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 — Catheter ablation of ventricular tachycardia ( VT )  is effective and particularly useful in patients with frequent defibrillator interventions . Various substrate modification techniques have been described for unmappable or hemodynamically intolerable VT . Noninducibility is the most frequently used end point but is associated with significant limitations , so the optimal end point remains unclear . We hypothesized that elimination of local abnormal ventricular activities ( LAVAs ) during sinus rhythm or ventricular pacing would be a useful and effective end point for substrate-based VT ablation . As an adjunct to this strategy , we used a new high-density mapping catheter and frequently used epicardial mapping . Methods and Results — Seventy patients ( age , 67±11 years ; 7 female ) with VT and structurally abnormal ventricle(s ) were prospect ively enrolled .  Conventional mapping was performed in sinus rhythm in all , and a high-density Pentaray mapping catheter was used in the endocardium ( n=35 ) and epicardially . LAVAs were recorded in 67 patients ( 95.7 % ; 95 % confidence interval , 89.2–98.9 ) . Catheter ablation was performed targeting LAVA with an irrigated-tip catheter placed endocardially via a transseptal or retro grade aortic approach or epicardially via the subxiphoid approach . LAVAs were successfully abolished or dissociated in 47 of 67 patients ( 70.1 % ; 95 % confidence interval , 58.7–80.1 ) . In multivariate analysis , LAVA elimination was independently associated with a reduction in recurrent VT or death ( hazard ratio , 0.49 ; 95 % confidence interval , 0.26–0.95 ; P=0.035 ) during long-term follow-up ( median , 22 months ) . Conclusions — LAVAs can be identified in most patients with scar-related VT . Elimination of LAVAs is feasible and safe and is associated with superior survival free from recurrent VT BACKGROUND For patients who have a ventricular tachyarrhythmic event , implantable cardioverter-defibrillators ( ICDs ) are a mainstay of therapy to prevent sudden death . However , ICD shocks are painful , can result in clinical depression , and do not offer complete protection against death from arrhythmia . We design ed this r and omized trial to examine whether prophylactic radiofrequency catheter ablation of arrhythmogenic ventricular tissue would reduce the incidence of ICD therapy . METHODS Eligible patients with a history of a myocardial infa rct ion underwent defibrillator implantation for spontaneous ventricular tachycardia or fibrillation . The patients did not receive  antiarrhythmic drugs .  Patients were r and omly assigned to  defibrillator implantation alone or defibrillator implantation with adjunctive catheter ablation  ( 64 patients in each group ) . Ablation was performed with the use of a substrate-based approach in which the myocardial scar is mapped and ablated while the heart remains predominantly in sinus rhythm . The primary end point was survival free from any appropriate ICD therapy . RESULTS The mortality rate 30 days after ablation was zero , and there were no significant changes in ventricular function or functional class during the mean ( + /-SD ) follow-up period of 22.5+/-5.5 months . Twenty-one patients assigned to defibrillator implantation alone ( 33 % ) and eight patients assigned to defibrillator implantation plus ablation ( 12 % ) received appropriate ICD therapy ( antitachycardia pacing or shocks ) ( hazard ratio in the ablation group , 0.35 ; 95 % confidence interval , 0.15 to 0.78 , P=0.007 ) . Among these patients , 20 in the control group ( 31 % ) and 6 in the ablation group ( 9 % ) received shocks ( P=0.003 ) . Mortality was not increased in the group assigned to ablation as compared with the control group ( 9 % vs. 17 % , P=0.29 ) . CONCLUSIONS In this r and omized trial , prophylactic substrate-based catheter ablation reduced the incidence of ICD therapy in patients with a history of myocardial infa rct ion who received ICDs for the secondary prevention of sudden death . ( Current Controlled Trials number , IS RCT N62488166 [ controlled-trials.com ] . ) One hundred and one patients with sustained unimorphic ventricular tachycardia underwent programmed ventricular stimulation with one of two protocol s. Fifty patients underwent programmed stimulation with protocol A , which consisted of burst overdrive pacing , single , double , and triple extrastimuli at the right ventricular apex , right ventricular outflow tract , or septum , and then at the left ventricular apex . Fifty-one patients underwent programmed stimulation with protocol B  , which consisted of burst overdrive pacing , single and double extrastimuli at the right ventricular apex , right ventricular outflow tract or septum , and at the left ventricular apex , followed by triple extrastimuli at these sites . The stimulation protocol was continued until sustained ventricular tachycardia or rapid , polymorphic ventricular tachycardia greater than 10 sec in duration was induced . With protocol A , clinical and non clinical ventricular tachycardia was induced in 76 % and 36 % of patients , respectively ; with protocol B , clinical and non clinical ventricular tachycardia was induced in 85 % and 38 % of patients , respectively . Direct-current countershock for sustained polymorphic ventricular tachycardia was required in 10 % of patients studied under protocol A , compared with in 2 % of patients studied under protocol B. With protocol A , near-maximal yield of induced clinical ( 72 % ) and non clinical ventricular tachycardia ( 30 % ) was attained after the use of triple extrastimuli at the first stimulation site . The yield of stimulation at a second right ventricular site and of left ventricular stimulation was only an additional 2 % each . With protocol B , triple extrastimuli increased the yield of induced clinical ventricular tachycardia from 61 % to 85 % . ( ABSTRACT TRUNCATED AT 250 WORDS BACKGROUND Recurrent sustained ventricular tachycardia ( VT ) is not responsive to antiarrhythmic drugs in the majority of patients , who therefore need therapy with nonpharmacological methods . We evaluated prospect ively the feasibility , safety , and efficacy of transcatheter radiofrequency ( RF ) ablation of VT in 21 selected patients with ischemic heart disease and VT . METHODS AND RESULTS Twenty-one patients with ischemic heart disease and recurrent , drug-refractory VT documented by 12-lead ECG were selected who had sufficient hemodynamic tolerance of VT to undergo transcatheter mapping . Documented clinical VT was reproduced by programmed cardiac stimulation ( PCS ) , and the site of origin was localized by a combination of techniques , including pace mapping , activation-sequence mapping , recordings of middiastolic potentials , and application of re setting and entrainment principles . RF current at 55 V was applied ( 3.8 + /- 3.1 applications per patient ) for as long as 30 seconds at a time to target sites . Twenty-four distinct clinical VTs ( mean cycle length , 445 + /- 52 milliseconds ) were mapped and ablated in 21 patients . In 17 of 21 patients ( 81 % ) , the procedure was acutely successful , and the target clinical VT could no longer be induced by PCS after the procedure , whereas in 4 patients , clinical VT remained inducible . By contrast , VTs with shorter cycle length and different QRS morphology than the ablated VT could still be induced by PCS in 12 of 21 patients . One patient died in intractable congestive heart failure 10 days after the procedure , and the remaining 20 are alive at the end of the follow-up period . The majority of the patients continued to be treated with at least one additional mode of antiarrhythmic therapy ; 12 patients were still taking antiarrhythmic drugs , and 9 patients received an implantable cardioverter/defibrillator . During a mean follow-up period of 13.2 + /- 5.0 months , 9 of 20 patients ( 45 % ) had recurrent VT . In 4 patients , the recurrent VT was different than the previously ablated one . Clinical VT recurred in all 4 patients in whom RF ablation had been acutely unsuccessful . Four patients with recurrent VT underwent repeat RF ablation procedures that were acutely successful and had no further recurrence . CONCLUSION Transcatheter RF ablation is feasible but has only moderately high efficacy in a small , selected group of patients with ischemic heart disease and drug-refractory , highly frequent , hemodynamically tolerated , sustained VT . In the majority of the patients , this treatment technique is palliative rather than definitive , and many of the patients continue to require other methods of antiarrhythmic therapy BACKGROUND This study evaluated the cost-effectiveness of catheter ablation therapy versus amiodarone for treating ventricular tachycardia ( VT ) in patients with structural heart disease . The analysis used a societal perspective for a hypothetical cohort of VT patients with implantable cardioverter-defibrillators , who were experiencing frequent shocks . METHODS AND RESULTS We calculated incremental cost-effectiveness of ablation relative to amiodarone over 5 years after treatment initiation . Event probabilities were from the Chilli r and omized clinical trial ( Chilli Cooled Ablation System , Cardiac Pathways Corporation , Sunnyvale , Calif ) , the literature , and a consensus panel . Costs were from 1998 national Medicare reimbursement schedules . Quality -of-life weights ( utilities ) were estimated using an established preference measurement technique . In a hypothetical cohort of 10 000 patients , 5-year costs were higher for patients undergoing ablation compared with amiodarone therapy ( $ 21 795 versus $ 19 075 ) . Ablation also produced a greater increase in quality of life ( 2.78 versus 2.65 quality -adjusted life-years [ QALYs ] ) . This yielded a cost-effectiveness ratio of $ 20 923 per QALY gained for ablation compared with amiodarone . Results were relatively insensitive to assumptions about ablation success and durability . In less severe patients with good ejection fractions who suffer their first VT episode , the incremental cost-effectiveness ratio was $ 6028 per QALY gained . These cost-effectiveness ratios are within the range generally thought to warrant technology adoption . CONCLUSIONS This study demonstrates that , from a societal perspective , catheter ablation appears to be a cost-effective alternative to amiodarone for treating VT patients Reproduction of  spontaneously occurring ventricular tachycardia ( VT ) and induction of previously undocumented VT were studied prospect ively in 98 patients : 48 with documented sustained VT or ventricular fibrillation , 25 with nonsustained or exercise-induced VT , and 25 with no documented VT . Patients received 1 to 4 ventricular extrastimuli and ventricular burst pacing at 2 right ventricular ( RV ) sites , first at twice late diastolic threshold , and then at 10 mA using a prospect i ve , t and em study design . Spontaneously occurring VT was reproduced in 37 of 48 patients ( 77 % ) at twice late diastolic threshold and in 1 other patient ( 2 % ) at 10 mA. VT was reproduced at both RV sites in 17 of 48 patients ( 35 % ) and at 1 site in 20 of 48 patients ( 42 % ) at twice late diastolic threshold . A previously undocumented VT was induced in 7 of 25 patients ( 28 % ) with no documented VT at twice diastolic threshold and 14 of 25 patients ( 56 % ) at 10 mA. A previously undocumented VT was induced in 33 of 73 patients ( 45 % ) with a history of sustained or nonsustained VT at twice late diastolic threshold and in 47 of 73 patients ( 64 % ) at 10 mA. In patients with documented sustained VT , the use of up to 4 ventricular extrastimuli at multiple RV sites increases the sensitivity of the test . In patients without documented VT , the induction of previously undocumented VT with more than 3 ventricular extrastimuli limits the specificity of the test . Increased current provides only a slight advantage over 4 ventricular extrastimuli at twice late diastolic threshold in terms of reproduction of spontaneously occurring VT , but leads to a marked increase in induction of previously undocumented VT Background — Electrical storm ( ES ) caused by recurrent episodes of ventricular tachycardia ( VT ) can cause sudden death in patients with implantable cardioverter-defibrillators and adversely affects prognosis in survivors . Catheter ablation has been proposed for treating ES , but its long-term effect in a large population has never been verified . Methods and Results — Ninety-five consecutive patients with coronary artery disease ( 72 patients ) , idiopathic dilated cardiomyopathy ( 10 patients ) , and arrhythmogenic right ventricular dysplasia/cardiomyopathy ( 13 patients ) undergoing catheter ablation for drug-refractory ES  were prospect ively evaluated . Short-term efficacy 
    Output:
    
agent
Noninducibility of VT after VT ablation is associated with improved arrhythmia-free survival and all-cause mortality
***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 — Catheter ablation of ventricular tachycardia ( VT )  is effective and particularly useful in patients with frequent defibrillator interventions . Various substrate modification techniques have been described for unmappable or hemodynamically intolerable VT . Noninducibility is the most frequently used end point but is associated with significant limitations , so the optimal end point remains unclear . We hypothesized that elimination of local abnormal ventricular activities ( LAVAs ) during sinus rhythm or ventricular pacing would be a useful and effective end point for substrate-based VT ablation . As an adjunct to this strategy , we used a new high-density mapping catheter and frequently used epicardial mapping . Methods and Results — Seventy patients ( age , 67±11 years ; 7 female ) with VT and structurally abnormal ventricle(s ) were prospect ively enrolled .  Conventional mapping was performed in sinus rhythm in all , and a high-density Pentaray mapping catheter was used in the endocardium ( n=35 ) and epicardially . LAVAs were recorded in 67 patients ( 95.7 % ; 95 % confidence interval , 89.2–98.9 ) . Catheter ablation was performed targeting LAVA with an irrigated-tip catheter placed endocardially via a transseptal or retro grade aortic approach or epicardially via the subxiphoid approach . LAVAs were successfully abolished or dissociated in 47 of 67 patients ( 70.1 % ; 95 % confidence interval , 58.7–80.1 ) . In multivariate analysis , LAVA elimination was independently associated with a reduction in recurrent VT or death ( hazard ratio , 0.49 ; 95 % confidence interval , 0.26–0.95 ; P=0.035 ) during long-term follow-up ( median , 22 months ) . Conclusions — LAVAs can be identified in most patients with scar-related VT . Elimination of LAVAs is feasible and safe and is associated with superior survival free from recurrent VT BACKGROUND For patients who have a ventricular tachyarrhythmic event , implantable cardioverter-defibrillators ( ICDs ) are a mainstay of therapy to prevent sudden death . However , ICD shocks are painful , can result in clinical depression , and do not offer complete protection against death from arrhythmia . We design ed this r and omized trial to examine whether prophylactic radiofrequency catheter ablation of arrhythmogenic ventricular tissue would reduce the incidence of ICD therapy . METHODS Eligible patients with a history of a myocardial infa rct ion underwent defibrillator implantation for spontaneous ventricular tachycardia or fibrillation . The patients did not receive  antiarrhythmic drugs .  Patients were r and omly assigned to  defibrillator implantation alone or defibrillator implantation with adjunctive catheter ablation  ( 64 patients in each group ) . Ablation was performed with the use of a substrate-based approach in which the myocardial scar is mapped and ablated while the heart remains predominantly in sinus rhythm . The primary end point was survival free from any appropriate ICD therapy . RESULTS The mortality rate 30 days after ablation was zero , and there were no significant changes in ventricular function or functional class during the mean ( + /-SD ) follow-up period of 22.5+/-5.5 months . Twenty-one patients assigned to defibrillator implantation alone ( 33 % ) and eight patients assigned to defibrillator implantation plus ablation ( 12 % ) received appropriate ICD therapy ( antitachycardia pacing or shocks ) ( hazard ratio in the ablation group , 0.35 ; 95 % confidence interval , 0.15 to 0.78 , P=0.007 ) . Among these patients , 20 in the control group ( 31 % ) and 6 in the ablation group ( 9 % ) received shocks ( P=0.003 ) . Mortality was not increased in the group assigned to ablation as compared with the control group ( 9 % vs. 17 % , P=0.29 ) . CONCLUSIONS In this r and omized trial , prophylactic substrate-based catheter ablation reduced the incidence of ICD therapy in patients with a history of myocardial infa rct ion who received ICDs for the secondary prevention of sudden death . ( Current Controlled Trials number , IS RCT N62488166 [ controlled-trials.com ] . ) One hundred and one patients with sustained unimorphic ventricular tachycardia underwent programmed ventricular stimulation with one of two protocol s. Fifty patients underwent programmed stimulation with protocol A , which consisted of burst overdrive pacing , single , double , and triple extrastimuli at the right ventricular apex , right ventricular outflow tract , or septum , and then at the left ventricular apex . Fifty-one patients underwent programmed stimulation with protocol B  , which consisted of burst overdrive pacing , single and double extrastimuli at the right ventricular apex , right ventricular outflow tract or septum , and at the left ventricular apex , followed by triple extrastimuli at these sites . The stimulation protocol was continued until sustained ventricular tachycardia or rapid , polymorphic ventricular tachycardia greater than 10 sec in duration was induced . With protocol A , clinical and non clinical ventricular tachycardia was induced in 76 % and 36 % of patients , respectively ; with protocol B , clinical and non clinical ventricular tachycardia was induced in 85 % and 38 % of patients , respectively . Direct-current countershock for sustained polymorphic ventricular tachycardia was required in 10 % of patients studied under protocol A , compared with in 2 % of patients studied under protocol B. With protocol A , near-maximal yield of induced clinical ( 72 % ) and non clinical ventricular tachycardia ( 30 % ) was attained after the use of triple extrastimuli at the first stimulation site . The yield of stimulation at a second right ventricular site and of left ventricular stimulation was only an additional 2 % each . With protocol B , triple extrastimuli increased the yield of induced clinical ventricular tachycardia from 61 % to 85 % . ( ABSTRACT TRUNCATED AT 250 WORDS BACKGROUND Recurrent sustained ventricular tachycardia ( VT ) is not responsive to antiarrhythmic drugs in the majority of patients , who therefore need therapy with nonpharmacological methods . We evaluated prospect ively the feasibility , safety , and efficacy of transcatheter radiofrequency ( RF ) ablation of VT in 21 selected patients with ischemic heart disease and VT . METHODS AND RESULTS Twenty-one patients with ischemic heart disease and recurrent , drug-refractory VT documented by 12-lead ECG were selected who had sufficient hemodynamic tolerance of VT to undergo transcatheter mapping . Documented clinical VT was reproduced by programmed cardiac stimulation ( PCS ) , and the site of origin was localized by a combination of techniques , including pace mapping , activation-sequence mapping , recordings of middiastolic potentials , and application of re setting and entrainment principles . RF current at 55 V was applied ( 3.8 + /- 3.1 applications per patient ) for as long as 30 seconds at a time to target sites . Twenty-four distinct clinical VTs ( mean cycle length , 445 + /- 52 milliseconds ) were mapped and ablated in 21 patients . In 17 of 21 patients ( 81 % ) , the procedure was acutely successful , and the target clinical VT could no longer be induced by PCS after the procedure , whereas in 4 patients , clinical VT remained inducible . By contrast , VTs with shorter cycle length and different QRS morphology than the ablated VT could still be induced by PCS in 12 of 21 patients . One patient died in intractable congestive heart failure 10 days after the procedure , and the remaining 20 are alive at the end of the follow-up period . The majority of the patients continued to be treated with at least one additional mode of antiarrhythmic therapy ; 12 patients were still taking antiarrhythmic drugs , and 9 patients received an implantable cardioverter/defibrillator . During a mean follow-up period of 13.2 + /- 5.0 months , 9 of 20 patients ( 45 % ) had recurrent VT . In 4 patients , the recurrent VT was different than the previously ablated one . Clinical VT recurred in all 4 patients in whom RF ablation had been acutely unsuccessful . Four patients with recurrent VT underwent repeat RF ablation procedures that were acutely successful and had no further recurrence . CONCLUSION Transcatheter RF ablation is feasible but has only moderately high efficacy in a small , selected group of patients with ischemic heart disease and drug-refractory , highly frequent , hemodynamically tolerated , sustained VT . In the majority of the patients , this treatment technique is palliative rather than definitive , and many of the patients continue to require other methods of antiarrhythmic therapy BACKGROUND This study evaluated the cost-effectiveness of catheter ablation therapy versus amiodarone for treating ventricular tachycardia ( VT ) in patients with structural heart disease . The analysis used a societal perspective for a hypothetical cohort of VT patients with implantable cardioverter-defibrillators , who were experiencing frequent shocks . METHODS AND RESULTS We calculated incremental cost-effectiveness of ablation relative to amiodarone over 5 years after treatment initiation . Event probabilities were from the Chilli r and omized clinical trial ( Chilli Cooled Ablation System , Cardiac Pathways Corporation , Sunnyvale , Calif ) , the literature , and a consensus panel . Costs were from 1998 national Medicare reimbursement schedules . Quality -of-life weights ( utilities ) were estimated using an established preference measurement technique . In a hypothetical cohort of 10 000 patients , 5-year costs were higher for patients undergoing ablation compared with amiodarone therapy ( $ 21 795 versus $ 19 075 ) . Ablation also produced a greater increase in quality of life ( 2.78 versus 2.65 quality -adjusted life-years [ QALYs ] ) . This yielded a cost-effectiveness ratio of $ 20 923 per QALY gained for ablation compared with amiodarone . Results were relatively insensitive to assumptions about ablation success and durability . In less severe patients with good ejection fractions who suffer their first VT episode , the incremental cost-effectiveness ratio was $ 6028 per QALY gained . These cost-effectiveness ratios are within the range generally thought to warrant technology adoption . CONCLUSIONS This study demonstrates that , from a societal perspective , catheter ablation appears to be a cost-effective alternative to amiodarone for treating VT patients Reproduction of  spontaneously occurring ventricular tachycardia ( VT ) and induction of previously undocumented VT were studied prospect ively in 98 patients : 48 with documented sustained VT or ventricular fibrillation , 25 with nonsustained or exercise-induced VT , and 25 with no documented VT . Patients received 1 to 4 ventricular extrastimuli and ventricular burst pacing at 2 right ventricular ( RV ) sites , first at twice late diastolic threshold , and then at 10 mA using a prospect i ve , t and em study design . Spontaneously occurring VT was reproduced in 37 of 48 patients ( 77 % ) at twice late diastolic threshold and in 1 other patient ( 2 % ) at 10 mA. VT was reproduced at both RV sites in 17 of 48 patients ( 35 % ) and at 1 site in 20 of 48 patients ( 42 % ) at twice late diastolic threshold . A previously undocumented VT was induced in 7 of 25 patients ( 28 % ) with no documented VT at twice diastolic threshold and 14 of 25 patients ( 56 % ) at 10 mA. A previously undocumented VT was induced in 33 of 73 patients ( 45 % ) with a history of sustained or nonsustained VT at twice late diastolic threshold and in 47 of 73 patients ( 64 % ) at 10 mA. In patients with documented sustained VT , the use of up to 4 ventricular extrastimuli at multiple RV sites increases the sensitivity of the test . In patients without documented VT , the induction of previously undocumented VT with more than 3 ventricular extrastimuli limits the specificity of the test . Increased current provides only a slight advantage over 4 ventricular extrastimuli at twice late diastolic threshold in terms of reproduction of spontaneously occurring VT , but leads to a marked increase in induction of previously undocumented VT Background — Electrical storm ( ES ) caused by recurrent episodes of ventricular tachycardia ( VT ) can cause sudden death in patients with implantable cardioverter-defibrillators and adversely affects prognosis in survivors . Catheter ablation has been proposed for treating ES , but its long-term effect in a large population has never been verified . Methods and Results — Ninety-five consecutive patients with coronary artery disease ( 72 patients ) , idiopathic dilated cardiomyopathy ( 10 patients ) , and arrhythmogenic right ventricular dysplasia/cardiomyopathy ( 13 patients ) undergoing catheter ablation for drug-refractory ES  were prospect ively evaluated . Short-term efficacy 
    Output:
    