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1Laboratory of Cardiac Energetics, National Heart, Lung, and Blood Institute, Bethesda 20892; 2Department of Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore 21205; and 3Division of Cardiology, Department of Medicine, Johns Hopkins Medical Institutions, Baltimore, Maryland 21287
Submitted 10 April 2003 ; accepted in final form 2 July 2003
Cardiac resynchronization therapy has been most typically achieved by biventricular stimulation. However, left ventricular (LV) free-wall pacing appears equally effective in acute and chronic clinical studies. Recent data suggest electrical synchrony measured epicardially is not required to yield effective mechanical synchronization, whereas endocardial mapping data suggest synchrony (fusion with intrinsic conduction) is important. To better understand this disparity, we simultaneously mapped both endocardial and epicardial electrical activation during LV free-wall pacing at varying atrioventricular delays (AV delay 0150 ms) in six normal dogs with the use of a 64-electrode LV endocardial basket and a 128-electrode epicardial sock. The transition from dyssynchronous LV-paced activation to synchronous RA-paced activation was studied by constructing activation time maps for both endo- and epicardial surfaces as a function of increasing AV delay. The AV delay at the transition from dyssynchronous to synchronous activation was defined as the transition delay (AVt). AVt was variable among experiments, in the range of 4493 ms on the epicardium and 47105 ms on the endocardium. Differences in endo- and epicardial AVt were smaller (17 to +12 ms) and not significant on average (5.0 ± 5.2 ms). In no instance was the transition to synchrony complete on one surface without substantial concurrent transition on the other surface. We conclude that both epicardial and endocardial synchrony due to fusion of native with ventricular stimulation occur nearly concurrently. Assessment of electrical epicardial delay, as often used clinically during cardiac resynchronization therapy lead placement, should provide adequate assessment of stimulation delay for inner wall layers as well.
resynchronization; mapping; heart failure
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