Stimulus intensity in left ventricular leads and response to cardiac resynchronization therapy.

Increased left ventricular (lv) stimulus intensity has been shown to improve conduction velocity and cardiac output. however,high-output pacing would shorten device battery life. our prospective trial analyzed the clinical effects of high- versus low-output lv pacing. thirty-nine patients undergoing initial cardiac resynchronization therapy device implantation with bipolar lv leads were assigned to 3 months of either high-output lv pacing (hi) or low-output lv pacing (lo) in a randomized,blinded crossover fashion. hi and lo settings were determined with a rigorous intraoperative protocol specific to each patient. clinical and echocardiographic data were obtained at randomization,at 3 months,and a subsequent 3 months after crossover. mean age was 66.4±9.8 years,and mean qrs duration was 159.3±23.1 ms. compared to baseline,both arms had significant improvements in minnesota living with heart failure score (given as mean [95% confidence interval]) (baseline versus lo: 43.3 [35.5 to 51.1] versus 21.3 [14.6 to 28.0],p<0.01; baseline versus hi: 43.3 [35.5 to 51.1] versus 23.6 [16.1 to 31.1],p<0.01) and 6-minute walk distance (baseline versus lo: 692 ft [581 to 804] versus 995 ft [876 to 1114],p<0.01; baseline versus hi: 699 ft [585 to 813] versus 982 ft [857 to 1106],p<0.01). although both hi and lo arms had some echocardiographic parameters that significantly improved compared to baseline (baseline end-diastolic diameter 5.7 cm [5.5 to 6.0] versus lo 5.5 cm [5.1 to 5.8],p<0.01; baseline end-systolic diameter 4.9 cm [4.6 to 5.3] versus hi 4.7 cm [4.3 to 5.0],p<0.05),there were no significant differences observed when comparing the hi- versus lo-output arms. low-output lv pacing with a relatively narrow safety margin above capture threshold affords significant improvement from baseline and is clinically equivalent to high-output lv pacing. these data support a strategy of minimizing the programmed lv safety margin to increase battery life in cardiac resynchronization therapy devices. url: http://www.clinicaltrials.gov. unique identifier: nct01060449.