Pharmacological trials including patients with more severe heart failure were more likely to show a significant improvement with therapy than trials of milder heart failure .
Using mean values in these trials , the age of patients appeared a more important determinant of 6MWT distance than New York Heart Association classification .
The 6MWT has not yet been proven to be a robust test for the identification of effective pharmacological interventions although it appears useful for the assessment of cardiac resynchronization therapy .
The results of the 6MWT were concordant with changes in symptoms , suggesting that it may be used as supportive evidence for symptom benefit .
AIMS The 6 min walk test ( 6MWT ) is commonly used in clinical trials to assess treatments for heart failure , but its ability to distinguish between effective and ineffective treatments is question able .
The aim of this study is to investigate , using a systematic literature review , the utility of the 6MWT as a measure of the effectiveness of treatment in r and omized controlled trials of heart failure .
Effects of cardiac resynchronization therapy on heart rate variability in patients with chronic systolic heart failure and intraventricular conduction delay.
C resynchronization therapy ( CRT ) by atriobiventricular pacing has been proposed to treat severe heart failure in patients with intraventricular conduction delay result ing in ventricular mechanical discoordination . The clinical efficacy of CRT was recently demonstrated in a single-blind , r and omized , crossover trial , namely the MUltisite STimulation In Cardiomyopathies ( MUSTIC ) study .1 The purpose of this sub study was to assess the effect of CRT on heart rate variability ( HRV ) and to analyze its correlation with clinical efficacy . • • • All patients provided written informed consent before enrollment . All had severe heart failure due to idiopathic or ischemic left ventricular systolic dysfunction , left ventricular ejection fraction 35 % , and end-diastolic diameter 60 mm . All patients were in sinus rhythm with a QRS interval 150 ms and no classic indication for pacemaker implantation.2 Patients had been in New York Heart Association ( NYHA ) class III for 1 month before inclusion while receiving individually optimized treatment , including diuretics and angiotensin-converting enzyme inhibitors at the maximum tolerated dose . Exclusion criteria have been already reported.1 The study included a 6-month r and omized crossover phase during which atriobiventricular ( active ) pacing was compared with inhibited ( inactive ) ventricular pacing at the basic rate of 40 beats/min , each for a period of 3 months in r and om order ( Figure 1 ) . Implantation was performed after a 1-month observation period to verify the stability of heart failure .  Pacemakers were programmed as inactive after implantation . Patients were r and omly assigned to experimental groups within the following 2 weeks after verification of pacemaker proper performance . Treatment order r and omization followed a block design with stratification according to center . The single-blind , crossover phase was followed by a complementary 6-month period during which the pacing system was programmed according to patients ’ preferences . All leads were implanted transvenously . The left ventricular lead was placed in a tributary of the coronary sinus according to a previously described method .3 Specially design ed electrodes were used . The preferred target site was the lateral wall . The pacemakers were triple-output devices using st and ard dual-chamber technology , with built-in adapters to synchronize pacing in both ventricles . Pacemakers were programmed as either active or inactive at r and omization . The baseline pacing rate was set at 40 beats/min and the upper rate limit at 85 % of the highest predictable heart rate according to patients ’ age and gender . Each patient underwent Doppler echocardiography to determine their optimal atrioventricular delay ( electrical delay between atrial and ventricular excitation ) during atriobiventricular pacing . No modification of medical treatment except diuretic dose adjustment was permitted between enrollment and the end of the crossover phase of the study . Twenty-four-hour ambulatory electrocardiograms with a 2-channel recorder ( ELA Medical , le PlessisRobinson , France ) were obtained in all subjects during normal activity at baseline , at r and omization , at the end of each of the 2 crossover periods , and at the end of each longitudinal follow-up period ( 9 and 12 months ) . Tapes were replayed through a Elatec analyzer ( ELA Medical ) . HRV analysis used specifically vali date d software.4 Ambulatory electrocardiographic recordings  that lasted 16 hours and whose analyzable proportion was 90 % were excluded to avoid bias linked to HRV circadian variations . After initial arrhythmia analysis and editing , the remaining normal-to-normal RR intervals in suitable recordings were measured and HRV time-domain analyses were performed according to published guidelines .5 For the purpose s of this study , 4 different time-domain HRV indexes were measured : ( 1 ) the SD of the normal-to-normal ( NN ) interval over the recording duration ( SDNN ) ; ( 2 ) the SD of the 5-minute mean NN interval over the entire recording ( SDANN [ milliseconds ] ) . Because SDANN values are obtained from successive 5-minute periods , they reflect heart rate changes caused by 5-minute cycles . They reflect long-term variations but provide no short-term variability data ; ( 3 ) the square root of the mean squared successive differences between adjacent RR intervals over the entire recording ( rMSSD [ milliseconds ] ) . This correlates more with the parasympathetic ( vagal ) activity ; ( 4 ) proportion of successive interval differences 50 ms as computed over the entire recording ( pNN50 [ percent ] ) . This also reflects parasympathetic activity . From the Departement de Cardiologie et Maladies Vasculaires , Centre Cardio-Pneumologique , Hopital Pontchaillou-CHU , Rennes , France . Dr. Daubert ’s address is : Departement de Cardiologie et Maladies Vasculaires , Centre Cardio-Pneumologique , Hopital PontchaillouCHU , 35033 Rennes Cedex , France . E-mail : jean-claude . daubert@chu-rennes.fr . Manuscript received August 23 , 2002 ; revised manuscript received and accepted January 23 , 2003
Pharmacological trials including patients with more severe heart failure were more likely to show a significant improvement with therapy than trials of milder heart failure .
Using mean values in these trials , the age of patients appeared a more important determinant of 6MWT distance than New York Heart Association classification .
The 6MWT has not yet been proven to be a robust test for the identification of effective pharmacological interventions although it appears useful for the assessment of cardiac resynchronization therapy .
The results of the 6MWT were concordant with changes in symptoms , suggesting that it may be used as supportive evidence for symptom benefit .
AIMS The 6 min walk test ( 6MWT ) is commonly used in clinical trials to assess treatments for heart failure , but its ability to distinguish between effective and ineffective treatments is question able .
The aim of this study is to investigate , using a systematic literature review , the utility of the 6MWT as a measure of the effectiveness of treatment in r and omized controlled trials of heart failure .