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Figure 1 Time line depicting study protocol. Electrocardiograms, blood pressure, and gated blood pool scans were obtained at each time point indicated by the vertical arrows. Between studies, pacemakers were programmed to result in either normal atrioventricular (AV) conduction (AAI) or ventricular pacing (DDD mode with short AV delay), as indicated by the programmed mode. The mode during testing is indicated on top. MTVP = mid-term ventricular pacing for at least one week; STVP = short-term ventricular pacing for 2 h.