human
***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: BACKGROUND In a previous study of 225 patients with sick-sinus syndrome r and omised to either single-chamber atrial pacing ( n=110 ) or single-chamber ventricular pacing ( n=115 ) , we found that after a mean follow-up of 3.3 years , atrial pacing was associated with significantly less atrial fibrillation and thromboembolism whereas there was no significant difference in mortality and heart failure between the two groups . We aim ed to find out whether this beneficial effect of atrial pacing is maintained during extended follow-up of up to 8 years . METHODS Follow-up visits for all patients were at 3 months , 12 months , then once a year at which patients had a physical examination , ECG recording , and pacemaker check-up . Endpoints were mortality , cardiovascular death , atrial fibrillation , thromboembolic events , heart failure , and atrioventricular block . Data was analysed on Dec 31 , 1996 . FINDINGS At long-term follow-up , 39 patients from the atrial group had died versus 57 from the ventricular group ( relative risk 0.66 [ 95 % CI 0.44 - 0.99 ] ; p=0.045 ) . 19 patients from the atrial group and 39 patients from the ventricular group died from a cardiovascular cause ( 0.47 [ 0.27 - 0.82 ] ; p=0.0065 ) . The cumulative incidences of atrial fibrillation and chronic atrial fibrillation were also significantly lower in the atrial group than in the ventricular group ( 0.54 [ 0.33 - 0.89 ] , p=0.012 and 0.35 [ 0.16 - 0.76 ] , p=0.004 , respectively ) . Thromboembolic events occurred in 13 patients in the atrial group and 26 in the ventricular group ( 0.47 [ 0.24 - 0.92 ] , p=0.023 ) . Heart failure was less severe in the atrial group than in the ventricular group ( p<0.05 ) . In multivariate analysis , atrial pacing was significantly associated with freedom from thromboembolic events ( 0.47 [ 0.24 - 0.92 ] , p=0.028 ) and survival from cardiovascular death ( 0.52 [ 0.30 - 0.91 ] , p=0.022 ) , but no longer with overall survival ( 0.71 [ 0.46 - 1.08 ] , p=0.11 ) or chronic atrial fibrillation ( 0.45 [ 0.20 - 1.05 ] , p=0.063 ) . Atrioventricular block occurred in four patients in the atrial group ( 0.6 % annual risk ) . INTERPRETATION The beneficial effect of atrial pacing found in our previous study is enhanced substantially over time . Patients with sick-sinus syndrome should be treated with an atrial rather than ventricular-pacing system because after long-term follow-up , atrial pacing is associated with a significantly higher survival , less atrial fibrillation , fewer thromboembolic complications , less heart failure , and a low-risk of atrioventricular block Reproducibility and validity are prerequisites for a useful clinical scale . We therefore prospect ively tested the reproducibility and validity of the New York Heart Association criteria and the Canadian Cardiovascular Society criteria for the assessment of cardiac functional class  and compared these criteria with a new Specific Activity Scale based on the metabolic costs of specific activities . The New York Heart Association estimates made by two physicians had a reproducibility of only 56 % , and only 51 % of the estimates agreed with treadmill exercise performance . Functional estimates based on the Canadian Cardiovascular Society criteria were significantly more reproducible ( 73 % ) , but not significantly more valid . The Specific Activity Scale was as reproducible as the Canadian Cardiovascular Society criteria , and its 68 % validity was significantly higher than the validities of the other systems . The easily administered Specific Activity Scale was equally reproducible and valid when used by a nonphysician . It was especially better than the other systems for the evaluation of true class II patients and was significantly less likely to underestimate treadmill performance . Although no set of questions can perfectly predict exercise tolerance , the Specific Activity Scale deserves wider prospect i ve testing BACKGROUND Both " physiologic " ( dual-chamber or atrial only ) or ventricular-pacing-only permanent pacemakers provide chronotropic competence , with unknown health-related quality of life ( QOL ) differences between these options . The QOL studies within the Canadian Trial of Physiologic Pacing were performed to assess whether QOL differences exist in patients r and omized to these 2 pacing modes . METHODS Two QOL protocol s were performed : 1 ) a sub study of 269 patients with detailed QOL measures ( The Medical Outcomes Study , Short-Form [ SF-36 ] , the Pacemaker Syndrome Scale , an activity scale , and a pacemaker-specific scale ) at baseline and 6 months after implantation ; and 2 ) a parent study assessment of QOL in 1721 patients with a 12-item QOL instrument package ( SF-6 , " ladder of life , " and pacemaker syndrome scale ) given 6 months after implantation only . RESULTS In the sub study , pacing was associated with an average significant ( P < .05 ) 0.36 SD unit improvement in QOL across all domains ( SF-36 : 38 + /- 9 to 41 + /- 11 for physical scores , 47 + /- 11 to 52 + /- 9 for mental health scores , both P < .001 ) . Similar improvements were seen with the pacemaker-specific scales . There were no significant differences in the absolute or relative improvement in QOL between assigned pacing modes . The parent study similarly showed no differences in QOL between pacing modalities . Presyncope occurred in 31 % of patients in the physiological pacing group , compared with 38 % of the patients in the ventricular pacing group ( P < .01 ) . No other symptoms were different between the 2 groups . Pacemaker dependency , defined as an escape heart rate < 50 beats per minute , did not influence the lack of difference in QOL scores between the 2 assigned pacing modes . CONCLUSION In this largest r and omized assessment of QOL in patients with pacemakers , with the instruments used , there was no significant health-related QOL difference seen between " physiologic " pacing and ventricular pacing Objective To determine the rate of late complications following first implantation or elective unit replacement of a permanent pacemaker system .  Design Analysis of pacemaker data and complications prospect ively acquired on a computerised data base . Complications were studied over an 11 year period from January 1984 to December 1994 . Setting Tertiary referral cardiothoracic centre . Patients Records of 2621 patients were analysed retrospectively . Main outcome measures Complications requiring repeat procedures occurring more than six weeks after pacemaker implantation or elective unit replacement . Results The overall rate of late complications was significantly lower after first implantation of a permanent pacemaker ( 34 cases , complication rate 1.4 % , 95 % confidence interval 0.9 % to 1.9 % ) than after elective unit replacement ( 16 cases , complication rate 6.5 % ( 3.3 % to 9.7 % ) . There were 20 cases of erosion , 18 infections , five electrode problems , and seven miscellaneous problems . Complications were more common with inexperienced operators ( 18.9 % ( 6.0 % to 31.8 % ) ) than with experienced operators ( 0.9 % ( 0.3 % to 1.5 % ) ) . Conclusions The incidence of late complications following pacemaker implantation is low and compares favourably with early complication rates . The majority are caused by erosion and infection . Patients who have undergone elective unit replacement are at particular risk The hemodynamic effects of two different pacing modes -- rate adaptive atrial ( AAIR ) versus dual chamber ( DDDR ) pacing -- were assessed in 12 patients with DDDR pacemakers during upright bicycle exercise first-pass radionuclide angiography using a multiwire gamma camera with tantalum-178 as a tracer . All patients had sinus node disease with intact AV conduction . Patients exercised to the same heart rate in r and om order in these two different pacing modes , AAIR and DDDR with AV delay ( of 100 msec ) selected to maintain 100 % ventricular capture . Cardiac output increased significantly above baseline values during exercise in both pacing modes : 154 + /- 41 % ( mean + /- SEM , P = 0.002 ) with AAIR , versus 95 + /- 24 % ( P = 0.004 ) with DDDR ( P = NS between the two modes ) . The peak filling rate , likewise , increased in both pacing modes ( 2.3 + /- 0.21 end-diastolic volumes/sec to 3.8 + /- 0.31 end-diastolic volumes/sec in AAIR [ P = 0.0004 ] and 2.2 + /- 0.18 end-diastolic volumes/sec to 3.4 + /- 0.27 end-diastolic volumes/sec in DDDR [ P = 0.0008 ] ) . LV ejection fraction was normal at rest ( 60 + /- 4 % , SEM ) and did not significantly change with submaximal exercise in either pacing mode ( both 56 % , P = NS ) . No significant changes in end-diastolic volume or stroke volume indexes occurred with exercise in either pacing mode . Our study demonstrates that in patients with normal resting LV function , AAIR and DDDR pacing are equally effective in attaining appropriate increases in cardiac output and LV filling during exercise Pacemakers are frequently implanted , yet accurate prospect i ve data on implant complications are limited . Elderly patients may be at increased risk of implant complications and are increasingly being referred for pacemaker implantation . The purpose of the present analysis was to define the incidence and possible predictors of serious complications of dual chamber permanent pacemaker implantation  in the elderly . Therefore , we sought to prospect ively identify the incidence and predictors of pacemaker implant complications in a large multicenter trial involving patients receiving a dual chamber pacemaker .  The Pacemaker Selection in the Elderly ( PASE ) study was a prospect i ve trial design ed to evaluate quality of life in  dual chamber pacemaker recipients age 65 years or older r and omized to DDDR versus VVIR programming . In addition to being age 65 years or older , patients enrolled in this study were in normal sinus rhythm , and had st and ard indications for permanent pacemaker implantation . All patients received dual chamber pacemakers and were r and omized to DDDR versus VVIR pacing . Pacemaker implant complications were collected on st and ardized forms which were completed at pacemaker implantation and during follow-up appointments . In this study of 407 patients , there were 26 complications occurring in 25 patients ( 6.1 % ) . The most frequent complication was lead dislodgment which occurred in 9 patients . This was followed by pneumothorax ( 8 patients ) and cardiac perforations ( 4 patients ) . In 18 patients ( 4.4 % ) repeat surgical procedures ( including chest tubes ) were required . Complications were noted prior to discharge in only 18 patients . There were no significant predictors of overall complications . Pneumothorax was more frequent in patients ≤75 years old , and was observed only in patients with subclavian venous access . In conclusion , complications from pacemaker implantation in the elderly are seen in 6.1 % of patients and 4.4 % of patients require a repeat surgical procedure . Other than advanced age and lower weight predicting for pneumothorax , there are no significant clinical predictors of Background —Some current pacing systems can automatically detect and record atrial tachyarrhythmias that may be asymptomatic . We prospect ively studied a 312-patient ( pt ) subgroup of MOST ( MOde Selection Trial ) , a 2010-patient , 6-year r and omized trial of DDDR versus VVIR pacing in sinus node dysfunction ( SND ) . The purpose of the study was to correlate atrial high rate events ( AHREs ) detected by pacemaker diagnostics with clinical outcomes . Methods and Results —Pacemakers were programmed to log an AHRE when the atrial rate was > 220 bpm for 10 consecutive beats . Analysis was confined to patients with at least 1 AHRE duration exceeding 5 minutes . The 312 patients were median age 74 years , 55 % female , and 60 % had a history of SVT . 160 of 312 ( 51.3 % ) patients enrolled had at least 1 AHRE > 5 minutes duration over median follow-up of 27 months . Cox proportional hazards analysis assessed the relationship of AHREs with clinical events , adjusting for prognostic variables and baseline covariates . The presence of any AHRE was an independent predictor of the following : total mortality ( hazard ratio AHRE versus no AHRE and 95 % confidence intervals=2.48 [ 1.25 , 4.91 ] , P = 0.0092 ) ; death or nonfatal stroke ( 2.79 [ 1.51 , 5.15 ] , P = 0.0011 ) ; and atrial fibrillation ( 5.93 [ 2.88 , 12.2 ] , P = 0.0001 ) . There was no significant effect of pacing mode on the presence or absence 
    Output:
    
agent
No statistically significant difference was found between the pacing modes for mortality , heart failure , stroke , chronic atrial fibrillation or quality of life .
However , the risk of developing heart failure may vary with age and device .
The risk of heart failure may have an impact on the decision to use dual-chamber or single-chamber atrial pacemakers .
Results from an analysis based on age ( > 75 years or ≤ 75 years ) and risk of heart failure indicate that dual-chamber pacemakers dominate single-chamber atrial pacemakers ( i.e. are less expensive and more effective ) in older patients , whereas dual-chamber pacemakers are dominated by ( i.e. more expensive and less effective ) single-chamber atrial pacemakers in younger patients .
In patients with SSS without evidence of impaired AV conduction , dual-chamber pacemakers appear to be cost-effective compared with single-chamber atrial pacemakers .
***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: BACKGROUND In a previous study of 225 patients with sick-sinus syndrome r and omised to either single-chamber atrial pacing ( n=110 ) or single-chamber ventricular pacing ( n=115 ) , we found that after a mean follow-up of 3.3 years , atrial pacing was associated with significantly less atrial fibrillation and thromboembolism whereas there was no significant difference in mortality and heart failure between the two groups . We aim ed to find out whether this beneficial effect of atrial pacing is maintained during extended follow-up of up to 8 years . METHODS Follow-up visits for all patients were at 3 months , 12 months , then once a year at which patients had a physical examination , ECG recording , and pacemaker check-up . Endpoints were mortality , cardiovascular death , atrial fibrillation , thromboembolic events , heart failure , and atrioventricular block . Data was analysed on Dec 31 , 1996 . FINDINGS At long-term follow-up , 39 patients from the atrial group had died versus 57 from the ventricular group ( relative risk 0.66 [ 95 % CI 0.44 - 0.99 ] ; p=0.045 ) . 19 patients from the atrial group and 39 patients from the ventricular group died from a cardiovascular cause ( 0.47 [ 0.27 - 0.82 ] ; p=0.0065 ) . The cumulative incidences of atrial fibrillation and chronic atrial fibrillation were also significantly lower in the atrial group than in the ventricular group ( 0.54 [ 0.33 - 0.89 ] , p=0.012 and 0.35 [ 0.16 - 0.76 ] , p=0.004 , respectively ) . Thromboembolic events occurred in 13 patients in the atrial group and 26 in the ventricular group ( 0.47 [ 0.24 - 0.92 ] , p=0.023 ) . Heart failure was less severe in the atrial group than in the ventricular group ( p<0.05 ) . In multivariate analysis , atrial pacing was significantly associated with freedom from thromboembolic events ( 0.47 [ 0.24 - 0.92 ] , p=0.028 ) and survival from cardiovascular death ( 0.52 [ 0.30 - 0.91 ] , p=0.022 ) , but no longer with overall survival ( 0.71 [ 0.46 - 1.08 ] , p=0.11 ) or chronic atrial fibrillation ( 0.45 [ 0.20 - 1.05 ] , p=0.063 ) . Atrioventricular block occurred in four patients in the atrial group ( 0.6 % annual risk ) . INTERPRETATION The beneficial effect of atrial pacing found in our previous study is enhanced substantially over time . Patients with sick-sinus syndrome should be treated with an atrial rather than ventricular-pacing system because after long-term follow-up , atrial pacing is associated with a significantly higher survival , less atrial fibrillation , fewer thromboembolic complications , less heart failure , and a low-risk of atrioventricular block Reproducibility and validity are prerequisites for a useful clinical scale . We therefore prospect ively tested the reproducibility and validity of the New York Heart Association criteria and the Canadian Cardiovascular Society criteria for the assessment of cardiac functional class  and compared these criteria with a new Specific Activity Scale based on the metabolic costs of specific activities . The New York Heart Association estimates made by two physicians had a reproducibility of only 56 % , and only 51 % of the estimates agreed with treadmill exercise performance . Functional estimates based on the Canadian Cardiovascular Society criteria were significantly more reproducible ( 73 % ) , but not significantly more valid . The Specific Activity Scale was as reproducible as the Canadian Cardiovascular Society criteria , and its 68 % validity was significantly higher than the validities of the other systems . The easily administered Specific Activity Scale was equally reproducible and valid when used by a nonphysician . It was especially better than the other systems for the evaluation of true class II patients and was significantly less likely to underestimate treadmill performance . Although no set of questions can perfectly predict exercise tolerance , the Specific Activity Scale deserves wider prospect i ve testing BACKGROUND Both " physiologic " ( dual-chamber or atrial only ) or ventricular-pacing-only permanent pacemakers provide chronotropic competence , with unknown health-related quality of life ( QOL ) differences between these options . The QOL studies within the Canadian Trial of Physiologic Pacing were performed to assess whether QOL differences exist in patients r and omized to these 2 pacing modes . METHODS Two QOL protocol s were performed : 1 ) a sub study of 269 patients with detailed QOL measures ( The Medical Outcomes Study , Short-Form [ SF-36 ] , the Pacemaker Syndrome Scale , an activity scale , and a pacemaker-specific scale ) at baseline and 6 months after implantation ; and 2 ) a parent study assessment of QOL in 1721 patients with a 12-item QOL instrument package ( SF-6 , " ladder of life , " and pacemaker syndrome scale ) given 6 months after implantation only . RESULTS In the sub study , pacing was associated with an average significant ( P < .05 ) 0.36 SD unit improvement in QOL across all domains ( SF-36 : 38 + /- 9 to 41 + /- 11 for physical scores , 47 + /- 11 to 52 + /- 9 for mental health scores , both P < .001 ) . Similar improvements were seen with the pacemaker-specific scales . There were no significant differences in the absolute or relative improvement in QOL between assigned pacing modes . The parent study similarly showed no differences in QOL between pacing modalities . Presyncope occurred in 31 % of patients in the physiological pacing group , compared with 38 % of the patients in the ventricular pacing group ( P < .01 ) . No other symptoms were different between the 2 groups . Pacemaker dependency , defined as an escape heart rate < 50 beats per minute , did not influence the lack of difference in QOL scores between the 2 assigned pacing modes . CONCLUSION In this largest r and omized assessment of QOL in patients with pacemakers , with the instruments used , there was no significant health-related QOL difference seen between " physiologic " pacing and ventricular pacing Objective To determine the rate of late complications following first implantation or elective unit replacement of a permanent pacemaker system .  Design Analysis of pacemaker data and complications prospect ively acquired on a computerised data base . Complications were studied over an 11 year period from January 1984 to December 1994 . Setting Tertiary referral cardiothoracic centre . Patients Records of 2621 patients were analysed retrospectively . Main outcome measures Complications requiring repeat procedures occurring more than six weeks after pacemaker implantation or elective unit replacement . Results The overall rate of late complications was significantly lower after first implantation of a permanent pacemaker ( 34 cases , complication rate 1.4 % , 95 % confidence interval 0.9 % to 1.9 % ) than after elective unit replacement ( 16 cases , complication rate 6.5 % ( 3.3 % to 9.7 % ) . There were 20 cases of erosion , 18 infections , five electrode problems , and seven miscellaneous problems . Complications were more common with inexperienced operators ( 18.9 % ( 6.0 % to 31.8 % ) ) than with experienced operators ( 0.9 % ( 0.3 % to 1.5 % ) ) . Conclusions The incidence of late complications following pacemaker implantation is low and compares favourably with early complication rates . The majority are caused by erosion and infection . Patients who have undergone elective unit replacement are at particular risk The hemodynamic effects of two different pacing modes -- rate adaptive atrial ( AAIR ) versus dual chamber ( DDDR ) pacing -- were assessed in 12 patients with DDDR pacemakers during upright bicycle exercise first-pass radionuclide angiography using a multiwire gamma camera with tantalum-178 as a tracer . All patients had sinus node disease with intact AV conduction . Patients exercised to the same heart rate in r and om order in these two different pacing modes , AAIR and DDDR with AV delay ( of 100 msec ) selected to maintain 100 % ventricular capture . Cardiac output increased significantly above baseline values during exercise in both pacing modes : 154 + /- 41 % ( mean + /- SEM , P = 0.002 ) with AAIR , versus 95 + /- 24 % ( P = 0.004 ) with DDDR ( P = NS between the two modes ) . The peak filling rate , likewise , increased in both pacing modes ( 2.3 + /- 0.21 end-diastolic volumes/sec to 3.8 + /- 0.31 end-diastolic volumes/sec in AAIR [ P = 0.0004 ] and 2.2 + /- 0.18 end-diastolic volumes/sec to 3.4 + /- 0.27 end-diastolic volumes/sec in DDDR [ P = 0.0008 ] ) . LV ejection fraction was normal at rest ( 60 + /- 4 % , SEM ) and did not significantly change with submaximal exercise in either pacing mode ( both 56 % , P = NS ) . No significant changes in end-diastolic volume or stroke volume indexes occurred with exercise in either pacing mode . Our study demonstrates that in patients with normal resting LV function , AAIR and DDDR pacing are equally effective in attaining appropriate increases in cardiac output and LV filling during exercise Pacemakers are frequently implanted , yet accurate prospect i ve data on implant complications are limited . Elderly patients may be at increased risk of implant complications and are increasingly being referred for pacemaker implantation . The purpose of the present analysis was to define the incidence and possible predictors of serious complications of dual chamber permanent pacemaker implantation  in the elderly . Therefore , we sought to prospect ively identify the incidence and predictors of pacemaker implant complications in a large multicenter trial involving patients receiving a dual chamber pacemaker .  The Pacemaker Selection in the Elderly ( PASE ) study was a prospect i ve trial design ed to evaluate quality of life in  dual chamber pacemaker recipients age 65 years or older r and omized to DDDR versus VVIR programming . In addition to being age 65 years or older , patients enrolled in this study were in normal sinus rhythm , and had st and ard indications for permanent pacemaker implantation . All patients received dual chamber pacemakers and were r and omized to DDDR versus VVIR pacing . Pacemaker implant complications were collected on st and ardized forms which were completed at pacemaker implantation and during follow-up appointments . In this study of 407 patients , there were 26 complications occurring in 25 patients ( 6.1 % ) . The most frequent complication was lead dislodgment which occurred in 9 patients . This was followed by pneumothorax ( 8 patients ) and cardiac perforations ( 4 patients ) . In 18 patients ( 4.4 % ) repeat surgical procedures ( including chest tubes ) were required . Complications were noted prior to discharge in only 18 patients . There were no significant predictors of overall complications . Pneumothorax was more frequent in patients ≤75 years old , and was observed only in patients with subclavian venous access . In conclusion , complications from pacemaker implantation in the elderly are seen in 6.1 % of patients and 4.4 % of patients require a repeat surgical procedure . Other than advanced age and lower weight predicting for pneumothorax , there are no significant clinical predictors of Background —Some current pacing systems can automatically detect and record atrial tachyarrhythmias that may be asymptomatic . We prospect ively studied a 312-patient ( pt ) subgroup of MOST ( MOde Selection Trial ) , a 2010-patient , 6-year r and omized trial of DDDR versus VVIR pacing in sinus node dysfunction ( SND ) . The purpose of the study was to correlate atrial high rate events ( AHREs ) detected by pacemaker diagnostics with clinical outcomes . Methods and Results —Pacemakers were programmed to log an AHRE when the atrial rate was > 220 bpm for 10 consecutive beats . Analysis was confined to patients with at least 1 AHRE duration exceeding 5 minutes . The 312 patients were median age 74 years , 55 % female , and 60 % had a history of SVT . 160 of 312 ( 51.3 % ) patients enrolled had at least 1 AHRE > 5 minutes duration over median follow-up of 27 months . Cox proportional hazards analysis assessed the relationship of AHREs with clinical events , adjusting for prognostic variables and baseline covariates . The presence of any AHRE was an independent predictor of the following : total mortality ( hazard ratio AHRE versus no AHRE and 95 % confidence intervals=2.48 [ 1.25 , 4.91 ] , P = 0.0092 ) ; death or nonfatal stroke ( 2.79 [ 1.51 , 5.15 ] , P = 0.0011 ) ; and atrial fibrillation ( 5.93 [ 2.88 , 12.2 ] , P = 0.0001 ) . There was no significant effect of pacing mode on the presence or absence 
    Output:
    