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 —Atrial  fibrillation ( AF ) frequently complicates congestive heart failure ( CHF ) . However , the electrophysiological substrate for AF in humans with CHF remains unknown . We evaluated the electrophysiological and electroanatomic characteristics of the atria in patients with CHF . Methods and Results —Twenty-one patients ( aged 53.7±13.6 years ) with symptomatic CHF ( left ventricular ejection fraction 25.5±6.0 % ) and 21 age-matched controls were studied . The following were evaluated : effective refractory periods ( ERPs ) from the high and low lateral right atrium ( LRA ) , high septal right atrium , and distal coronary sinus ( CS ) ; conduction time along the CS and LRA ; corrected sinus node recovery times ; P-wave duration ; and conduction at the crista terminalis . In a subset , electroanatomic mapping was performed to determine atrial activation , regional conduction velocity , double potentials , fractionated electrograms , regional voltage , and areas of electrical silence .  Patients with CHF demonstrated an increase in atrial ERP with no change in the heterogeneity of refractoriness , an increase of atrial conduction time along the LRA and the CS , prolongation of the P-wave duration and corrected sinus node recovery times , and greater number and duration of double potentials along the crista terminalis . Electroanatomic mapping demonstrated regional conduction slowing with a greater number of electrograms with fractionation or double potentials , associated with areas of low voltage and electrical silence ( scar ) . Patients with CHF demonstrated an increased propensity for AF with single extrastimuli , and induced AF was more often sustained . Conclusions —Atrial remodeling due to CHF is characterized by structural changes , abnormalities of conduction , sinus node dysfunction , and increased refractoriness . These abnormalities may be responsible in part for the increased propensity for AF in CHF Background — Isolated atrial fibrillation ( AF ) is associated with mild enlargement of the left atrium ( LA ) and left ventricular ( LV ) diastolic dysfunction . The impact of ablation of isolated AF on left chamber size and function is unclear , and whether diastolic dysfunction is the cause or the consequence of AF remains unknown . The objective of this prospect i ve study was to evaluate the impact of sinus rhythm restoration by catheter ablation on LV diastolic dysfunction , LA morphology , and mechanical function . Methods and Results — Forty-eight patients with isolated AF were studied by serial echocardiographic studies at baseline and at 1- , 3- , 6- , 9- , and 12-month intervals after radiofrequency ablation .  LA dimensions and mechanical function and LV systolic and diastolic functions were evaluated at each time interval . Diastolic function was assessed with conventional Doppler parameters and new indexes such as tissue Doppler imaging , mitral flow propagation velocity , and combined criteria . LV diastolic dysfunction was present in paroxysmal and chronic AF patients with a reduction of tissue Doppler imaging lateral early diastolic peak velocity in 37 % ( P<0.001 ) and 48 % ( P<0.01 ) , respectively , compared with healthy control subjects . At the end of the follow-up , LA area decreased significantly by 18 % ( P<0.001 ) in paroxysmal and 23 % ( P<0.05 ) in chronic AF patients . Diastolic function improved significantly with an increase in lateral early diastolic peak velocity of 29 % ( P<0.001 ) in paroxysmal AF and 46 % ( P<0.05 ) in chronic AF patients . A significant increase in LV ejection fraction was also noted for both groups : 7.7 % and 18.8 % , respectively . Conclusions — This study demonstrates reverse morphological remodeling of the LA and improvement of LV diastolic and systolic functions after restoration of sinus rhythm by ablation for isolated AF . Because patients with isolated AF have none of the traditional causes of LV diastolic dysfunction , our findings suggest that AF may be partly the cause rather than the consequence of diastolic dysfunction AIMS In congestive heart failure ( CHF ) patients with persistent atrial fibrillation ( AF ) , direct current cardioversion ( DCC ) may reveal participation of tachycardiamediated process to left ventricular ( LV ) dysfunction by restoring sinus rhythm ( SR ) . However , if DCC fails to restore SR , patients ' management remains challenging . The aim of the study was to assess the AF catheter ablation benefit in a selected group of CHF patients with LV ejection fraction ( LVEF ) < 40 % and persistent AF unresponsive to DCC , in whom a tachycardia-mediated process is thought to be predominant . METHODS AND RESULTS Between January 2008 and September 2011 , among 129 CHF patients with persistent AF referred to our institution , 34 ( 63.8 ± 9-year old , 24 men ) presented AF refractory to DCC with an estimated high likelihood of tachycardia-mediated LV dysfunction according to a specific set of criteria . These 34 patients underwent stepwise AF ablation and were closely followed up . After a mean 1.9 AF ablation procedures per patient and 17.6 ± 7 months after the last procedure , all patients were in SR . The New York Heart Association class improved from 2.8 ± 0.3 to 1 ± 0.2 ( P < 0.001 ) and the LVEF increased from 30.4 ± 6 to 54.6 ± 6 % ( P < 0.0001 ) after 3 - 6 months of SR , with a persistent benefit as long as the SR was maintained . CONCLUSION Atrial fibrillation catheter ablation in selected CHF patients with persistent AF refractory to DCC and without any other evidence for secondary LV dysfunction leads to a substantial LVEF improvement in the majority of them . However , redo procedures are frequent in order to achieve mid-term SR maintenance Small , single-center studies suggest that catheter ablation of atrial fibrillation ( AF )  can improve ventricular function and reduce symptoms in patients with left ventricular ( LV ) dysfunction . However , ablation has not been compared with a pharmacologic strategy for AF . The authors evaluated patients with AF and symptomatic LV dysfunction ( ejection fraction < or = 45 % ) referred for pulmonary vein isolation ( PVI ) . They compared these patients with a matched cohort treated medically for AF and LV dysfunction via a retrospective case-control method . Fifteen patients ( 14 men , 56+/-11 years , 10 [ 67 % ] paroxysmal AF ) with AF for 4+/-3 years underwent PVI .  Baseline ejection fraction was 37%+/-6 % and New York Heart Association ( NYHA ) class was 2.0+/-1.0 . Fifteen controls ( 13 men , 63+/-14 years , 11 [ 73 % ] paroxysmal AF ) with AF for 5+/-4 years were treated medically for AF . Baseline ejection fraction was 34%+/-11 % and NYHA class was 2.0+/-0.7 . The groups were similar in all respects . During a follow-up of 16+/-13 months after complete PVI , ejection fraction improved ( P=.001 ) to 50%+/-13 % and normalized in 8 patients ( 53 % ) . NYHA class improved to 1.3+/-0.5 ( P=.01 ) . In the medically treated group , after follow-up of 16+/-12 months , no improvement in ejection fraction ( 36%+/-12 % ) or NYHA class ( 1.8+/-0.7 ) was seen . Compared with pharmacologic therapy , PVI significantly improved LV function and NYHA class in patients with AF and symptomatic LV dysfunction . These provocative findings provide potent rationale for a r and omized clinical trial comparing ablation with pharmacologic therapy OBJECTIVES We aim ed to determine the safety and efficacy of pulmonary vein isolation ( PVI ) in atrial fibrillation ( AF ) patients with impaired left ventricular ( LV ) systolic function . BACKGROUND To date , PVI has been performed primarily in patients with normal LV function . Yet , many AF patients have impaired LV systolic function . The outcomes of PVI in patients with impaired LV systolic function are unknown . METHODS We included 377 consecutive patients undergoing PVI between December 2000 and January 2003 . Ninety-four patients had impaired LV function ( ejection fraction [ EF ] < 40 % ) , and they comprised the study group . The control group was the remaining 283 patients who had a normal EF . End points included AF recurrence and changes in EF and quality of life ( QoL ) . RESULTS Mean EF was 36 % in our study group , compared with 54 % in controls . After initial PVI , 73 % of patients with impaired EF and 87 % of patients with normal EF were free of AF recurrence at 14 + /- 6 months ( p = 0.03 ) . In the study group , there was a nonsignificant increase in EF of 4.6 % and significant improvement in QoL. Complication rates were low and included a 1 % risk of pulmonary vein stenosis . CONCLUSIONS Although the AF recurrence rate after initial PVI in impaired EF patients was higher than in normal EF subjects , nearly three-fourths of patients with impaired EF remained AF-free . Although our sample size was nonr and omized , our results suggest PVI may be a feasible therapeutic option in AF patients with impaired EF . R and omized studies with more patients and longer follow-up are warranted Objective To determine whether or not radiofrequency ablation ( RFA ) for persistent atrial fibrillation in patients with advanced heart failure leads to improvements in cardiac function . Setting Patients were recruited from heart failure outpatient clinics in Scotl and . Design and intervention Patients with advanced heart failure and severe left ventricular dysfunction were r and omised to RFA ( rhythm control ) or  continued medical treatment  ( rate control ) . Patients were followed up for a minimum of 6 months . Main outcome measure Change in left ventricular ejection fraction ( LVEF ) measured by cardiovascular MRI . Results 22 patients were r and omised to RFA and 19 to medical treatment . In the RFA group , 50 % of patients were in sinus rhythm at the end of the study ( compared with none in the medical treatment group ) . The increase in cardiovascular magnetic resonance ( CMR ) LVEF in the RFA group was 4.5±11.1 % compared with 2.8±6.7 % in the medical treatment group ( p=0.6 ) . The RFA group had a greater increase in radionuclide LVEF ( a prespecified secondary end point ) than patients in the medical treatment group ( + 8.2±12.0 % vs + 1.4±5.9 % ; p=0.032 ) . RFA did not improve N-terminal pro-B-type natriuretic peptide , 6 min walk distance or quality of life . The rate of serious complications related to RFA was 15 % . Conclusions RFA result ed in long-term restoration of sinus rhythm in only 50 % of patients . RFA did not improve CMR LVEF compared with a strategy of rate control . RFA did improve radionuclide LVEF but did not improve other secondary outcomes and was associated with a significant rate of serious complications . Clinical trials registration number NCT00292162 AIMS In the setting of congestive heart failure ( CHF ) , atrial fibrillation ( AF ) ablation can improve clinical status and the left ventricular ejection fraction ( LVEF ) value . However , the impact of AF ablation on the implantable cardioverter defibrillator ( ICD ) indication has never been specifically addressed . METHODS AND RESULTS Study subject were six CHF ( mean age 61.1 + /- 6.9 years , mean LVEF 25.8 + /- 7.3 % ) patients refractory to conventional medical treatment with long-lasting AF unresponsive to external cardioversion . Five patients had an idiopathic dilated cardiomyopathy ( DCM ) and one had an ischaemic cardiomyopathy ( ICM ) . Their New York Heart Association ( NYHA ) class was III-IV . Two patients had renal insufficiency . No patient had left ventricular delay . All patients underwent AF ablation .  LVEF and NYHA class were dramatically improved in the five DCM patients . New York Heart Association class , but not the LVEF , was improved in the ICM patient . A redo ablative procedure was undertaken in four of five DCM patients and in the ICM patient due to arrhythmia recurrence . Left ventricular ejection fraction and NYHA were improved again in the DCM patients ( 56 + /- 4.4 % , I-II , respectively ) and led to ICD indication preclusion . The LVEF remained low in the ICM patient ( 30 % ) and led to ICD insertion . Sinus rhythm has been stable during the 18.1 + /- 5.7 months follow-up period . CONCLUSION  Atrial fibrillation ablation in CHF patients can improve both the clinical status of patients and their LVEF , especially among those affected by DCM . The LVEF improvement has the potential to preclude the indication for a primary prevention ICD insertion Background —Restoring sinus rhythm in patients with heart failure ( HF ) and atrial fibrillation ( AF ) may improve left ventricular ( LV ) function and HF symptoms . We sought to compare the effect of a catheter ablation strategy with that of a medical rate control strategy in patients with persistent AF and HF . Methods and Results — Patients with persistent AF , symptomatic HF , and LV ejection fraction < 50 % were r and omized to catheter ablation or medical rate control . The 
    Output:
    
agent
Catheter ablation may be an effective therapy in AF patients with left ventricular systolic impairment , and can be associated with improvements in left ventricular function , quality of life , exercise capacity , and modest rates of serious adverse events
***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 —Atrial  fibrillation ( AF ) frequently complicates congestive heart failure ( CHF ) . However , the electrophysiological substrate for AF in humans with CHF remains unknown . We evaluated the electrophysiological and electroanatomic characteristics of the atria in patients with CHF . Methods and Results —Twenty-one patients ( aged 53.7±13.6 years ) with symptomatic CHF ( left ventricular ejection fraction 25.5±6.0 % ) and 21 age-matched controls were studied . The following were evaluated : effective refractory periods ( ERPs ) from the high and low lateral right atrium ( LRA ) , high septal right atrium , and distal coronary sinus ( CS ) ; conduction time along the CS and LRA ; corrected sinus node recovery times ; P-wave duration ; and conduction at the crista terminalis . In a subset , electroanatomic mapping was performed to determine atrial activation , regional conduction velocity , double potentials , fractionated electrograms , regional voltage , and areas of electrical silence .  Patients with CHF demonstrated an increase in atrial ERP with no change in the heterogeneity of refractoriness , an increase of atrial conduction time along the LRA and the CS , prolongation of the P-wave duration and corrected sinus node recovery times , and greater number and duration of double potentials along the crista terminalis . Electroanatomic mapping demonstrated regional conduction slowing with a greater number of electrograms with fractionation or double potentials , associated with areas of low voltage and electrical silence ( scar ) . Patients with CHF demonstrated an increased propensity for AF with single extrastimuli , and induced AF was more often sustained . Conclusions —Atrial remodeling due to CHF is characterized by structural changes , abnormalities of conduction , sinus node dysfunction , and increased refractoriness . These abnormalities may be responsible in part for the increased propensity for AF in CHF Background — Isolated atrial fibrillation ( AF ) is associated with mild enlargement of the left atrium ( LA ) and left ventricular ( LV ) diastolic dysfunction . The impact of ablation of isolated AF on left chamber size and function is unclear , and whether diastolic dysfunction is the cause or the consequence of AF remains unknown . The objective of this prospect i ve study was to evaluate the impact of sinus rhythm restoration by catheter ablation on LV diastolic dysfunction , LA morphology , and mechanical function . Methods and Results — Forty-eight patients with isolated AF were studied by serial echocardiographic studies at baseline and at 1- , 3- , 6- , 9- , and 12-month intervals after radiofrequency ablation .  LA dimensions and mechanical function and LV systolic and diastolic functions were evaluated at each time interval . Diastolic function was assessed with conventional Doppler parameters and new indexes such as tissue Doppler imaging , mitral flow propagation velocity , and combined criteria . LV diastolic dysfunction was present in paroxysmal and chronic AF patients with a reduction of tissue Doppler imaging lateral early diastolic peak velocity in 37 % ( P<0.001 ) and 48 % ( P<0.01 ) , respectively , compared with healthy control subjects . At the end of the follow-up , LA area decreased significantly by 18 % ( P<0.001 ) in paroxysmal and 23 % ( P<0.05 ) in chronic AF patients . Diastolic function improved significantly with an increase in lateral early diastolic peak velocity of 29 % ( P<0.001 ) in paroxysmal AF and 46 % ( P<0.05 ) in chronic AF patients . A significant increase in LV ejection fraction was also noted for both groups : 7.7 % and 18.8 % , respectively . Conclusions — This study demonstrates reverse morphological remodeling of the LA and improvement of LV diastolic and systolic functions after restoration of sinus rhythm by ablation for isolated AF . Because patients with isolated AF have none of the traditional causes of LV diastolic dysfunction , our findings suggest that AF may be partly the cause rather than the consequence of diastolic dysfunction AIMS In congestive heart failure ( CHF ) patients with persistent atrial fibrillation ( AF ) , direct current cardioversion ( DCC ) may reveal participation of tachycardiamediated process to left ventricular ( LV ) dysfunction by restoring sinus rhythm ( SR ) . However , if DCC fails to restore SR , patients ' management remains challenging . The aim of the study was to assess the AF catheter ablation benefit in a selected group of CHF patients with LV ejection fraction ( LVEF ) < 40 % and persistent AF unresponsive to DCC , in whom a tachycardia-mediated process is thought to be predominant . METHODS AND RESULTS Between January 2008 and September 2011 , among 129 CHF patients with persistent AF referred to our institution , 34 ( 63.8 ± 9-year old , 24 men ) presented AF refractory to DCC with an estimated high likelihood of tachycardia-mediated LV dysfunction according to a specific set of criteria . These 34 patients underwent stepwise AF ablation and were closely followed up . After a mean 1.9 AF ablation procedures per patient and 17.6 ± 7 months after the last procedure , all patients were in SR . The New York Heart Association class improved from 2.8 ± 0.3 to 1 ± 0.2 ( P < 0.001 ) and the LVEF increased from 30.4 ± 6 to 54.6 ± 6 % ( P < 0.0001 ) after 3 - 6 months of SR , with a persistent benefit as long as the SR was maintained . CONCLUSION Atrial fibrillation catheter ablation in selected CHF patients with persistent AF refractory to DCC and without any other evidence for secondary LV dysfunction leads to a substantial LVEF improvement in the majority of them . However , redo procedures are frequent in order to achieve mid-term SR maintenance Small , single-center studies suggest that catheter ablation of atrial fibrillation ( AF )  can improve ventricular function and reduce symptoms in patients with left ventricular ( LV ) dysfunction . However , ablation has not been compared with a pharmacologic strategy for AF . The authors evaluated patients with AF and symptomatic LV dysfunction ( ejection fraction < or = 45 % ) referred for pulmonary vein isolation ( PVI ) . They compared these patients with a matched cohort treated medically for AF and LV dysfunction via a retrospective case-control method . Fifteen patients ( 14 men , 56+/-11 years , 10 [ 67 % ] paroxysmal AF ) with AF for 4+/-3 years underwent PVI .  Baseline ejection fraction was 37%+/-6 % and New York Heart Association ( NYHA ) class was 2.0+/-1.0 . Fifteen controls ( 13 men , 63+/-14 years , 11 [ 73 % ] paroxysmal AF ) with AF for 5+/-4 years were treated medically for AF . Baseline ejection fraction was 34%+/-11 % and NYHA class was 2.0+/-0.7 . The groups were similar in all respects . During a follow-up of 16+/-13 months after complete PVI , ejection fraction improved ( P=.001 ) to 50%+/-13 % and normalized in 8 patients ( 53 % ) . NYHA class improved to 1.3+/-0.5 ( P=.01 ) . In the medically treated group , after follow-up of 16+/-12 months , no improvement in ejection fraction ( 36%+/-12 % ) or NYHA class ( 1.8+/-0.7 ) was seen . Compared with pharmacologic therapy , PVI significantly improved LV function and NYHA class in patients with AF and symptomatic LV dysfunction . These provocative findings provide potent rationale for a r and omized clinical trial comparing ablation with pharmacologic therapy OBJECTIVES We aim ed to determine the safety and efficacy of pulmonary vein isolation ( PVI ) in atrial fibrillation ( AF ) patients with impaired left ventricular ( LV ) systolic function . BACKGROUND To date , PVI has been performed primarily in patients with normal LV function . Yet , many AF patients have impaired LV systolic function . The outcomes of PVI in patients with impaired LV systolic function are unknown . METHODS We included 377 consecutive patients undergoing PVI between December 2000 and January 2003 . Ninety-four patients had impaired LV function ( ejection fraction [ EF ] < 40 % ) , and they comprised the study group . The control group was the remaining 283 patients who had a normal EF . End points included AF recurrence and changes in EF and quality of life ( QoL ) . RESULTS Mean EF was 36 % in our study group , compared with 54 % in controls . After initial PVI , 73 % of patients with impaired EF and 87 % of patients with normal EF were free of AF recurrence at 14 + /- 6 months ( p = 0.03 ) . In the study group , there was a nonsignificant increase in EF of 4.6 % and significant improvement in QoL. Complication rates were low and included a 1 % risk of pulmonary vein stenosis . CONCLUSIONS Although the AF recurrence rate after initial PVI in impaired EF patients was higher than in normal EF subjects , nearly three-fourths of patients with impaired EF remained AF-free . Although our sample size was nonr and omized , our results suggest PVI may be a feasible therapeutic option in AF patients with impaired EF . R and omized studies with more patients and longer follow-up are warranted Objective To determine whether or not radiofrequency ablation ( RFA ) for persistent atrial fibrillation in patients with advanced heart failure leads to improvements in cardiac function . Setting Patients were recruited from heart failure outpatient clinics in Scotl and . Design and intervention Patients with advanced heart failure and severe left ventricular dysfunction were r and omised to RFA ( rhythm control ) or  continued medical treatment  ( rate control ) . Patients were followed up for a minimum of 6 months . Main outcome measure Change in left ventricular ejection fraction ( LVEF ) measured by cardiovascular MRI . Results 22 patients were r and omised to RFA and 19 to medical treatment . In the RFA group , 50 % of patients were in sinus rhythm at the end of the study ( compared with none in the medical treatment group ) . The increase in cardiovascular magnetic resonance ( CMR ) LVEF in the RFA group was 4.5±11.1 % compared with 2.8±6.7 % in the medical treatment group ( p=0.6 ) . The RFA group had a greater increase in radionuclide LVEF ( a prespecified secondary end point ) than patients in the medical treatment group ( + 8.2±12.0 % vs + 1.4±5.9 % ; p=0.032 ) . RFA did not improve N-terminal pro-B-type natriuretic peptide , 6 min walk distance or quality of life . The rate of serious complications related to RFA was 15 % . Conclusions RFA result ed in long-term restoration of sinus rhythm in only 50 % of patients . RFA did not improve CMR LVEF compared with a strategy of rate control . RFA did improve radionuclide LVEF but did not improve other secondary outcomes and was associated with a significant rate of serious complications . Clinical trials registration number NCT00292162 AIMS In the setting of congestive heart failure ( CHF ) , atrial fibrillation ( AF ) ablation can improve clinical status and the left ventricular ejection fraction ( LVEF ) value . However , the impact of AF ablation on the implantable cardioverter defibrillator ( ICD ) indication has never been specifically addressed . METHODS AND RESULTS Study subject were six CHF ( mean age 61.1 + /- 6.9 years , mean LVEF 25.8 + /- 7.3 % ) patients refractory to conventional medical treatment with long-lasting AF unresponsive to external cardioversion . Five patients had an idiopathic dilated cardiomyopathy ( DCM ) and one had an ischaemic cardiomyopathy ( ICM ) . Their New York Heart Association ( NYHA ) class was III-IV . Two patients had renal insufficiency . No patient had left ventricular delay . All patients underwent AF ablation .  LVEF and NYHA class were dramatically improved in the five DCM patients . New York Heart Association class , but not the LVEF , was improved in the ICM patient . A redo ablative procedure was undertaken in four of five DCM patients and in the ICM patient due to arrhythmia recurrence . Left ventricular ejection fraction and NYHA were improved again in the DCM patients ( 56 + /- 4.4 % , I-II , respectively ) and led to ICD indication preclusion . The LVEF remained low in the ICM patient ( 30 % ) and led to ICD insertion . Sinus rhythm has been stable during the 18.1 + /- 5.7 months follow-up period . CONCLUSION  Atrial fibrillation ablation in CHF patients can improve both the clinical status of patients and their LVEF , especially among those affected by DCM . The LVEF improvement has the potential to preclude the indication for a primary prevention ICD insertion Background —Restoring sinus rhythm in patients with heart failure ( HF ) and atrial fibrillation ( AF ) may improve left ventricular ( LV ) function and HF symptoms . We sought to compare the effect of a catheter ablation strategy with that of a medical rate control strategy in patients with persistent AF and HF . Methods and Results — Patients with persistent AF , symptomatic HF , and LV ejection fraction < 50 % were r and omized to catheter ablation or medical rate control . The 
    Output:
    