Results
Study population
A total of 101 patients were enrolled in the study. After three patients were withdrawn for valve replacement and limited life-expectancy, a hemodynamic evaluation was attempted in 98 patients and successful in 92 patients. The coronary sinus could not be cannulated in two patients; a lateral or posterior LV coronary vein was inaccessible in two patients; and there was dissection of the coronary venous intima in two patients. Three other patients were withdrawn after hemodynamic evaluation due to consent withdrawal, recurrent atrial tachycardia, and infection. The remaining 89 patients were randomized. The results of all randomized patients have been reported at a conference (28). Three of these patients received RV pacing for right bundle branch block. They have been excluded from the present analysis in order to report the results on the 86 randomized patients receiving LV pacing. Table 1lists their baseline clinical characteristics. The intraventricular conduction delay was diagnosed as left bundle branch block in 76 patients (88%) and right bundle branch block in 1 patient (1%); it was nonspecific in 9 patients (11%). All patients were symptomatic despite optimal pharmacologic treatment at baseline, including angiotensin-converting enzyme inhibitors or angiotensin II receptor blockers in 99% of patients and beta-blockers in 73% of patients. Study investigators were prospectively instructed to not modify the patients' medications during the crossover study, except for diuretics, unless such a change would be required for patient safety. There were no significant changes in medication from baseline to the conclusion of the crossover study in any patient group.