine induced a transient contraction, apparently by a rise in [Ca(2+)](cyt) due to Ca(2+) release from the intracellular stores. The transient contraction lasted for 3-4 min until the Ca(2+) store was depleted. Restoration of extracellular Ca(2+) in the presence of phentolamine produced a contraction potentially due to a rise in [Ca(2+)](cyt) via CCE. The store-operated Ca(2+) channel blocker Ni(2+) reduced the store depletion-activated Ca(2+) currents, decreased CCE, and inhibited the CCE-mediated contraction. In single PASMCs, we identified, using RT-PCR, five transient receptor potential gene transcripts. These results suggest that CCE, potentially through transient receptor potential-encoded Ca(2+) channels, plays an important role in agonist-mediated PA contraction.

Activation of K+ channels induces apoptosis in vascular smooth muscle cells

Intracellular K+ plays an important role in controlling the cytoplasmic ion homeostasis for maintaining cell volume and inhibiting apoptotic enzymes in the cytosol and nucleus. Cytoplasmic K+ concentration is mainly regulated by K+ uptake via Na+-K+-ATPase and K+ efflux through K+ channels in the plasma membrane. Carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP), a protonophore that dissipates the H+ gradient across the inner membrane of mitochondria, induces apoptosis in many cell types. In rat and human pulmonary artery smooth muscle cells (PASMC), FCCP opened the large-conductance, voltage- and Ca2+-sensitive KK+ (maxi-K) channels, increased K+ currents through maxi-K channels [I(K(Ca))], and induced apoptosis. Tetraethylammonia (1 mM) and iberiotoxin (100 nM) decreased I(K(Ca)) by blocking the sarcolemmal maxi-K channels and inhibited the FCCP-induced apoptosis in PASMC cultured in media containing serum and growth factors. Furthermore, inhibition of K+ efflux by raising extracellular K+ concentration from 5 to 40 mM also attenuated PASMC apoptosis induced by FCCP and the K+ ionophore valinomycin. These results suggest that FCCP-mediated apoptosis in PASMC is partially due to an increase of maxi-K channel activity. The resultant K+ loss through opened maxi-K channels may serve as a trigger for cell shrinkage and caspase activation, which are major characteristics of apoptosis in pulmonary vascular smooth muscle cells.

Upregulated TRP and enhanced capacitative Ca(2+) entry in human pulmonary artery myocytes during proliferation

A rise in cytosolic Ca(2+) concentration ([Ca(2+)](cyt)) due to Ca(2+) release from intracellular Ca(2+) stores and Ca(2+) influx through plasmalemmal Ca(2+) channels plays a critical role in mitogen-mediated cell growth. Depletion of intracellular Ca(2+) stores triggers capacitative Ca(2+) entry (CCE), a mechanism involved in maintaining Ca(2+) influx and refilling intracellular Ca(2+) stores. Transient receptor potential (TRP) genes have been demonstrated to encode the store-operated Ca(2+) channels that are activated by Ca(2+) store depletion. In this study, we examined whether CCE, activity of store-operated Ca(2+) channels, and human TRP1 (hTRP1) expression are essential in human pulmonary arterial smooth muscle cell (PASMC) proliferation. Chelation of extracellular Ca(2+) and depletion of intracellularly stored Ca(2+) inhibited PASMC growth in media containing serum and growth factors. Resting [Ca(2+)](cyt) as well as the increases in [Ca(2+)](cyt) due to Ca(2+) release and CCE were all significantly greater in proliferating PASMC than in growth-arrested cells. Consistently, whole cell inward currents activated by depletion of intracellular Ca(2+) stores and the mRNA level of hTRP1 were much greater in proliferating PASMC than in growth-arrested cells. These results suggest that elevated [Ca(2+)](cyt) and intracellularly stored [Ca(2+)] play an important role in pulmonary vascular smooth muscle cell growth. CCE, potentially via hTRP1-encoded Ca(2+)-permeable channels, may be an important mechanism required to maintain the elevated [Ca(2+)](cyt) and stored [Ca(2+)] in human PASMC during proliferation.

The mode selection trial (MOST) in sinus node dysfunction: design, rationale, and baseline characteristics of the first 1000 patients

BACKGROUND

More than 200,000 permanent pacemakers will be implanted in the United States in 2000 at a cost of more than $2 billion. Sick sinus syndrome (SSS) will likely account for approximately half of all cases necessitating implantation. Pacemaker technology permits the selection of ventricular (single-chamber) or dual-chamber devices. However, clinical and outcomes data are inadequate to support a clear recommendation that one or the other type of device be used.

METHODS

The Mode Selection Trial (MOST) is a single-blind study supported by the National Heart, Lung, and Blood Institute designed to enroll 2000 patients with SSS. All patients will receive a DDDR pacemaker programmed to VVIR or DDDR before implantation. The average time of follow-up will be 3 years. MOST has a >90% power to detect a 25% reduction in the primary end point-nonfatal stroke or total (all cause) mortality-in the DDDR-treated group. Secondary end points will include health-related quality of life and cost effectiveness, atrial fibrillation, and development of pacemaker syndrome. Prespecified subgroups for analysis will include women and the elderly. Enrollment was completed in October 1999, with a total of 2010 patients.

RESULTS

The median age of the first 1000 enrolled patients is 74 years, with 25% of patients 80 years or older. Women comprise 49%, and 17% are nonwhite, predominantly black (13%). Before pacemaker implantation, 22% of patients reported a history of congestive heart failure, 11% coronary angioplasty, and 25% coronary bypass surgery. Supraventricular tachycardia including atrial fibrillation was present in 53% of patients. A prior stroke was reported by 12%. Antiarrhythmic therapy was in use in 18% of patients.

CONCLUSIONS

MOST will fill the clinical need for carefully designed prospective studies to define the benefits of dual-chamber versus single-chamber ventricular pacing in patients with SSS. The MOST population is typical of the overall pacemaker population in the United States. Thus the final results of MOST should be clinically generalizable.