Use of microelectrode near-field signals to determine catheter contact

Electrogram voltage and pacing threshold before ablation, measured by mini-electrodes, predict parameters indicative of transmural lesions in the human atrium

PURPOSE

An important attenuation of the atrial signal recorded with mini-electrodes (ME) embedded in an 8-mm tip was associated with a transmural radiofrequency lesion. Our aim was to assess if parameters obtained from ME or conventional bipoles before applications predict successful atrial lesions.

METHODS

We prospectively included 33 consecutive patients undergoing cavotricuspid isthmus (CTI) ablation. Electrogram voltages and pacing thresholds were measured with ME and conventional bipoles before and after radiofrequency (RF) applications. The time before the loss of capture during applications was recorded. Lesions were considered successful, in accordance with preclinical data, if ME voltage decreased > 54%.

RESULTS

Of 207 applications, 107 could be analyzed. During applications, voltages decreased more in the ME than in the conventional bipoles (66.8 ± 26.1% vs 37.5 ± 42.5%, P = 0.001). Likewise, pacing threshold increased significantly more using the ME (86.3 ± 22.9% ME, 52.6 ± 35.6% conventional, P = 0.001). ME pre-ablation voltages were significantly higher and pacing thresholds significantly lower in successful lesions (voltage 0.88 ± 0.71 vs 0.26 ± 0.18 mV, P = 0.0001; threshold 1.6 ± 1.7 vs 2.8 ± 3.0, P = 0.04). Neither of these parameters with conventional bipoles nor time to loss of capture showed differences. A ME voltage > 0.33 mV and a pacing threshold < 1.5 mA predicted a successful lesion with 0.78 and 0.6 sensitivity and 0.78 and 0.59 specificity.

CONCLUSIONS

Certain pre-ablation parameters derived from ME such as electrogram voltage and pacing threshold differ from those obtained by a conventional configuration and can predict a successful atrial lesion.

First clinical use of novel ablation catheter incorporating local impedance data

INTRODUCTION

Successful catheter ablation is limited by both poor spatial resolution of abnormal local signals and inability to deliver an effective lesion due to poor tissue contact. We report first worldwide use of the Intellanav MiFi OI catheter (Boston Scientific), providing ultra-high density mapping and incorporating a "DirectSense" algorithm to measure local tissue impedance (LI).

METHODS AND RESULTS

31 patients (65±6 years, 20 male) underwent ablation. LI from the catheter, generator impedance (GI) and maximum electrogram amplitude were recorded in the blood pool, and in regions from healthy to dense scar before, during and after ablation. The catheter demonstrated clear nearfield signal where standard bipolar recordings included farfield signal. LI was lower in dense scar than either healthy tissue or blood pool, and demonstrated an exponential relationship with maximum electrogram amplitude. Maximum LI drop on ablation linearly correlated with initial LI. The median LI drop for successful lesions, resulting in lack of local tissue capture, was 16.0Ω (12.1-19.8 Ω) for LV and 14.6 Ω (10.0-18.3 Ω) for LA, which was larger than for unsuccessful lesions (LV: 9.4 Ω [5.4-15.6 Ω] P = 0.001; LA: 6.8 Ω [4.7-13.0 Ω], P = 0.049). LI percentage drop was also significantly larger for successful than unsuccessful lesions (LV: 17.1 Ω [14.0-19.6 Ω] vs. 10.6 Ω (7.1-16.5 Ω) P = 0.002; LA: 14.2 Ω [10.8-19.5 Ω] vs. 7.5Ω [5.1-11.0 Ω], P = 0.005).

CONCLUSION

This novel catheter gives reproducible recordings of local impedance, which are dependent on scar level. Absolute LI drop, and also percentage drop, on ablation may give an indication of tissue contact and subsequent effective lesion formation.