Hemodynamic Surveillance of Ventricular Pacing Effectiveness with the Transvalvular Impedance Sensor

Abstract

The Transvalvular Impedance (TVI) is derived between atrial and ventricular pacing electrodes. A sharp TVI increase in systole is an ejection marker, allowing the hemodynamic surveillance of ventricular stimulation effectiveness in pacemaker patients. At routine follow-up checks, the ventricular threshold test was managed by the stimulator with the supervision of a physician, who monitored the surface ECG. When the energy scan resulted in capture loss, the TVI system must detect the failure and increase the output voltage. A TVI signal suitable to this purpose was present in 85% of the tested patients. A total of 230 capture failures, induced in 115 patients in both supine and sitting upright positions, were all promptly recognized by real-time TVI analysis (100% sensitivity). The procedure was never interrupted by the physician, as the automatic energy regulation ensured full patient's safety. The pulse energy was then set at 4 times the threshold to test the alarm specificity during daily activity (sitting, standing up, and walking). The median prevalence of false alarms was 0.336%. The study shows that TVI-based ejection assessment is a valuable approach to the verification of pacing reliability and the autoregulation of ventricular stimulation energy.

Figure 1

Real-time telemetry from the implanted pacemaker. Event markers (upper tracing; short bar = atrial sensing; long bar = ventricular pacing) and transvalvular impedance (TVI; middle tracing; recording in ventricular tip configuration) are matched with the surface ECG (lead II; lower tracing). The horizontal grey bars represent the TVI blanking period following the ventricular spike emission. Atrium-driven (a) and VVI stimulation (b) are compared in the same patient.

Figure 2

Real-time telemetry of event markers (1st tracing) and transvalvalvular impedance (2nd tracing) with simultaneous surface ECG recording (I, III, and aVR from the 3rd to bottom tracings, all with the same voltage scale) during ventricular threshold analysis in VVI. On the markers tracing, long bars represent ventricular pacing and short bars atrial sensing. The 6th spike energy was below the threshold. The capture failure was recognized by the TVI system and the pacemaker promptly increased the pulse amplitude, restoring effective ventricular stimulation.

Figure 3

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.