***TASK*** the task is to summarize an input biomedical literature in six sentences 
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    Input: BACKGROUND Obstructive sleep apnea syndrome ( OSAS ) has been associated with increased morbidity and mortality , principally from cardiovascular disease , but the impact of nasal continuous positive airway pressure ( CPAP ) therapy is unclear . METHODS We performed a long-term follow-up study of 168 patients with OSAS who had begun receiving CPAP therapy at least 5 years previously , most of whom had been prospect ively followed up , having been the subject of an earlier report on cardiovascular risk factors in OSAS patients . The average follow-up period was 7.5 years . We compared the cardiovascular outcomes of those patients who were intolerant of CPAP ( untreated group , 61 patients ) with those continuing CPAP therapy ( 107 patients ) . RESULTS CPAP-treated patients had a higher median apnea-hypopnea index score than the untreated group ( 48.3 [ interquartile range ( IQR ) , 33.6 to 66.4 ] vs 36.7 [ IQR , 27.4 to 55 ] , respectively ; p = 0.02 ) , but age , body mass index , and time since diagnosis were similar . Deaths from cardiovascular disease were more common in the untreated group than in the CPAP-treated group during follow-up ( 14.8 % vs 1.9 % , respectively ; p = 0.009 [ log rank test ] ) , but no significant differences were found in the development of new cases of hypertension , cardiac disorder , or stroke . Total cardiovascular events ( ie , death and new cardiovascular disease combined ) were more common in the untreated group than in the CPAP-treated group ( 31 % vs 18 % , respectively ; p < 0.05 ) . CONCLUSIONS The data support a protective effect of CPAP therapy against death from cardiovascular disease in patients with OSAS STUDY OBJECTIVES A high incidence of nocturnal cardiac rhythm disturbances among patients with obstructive sleep apnea ( OSA ) syndrome has been described in some reports , but not in others . We wished to examine the prevalence of significant cardiac rhythm disturbance in patients with established moderate to severe OSA syndrome and , in particular , to assess the impact of nasal continuous positive airway pressure ( nCPAP ) therapy . DESIGN AND SETTING A prospect i ve study of consecutive eligible patients in a dedicated sleep disorders unit of a university teaching hospital . MEASUREMENTS AND RESULTS  Holter monitoring  was performed for 18 h in 45 patients with previously diagnosed OSA syndrome ( mean [ SD ] apnea/hypopnea frequency [ AHI ] of 50 [23]/h ) and repeated within 2 to 3 days after institution of nCPAP therapy .  Investigators were blinded to the patients ' treatments during data analysis . Thirty-five patients were found to have some cardiac rhythm disturbance , but only 8 had pathologically significant disturbances ( ventricular tachycardia or fibrillation , complex ventricular ectopy , new-onset supraventricular tachycardia other than sinus tachycardia , pauses of > 2 s , and second- or third-degree heart block ) . Significant rhythm disturbances occurred only during the nighttime , and there was a significant correlation between OSA severity and the severity of rhythm disturbance ( p = 0.04 , r = 0.301 ) . No significant correlation was found between OSA severity and any other anthropometric parameter measured . nCPAP therapy result ed in abolition of rhythm disturbance in seven of these eight patients ; the eighth patient was found to have coexisting severe aortic valve disease requiring valve replacement . CONCLUSION The data indicate that OSA syndrome predisposes to clinical ly significant cardiac rhythm disturbances that can be successfully controlled by nCPAP therapy The prevalence and clinical significance of sleep-related breathing disorders ( SRBDs ) in patients with cardiac disease and a history of life-threatening ventricular tachyarrhythmias is unclear . Forty consecutive recipients of implantable cardioverter defibrillators ( ICDs ) with cardiac disease and a documented history of spontaneous , life-threatening , ventricular tachyarrhythmias underwent full night polysomnography .  SRBDs were diagnosed if the apnea/hypopnea index was > 10 . SRBD were diagnosed in 16 of 40 patients ( 40 % ) : central sleep apnea ( CSA ) was present in 9 of these 16 patients ( 56 % ) , 8 of whom had associated Cheyne-Stoke respiration . Seven of the 16 patients with SRBD ( 44 % ) had obstructive sleep apnea ( OSA ) . Patients with and without SRBDs were comparable with respect to left ventricular ejection fraction , NYHA classification , underlying heart disease , ICD indications , and concomitant antiarrhythmic drug and beta-blocker therapy . Patients were followed prospect ively for 2 years . ICD-treated ventricular tachyarrhythmias occurred in 10 of 24 patients ( 42 % ) without SRBD , in 4 of 9 patients ( 44 % ) with CSA , and in 3 of 7 patients ( 44 % ) with OSA ( NS ) . The numbers and circadian distributions of episodes recorded during follow-up in patients without SRBD versus with CSA or OSA were not significantly different ( 14 + /- 25 , median = 4 vs 4 + /- 5 , median = 2.5 vs 15 + /- 15 , median = 7 , respectively ) . The 2-year mortality , which was entirely attributable to nonsudden cardiac events , was highest in patients with CSA ( 4/9 [ 44 % ] , vs 0/7 [ 0 % ] with OSA , vs 3/24 patients ( 12.5 % ) without SRBD ; P < 0.05 ) Patients with coronary artery disease , depressed left ventricular ejection fraction , and nonsustained ventricular tachycardia ( VT ) have a high mortality rate due to arrhythmic ( arrhythmic death/cardiac arrest ) and other cardiac causes . The Multicenter UnSustained Tachycardia Trial ( MUSTT ) investigated whether electrophysiologic study ( EPS ) was helpful in choosing drug or defibrillator therapy in patients induced into sustained VT . The events committee attempted to categorize follow-up events in patients in MUSTT and to present a detailed breakdown of events . A derivative of the Hinkle-Thaler classification was used , incorporating lessons from other multicenter studies . The committee was blinded to results of EPS and implantable cardioverter-defibrillator ( ICD ) or other antiarrhythmic therapy status of patients . The primary end point was cardiac arrest or death from arrhythmia . Secondary end points were death from all causes , cardiac causes , and spontaneous sustained VT . Classifications were death and cardiac arrest . Each was similarly divided as arrhythmic with 14 subcategories , e.g. , unwitnessed or related to EPS and nonarrhythmic with 10 subcategories , e.g. , ischemia . Terminal VF in progressive heart failure was considered nonarrhythmic . Events were review ed by 2 members . Disagreements were resolved by the 2 members or , if needed , by the full committee . Of the 2,202 patients in MUSTT , there were 902 deaths . Sustained VT  requiring cardioversion occurred in 182 patients . An additional 94 patients had resuscitated cardiac arrests .  Events occurred in 1,027 patients , and all were review ed . The 3 leading events were deaths that were classed as sudden/unwitnessed ( 23 % of 902 ) , due to progressive heart failure ( 22 % ) , or due to noncardiovascular causes ( 18 % ) . Arrhythmic deaths or cardiac arrests were highest in inducible patients r and omized to no antiarrhythmic therapy ; next were inducible patients receiving an ICD ; and lowest were in patients who were noninducible . In conclusion , the classification system provided a detailed breakdown of events in consistent categories , showing utility for event analysis and interpretation and development of therapeutic strategies . The classifications assigned by the committee were used in all MUSTT outcomes reports , thus affecting all reported outcomes and overall interpretations of the MUSTT AIMS The preliminary evidence supports an association between obstructive sleep apnoea ( OSA ) , disturbed cardiac repolarization , and consequent cardiac dysrhythmias . The aim of the current trial was to assess the effects of continuous positive airway pressure ( CPAP ) therapy withdrawal on the measures of cardiac repolarization in patients with OSA . METHODS AND RESULTS Forty-one OSA patients established on CPAP treatment were r and omized to either CPAP withdrawal ( subtherapeutic CPAP ) or continue therapeutic CPAP for 2 weeks .  Polysomnography  was performed , and indices of cardiac repolarization ( QT(c ) , TpTe(c ) intervals ) and dispersion of repolarization ( TpTe/QT ratio ) were derived from 12-lead electrocardiography ( ECG ) at baseline and 2 weeks . Continuous positive airway pressure withdrawal led to a recurrence of OSA . Compared with therapeutic CPAP , subtherapeutic CPAP for 2 weeks was associated with a significant increase in the length of the QT(c ) and TpTe(c ) intervals ( mean difference between groups 21.4 ms , 95 % CI 11.3 - 1.6 ms , P < 0.001 and 14.4 ms , 95 % CI 7.2 - 21.5 ms , P < 0.001 , respectively ) and in the TpTe/QT ratio ( mean difference between groups 0.02 , 95 % CI 0.00 - 0.03 , P = 0.020 ) . There was a statistically significant correlation between the change in apnoea/hypopnoea index ( AHI ) from baseline , and both the change in the QT(c ) interval and the TpTe(c ) interval ( r = 0.60 , 95 % CI 0.36 - 0.77 , P < 0.001 and r = 0.45 , 95 % CI 0.17 - 0.67 , P = 0.003 , n = 41 , respectively ) . CONCLUSION Continuous positive airway pressure withdrawal is associated with the prolongation of the QT(c ) and TpTe(c ) intervals and TpTe/QT ratio , which may provide a possible mechanistic link between OSA , cardiac dysrhythmias , and thus sudden cardiac death BACKGROUND Limited data have suggested that sleep-disordered breathing , a condition of repeated episodes of apnea and hypopnea during sleep , is prevalent among adults . Data from the Wisconsin Sleep Cohort Study , a longitudinal study of the natural history of cardiopulmonary disorders of sleep , were used to estimate the prevalence of undiagnosed sleep-disordered breathing among adults and address its importance to the public health . METHODS A r and om sample of 602 employed men and women 30 to 60 years old were studied by overnight polysomnography to determine the frequency of episodes of apnea and hypopnea per hour of sleep ( the apnea-hypopnea score ) . We measured the age- and sex-specific prevalence of sleep-disordered breathing in this group using three cutoff points for the apnea-hypopnea score ( > or = 5 , > or = 10 , and > or = 15 ) ; we used logistic regression to investigate risk factors . RESULTS The estimated prevalence of sleep-disordered breathing , defined as an apnea-hypopnea score of 5 or higher , was 9 percent for women and 24 percent for men . We estimated that 2 percent of women and 4 percent of men in the middle-aged work force meet the minimal diagnostic criteria for the sleep apnea syndrome ( an apnea-hypopnea score of 5 or higher and daytime hypersomnolence ) . Male sex and obesity were strongly associated with the presence of sleep-disordered breathing . Habitual snorers , both men and women , tended to have a higher prevalence of apnea-hypopnea scores of 15 or higher . CONCLUSIONS The prevalence of undiagnosed sleep-disordered breathing is high among men and is much higher than previously suspected among women . Undiagnosed sleep-disordered breathing is associated with daytime hypersomnolence It was recognized that sleep-disordered breathing ( SDB ) is associated with cardiac arrhythmia and sudden cardiac death . However , it was unclear whether the presence of SDB increased the risk of life-threatening ventricular arrhythmia in patients with heart failure ( HF ) with an implantable cardioverter-defibrillator ( ICD ) . Seventy-one patients with HF and an ICD who were followed up for 180 days after a sleep study were prospect ively studied . All patients had an ejection fraction < or=35 % . SDB was defined as an apnea-hypopnea index > or=10 events/hour on the sleep study . The frequency of appropriate ICD therapy and the day-night pattern of ICD therapies were compared between patients with and without SDB . SDB was diagnosed in 47 of 71 patients ( 66 % ) . There were no statistical differences between patients with and without SDB in baseline cardiac function . However , appropriate ICD therapies occurred more frequently in patients with ( 43 % ) than without SDB ( 17 % ; p = 0.029 ) . On multivariate analysis , the presence of SDB was an independent predictor for appropriate ICD therapy ( hazard ratio 4.05 , 95 % confidence interval 1.20 to 13.65 , p = 0.015 ) . Moreover , the rate of total ICD therapy from midnight to 
    Output:
    
Patients with OSA were noted to have higher odds of ventricular ectopy , and were at a higher risk for ventricular arrhythmias .
Associations included higher QTc dispersion and HR variability .
We did not , however , find any clear evidence for a direct correlation between increased apnea hypopnea index and increased VT or VF .
In a systemic review of studies , patients with OSA were noted to have higher odds of ventricular ectopy and arrhythmias .
A single study showed that CPAP may help lower arrhythmogenicity ; however , it was unclear if CPAP lowered the risk of VT .