***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 
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    Input: Within six hours of suspected acute myocardial infa rct ion , 791 patients entered a r and omised double blind study of combined intravenous and oral tocainide for the prophylaxis of primary ventricular fibrillation . Acute myocardial infa rct ion was confirmed in 559 patients , of whom 278 had received tocainide .  The study was terminated on the basis of a sequential statistical analysis which showed that in these patients tocainide was unlikely to reduce the incidence of primary ventricular fibrillation by as much as 50 % , primary ventricular fibrillation having occurred in 4 % of the tocainide and 2 % of the placebo patients . Significantly fewer tocainide treated patients were withdrawn for other serious ventricular arrhythmias . Mortality ( 1 % in the tocainide group and 2 % in the placebo group ) was low with no statistically significant differences between the active and placebo groups . Unwanted effects of treatment were infrequent and rarely troublesome both in patients with and without acute myocardial infa rct ion . These results suggest that in the dosage used in this study tocainide does not exert an antifibrillatory action in the early phase of acute myocardial infa rct ion Sixty patients with a first acute myocardial infa rct ion and no current treatment with cardioactive drugs were included in a prospect i ve study of the relationship between serum potassium concentration and the early occurrence of ventricular tachycardia and premature ventricular contractions ( PVCs ) . Serum potassium level ( range 2.5 to 5 mmol/liter ) was estimated 3.8 + /- 2.5 hr ( mean + /- SD ) after the onset of the infa rct ion , and Holter monitoring was performed during the subsequent 12 hr . In multivariate analysis , serum potassium level was negatively and age positively related to ventricular tachycardia . Among the subclasses of PVCs ( frequent unifocal , multifocal , couplets , bigeminy ) , serum potassium concentration was negatively related to the frequent unifocal subclass ; hypertension was related to couplets and to the presence of any of the subclasses , and serum aspartate aminotransferase concentration was related to multifocal PVCs . Heart failure leading to death was related to all subclasses of PVC . Serum potassium concentration is an independent inverse predictor of the occurrence of ventricular tachycardia and frequent unifocal PVCs early in acute myocardial infa rct ion OBJECTIVE To determine the changing risk of ventricular fibrillation , the prognostic implication s , and the potential long term prognostic benefit of earlier hospital admission , after acute myocardial infa rct ion . DESIGN Prospect i ve observational study . SETTING A district general hospital in east London . PATIENTS 1225 consecutive patients admitted to a coronary care unit with acute myocardial infa rct ion . MAIN OUTCOME MEASURES Time of onset of pain and ventricular fibrillation , and long term survival of patients admitted with acute myocardial infa rct ion . RESULTS The rate of ventricular fibrillation in these hospital in patients was high in the first hour from onset of pain ( 118 events/1000 persons/h ; 95 % confidence interval ( CI ) 50.7 to 231 ) and fell rapidly to an almost constant low level by six hours ; 27.4 % of patients with early ventricular fibrillation died in hospital , compared with 11.6 % of those without ( p < 0.0001 ) , but mortality in patients who survived to hospital discharge was not altered by early ventricular fibrillation ( five year survival : 75.0 % ( 95 % CI 60.0 % to 84.8 % ) with ventricular fibrillation v 73.3 % ( 95 % CI 69.6 % to 76.6 % ) without ventricular fibrillation ) . CONCLUSIONS Patients successfully resuscitated from early ventricular fibrillation have the same prognosis as those without ventricular fibrillation after acute myocardial infa rct ion . Faster access to facilities for resuscitation must be achieved if major improvements in the persistently high case fatality of patients after acute myocardial infa rct ion are to be made In 5,839 consecutive patients with acute myocardial infa rct ion ( AMI ) , hospitalized between July 1981 and July 1983 in 14 coronary care units in Israel , the incidence of primary ventricular fibrillation ( VF ) was 2.1 % . Patients with primary VF resembled counterparts without VF in terms of age , gender , frequency of previous AMI and past cigarette smoking habits . The hospital course of patients with primary VF revealed increased incidence of primary atrial fibrillation and atrioventricular block . Increased serum levels of glutamic oxaloacetic transaminase and lactic dehydrogenase were noted among the patients with primary VF . In-hospital mortality rate was 18.8 % in 122 patients with primary VF compared with 8.5 % in 3,707 patients forming the reference group ( p less than 0.01 ) . Adjustment by age using logistic function yielded an estimate of 2.86 for relative mortality odds associated with primary VF , and further adjustment by gender , history of AMI , systemic hypertension , and by enzymatically estimated infa rct size slightly reduced the estimated odds , at 2.52 ( 95 % confidence interval , 1.42 to 4.46 ) . Prognosis after discharge from the hospital was independent of primary VF . In conclusion , primary VF exerts an independent , significant effect on in-hospital mortality OBJECTIVES This study sought to examine the relations among patient characteristics , time to thrombolysis  and outcomes in the international GUSTO-I trial . BACKGROUND Studies have shown better left ventricular function and decreased infa rct size as well as increased survival with earlier thrombolysis , but the relative benefits of various thrombolytic agents with earlier administration are uncertain . METHODS We evaluated the relations of baseline characteristics to three prospect ively defined time variables :  symptom onset to treatment , symptom onset to hospital arrival ( presentation delay ) and hospital arrival to treatment ( treatment delay ) .  We also examined the relations of delays to clinical outcomes and to the relative 30-day mortality benefit with accelerated tissue-type plasminogen activator ( t-PA ) versus streptokinase . RESULTS Female , elderly , diabetic and hypertensive patients had longer delays at all stages . Previous infa rct ion or bypass surgery was an additional risk factor for treatment delay . Early thrombolysis was associated with lower overall mortality rate ( < 2 h , 5.5 % ; > 4 h , 9.0 % ) , but no additional relative benefit result ed from earlier treatment with accelerated t-PA versus streptokinase ( p = 0.38 ) . Longer presentation and treatment delays were both associated with increased mortality rate ( presentation delay < 1 h , 5.6 % and > 4 h , 8.6 % ; treatment delay < 1 h , 5.4 % , and > 90 min , 8.1 % ) . As time to treatment increased , the incidence of recurrent ischemia or reinfa rct ion decreased , but the rates of shock , heart failure and stroke increased . CONCLUSIONS Earlier treatment result ed in better outcomes , regardless of thrombolytic strategy . Elderly , female and diabetic patients were treated later , adding to their already substantial risk 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 % ; p = 0.007 ) , serum potassium supplements ( 90.2 % vs 43 . 1 % ; p = 0.000005 ) , and antiarrhythmic drugs ( 78.0 % vs 50.4 % ; p = 0 . 0007 ) in the LK patients . No difference was detected between the LK and NK patients in total mortality ( 24.4 % vs. 18.3 % ; p = 0.34 ) , cardiac mortality ( 17.1 % vs. 15.3 % ; p = 0.52 ) , atrial fibrillation ( 14.6 % vs 13.9 % ; p = 0.89 ) , and ventricular tachycardia ( 22.0 % vs. 16.0 % ; p = 0.32 ) , but ventricular fibrillation ( VF ) occurred more often ( 24.4 % vs 13.0 % ; p = 0.04 ) in the LK patients . However , proportions of VF occurring in the emergency department , CCU , or wards in the two cohorts were not different , but they were higher during the time interval prior to emergency department admission in LK patients ( 17.1 % vs 2.1 % ; p = 0.00001 ) . CONCLUSIONS LK is seen in approximately 8 % of patients with MI in the emergency department ; LK is associated with low emergency department magnesium , and low serum potassium levels in the CCU and throughout hospitalization . LK has no relationship to preadmission use of diuretics , it is associated with early presentation to the emergency department , and it is not a predictor of increased morbidity or mortality Low plasma potassium and magnesium concentrations have been advanced as risk factors for ventricular fibrillation ( VF ) . For potassium , this assertion is based almost exclusively on retrospective data ; for magnesium the evidence shows an association with ventricular arrhythmias but no direct association with VF . We studied the relationship between these electrolytes and VF prospect ively .  Plasma potassium and serum magnesium concentrations were measured on admission to our coronary care unit .  Drug therapy , time from onset of symptoms , ECG , enzyme changes and clinical status were all recorded . VF was confirmed by analysis of 24 h monitoring tapes .  Mean plasma potassium in the 21 patients with VF who had measurements prior to their arrhythmia was 3.49 + /- 0.54 mmol/l , lower than that of the 1165 patients without VF ( mean K 3.88 + /- 0.57 mmol/l , p < 0.05 ) . Plasma potassium concentrations in the 17 patients with myocardial infa rct ion and VF were lower ( mean 3.58 + /- 0.41 mmol/l ) than in those without VF ( n = 417 , mean 3.89 + /- 0.61 mmol/l ) ( p < 0.05 ) . Mean serum magnesium in the 12 patients with VF , measured prior to their arrhythmia ( all with myocardial infa rct ion ) was 0.80 + /- 0.07 mmol/l , which was not different from the mean for patients without VF ( n = 781 , 0.82 + /- 0.09 mmol/l ) or from the mean of 0.81 + /- 0.08 mmol/l for those with infa rct ion but not VF ( n = 331 ) . Low plasma potassium concentrations are associated with increased risk of ventricular fibrillation , but low serum magnesium concentrations are not To determine whether epinephrine-induced hypokalemia is due to beta2-adrenoceptor stimulation , and whether hypokalemia can occur at physiologic concentrations of the agonist , epinephrine was infused into six 
    Output:
    
PVF was not associated with a history of myocardial infa rct ion or hypertension .
CONCLUSION Patients who developed a vali date d PVF presented with characteristics of both abrupt coronary occlusion and early hospital admission .
This review provides no evidence for risk factors for PVF other than ST-elevation and time from onset of symptoms .