Left Ventricular-Only Pacing in Heart Failure Patients with Normal Atrioventricular Conduction Improves Global Function and Left Ventricular Regional Mechanics Compared with Biventricular Pacing: An Adaptive Cardiac Resynchronization Therapy Sub-Study

AIMS: Right ventricular (RV) pacing can impair left ventricular (LV) function. When timed with native RV activation, LV-only pacing may cause greater improvements in LV function than biventricular pacing. This study compared the chronic effects of cardiac resynchronization therapy (CRT) on LV mechanics between biventricular pacing and LV-only pacing in patients with normal atrioventricular (AV) conduction. METHODS AND RESULTS: The Adaptive CRT (aCRT) algorithm provides LV-only pacing timed with native RV activation when the AV interval is normal (≤200 ms during sinus rhythm). We studied patients from the aCRT trial with normal AV conduction at their baseline visit and compared changes in cardiac function after 12 months of treatment with conventional biventricular or mostly (≥80%) LV-only pacing. Speckle tracking echocardiography was used to assess LV myocardial strain before and after treatment. Despite similar improvements in Packer's clinical composite scores and LV volumes, LV-only paced patients (n = 70) had a greater improvement in LV ejection fraction (8.5 ± 11.3% vs. 5.5 ± 10.3%, P = 0.038) and global LV radial strain (6.3 ± 8.6% vs. 4.0 ± 10.1%, P = 0.046) than those randomized to biventricular pacing (n = 91). Strain was improved to a greater extent near the RV pacing lead, in septal and apical regions (P < 0.05 for both regions), in patients receiving LV-only pacing. CONCLUSION: In heart failure patients with normal AV conduction, LV-only pacing timed with native RV activation may result in greater improvements in LV ejection fraction and myocardial strain compared with biventricular pacing due to better apical and septal function.