Autocapture enhancements: unipolar and bipolar lead compatibility and bipolar pacing capability on bipolar leads

Hemodynamic Surveillance of Ventricular Pacing Effectiveness with the Transvalvular Impedance Sensor

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.

Effect of atrial lead position on atrial automatic capture verification

INTRODUCTION

Optimizing atrial automatic capture verification based on atrial-evoked response (AER) detection requires maximizing the signal artifact ratio (SAR), that is, AER to stimulation artifact (ART). This study evaluated the effect of bipolar atrial lead position on sensed AER, ART, and SAR.

METHODS AND RESULTS

A custom-made external research system (INSIGNIA(AC), Boston Scientific Corp. St Paul, MN, USA) was used to perform an automatic voltage step-down atrial pacing protocol at three different right atrial lead positions (A-appendage, L-lateral wall, and S-septal wall) in each studied patient. The atrial pacing and the AER sensing configurations were independent. The pacing was unipolar in an A(tip)-Can configuration while sensing was in A(ring)-I(ndiff). Data from 16 patients (mean age 71.1 +/- 9.6 years) and six-lead models from five different manufacturers were analyzed. Study results show that with all lead types, the atrial lead placement had no significant effect on AER(min), ART(max), and SAR(min) and only one patient had an SAR that was not sufficient to support successful automatic capture verification at all tested atrial pacing sites.

CONCLUSION

The atrial pacing site has minimal effect on AER sensing when using an independent pace/sense configuration. The leads placed at all tested sites were found to have the parameters sufficient to support the atrial automatic capture verification in all but one patient.

Clinical Performance of a Ventricular Automatic Capture Verification Algorithm

BACKGROUND

This study was conducted to evaluate the clinical performance of the ventricular automatic capture feature as implemented in the Insignia I Ultra pacemaker system (Guidant) utilizing a variety of ventricular leads. Currently, the optimal programming of the pacemaker output considers both pacemaker efficiency (prolonging battery longevity) and patient safety (adequate safety margin). The ability of a pacemaker to automatically adjust the ventricular output above the pacing threshold while maintaining the appropriate safety margin has been explored since the early 1970s and is only available today in conjunction with a specific low polarization lead system.

METHODS

One hundred and five patients were enrolled from 17 European centers utilizing 31 different types of ventricular leads were followed through their 3-month follow-up visit. There were no restrictions on the type of ventricular leads used.

RESULTS

The average mean difference between the commanded autothreshold test (0.652 + 0.335 V) and the manual threshold test (0.651 + 0.335 V) was 0.001 + 0.49 (P < 0.0001). The average mean difference between the ambulatory autothreshold test (0.696 + 0.322 V) and the commanded autothreshold test (0.682 + 0.315 V) was 0.002 + 0.74 (P < 0.0001). Holter recordings confirmed that there were no loss of capture incidences without a backup pulse being delivered. In addition, the mean number of backup pulses delivered in a 24-hour period was less than 0.1% of the total number of paced beats.

CONCLUSIONS

This study provided that the automatic capture feature while using a variety of leads accurately determines the ventricular stimulation threshold and safely delivers a backup pulse when required.