document: cardiac resynchronisation therapy ( crt ) has become an important treatment for patients with heart failure and left ventricular ( lv ) dyssynchrony [ 13 ] . 
   however , clinical non - response to crt is reported in 2535  % of patients . 
   although a large variety of causes for a suboptimal response have been cited , most attention has been focused on the selection of patients eligible for crt , and less on inadequate delivery of crt therapy . however , even with growing experience and improved materials and tools , the optimal position can not always be reached in one of the tributaries of the coronary sinus . 
   this can be due to the absence of suitable side branches in the posterolateral area , coronary vein stenosis , lead instability , high stimulation threshold , phrenic nerve stimulation , or a combination of the above [ 57 ] . 
   we studied the acute haemodynamic response ( ahr ) of the implanted system and alternative left ventricular endocardial pacing sites in patients clinically not responding to crt . 
   we asked patients who remained in new york heart failure class iii or iv despite at least 6 months of crt and adequate medical therapy and with no therapeutic options left to undergo an acute haemodynamic study in search of improving existing crt , as previously described [ 8 , 9 ] . 
   twenty - four non - consecutive patients , 23 males , age 72.8    9.1 years , mean ejection fraction 22.5    7.1  % , agreed to undergo this test ( table  1 ) . 
   the ecg prior to implantation showed left bundle branch block ( lbbb ) in 12 , non - lbbb in 4 , and right ventricular ( rv ) pacing in 8 patients . 
   table 1characteristics of clinical non - responders ( 24 patients)patientgenderage ( years)nyha classicm / dcmejection fraction ( % ) qrs morphologyqrs width ( ms)pt . 01m56ivdcm13lbbb135pt . 
   ivicm17rvp210average23m/1f72.8    9.13.2    0.36dcm22.5    7.112lbbb/8rvp175    22patient characteristics of 24 clinical non - responders to crt . 
   nyha class new york heart association class , dcm dilated cardiomyopathy , icm ischaemic cardiomyopathy , lbbb left bundle branch block , non - lbbb non left bundle branch block , pt . 
   characteristics of clinical non - responders ( 24 patients ) patient characteristics of 24 clinical non - responders to crt . 
   nyha class new york heart association class , dcm dilated cardiomyopathy , icm ischaemic cardiomyopathy , lbbb left bundle branch block , non - lbbb non left bundle branch block , pt . 
   a 6f multipurpose angioplasty guiding catheter was introduced into the lv after a standard transseptal catheterisation . in one patient 
   , the guiding catheter was introduced through the radial artery following coronary angiography . through this guiding catheter , endocardial pacing and measurements of lvdp / dtmax 
   were accomplished by roving a medtronic 6416 temporary bipolar screw - in lead ( medtronic inc . 
   minneapolis , mn . ) and a radi pressure wire ( radi medical , a st jude medical company , st . 
   initially the atrioventricular and interventricular intervals of the implanted system were optimised to obtain the maximal lvdp / dtmax . 
   lv pacing was performed from basal posterolateral , mid - posterolateral , lv apical and lv septal locations , and optimal ahr obtained after optimisation of the crt system for all positions . 
   if none of the 4 endocardial positions were opposite the position of the coronary sinus lead , an additional measurement was done at this location . a rise in lvdp / dtmax 
   15  % from baseline was considered to be a positive haemodynamic response . in all patients with an ahr of   15  % during lv endocardial pacing , the interval between the onset of the qrs complex and the intrinsic activation at the lv electrode ( q - lv interval ) was measured and the ratio between q - lv / qrs width interval calculated . 
   this ratio expresses the relation between q - lv interval and qrs width , which is a better indicator for late or early lv sensing than the absolute value of q - lv . 
   notwithstanding that all patients were clinical non - responders , in 5 patients lvdp / dtmax with the implanted coronary sinus system increased   15  % after optimisation : average 30.2  % , 15.644.5  % ( table  2 ) . in 3 out of these 5 patients with the coronary sinus lead in a posterolateral position , endocardial pacing did not increase the lvdp / dtmax substantially ( ahr less than 3  % and even an adverse effect from lv endocardial pacing was observed in one patient ) . in one of the two remaining patients with an apical position of the coronary sinus lead , 
   the ahr could be increased during lv endocardial pacing from 19.766  % and we considered the increase sufficient to justify the upgrade to lv endocardial pacing ( fig .  1 ) . 
   table 2individual haemodynamic results of all clinical non - responders ( 24 patients)patientqrs morphologybaseline lvdp / dtmax ( mmhg / s)position cs leadahr cs lead ( % ) ahr cs - level - endo(%)lv endo optimal positionahr lvendo ( % ) pt . 
   07non - lbbb893pl - mid  23.4lv septal  21.5pt . 08lbbb827pl - bas44.951.0pl - bas51.0pt . 
   24rvp489lv apical12.717.2pl - mid24.1average891    2478.7    15.810.5    8.919.6    17.5haemodynamic measurements of 24 clinical nonresponders to crt . 
   baseline lvdp / dtmax lvdp / dtmax with intrinsic rhythm or right ventricular pacing , ahr cs lead acute haemodynamic response from the coronary sinus ( cs ) lead expressed as percentage rise in lvdp / dtmax from baseline , ahr cs level endo acute haemodynamic response at an endocardial location opposite the cs lead , lv endo optimal position anatomic site with the highest ahr , ahr lv endo acute haemodynamic response from the optimal endocardial position . 
   grey shaded patients have an ahr from the cs lead   15  % and are considered haemodynamic responders , pl - bas basal posterolateral , pl - mid mid - posterolateral , rvp right ventricular pacing . 
   individual haemodynamic results of all clinical non - responders ( 24 patients ) haemodynamic measurements of 24 clinical nonresponders to crt . 
   baseline lvdp / dtmax lvdp / dtmax with intrinsic rhythm or right ventricular pacing , ahr cs lead acute haemodynamic response from the coronary sinus ( cs ) lead expressed as percentage rise in lvdp / dtmax from baseline , ahr cs level endo acute haemodynamic response at an endocardial location opposite the cs lead , lv endo optimal position anatomic site with the highest ahr , ahr lv endo acute haemodynamic response from the optimal endocardial position . 
   grey shaded patients have an ahr from the cs lead   15  % and are considered haemodynamic responders , pl - bas basal posterolateral , pl - mid mid - posterolateral , rvp right ventricular pacing . 
   all views are in left anterior oblique ( lao ) showing the haemodynamic effects of stimulation from the coronary sinus lead and lv endocardial stimulation in the mid - posterolateral area ( left upper panel ) , basal posterolateral area ( left lower panel ) , lv septum ( right upper panel ) and lead positions after lv endocardial implantation of a permanent lead in the lv basal posterolateral segment . 
   arrows indicate the position of the bipolar pacing lead angiographic pictures of the haemodynamic study in patient no . 
   all views are in left anterior oblique ( lao ) showing the haemodynamic effects of stimulation from the coronary sinus lead and lv endocardial stimulation in the mid - posterolateral area ( left upper panel ) , basal posterolateral area ( left lower panel ) , lv septum ( right upper panel ) and lead positions after lv endocardial implantation of a permanent lead in the lv basal posterolateral segment . 
   arrows indicate the position of the bipolar pacing lead in the 19 patients with an ahr from the implanted system <  15  % , 9 patients had an increase in ahr above the 15  % limit . 
   the results of the total group of 24 patients showed a positive response in 11 patients with an apical lead position in 7 , anterolateral in 2 and mid - posterolateral in 2 patients . 
   a negative response of endocardial pacing was observed in 13 patients with a basal posterolateral lead position in 3 , mid - posterolateral in 8 and apical in 2 patients . in 5 out of the 9 acute haemodynamic non - responders 
   ( ahr <  15  % ) with lbbb , the ahr could be increased above the 15  % level by lv endocardial pacing . 
   the average ahr with the coronary sinus system was 9.6  % ( 5.814.9  % ) and at the lv endocardial optimal position 25.8  % ( 19.034.3  % ) . 
   the average qrs width in these patients was 169  ms ( 135198  ms ) and the average q - lv at the optimal lv endocardial pacing site 157  ms ( 128176  ms ) , resulting in a q - lv / qrs ratio of 93  % . 
   the position of the original coronary sinus lead was apical in 3 , anterolateral in 1 and mid - posterolateral in 1 patient ( fig .  2 ) . 
   2recordings of the temporary study of patient no . 22 with a lbbb showing the haemodynamic effects and the timing of the lv endocardial electrogram from the different positions recordings of the temporary study of patient no . 
   22 with a lbbb showing the haemodynamic effects and the timing of the lv endocardial electrogram from the different positions in the remaining 4 patients , the average ahr at the optimal endocardial position increased <  15  % , with an average of 7.3  % ( 1.79.9  % ) . 
   the average qrs width in these patients was 176  ms ( 149209  ms ) and the average q - lv 136  ms ( 100174  ms ) , resulting in a q - lv / qrs ratio of 83  % . 
   of these , only one patient with rbbb , combined with left anterior hemiblock , showed an increase in the ahr , from   9.1  % ( apical coronary sinus position ) to 25.8  % at an endocardial basal posterolateral position . 
   3 ) ; one had a non - specific intraventricular conduction delay with a qrs complex of 175  ms . 
   the coronary sinus lead position was mid - posterolateral in 2 and apical in 1 patient . 
   3recordings of a temporary study of patient no.18 with non - lbbb , showing the haemodynamic effects and the timing of the lv endocardial electrogram from the different positions . 
   this recording illustrates that there is no conduction delay in the lv and a minimal haemodynamic effect recordings of a temporary study of patient no.18 with non - lbbb , showing the haemodynamic effects and the timing of the lv endocardial electrogram from the different positions . 
   this recording illustrates that there is no conduction delay in the lv and a minimal haemodynamic effect three out of the 6 patients with rv pacing became haemodynamic responders ( lv dp / dtmax from average 9.7  % , ( 9.312.7  % ) increased to 21.8  % ( 16.624.8  % ) ) . 
   in the other 3 patients the average ahr increased from 2.9  % ( 1.14.0  % ) to 9.7  % ( 7.811.4  % ) . in 2 patients the coronary sinus lead was in a mid - posterolateral position , one in an apical position . 
   individual details are summarised in table  2 and a flow chart overview in fig .  4 . 
   4flow chart of the study showing the haemodynamic results in relation to the coronary sinus lead positions . 
   ahr acute haemodynamic response , ant lat anterolateral , bas basal , cs coronary sinus , endo endocardial , lbbb left bundle branch block , lv left ventricular , pl posterolateral , pts patients , rv right ventricular flow chart of the study showing the haemodynamic results in relation to the coronary sinus lead positions . ahr acute haemodynamic response , ant lat anterolateral , bas basal , cs coronary sinus , endo endocardial , lbbb left bundle branch block , lv left ventricular , pl posterolateral , pts patients , rv right ventricular when pacing endocardially , opposite the epicardial coronary sinus lead , we found that lvdp / dtmax did not differ significantly for any of the patients : lvdp / dtmax from the coronary sinus averaged 1046    292  mmhg / s vs. 1068    296  mmhg / s from the corresponding lv endocardial site ( p  =  0.37 ) . 
   we found that basal or mid - posterolateral segments had the highest ahr of the tested endocardial sites in all 14 patients who showed an ahr   15  % rise in lvdp / dtmax compared with baseline . because either the basal or mid - posterolateral segment had the highest ahr , we also calculated the combined best results from basal posterolateral and mid - posterolateral ( pl - best ) . 
   pl - best had a rise to 30.2    13.6  % in lvdp / dtmax , basal posterolateral 27.7    15.2  % , mid - posterolateral 24.6    12.6  % , lv apical 14.8    9.1  % and lv septal 17.0    11.2  % . 
   we also found that in 12 out of the 14 patients ( 85  % ) with an ahr   15  % , the lv endocardial site with the longest time interval between the onset of the qrs complex and lv sensing ( q - lv interval ) resulted in the best haemodynamic response . 
   the average qrs width was 133    22  ms ( range 120205  ms ) and average q - lv interval 155    26  ms ( 128205  ms ) . 
   the average q - lv / qrs width ratio , which is q - lv expressed as a percentage of qrs width , was 90  % . 
   table 3haemodynamic results for all 4 endocardial locations and maximum q - lv interval for 14 patients that showed a rise in lvdp / dtmax   15  % from endocardial pacingpts.ahr pl - best ( % ) ahr pl - basal ( % ) ahr pl - mid ( % ) ahr lv apical ( % ) ahr lv septal ( % ) qrs width ( ms)max q - lv interval ( ms)location longest q - lvpt.0124.224.22.71.72.1135128pl - baspt.0331.631.625.84.826.1174165pl - baspt.0424.818.724.814.219.6196205pl - midpt.0520.120.118.018.111.8165163pl - midpt.0851.051.046.022.029.2154138pl - baspt.1219.013.519.017.613.7198176pl - midpt.1316.55.316.68.89.6152128pl - midpt.1566.066.050.231.347.3200181pl - midpt.1625.825.814.1  0.612.2175147pl - baspt.2019.719.716.78.916.3156124pl - midpt.2134.928.034.916.96.9174132pl - midpt.2234.334.320.315.614.4175155pl - baspt.2331.026.231.026.718.6160138pl - midpt.2424.122.924.117.211.5210192pl - mid30.2    13.627.7    15.224.6    12.614.8    9.117.1    11.2173    22155    26 
   ahr acute haemodynamic response expressed as the percentage rise in lvdp / dt from baseline , pl - best best result from either basal posterolateral ( pl - bas ) or mid - posterolateral ( pl - mid ) region , max q - lv longest interval measured between onset of the qrs complex and intrinsic activation at the lv electrode . 
   grey shaded area indicates 2 patient in whom the longest q - lv interval did not correspond with the best haemodynamic response . 
   haemodynamic results for all 4 endocardial locations and maximum q - lv interval for 14 patients that showed a rise in lvdp / dtmax   15  % from endocardial pacing 
   ahr acute haemodynamic response expressed as the percentage rise in lvdp / dt from baseline , pl - best best result from either basal posterolateral ( pl - bas ) or mid - posterolateral ( pl - mid ) region , max q - lv longest interval measured between onset of the qrs complex and intrinsic activation at the lv electrode . 
   grey shaded area indicates 2 patient in whom the longest q - lv interval did not correspond with the best haemodynamic response . 
   ten patients were considered possible candidates for lv endocardial pacing : 9 patients in whom a rise in lvdp / dtmax   15  % level was only obtained by endocardial pacing , and the patient that showed a substantial additional rise in ahr with lv pacing compared with coronary sinus pacing ( patient 15 ) . 
   of the remaining 9 patients , and after deliberation with the patients about the possible benefits and risks , 5 of them finally agreed to lv endocardial implant at the optimal lv site as indicated from the acute study . 
   all five patients improved clinically with a reduction of at least 1 class in the nyha score after 6 months of follow - up . 
   two patients with a positive response in the temporary study refrained from implantation of an lv endocardial lead . 
   one patient with a positive ahr from endocardial pacing also improved significantly after changing stimulation from the distal to the proximal electrode with a more basal position , and became a clinical responder after optimisation of the atrioventricular and interventricular interval . 
   in one patient , the deterioration of his condition after initial improvement proved to be the result of a blunted chronotropic response after increasing beta - blocker dosage following an episode of atrial fibrillation resulting in an inappropriate icd shock . 
   notwithstanding that all patients were clinical non - responders , in 5 patients lvdp / dtmax with the implanted coronary sinus system increased   15  % after optimisation : average 30.2  % , 15.644.5  % ( table  2 ) . in 3 out of these 5 patients with the coronary sinus lead in a posterolateral position , endocardial pacing did not increase the lvdp / dtmax substantially ( ahr less than 3  % and even an adverse effect from lv endocardial pacing was observed in one patient ) . in one of the two remaining patients with an apical position of the coronary sinus lead , 
   the ahr could be increased during lv endocardial pacing from 19.766  % and we considered the increase sufficient to justify the upgrade to lv endocardial pacing ( fig .  1 ) . 
   table 2individual haemodynamic results of all clinical non - responders ( 24 patients)patientqrs morphologybaseline lvdp / dtmax ( mmhg / s)position cs leadahr cs lead ( % ) ahr cs - level - endo(%)lv endo optimal positionahr lvendo ( % ) pt . 
   07non - lbbb893pl - mid  23.4lv septal  21.5pt . 08lbbb827pl - bas44.951.0pl - bas51.0pt . 
   24rvp489lv apical12.717.2pl - mid24.1average891    2478.7    15.810.5    8.919.6    17.5haemodynamic measurements of 24 clinical nonresponders to crt . 
   baseline lvdp / dtmax lvdp / dtmax with intrinsic rhythm or right ventricular pacing , ahr cs lead acute haemodynamic response from the coronary sinus ( cs ) lead expressed as percentage rise in lvdp / dtmax from baseline , ahr cs level endo acute haemodynamic response at an endocardial location opposite the cs lead , lv endo optimal position anatomic site with the highest ahr , ahr lv endo acute haemodynamic response from the optimal endocardial position . 
   grey shaded patients have an ahr from the cs lead   15  % and are considered haemodynamic responders , pl - bas basal posterolateral , pl - mid mid - posterolateral , rvp right ventricular pacing . 
   individual haemodynamic results of all clinical non - responders ( 24 patients ) haemodynamic measurements of 24 clinical nonresponders to crt . 
   baseline lvdp / dtmax lvdp / dtmax with intrinsic rhythm or right ventricular pacing , ahr cs lead acute haemodynamic response from the coronary sinus ( cs ) lead expressed as percentage rise in lvdp / dtmax from baseline , ahr cs level endo acute haemodynamic response at an endocardial location opposite the cs lead , lv endo optimal position anatomic site with the highest ahr , ahr lv endo acute haemodynamic response from the optimal endocardial position . 
   grey shaded patients have an ahr from the cs lead   15  % and are considered haemodynamic responders , pl - bas basal posterolateral , pl - mid mid - posterolateral , rvp right ventricular pacing . 
   all views are in left anterior oblique ( lao ) showing the haemodynamic effects of stimulation from the coronary sinus lead and lv endocardial stimulation in the mid - posterolateral area ( left upper panel ) , basal posterolateral area ( left lower panel ) , lv septum ( right upper panel ) and lead positions after lv endocardial implantation of a permanent lead in the lv basal posterolateral segment . 
   arrows indicate the position of the bipolar pacing lead angiographic pictures of the haemodynamic study in patient no . 
   all views are in left anterior oblique ( lao ) showing the haemodynamic effects of stimulation from the coronary sinus lead and lv endocardial stimulation in the mid - posterolateral area ( left upper panel ) , basal posterolateral area ( left lower panel ) , lv septum ( right upper panel ) and lead positions after lv endocardial implantation of a permanent lead in the lv basal posterolateral segment . 
   arrows indicate the position of the bipolar pacing lead in the 19 patients with an ahr from the implanted system <  15  % , 9 patients had an increase in ahr above the 15  % limit . 
   the results of the total group of 24 patients showed a positive response in 11 patients with an apical lead position in 7 , anterolateral in 2 and mid - posterolateral in 2 patients . 
   a negative response of endocardial pacing was observed in 13 patients with a basal posterolateral lead position in 3 , mid - posterolateral in 8 and apical in 2 patients . 
   in 5 out of the 9 acute haemodynamic non - responders ( ahr <  15  % ) with lbbb , the ahr could be increased above the 15  % level by lv endocardial pacing . 
   the average ahr with the coronary sinus system was 9.6  % ( 5.814.9  % ) and at the lv endocardial optimal position 25.8  % ( 19.034.3  % ) . 
   the average qrs width in these patients was 169  ms ( 135198  ms ) and the average q - lv at the optimal lv endocardial pacing site 157  ms ( 128176  ms ) , resulting in a q - lv / qrs ratio of 93  % . 
   the position of the original coronary sinus lead was apical in 3 , anterolateral in 1 and mid - posterolateral in 1 patient ( fig .  2 ) . 
   2recordings of the temporary study of patient no . 22 with a lbbb showing the haemodynamic effects and the timing of the lv endocardial electrogram from the different positions recordings of the temporary study of patient no . 22 with a lbbb showing the haemodynamic effects and the timing of the lv endocardial electrogram from the different positions in the remaining 4 patients , the average ahr at the optimal endocardial position increased <  15  % , with an average of 7.3  % ( 1.79.9  % ) . 
   the average qrs width in these patients was 176  ms ( 149209  ms ) and the average q - lv 136  ms ( 100174  ms ) , resulting in a q - lv / qrs ratio of 83  % . 
   four patients did not have lbbb . of these , only one patient with rbbb , combined with left anterior hemiblock , showed an increase in the ahr , from   9.1  % ( apical coronary sinus position ) to 25.8  % at an endocardial basal posterolateral position . 
   3 ) ; one had a non - specific intraventricular conduction delay with a qrs complex of 175  ms . 
   the coronary sinus lead position was mid - posterolateral in 2 and apical in 1 patient . 
   3recordings of a temporary study of patient no.18 with non - lbbb , showing the haemodynamic effects and the timing of the lv endocardial electrogram from the different positions . 
   this recording illustrates that there is no conduction delay in the lv and a minimal haemodynamic effect recordings of a temporary study of patient no.18 with non - lbbb , showing the haemodynamic effects and the timing of the lv endocardial electrogram from the different positions . 
   this recording illustrates that there is no conduction delay in the lv and a minimal haemodynamic effect 
   three out of the 6 patients with rv pacing became haemodynamic responders ( lv dp / dtmax from average 9.7  % , ( 9.312.7  % ) increased to 21.8  % ( 16.624.8  % ) ) . 
   in the other 3 patients the average ahr increased from 2.9  % ( 1.14.0  % ) to 9.7  % ( 7.811.4  % ) . in 2 patients the coronary sinus lead was in a mid - posterolateral position , one in an apical position . 
   individual details are summarised in table  2 and a flow chart overview in fig .  4 . 
   4flow chart of the study showing the haemodynamic results in relation to the coronary sinus lead positions . 
   ahr acute haemodynamic response , ant lat anterolateral , bas basal , cs coronary sinus , endo endocardial , lbbb left bundle branch block , lv left ventricular , pl posterolateral , pts patients , rv right ventricular flow chart of the study showing the haemodynamic results in relation to the coronary sinus lead positions . 
   ahr acute haemodynamic response , ant lat anterolateral , bas basal , cs coronary sinus , endo endocardial , lbbb left bundle branch block , lv left ventricular , pl posterolateral , pts patients , rv right ventricular 
   when pacing endocardially , opposite the epicardial coronary sinus lead , we found that lvdp / dtmax did not differ significantly for any of the patients : lvdp / dtmax from the coronary sinus averaged 1046    292  mmhg / s vs. 1068    296  mmhg / s from the corresponding lv endocardial site ( p  =  0.37 ) . 
   we found that basal or mid - posterolateral segments had the highest ahr of the tested endocardial sites in all 14 patients who showed an ahr   15  % rise in lvdp / dtmax compared with baseline . because either the basal or mid - posterolateral segment had the highest ahr , we also calculated the combined best results from basal posterolateral and mid - posterolateral ( pl - best ) . 
   pl - best had a rise to 30.2    13.6  % in lvdp / dtmax , basal posterolateral 27.7    15.2  % , mid - posterolateral 24.6    12.6  % , lv apical 14.8    9.1  % and lv septal 17.0    11.2  % . 
   we also found that in 12 out of the 14 patients ( 85  % ) with an ahr   15  % , the lv endocardial site with the longest time interval between the onset of the qrs complex and lv sensing ( q - lv interval ) resulted in the best haemodynamic response . 
   the average qrs width was 133    22  ms ( range 120205  ms ) and average q - lv interval 155    26  ms ( 128205  ms ) . the average q - lv / qrs width ratio , which is q - lv expressed as a percentage of qrs width , was 90  % . 
   table 3haemodynamic results for all 4 endocardial locations and maximum q - lv interval for 14 patients that showed a rise in lvdp / dtmax   15  % from endocardial pacingpts.ahr pl - best ( % ) ahr pl - basal ( % ) ahr pl - mid ( % ) ahr lv apical ( % ) ahr lv septal ( % ) qrs width ( ms)max q - lv interval ( ms)location longest q - lvpt.0124.224.22.71.72.1135128pl - baspt.0331.631.625.84.826.1174165pl - baspt.0424.818.724.814.219.6196205pl - midpt.0520.120.118.018.111.8165163pl - midpt.0851.051.046.022.029.2154138pl - baspt.1219.013.519.017.613.7198176pl - midpt.1316.55.316.68.89.6152128pl - midpt.1566.066.050.231.347.3200181pl - midpt.1625.825.814.1  0.612.2175147pl - baspt.2019.719.716.78.916.3156124pl - midpt.2134.928.034.916.96.9174132pl - midpt.2234.334.320.315.614.4175155pl - baspt.2331.026.231.026.718.6160138pl - midpt.2424.122.924.117.211.5210192pl - mid30.2    13.627.7    15.224.6    12.614.8 
   9.117.1    11.2173    22155    26 
   ahr acute haemodynamic response expressed as the percentage rise in lvdp / dt from baseline , pl - best best result from either basal posterolateral ( pl - bas ) or mid - posterolateral ( pl - mid ) region , max q - lv longest interval measured between onset of the qrs complex and intrinsic activation at the lv electrode . 
   grey shaded area indicates 2 patient in whom the longest q - lv interval did not correspond with the best haemodynamic response . 
   haemodynamic results for all 4 endocardial locations and maximum q - lv interval for 14 patients that showed a rise in lvdp / dtmax   15  % from endocardial pacing 
   ahr acute haemodynamic response expressed as the percentage rise in lvdp / dt from baseline , pl - best best result from either basal posterolateral ( pl - bas ) or mid - posterolateral ( pl - mid ) region , max q - lv longest interval measured between onset of the qrs complex and intrinsic activation at the lv electrode . 
   grey shaded area indicates 2 patient in whom the longest q - lv interval did not correspond with the best haemodynamic response . 
   ten patients were considered possible candidates for lv endocardial pacing : 9 patients in whom a rise in lvdp / dtmax   15  % level was only obtained by endocardial pacing , and the patient that showed a substantial additional rise in ahr with lv pacing compared with coronary sinus pacing ( patient 15 ) . 
   of the remaining 9 patients , and after deliberation with the patients about the possible benefits and risks , 5 of them finally agreed to lv endocardial implant at the optimal lv site as indicated from the acute study . 
   all five patients improved clinically with a reduction of at least 1 class in the nyha score after 6 months of follow - up . 
   two patients with a positive response in the temporary study refrained from implantation of an lv endocardial lead . 
   one patient with a positive ahr from endocardial pacing also improved significantly after changing stimulation from the distal to the proximal electrode with a more basal position , and became a clinical responder after optimisation of the atrioventricular and interventricular interval . 
   in one patient , the deterioration of his condition after initial improvement proved to be the result of a blunted chronotropic response after increasing beta - blocker dosage following an episode of atrial fibrillation resulting in an inappropriate icd shock . 
   this observational study showed that endocardial lv pacing , guided by acute haemodynamic studies , could improve clinical outcome in patients not responding to conventional crt . 
   it also demonstrated the importance of lead location , as the clinical response improved with a posterolateral position of the lead instead of the original apical or anterolateral lead location . 
   conversely , none of the patients who already had a coronary sinus lead in a posterolateral position improved sufficiently with endocardial pacing at any site during the acute haemodynamic study to justify endocardial lead implant . 
   this is in line with the madit - crt trial , where the apical and anterior positions of the lv lead had a lower clinical response . 
   noteworthy , and similar to what has previously been reported , endocardial pacing opposite the coronary sinus pacing site did not improve the ahr in our study [ 1113 ] . 
   this is in contrast with animal experiments that show significantly better haemodynamic results with endocardial vs. epicardial pacing at the same location . 
   there is no clear single cause for this difference and it is most probably related to variance in the anatomical and electrophysiological substrate . 
   besides this , in animal experience the lead configuration guarantees an exact position of the endocardial lead opposite to the epicardial position ; this in contrast with human studies in which the endocardial lead is placed as close as possible to its epicardial counterpart . 
   therefore , although not examined in this and other studies , one either might speculate that epicardial pacing opposite the optimal endocardial sites , via the coronary sinus or surgically by thoracoscopy , might have resulted in similar benefits . if feasible , this might be a good alternative to avoid the uncertainty of thromboembolic complications with lv endocardial pacing . 
   our observational study also showed some limitations in the use of acute haemodynamic studies to predict clinical outcome . 
   first , five clinical non - responders showed a clear ahr according to the accepted criteria ( even with the higher than usual cut - off value of 15  % increase in lvdp / dtmax to exclude borderline cases ) but failed to respond clinically . 
   still , when a substantial further increase in lvdp / dtmax from endocardial pacing at a posterolateral position compared with the apical coronary sinus lead ( 66 vs. 19.7  % ) was obtained in one patient , endocardial lead implantation resulted in a positive clinical response . 
   this illustrates the limitation of cut - off values in crt studies of the 15  % level as surrogate for differentiating between clinical response and non - response , and that what is considered a positive haemodynamic response can still be significantly improved in the presence of an anterior or apical lead position . 
   a similar discrepancy is found with echocardiography as the observed presence or absence of decrease in lv end - diastolic volume or end - systolic volume and clinical response does not always correlate . to err on the safe side , we therefore proceeded to a permanent lv endocardial implantation when the final increase in ahr was at least 25  % . 
   the best ahr correlates well with the longest time interval between onset qrs and lv sensing in relation to the qrs width in the individual patient . 
   the results of the group of patients with non - lbbb are in line with what could be expected according to the literature . 
   the absence of response correlated well to the lack of conduction delay in any of the lv segments on the intracardiac lv electrogram . 
   the only responder to endocardial pacing in this group had a significant lv conduction delay due to the left anterior hemiblock that accompanied rbbb . 
   it is therefore questionable if one should proceed with endocardial mapping in this cohort of patients given the disappointing results . 
   this observational study showed that a temporary acute haemodynamic study could be useful in non - responders to establish the chance of improvement with alternative pacing sites before embarking on complex procedures as endocardial lv pacing . 
   it remains , however , uncertain what the optimal cut - off value for increase in lvdp / dtmax is before the improvement justifies intervention . 
   the longest q - lv interval is a reliable indicator for the optimal electrode position in the individual patient . 
   endocardial pacing opposite epicardial sites does not show acute haemodynamic improvement , so epicardial pacing at the optimal site may be a good alternative for endocardial lv lead placement . 
   although all patients who had a lv endocardial system implanted after a positive ahr improved clinically , larger randomised series are necessary to justify this technique before definitive conclusions can be drawn . 
   van gelder has received training and education on pacing and crt from st jude medical , is a consultant with radi pressure wire systems , a st jude medical company , and consultant for pacing and crt with sorin group crm sas . 
   b.m . van gelder has received training and education on pacing and crt from st jude medical , is a consultant with radi pressure wire systems , a st jude medical company , and consultant for pacing and crt with sorin group crm sas .
summary: introductionnon response to cardiac resynchronisation therapy ( crt ) may be related to the position of the coronary sinus lead.methodswe studied the acute haemodynamic response ( ahr ) from alternative left ventricular ( lv ) endocardial pacing sites in clinical non - responders to crt . 
   ahr and the interval from qrs onset to lv sensing ( q - lv interval ) from four different endocardial pacing sites were evaluated in 24 clinical non - responders . a rise in lvdp / dtmax   15  % from baseline 
   was considered a positive ahr . 
   we also compared the ahr from endocardial with the corresponding epicardial lead position.resultsthe implanted system showed an ahr   15  % in 5 patients . in 9 of the 19 remaining patients , ahr could be elevated to   15  % by endocardial lv pacing . 
   the optimal endocardial pacing site was posterolateral . 
   there was no significant difference in ahr between the epicardial and the corresponding endocardial position . 
   the longest q - lv interval corresponded with the best ahr in 12 out of the 14 patients with a positive ahr , with an average q - lv / qrs width ratio of 90  % .conclusionsacute haemodynamic testing may indicate an alternative endocardial pacing site with a positive ahr in clinical non - responders . 
   the q - lv interval is a strongly correlated with the optimal endocardial pacing site . 
   endocardial pacing opposite epicardial sites does not result in a better ahr .