Acute performance evaluation of a new ventricular automatic capture algorithm

Left ventricle pacing challenges in cardiac resynchronization therapy systems

Left ventricle (LV) pacing can be considered peculiar due to its different lead/tissue interface (epicardial pacing) and the small vein wedging lead locations with less reliable lead stability. The current technologies available for LV capture automatic confirmation adopt the evoked response (ER), as well as "LV pace to right ventricular (RV) sense" algorithms. The occurrence of anodal RV capture is today completely solved by the use of bipolar LV leads, while intriguing data are recently published regarding the unintentional LV anodal capture beside the cathodal one, which may enlarge the front wave of cardiac resynchronization therapy (CRT) delivery. The LV threshold behavior over time leading to ineffective CRT issues (subthreshold stimulation or concealed loss of capture), the extracardiac capture with phrenic nerve stimulation (PNS), the flexible electronic cathode reprogramming and the inadequate CRT delivery related to inadequate AV and VV pace timing (and its management by LV "dromotropic pace-conditioning") are discussed. Moreover, recently, His bundle pacing (HBP) and left bundle branch pacing (LBBP) have shown growing interest to prevent pacing-induced cardiomyopathy as well as for direct intentional CRT. The purpose of the present review is to explore these new challenges regarding LV pacing starting from old concepts.

Left ventricle automatic pacing threshold management in CRT systems: A comprehensive review

Modern cardiac resynchronization therapy (CRT) device-based threshold detection enables capture management and voltage output adjusting to combine consistent left ventricular (LV) pacing with acceptable battery drainage. The current technologies available for LV capture automatic confirmation in most cases require the evoked response, as well as "LV pace to right ventricular sense" algorithms. The LV pacing percentage counter may overestimate the CRT delivery which may be reduced due to pacing inhibition (by sensed LV activation) or inadequate capture due to subthreshold current or pacing into refractory tissue. Moreover, the LV threshold at implant and its behavior over time (as a marker of electrical viability) and the ineffective CRT issues (subthreshold stimulation or concealed loss of capture) are discussed. The purpose of the present review is to explore these new challenges regarding LV pacing automatic management.

Clinical Evaluation of Two Different Evoked Response Sensing Methods for Automatic Capture Detection in the Left Ventricle

BACKGROUND

This acute feasibility study compared two different automatic capture detection methodologies, the reduced coupling capacitor (RCC) and the independent pace/sense (IPS) methods, for the left ventricle (LV).

METHODS

LV threshold tests were performed in DDD mode, with LV-only and bi-ventricular (BiV) pacing using an external cardiac resynchronization therapy (CRT) defibrillator. Evoked response (ER) signals from LV leads were recorded using the LV(Tip) (LV(Tip)-->Can) and LV(Ring) (LV(Ring)-->Can) to empty pulse generator (Can) housing sensing vectors to evaluate the two methodologies. Pacing vector, pulse duration, atrioventricular delay, and interventricular delay were varied to assess their effects on ER. The minimum ER amplitude (ER(min)), signal-to-artifact ratio (SAR), and ER amplitude voltage dependence were evaluated. ER(min)>2 mV and SAR(min)>2 define potential automatic LV capture detection for the two methodologies.

RESULTS

Data collected from 43 patients (63.7 +/- 11.0 years) were analyzed, including unipolar and bipolar (14/29) LV leads. Neither ER sensing method was affected by changing the pacing vector. The LV(Tip)-->Can ER(min) was significantly decreased at the 1.0-ms pulse duration when compared to 0.4-ms (p < 0.05). During BiV pacing, LV(Tip)-->Can ER(min) increased at negative interventricular delays and decreased at positive interventricular delays relative to simultaneous pacing. LV(Tip)-->Can resulted in fewer patients with sufficient ER characteristics for capture detection, albeit only significantly at the extended pulse duration (79% vs 97%, p < 0.05) and at simultaneous and positive interventricular delays (81% vs 97%, p < 0.05).

CONCLUSIONS

Though LV capture detection was feasible using both investigated methods, the RCC method (LV(Tip)-->Can) sensitivity to the evaluated pacing parameters suggests the IPS method (LV(Ring)-->Can) provides a more robust performance.