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the reasons for this pandemic include the aging populations of both industrialized and developing nations and a growing incidence of obesity , diabetes , and hypertension .
are abnormalities of ventricular conduction , such as bundle branch blocks that alter the timing and pattern of ventricular contraction , so as to place the already failing heart at a further mechanical disadvantage .
these ventricular conduction delays produce suboptimal ventricular filling , a reduction in left ventricular ( lv ) contractility , prolonged duration of mitral regurgitation , and paradoxical septal wall motion . taken together , these mechanical manifestations of altered ventricular conduction have been termed ventricular dyssynchrony , .
ventricular dyssynchrony has been defined by a prolonged qrs duration , generally longer than 120  ms , on a surface electrocardiogram . by this definition ,
about one third of patients with systolic heart failure have ventricular dyssynchrony . in patients with heart failure , cardiac resynchronization therapy ( crt ) for 6 months
was associated with reduced end - diastolic and end - systolic volume , reduced lv mass , increased ejection fraction , reduced mitral regurgitant blood flow , and improved myocardial performance index as compared with controls , , , .
however , initial clinical studies comparing biv pacing with lv only pacing indicated that biv and lv pacing may provide a similar systolic function , , , , , . nonetheless , more evidence is required based on clinical trials conducted in different settings , to confirm this issue .
the present study addressed this important question by comparing the hemodynamic responses of biv versus lv only pacing in patients with a standard indication for ventricular pacing .
this before  after clinical trial was conducted at ekbatan hospital , affiliated with hamadan university of medical sciences , west of iran , from july 2012 to november 2014 .
the present study was approved by the ethic committee of the university ( d-3 - 16 - 35 - 9 - 4026 on 26 june 2012 ) .
the protocol was registered in the iranian registry of clinical trials ( irct201203169014n7 ) accepted on 3 july 2012 .
the patients with crt , who were referred to the electrophysiological clinic of ekbatan ( farshchian ) hospital , were enrolled if they fulfilled the following criteria : ( a ) lv ejection fraction less than or equal to 35% ; ( b ) a qrs duration greater than or equal to 0.12  s ; ( c ) sinus rhythm ; ( d ) indication for the treatment of new york heart association ( nyha ) functional class iii or ambulatory class iv heart failure symptoms with optimal recommended medical therapy ; and ( e ) had received crt at least 3 months previously .
patient characteristics were as follows : etiology ( non - ischemic , 24 patients ; ischemic , 20 patients ) ; morphology ( lbbb , 38 patients ; non - lbbb , 7 patients ) ; qrs interval ( lbbb group , 15832  ms ; non - lbbb group , 18538  ms ) .
all patients were on full medical treatments including loop diuretic ( furosemide ) , beta blocker ( long acting metoprolol or carvedilol ) and angiotensin converting enzyme inhibitors or angiotensin receptor blockers .
spironolactone was administered to all patients with a creatinine level less than 2.2  mg / dl and potassium level less than 5.5  meq / dl .
the hemodynamic status of the patients was assessed by echocardiography before setting ( as control ) and three months later ( as an intervention ) . after setting ,
an atrioventricular ( av ) delay was described as nominal in all patients , and echo - guided optimization was used in non - responsive patients . at the end of the study
the hemodynamic response of interest included : ( a ) lv end diastolic volume per ml ; ( b ) lv end systolic volume per ml ; ( c ) lv ejection fraction per percent ; and ( d ) velocity time integral of the aortic valve per cm . in order to minimize possible errors ,
all patients were evaluated with a specific echocardiography machine ( my lab 60 , esaote , italy ) .
all statistical analyses were performed at a significance level of 0.05 using statistical software stata 11 ( stata corp , college station , tx , usa ) .
we identified 45 patients who fulfilled the entry criteria ; one patient was excluded because of lv lead malfunction .
clinical response to crt was defined as improvement in the nyha classification by one class after crt implantation .
twenty seven ( 61% ) patients were female and 17 ( 39% ) were male .
the meansd age of the patients was 63.012.0 years with a minimum and a maximum of 26 and 83 years , respectively . during the study ,
no deaths and no serious ventricular arrhythmias or worsening clinical condition leading to hospitalization occurred .
the effect of biv pacing and lv only pacing on hemodynamic responses is shown in table 1 . according to these results , no statistically significant differences in hemodynamic responses were seen in the two groups .
given that the end diastolic and systolic volume is different in men and women , the results were analyzed by sex .
however , no statistically significant differences in the hemodynamic responses were seen between the two groups .
the main objective of this study was to compare the hemodynamic responses of biv pacing with those of lv pacing alone .
the benefits of lv pacing include ( 1 ) the transition from biv to lv pacing increases the longevity of the device and decreases the costs of repeated surgery ; ( 2 ) if the right ventricular ( rv ) threshold increases or rv lead is displaced , with maintaining an acceptable sensitivity , repeated surgery can be avoided by changing the pacing mode from biv to lv only pacing ; ( 3 ) in countries with limited resources where the cost of acquiring a pace and triple - chamber implantable cardioverter defibrillator ( crt ) is high , dual - chamber devices can be used on the right atrium and left ventricle position , which is cost efficient .
the results indicated that the benefits of the two procedures are similar . according to the european society of cardiology ( esc ) guidelines on cardiac pacing and crt ,
furthermore , a respective 21% of patients who did not respond clinically or echocardiographically to biv pacing responded to lv pacing mode .
moreover , a recently conducted meta - analysis has demonstrated that in patients with moderate - to - severe heart failure , these two pacing modalities did not differ with regard to death / heart transplantation or need for hospitalizations . in 2011 , thibault et al . conducted a multicenter , double - blind , crossover trial and compared the effects of lv and biv pacing on exercise tolerance and lv remodeling in 211 patients with an lv ejection fraction 35% , qrs120  ms , and symptoms of heart failure .
first , in patients with severe heart failure who need three - chamber crt , based on the guideline , using the lv mode may reduce the cost .
second , the time of implanting the lv mode is less than that of the biv mode .
thus , using the first approach can reduce the harmful exposure to radiation in both the patient and physician .
third , in cases where the right ventricular lead placement is difficult or even impossible for any reason , the lv mode can be considered as an alternative approach .
understanding the mechanism responsible for the lack of difference between lv and biv pacing was not an objective of this study .
as desynchronizing mostly affects the left ventricle , , , , , using lv pacing alone may be similar to biv pacing .
we conclude that lv pacing alone is not inferior to biv pacing , and the hemodynamic response was similar in the two groups
. however , more evidence , based on large clinical trials , is warranted in order to confirm our results .
this study was funded by the vic - chancellor of research and technology , hamadan university of medical sciences .
the authors declare that they have no conflicts of interest in relation to this work .
backgroundbiventricular ( biv ) pacing is the most common mode of delivering cardiac resynchronization therapy ( crt ) . however , initial clinical studies have indicated that left ventricular ( lv ) pacing is not inferior to biv pacing . 
 this study was conducted to address whether lv only pacing can provide the same hemodynamic response as biv pacing.methodsthis before  after clinical trial was conducted at ekbatan hospital , from july 2012 to november 2014 . 
 patients with a lv ejection fraction 35% and a qrs duration 0.12  s who had a standard indication for ventricular pacing were enrolled . 
 the crt devices of all patients had already been set for biv pacing . 
 therefore , their crt devices were set for lv only pacing for 3 months . 
 the hemodynamic status of the patients was assessed by echocardiography before setting the crt device to lv only pacing ( as a control ) and 3 months after ( as an intervention).resultsthere was no statistically significant difference between the effect of biv pacing and lv only pacing on the hemodynamic responses including lv ejection fraction , lv end diastolic and systolic volume , and velocity time integral of the aortic valve . moreover 
 , no significant difference was seen between men and women either.conclusionslv only pacing is not inferior to biv pacing , and the hemodynamic response was similar in the two groups . 
 however , the lv mode has a number of advantages over the biv mode . more evidence , based on large clinical trials , 
 is needed to confirm our results .