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Figures
- Figure 1.
Diagram of the mapping field (1 cm2 grid) and its position relative to the intact heart. Each small box within the grid (0.08×0.08 mm) represents a single recording site. Baseline pacing (S1) and first premature stimulus (S2) were always delivered from the same site (stimulus symbol). ECG shown below depicts last 2 beats of drivetrain (S1) followed by a single premature stimulus (S2). Shown is a normal heart in which VF was induced by delivery of a burst train of stimuli (100 Hz) during ECG T wave of S2 beat (S2-VFT) at a second site nearby (*). RA indicates right atrium; LA, left atrium; RV, right ventricle; LV, left ventricle; and LAD, left anterior descending coronary artery.
- Figure 2.
Dependence of depolarization and repolarization on premature coupling interval from a representative experiment (experiment 8). ECGs (top) and contour maps of depolarization (middle) and repolarization (bottom) during a premature stimulus delivered at a coupling interval near the baseline pacing cycle length (A), at an intermediate coupling interval (B), and at a short coupling interval near the effective refractory period (C). All values shown are in milliseconds unless otherwise indicated. The sites of baseline pacing and premature stimulation (stimulus symbol) were identical for each coupling interval. Dispersion of repolarization (ie, S2-DISP) was calculated for each S1S2 coupling interval shown.
- Figure 3.
Measuring vulnerability to VF (ie, S2-VFT) by burst stimulation (100 Hz) during vulnerable period of first premature (S2) beat. Shown are ECG (top) and 1 optically recorded ventricular transmembrane potential (bottom) measured during initiation of VF at 3 different S1S2 coupling intervals (A, 400 ms; B, 210 ms; C, 185 ms). For each coupling interval, the last 2 beats of drivetrain pacing (S1) and the first premature stimulus (S2) followed by the onset of VF are shown. S2-VFT is the average over 2 to 3 repeated initiations. In each panel, APD of the S2 beat is shown under each S2 action potential, and dashed lines indicate time interval when burst train was delivered.
- Figure 4.
A, Dependence of mean repolarization (S2-RT, open circles) and dispersion of repolarization (S2-DISP, filled circles) on S1S2 coupling interval from a representative experiment. B, Dependence of arrhythmia vulnerability (S2-VFT) on premature coupling interval from same representative experiment. Dispersion of repolarization (A, filled circles) and vulnerability to fibrillation (B) were modulated in a similar biphasic fashion, with minimum vulnerability (ie, maximum S2-VFT) and minimum dispersion occurring at the same S1S2 coupling interval (255 ms, dashed arrow).
- Figure 5.
Summery data for 8 experiments showing mean repolarization (S2-RT, A), dispersion of repolarization (S2-DISP, B), and vulnerability to fibrillation (S2-VFT, C) after premature stimulation for coupling intervals near baseline pacing rates (BASE), for intermediate coupling intervals (INTER), and for short coupling intervals near refractoriness (SHORT). All values shown are mean±SEM. Mean repolarization time decreased monotonically, whereas dispersion of repolarization and arrhythmia vulnerability were modulated analogously in a biphasic fashion.
Tables
Experiment No. Coupling Interval, ms S2-DISP, ms2 BASE INTER SHORT BASE INTER SHORT 1 300 255 230 103 78 110 2 300 245 220 43 16 136 3 300 250 220 110 36 121 4 300 270 230 47 23 108 5 400 250 220 18 9 24 6 350 230 195 64 59 123 7 400 230 215 24 7 14 8 400 220 205 46 10 48 Mean±SD 344±50 244±16 217±12 57±34 30±26 84±50 Δ −100 −27 −27 54 -
Summary of experimental data demonstrating the effect of premature stimulation coupling interval on dispersion (variance) of repolarization (S2-DISP). Shown are results for baseline stimulation (BASE), premature stimulation at an intermediate coupling interval (INTER), and premature stimulation at a short coupling interval near refractoriness (SHORT). The change in coupling interval and S2-DISP as S1S2 was decreased from BASE to INTER and INTER to SHORT is shown across the bottom (Δ). The intermediate coupling interval (INTER) was defined by the S1S2 coupling interval that resulted in minimal dispersion.
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