Real-time telemetry of event markers (1st tracing) and transvalvalvular impedance (2nd tracing) with simultaneous surface ECG recording (I, II, and aVR from the 3rd to bottom tracings, all with the same voltage scale) during ventricular threshold analysis in VDD. On the markers tracing, short bars represent atrial sensing, intermediate bars ventricular pacing, and the longest bars ventricular sensing in the pacemaker refractory period. From the 5th pulse onward the stimulation was below threshold and a narrow QRS replaced the pacing-evoked wide complex. Nevertheless, a properly timed TVI fluctuation was present, confirming the ejection occurrence, and the energy scan continued down to the minimum pulse amplitude available.
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