Disparity in Left Ventricular Stimulation Among Different Pacing Configurations in Cardiac Resynchronization Therapy

Abstract

Background-Cardiac resynchronization therapy (CRT) demands high energy utilization due to continuous biventricular pacing. Current technology allows 6 pacing configurations for a bipolar left ventricular (LV) lead. Understanding the energy requirements for each configuration will allow optimization of pacing output. Methods and Results-Pacing impedance, LV voltage threshold at 1.5 ms (rheobase) and 0.4 ms and chronaxie were obtained in 6 LV configurations in 49 consecutive patients undergoing CRT implantation or replacement. Strengthduration curves were derived using the Lapicque formula. Pacing impedances and voltage thresholds at 1.5 and 0.4 ms, calculated minimum threshold energy at chronaxie, current drain, energy thresholds at 0.4 ms, and strength-duration curves were statistically different between LV configurations (PϽ0.05). The lowest threshold energy requirements were found in Tip3right ventricular (RV) coil and Tip3 Can configuration. Energy strength-duration curves involving the ring as the cathode (Ring3 RV, Ring3 Can, and Ring3 Tip) had the highest LV thresholds. The pacing configuration with the lowest energy threshold correlated 89% of the time with the lowest voltage threshold at 0.4 ms. The probability to reach LV thresholds Ͻ1.5 V at 0.4 ms was increased from 51% with 2 LV configurations to 67% with 6 LV configurations. Conclusions-Pacing impedance, LV thresholds, minimum threshold energy at chronaxie, current drain, voltage, and energy strength-duration curves were statistically different between LV pacing configurations. LV pacing configuration with the lowest voltage threshold does not always reflects the lowest energy threshold, particularly in the presence of a low impedance configuration. The availability of 6 LV configurations increases the probability of optimizing LV pacing output. (Circ Arrhythm Electrophysiol. 2012;5:140-146.)Key Words: cardiac resynchronization therapy Ⅲ biventricular pacing Ⅲ pacing thresholds Ⅲ strength-duration curve C ardiac resynchronization therapy (CRT) has been developed as an adjunctive therapy in patients with congestive heart failure and left bundle-branch block. This therapy requires effective, safe, and permanent biventricular pacing to obtain clinical benefit and anatomic remodeling. 1 With implantation of a bipolar lead in the coronary sinus, current technology allows electronic programming of 6 different left ventricular (LV) pacing configurations or vectors. Frequently, LV pacing thresholds show a wide variation among LV pacing configurations in the same patient. To our knowledge, no prior studies have investigated the difference in LV thresholds and strength-duration curves between LV pacing configurations in the same patient. The main objective of this study was to determine and understand the difference of LV pacing thresholds and strength-duration curves among different LV pacing configurations, which in turn might provide insights to optimize LV pacing output and battery longevity. Clinical Perspective on p 146 MethodsThis prospective study inc...

Comparison of Different Pacing Strategies to Minimize Phrenic Nerve Stimulation in Cardiac Resynchronization Therapy

“…Few studies have compared PN voltage thresholds in different LV pacing configurations . We have previously shown that voltage thresholds cannot be equally compared between LV pacing configurations due to significant impedance differences between lead configurations . Our study expands on this principle, as we compared voltage and energy of PN threshold in all 6 configurations in the same patient, which corroborates that Tip→Ring has a low energy PN threshold despite a high‐voltage PN threshold, as previously reported …”

“…4 We have previously shown that voltage thresholds cannot be equally compared between LV pacing configurations due to significant impedance differences between lead configurations. 6,7 Our study expands on this principle, as we compared voltage and energy of PN threshold in all 6 configurations in the same patient, which corroborates that Tip→Ring has a low energy PN threshold despite a high-voltage PN threshold, as previously reported. 4 Two studies reported that Ring→RV coil and Tip→Ring had a significantly higher PN voltage threshold compared to Tip→RV coil .…”

“…[2][3][4][5] However, LV thresholds comparing energy or delivered current, are more accurate than voltage for LV pacing due to significant impedance differences between LV pacing configurations. 6 Since LV threshold may vary significantly with time and clinical circumstances, pacing output is traditionally programmed to twice the LV voltage threshold to allow 100% LV capture safety margin. 7 However, such programming is not always feasible in the presence of PNS.…”

“…Prior studies comparing PNS in different pacing configurations have only reported voltage thresholds . However, LV thresholds comparing energy or delivered current, are more accurate than voltage for LV pacing due to significant impedance differences between LV pacing configurations . Since LV threshold may vary significantly with time and clinical circumstances, pacing output is traditionally programmed to twice the LV voltage threshold to allow 100% LV capture safety margin .…”