***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 —The electrocardiographic PR interval increases with aging , differs by race , and is associated with atrial fibrillation ( AF ) , pacemaker implantation , and all-cause mortality . We sought to determine the associations between PR interval and heart failure , AF , and mortality in a biracial cohort of older adults . Methods and Results —The Health , Aging , and Body Composition ( Health ABC ) Study is a prospect i ve , biracial cohort . We used multivariable Cox proportional hazards models to examine PR interval ( hazard ratios expressed per SD increase ) and 10-year risks of heart failure , AF , and all-cause mortality . Multivariable models included demographic , anthropometric , and clinical variables in addition to established cardiovascular risk factors . We examined 2722 Health ABC participants ( aged 74±3 years , 51.9 % women , and 41 % black ) . We did not identify significant effect modification by race for the outcomes studied . After multivariable adjustment , every SD increase ( 29 ms ) in PR interval was associated with a 13 % greater 10-year risk of heart failure ( 95 % confidence interval , 1.02–1.25 ) and a 13 % increased risk of incident AF ( 95 % confidence interval , 1.04–1.23 ) . PR interval > 200 ms was associated with a 46 % increased risk of incident heart failure ( 95 % confidence interval , 1.11–1.93 ) . PR interval was not associated with increased all-cause mortality . Conclusions —We identified significant relationships of PR interval to heart failure and AF in older adults . Our findings extend prior investigations by examining PR interval and associations with adverse outcomes in a biracial cohort of older men and women BACKGROUND Prolonged interatrial conduction time ( IACT ) can be associated with abnormal left atrial ( LA ) function but has not been characterized in patients with left ventricular ( LV ) systolic dysfunction ( LVSD ) and QRS intervals > 130 ms . METHODS Two-dimensional Doppler echocardiography and Doppler tissue imaging ( DTI ) were performed in 41 patients with LVSD ( mean LV ejection fraction , 26 + /- 5 % ) and 41 similarly aged normal controls . Two-dimensional measurements included LV volume and ejection fraction and LA volume for the determination of LA emptying fraction and LA ejection fraction . IACT was defined as the time from the onset of the P wave to the onset of the DTI-derived late diastolic ( A ' ) velocity at the lateral mitral annulus . Two-dimensional Doppler measurements were reassessed in patients with LVSD 4 + /- 2 months after cardiac resynchronization therapy ( CRT ) . RESULTS IACT was longer in patients with compared to controls ( 105 + /- 25 vs 74 + /- 12 ms , P < .001 ) ; none of the controls had an IACT > 100 ms . In patients with LVSD , IACT was correlated modestly with measurements of LA volume ( r = .41-.48 , all P values < .009 ) but not with measurements of LA function .  Patients with LVSD with IACTs > 100 ms ( n = 20 ) prior to CRT had larger LA volumes and lower indices of LA function after CRT compared to those with IACTs < or = 100 ms . Significant reductions in LV end-systolic volumes and increases in LV ejection fractions occurred in both groups after CRT . CONCLUSION DTI-derived IACT can be prolonged in patients with severe LVSD and wide QRS intervals . An IACT > 100 ms can affect LA remodeling and function at early follow-up after CRT but does not influence the response in LV end-systolic volume or ejection fraction BACKGROUND AND PURPOSE First-degree atrioventricular ( AV ) block in relation to the outcome of cardiac resynchronization therapy ( CRT )  has not been well examined . METHODS Patients who received a CRT defibrillator or pacemaker between January 2002 and September 2010 at Mayo Clinic were classified into 2 groups : normal PR interval and prolonged PR interval . St and ard sensed ( 100 milliseconds ) and paced ( 130 milliseconds ) AV delay was programmed after CRT .  Clinical presentations and echocardiography were assessed before CRT and at a median of 6 months after CRT . RESULTS The normal PR interval group ( n=199 ) had greater improvements in heart failure functional class ( mean [ SD ] , 0.7 [ 0.8 ] vs 0.5 [ 0.9 ] ; P=.03 ) and left ventricular ejection fraction ( 9.4 % [ 12.4 % ] vs 5.9 % [ 9.5 % ] ; P=.007 ) than the prolonged PR group ( n=204 ) . CONCLUSION Compared with prolonged PR interval , the presence of normal PR interval was associated with a greater improvement in heart failure BACKGROUND Based on current patient selection criteria , a significant proportion of recipients of cardiac resynchronization therapy ( CRT )  do not respond to treatment . The purpose of this analysis is to identify predictors and characterize the timing of response to CRT  in patients with advanced heart failure . METHODS Patients r and omized to receive CRT in the MIRACLE and MIRACLE-ICD trials , design ed to assess the benefit of CRT compared with st and ard medical therapy in patients with advanced heart failure , left ventricular ejection fraction < 0.35 , and QRS > or = 130 milliseconds , were included for this analysis . Patients with an improvement of > or = 1 New York Heart Association ( NYHA ) class from baseline to the 6-month follow-up were considered responders and those who had no change or worse NYHA class or died were classified as nonresponders . Responders were subdivided into early ( within 1 - 3 months ) and late ( 6 months ) . RESULTS One hundred forty-three ( 64 % ) of 224 and 190 ( 61 % ) of 313 patients in the MIRACLE and MIRACLE-ICD trials , respectively , responded to therapy , with 81 ( 57 % ) of 143 and 100 ( 53 % ) of 190 responding early . Several but differing factors predicted CRT response and timing in the two trials with a high sensitivity ( 89%-90 % ) but , owing to a low specificity ( 31%-49 % ) , a modest predictive accuracy ( 66%-75 % ) . CONCLUSIONS Based on improvement of > or = 1 NYHA class , less than two thirds of patients enrolled in the MIRACLE or MIRACLE-ICD trials responded to CRT , with just more than half responding within the first month . Several factors predicted CRT response and timing , but given their modest predictive accuracy , comparable for both studies , additional methods for selecting c and i date s most likely to benefit from CRT are needed AIMS In CARE-HF , cardiac resynchronization therapy ( CRT ) lowered morbidity and mortality in patients with moderate to severe heart failure . We examined whether baseline and follow-up electrocardiographic characteristics might predict long-term outcome . METHODS AND RESULTS CARE-HF r and omly assigned 409 patients to medical therapy ( MT ) plus CRT , and 404 patients to MT alone .  Electrocardiographic measurements were made at baseline during sinus rhythm , and at 3 months during paced or spontaneous rhythm depending on treatment assignment . Favourable outcome was defined as freedom from death , urgent transplantation , or cardiovascular hospitalization . Among patients assigned to CRT , 39 % had unfavourable outcomes including 55 deaths . By single variable analysis , ( i ) prolonged PR interval , left QRS axis ( but not QRS duration ) , and left bundle branch block ( BBB ) at baseline , and ( ii ) heart rate , PR , and QRS duration at 3 months predicted unfavourable outcome . By multiple variable analysis , treatment assignment ( P = 0.0001 ) , PR ( P = 0.0004 ) , and right BBB ( P < 0.00013 ) at baseline predicted outcome , whereas baseline JTc and QRS duration at 3 months predicted all-cause mortality and heart failure hospitalization ( P = 0.0071 ) . CONCLUSION In CARE-HF , QRS duration at baseline did not predict outcome , but QRS at 3 months was a predictor by single variable analysis . Patients with prolonged PR interval and the 5 % of patients with right BBB had a particularly high event rate Purpose Heart failure ( HF ) is a major cause of morbidity and mortality , and ventricular dyssynchrony is an important contributor . The ReThinQ trial reported no improvement with cardiac resynchronization therapy ( CRT ) in HF patients with left ventricular ejection fraction ( LVEF ) < 35 % , narrow QRS ( < 130 ms ) , New York Heart Association ( NYHA ) class III , and echocardiographically detected dyssynchrony , in spite of echocardiographic optimization . We investigated whether a subset of narrow QRS patients might derive benefit from CRT , based on baseline PR interval . Methods We retrospectivelyanalyzed the 87 patients from ReThinQ who were r and omized to CRT . Patients were divided into two groups : baseline PR interval < 180 ms and baseline PR interval ≥180 ms . The primary outcome was change in VO2 max at 6 months ; secondary outcomes were change in LVEF , 6-min walk distance , and change in NYHA class . Results Forty-six patients had PR < 180 ms and 41 had PR ≥ 180 ms . The baseline characteristics were similar in the two groups . As compared to patients with a short PR interval , at 6 months , only patients with PR ≥ 180 ms showed a statistically significant increase in VO2 max from 12.2 to 13.6 mL/kg min ( P = 0.045 ) . Similarly , LVEF was significantly improved only in the long PR group ( 0.26 to 0.28 , P = 0.038 ) . A greater percentage of patients in the long PR group showed improvement by at least one NYHA class ( 59 vs. 35 % , P = 0.033 ) . Conclusions A longer baseline PR interval may allow more efficacious delivery of CRT by allowing programming of physiologic AV delays . A short baseline PR interval may contribute to LV under-filling and CRT non-response BACKGROUND The influence of PR prolongation on outcomes after  cardiac resynchronization therapy ( CRT )  is uncertain . OBJECTIVE To determine whether PR prolongation predicts outcomes in potential CRT c and i date s and whether CRT benefits these c and i date s regardless of baseline PR interval . METHODS A data base of 1520 patients fulfilling criteria for CRT implant ( the COMPANION Trial ) was examined . Patients assigned to normal ( PR < 200 ms ) or prolonged ( PR ≥ 200 ms ) cohorts were compared within the optimal pharmacologic therapy ( OPT ) and CRT groups regarding an endpoint of all-cause mortality or heart failure hospitalization . CRT was compared with OPT in normal and prolonged PR interval groups . An interaction test was performed to determine whether CRT influenced outcome as a function of PR interval . RESULTS PR prolongation was present in 52 % of COMPANION subjects . R and omization to CRT was associated with a reduction in the endpoint , but the strength of the association was greater for those with prolonged PR ( hazard ratio = 0.54 ; P < .01 ) versus normal PR ( hazard ratio = 0.71 ; P = .02 ) intervals . CRT ( vs OPT ) was associated with reduction in the endpoint for subjects with normal or prolonged PR intervals . Reduction in relative risk  ( CRT vs OPT ) was 29 % ( P = .02 ) for those with normal PR intervals but was 46 % ( P < .01 ) for those with PR prolongation . No interaction was detected between PR interval cohort and treatment ( P = .17 ) . CONCLUSIONS PR prolongation may affect mortality and heart failure hospitalizations in patients with systolic dysfunction , heart failure , and wide QRS complexes . The effect of PR prolongation may be attenuated by CRT The purpose of this study was to prospect ively determine the incidence of diastolic mitral and tricuspid regurgitation in atrioventricular ( AV ) block using Doppler echocardiography . The temporal relation between mitral and tricuspid diastolic insufficiency and the diastolic murmur recorded in patients with complete heart block was also investigated . Twenty-two consecutive patients with AV block ( referred to the Echo-Doppler laboratory for routine clinical studies ) , aged 18 to 87 years , were enrolled in the study . Eleven patients had third degree AV block and a ventricular-inhibited ( VVI ) pacemaker , two patients had second degree AV block , seven patients had first degree AV block , one patient had blocked premature atrial complexes and one patient had atrial flutter with 4:1 AV block .  Diastolic mitral regurgitation was detected in 20 patients , and diastolic tricuspid regurgitation in 21 . A mid-diastolic murmur was detected in all patients except in the three youngest . The murmur occurred before diastolic regurgitation and coincided with peak forward flow through the AV valve after atrial contraction . M-mode mitral valve echocardiograms obtained in nine patients demonstrated near closure of some portions of the mitral valve after atrial contraction . Effective closure of the valve , however , did not occur unless ventricular systole supervened . In conclusion , diastolic mitral and tricuspid regurgitation are almost universally present in patients with AV block and are associated with a diastolic murmur . The murmur coincides with forward AV valve flow . Diast 
    Output:
    
Conclusions Our systematic review and meta- analysis support the hypothesis that baseline prolonged PR interval is a predictor of all-cause mortality , heart failure hospitalization , and composite outcome in CRT patients