Annalisa Bucchi, Alexei N. Plotnikov, Iryna Shlapakova, Peter Danilo, Yelena Kryukova, Jihong Qu, Zhongju Lu, Huilin Liu, Zongming Pan, Irina Potapova, Bruce Ken Knight, Steven Girouard, Ira S. Cohen, Peter R. Brink, Richard B. Robinson and Michael R. Rosen
Circulation. 2006;114:992-999, originally published September 4, 2006
Definitions of experimental measurements. A, Schematic representation of an action potential during the last beat of a 50-beat baseline drive train (S1) and a single premature beat (S2). Superimposed are DTp, RTp, DTb, and RTb. The following intervals were calculated from these parameters: APDp (RTp−DTp), APDb (RTb−DTb), and DI (DTp−RTb). B, Stylized restitution curve along with the parameters used to estimate restitution kinetics (RK), where ΔAPD is the extent of APDp shortening over the range of DIs tested (ΔDI).
Restitution curves generated from optical action potentials (inset) measured simultaneously from two ventricular sites. The bold action potentials were recorded during the last beat of the constant cycle length drive train, and the remaining potentials were recorded at progressively shorter S1-S2 coupling intervals. The site at which APDb is longer (▪) has a faster time course of restitution (RK=0.47) compared with the site at which APDb is shorter (RK=0.29, •). The dashed lines connect data points recorded simultaneously during each S1-S2 coupling interval tested.
Spatial dispersion of restitution kinetics (RK) and APD during baseline pacing (APDb). Shown to the right of each contour map is a gray scale with corresponding numerical values in normalized units (RK) and milliseconds (APDb). Pacing was performed from the upper left corner (site A) of the mapping field for all measurements. Diagram shows the mapping field (1-cm2 grid) and its position relative to the intact heart preparation (bottom, left). RA indicates right atrium; LA, left atrium; RV, right ventricle; LV, left ventricle; and LAD, left anterior descending coronary artery. RK and APDb measured from each mapping site are plotted in the graph (bottom, right), demonstrating the strong correlation between these variables.
In propagating tissues, it is possible that electrotonic loading from the propagation wave front could influence restitution. If this were the case, restitution would be sensitive to propagation direction. To determine whether electrotonic loading influences restitution, the effect of propagation direction on RK and APDb was measured by repeating the restitution protocol from opposite sides of the mapping field (sites A and B in Fig 3). RK and APDb were not dependent on propagation direction, as evidenced by the alignment of data points along the line of identity (solid line). Therefore RK and APDb are largely determined by membrane ionic kinetics intrinsic to each recording site and not electrotonic loading.
