***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: Flaws in the design , conduct , analysis , and reporting of r and omised trials can cause the effect of an intervention to be underestimated or overestimated . The Cochrane Collaboration ’s tool for assessing risk of bias aims to make the process clearer and more BACKGROUND Atrial fibrillation is the most common sustained arrhythmia in the elderly . Serum potassium is associated with ventricular arrhythmias and cardiac arrest . Little is known about the association of serum potassium with atrial fibrillation . The objective of this study was to investigate the association of serum potassium and the risk of atrial fibrillation in a population based setting . METHODS The study was performed within the prospect i ve population -based Rotterdam Study . The study population consisted of 4059 participants without atrial fibrillation at baseline for whom baseline levels of serum potassium were measured .  Atrial fibrillation was ascertained from centre visit ECG assessment s as well as medical records . RESULTS During a mean follow up of 11.8 years ( SD=5.2 yr ) , 474 participants developed atrial fibrillation . Participants with hypokalemia ( < 3.5 mmol/l ) had a higher risk of atrial fibrillation ( HR : 1.63 , 95%CI : 1.03 - 2.56 ) than those with normokalemia ( 3.5 - 5.0 mmol/l ) . This association was independent of age , sex , serum magnesium , and other potential confounders . Especially in participants with a history of myocardial infa rct ion , those with hypokalemia had a higher risk of atrial fibrillation than those with normokalemia ( HR : 3.81 , 95%-CI : 1.51 - 9.61 ) . CONCLUSIONS In this study low serum levels of potassium were associated with a higher risk of atrial fibrillation Background : In acute coronary syndrome ( ACS ) , potassium levels < 3.5 mEq/L are associated with ventricular arrhythmias . Current guidelines therefore recommend a potassium target > 4.0 mEq/L in ACS . Our study evaluated the association between potassium levels , cardiac arrhythmias , and cardiovascular death in patients with non-ST-segment elevation myocardial infa rct ion or unstable angina . Methods : Potassium levels were measured in 6515 patients prior to r and omization to receive either ranolazine or a placebo in the MERLIN-TIMI 36 trial . A seven-day continuous electrocardiographic assessment was obtained to determine the incidence of non-sustained ventricular tachycardia ( NSVT ) and ventricular pauses . The association between potassium levels and cardiovascular death was evaluated using a Cox proportional hazards regression model with multivariable adjustment . Results : NSVT lasting for at least eight consecutive beats occurred more frequently at potassium levels < 3.5 mEq/L than at potassium levels ⩾5 mEq/L ( 10.1 vs. 4.5 % , p=0.03 for trend ) , whereas the inverse pattern was observed for ventricular pauses > 3 s , which occurred more frequently at potassium levels ⩾5 mEq/L than at potassium levels < 3.5 mEq/L ( 5.9 vs. 2.0 % , p=0.03 for trend ) . There was a U-shaped relationship between the potassium level at admission and both early and late risk of cardiovascular death . Compared with patients with potassium levels of 3.5 to < 4 mEq/L , a potassium level < 3.5 mEq/L was associated with an increased risk of cardiovascular death at day 14 ( 2.4 vs. 0.8 % , HRadj 3.1 , p=0.02 ) and at one year ( 6.4 vs. 3.0 % , HRadj 2.2 , p=0.01 ) . The risk of cardiovascular death at one year was also significantly increased at potassium levels ⩾4.5 mEq/L and a similar trend was noted at potassium levels ⩾5 mEq/L. Conclusions : The lowest risk of cardiovascular death was observed in patients with admission potassium levels between 3.5 and 4.5 mEq/L. Both lower and higher levels of potassium were associated with tachyarrhythmias and bradyarrhythmias , suggesting a potential mechanistic explanation for the increased risk of cardiovascular death at the extremes of potassium homeostasis Abstract Abnormal serum potassium levels are associated with an increased risk of ventricular arrhythmias and mortality in patients with acute myocardial infa rct ion ( AMI ) . The aim of the present study was to evaluate whether different levels of serum potassium , within the normal range , are associated with worse outcomes . The present study comprised 1277 patients with AMI and normal-range admission potassium levels ( 3.5–5.2 mEq/L ) , who were enrolled and prospect ively followed up in the Acute Coronary Syndrome Israeli Survey between 2010 and 2013 . Patients were divided into 4 quartiles based on admission potassium levels ; “ normal-low ” ( K ≥ 3.5 and K ⩽ 3.9 ) , “ normal-moderate ” ( K > 3.9 and K ⩽ 4.18 ) , “ normal-high ” ( K > 4.18 and K ⩽ 4.45 ) , and “ normal-very high ” ( K > 4.45 and K ⩽ 5.2 ) . We analyzed the association between admission serum potassium levels and 7 days in-hospital complication rates , and 30-day and 1-year all-cause mortality rates . Patients with “ normal-very high ” potassium displayed increased frequency of baseline clinical risk factors and experienced a higher rate of acute kidney injury during hospitalization compared with the “ normal-low ” group ( 7.7 % vs 2.4 % ; P = 0.002 ) . However , the rate of in-hospital ventricular arrhythmias was similar across the range of admission potassium levels ( overall P = 0.26 ) , Multivariate analysis showed that compared with “ low-normal ” potassium values , patients with “ normal-very high ” potassium levels experienced increased risk for 30-days ( adjusted hazard ratio 2.88 , 95 % confidence interval 1.05–7.87 , P = 0.039 ) and 1-year all-cause mortality ( adjusted hazard ratio 1.98 , 95 % confidence interval 1.05–3.75 , P = 0.034 ) . In patients admitted with AMI  , admission serum potassium levels of 4.45 to 5.2 mEq/L are not associated with in-hospital ventricular arrhythmias , but are associated with increased short and long-term mortality OBJECTIVE : To test the feasibility of creating a valid and reliable checklist with the following features : appropriate for assessing both r and omised and non-r and omised studies ; provision of both an overall score for study quality and a profile of scores not only for the quality of reporting , internal validity ( bias and confounding ) and power , but also for external validity . DESIGN : A pilot version was first developed , based on epidemiological principles , review s , and existing checklists for r and omised studies . Face and content validity were assessed by three experienced review ers and reliability was determined using two raters assessing 10 r and omised and 10 non-r and omised studies . Using different raters , the checklist was revised and tested for internal consistency ( Kuder-Richardson 20 ) , test-retest and inter-rater reliability ( Spearman correlation coefficient and sign rank test ; kappa statistics ) , criterion validity , and respondent burden . MAIN RESULTS : The performance of the checklist improved considerably after revision of a pilot version . The Quality Index had high internal consistency ( KR-20 : 0.89 ) as did the subscales apart from external validity ( KR-20 : 0.54 ) . Test-retest ( r 0.88 ) and inter-rater ( r 0.75 ) reliability of the Quality Index were good . Reliability of the subscales varied from good ( bias ) to poor ( external validity ) . The Quality Index correlated highly with an existing , established instrument for assessing r and omised studies ( r 0.90 ) . There was little difference between its performance with non-r and omised and with r and omised studies . Raters took about 20 minutes to assess each paper ( range 10 to 45 minutes ) . CONCLUSIONS : This study has shown that it is feasible to develop a checklist that can be used to assess the method ological quality not only of r and omised controlled trials but also non-r and omised studies . It has also shown that it is possible to produce a checklist that provides a profile of the paper , alerting review ers to its particular method ological strengths and weaknesses . Further work is required to improve the checklist and the training of raters in the assessment of external validity Aims In the Ongoing Telmisartan Alone and in Combination with Ramipril Trial ( ONTARGET ) , dual agent renin-angiotensin-aldosterone system ( RAAS ) blockade with angiotensin-converting-enzyme inhibitors ( ACEIs ) and angiotensin receptor blockers ( ARBs ) did not reduce the risk of renal and cardiovascular outcomes compared with the single use of either agent . Dual therapy however increased the incidence of hyperkalemia . We examined risk factors for hyper- and hyokalemia and hypothesized that both would be associated with worse cardiovascular and renal outcomes . Methods A post-hoc analysis of the  ONTARGET  trial comparing dual therapy ( ramipril and telmisartan ) vs monotherapy ( ramipril or telmisartan ) was performed . The association between serum potassium at week 6 on cardiovascular and renal outcomes during the 56 months follow-up was assessed by multivariate Cox analysis . The main cardiovascular outcome was the composite of cardiovascular death , myocardial infa rct ion , stroke , or hospitalization for heart failure . The renal outcome was defined as the composite of a doubling of serum creatinine or chronic dialysis . Results Six weeks after r and omization , hyperkalemia developed in 210 ( 2.7 % ) patients on dual therapy vs 264 ( 1.6 % ) patients on monotherapy ( p < 0.001 vs dual therapy ) . Hypokalemia developed in 87 ( 1.1 % ) patients on dual therapy vs 200 ( 1.2 % ) patients on monotherapy . Serum potassium was nonlinearly associated with cardiovascular and renal events with a nadir between 4.0–5.0 mmol/l for cardiovascular and 4.0–4.5 mmol/l for renal events such that subjects above or below these values exhibited higher risks . This association was independent of age , gender , diabetes , estimated glomerular filtration rate , systolic blood pressure and diuretic use . Conclusions With the pre caution s stipulated by the protocol of the ONTARGET trial , hypokalemia and hyperkalemia were infrequent events . Nevertheless , both high and low serum potassium were associated with an increased risk of cardiovascular and renal disease STUDY OBJECTIVES Although controversial , hypokalemia ( LK ) in patients with acute myocardial infa rct ion ( MI ) is thought to predict increased in-hospital morbidity , particularly cardiac arrhythmias , and mortality . Also , the mechanism of low serum potassium in the setting of MI has not been delineated . We evaluated the frequency , attributes , and outcome , and speculated on the mechanism of LK in patients with MI . DESIGN This was a prospect i ve cross-sectional study of 517 consecutive patients with MI admitted to the coronary care unit ( CCU ) .  Serum potassium was measured in the emergency department and repeatedly thereafter throughout hospitalization , and was used in the analysis , along with a large array of clinical and laboratory variables . RESULTS The patients were allocated to a LK and a normokalemic ( NK ) cohort , based on the emergency department serum potassium measurement . The 41 patients with LK ( 3.16+/-0.24 mEq/L ; 7.9 % of total ) were comparable on admission in their baseline assessment to the 476 patients with normal serum potassium ( 4.28+/-0.56 mEq/L ) , except for lower emergency department magnesium ( 1.48+/-0.15 mg/dL vs. 1.96+/-0.26 mg/dL ; p = 0.0005 ) and earlier presentation after onset of symptoms ( 3.0+/-4.1 h vs. 4.4+/- 6.2 h ; p = 0.05 ) . There was a poor correlation between serum potassium and magnesium on admission ( r = 0.14 ) . Peak creatine kinase ( CK ) and myocardial isomer of CK were higher in the LK patients ( 3,870+/-3 , 840 IU/L vs. 2,359+/-2,653 IU/L [ p = 0.018 ] and 358+/-312 IU/L vs. 228 + /- 258 IU/L [ p = 0.013 ] , respectively ) . Management of the two cohorts was the same , except for a higher rate of use of magnesium ( 14.6 % vs. 4.6 
    Output:
    
Conclusions Mortality , both short and long term , and the occurrence of ventricular arrhythmias in patients with acute myocardial infa rct ion seem to be negatively associated with hypokalemic serum potassium concentration .