CI-452766-1 ABRUPT TORQUE TRANSFER OCCURS FREQUENTLY DURING CONDUCTION SYSTEM PACING INSERTION IN AN EX-VIVO MODEL

Abstract

A fundamental challenge in conduction system pacing [CSP] is determining appropriate lead deployment. With either fixed core or stylet driven leads, the input number of turns may not match resultant rotations achieved by the helix. To date, no validated ex-vivo experimental model has been developed to enable quantitative assessment of the ratio of input turns to helix rotation. To develop a model system to quantitatively describe CSP lead tip to tissue response curves. Sixty-four fresh (<48h) ex-vivo ovine right ventricular septa were excised. Four different leads (1 fixed core (A), 3 stylet-driven (B,C,D)) were driven into the septal myocardium using support via a custom-engineered jig allowing control of input rotation and measurement of helix rotation. Leads were inserted using 15 turns applied proximally on the lead, with resultant helix rotation and tissue-interface characteristics observed at each 90° increment via high resolution photography. Output (helix) rotation vs input rotation response curves [RRC] were assessed using automated segmented linear regression. RRC linear models were statistically analysed using slope (to characterise input vs output response) and breakpoints (to characterise abrupt torque transfer [AAT]). A total of 3840 observations of ¼ turn at the proximal CSP lead were recorded. 16 repeated RRCs were created for each lead type. Mean input vs output slope across leads was 0.46 [95%CI 0.39, 0.52] implying muted output rotations compared to input rotations. Mean number of abrupt torque transfer events [ATT] during each 15 turn insertion (measured by linear break-points in RRC) was 7.2 [95%CI 6.6, 7.7]. In 57.8% (37/64) of lead insertions, there were uncontrolled abrupt torque transfer events [uATT] where the output response at the lead tip was more than the input rotation. An ex-vivo model system was created to examine the torque transfer relationship for CSP leads. Using a robust sample size, this model showed the relationship between input turns yields an overall muted response at the lead tip. However, during insertion, abrupt torque transfer events are common, with uncontrolled abrupt torque transfer events occurring during more than half the insertions. These findings are of clinical significance to CSP implanters to be aware of the potential abrupt torque transfer events, particularly when they are uncontrolled. These data suggest new lead designs may be required to increase the efficiency and safety of CSP.Tabled 1Slope and breakpoint analysis of rotation relationship curves.Lead TypeLead TypeMean RRC Slope [95%CI]Mean # ATT events per insertion [95%CI]Mean # uATT events per insertion [Range]Solid CoreLead A0.28 [0.15, 0.55]7.31 [6.08, 8.54]0.5 [0 to 3]Stylet DrivenLead B0.48 [0.37, 0.71]6.81 [5.57, 8.05]0.69 [ 0 to 3]Stylet DrivenLead C0.66 [0.55, 0.88]7.56 [6.50, 8.62]1.31 [ 0 to 6]Stylet DrivenLead D0.45 [0.35, 0.64]7.18 [6.11, 8.26]0.86 [ 0 to 2]ALL0.46 [0.39, 0.52]7.22 [6.08, 8.35]0.84 [0 to 6]Table 1: Slope and breakpoint analysis of rotation response curves shows that the output rotations delivered to the helix are substantially less than the input rotations. Abrupt torque transfer events occur when sudden changes in the rotations delivered at the helix are observed, and occur frequenty during 15 rotation insertion of physiological pacing leads. Uncontrolled abrupt torque transmission at the helix occurs when the helix rotation exceeds the immediate input rotation, indicating a sudden release of torque build-up from the lead. RRC = Rotation Response Curve. ATT = Abrupt Torque Transfer event where sudden change in slope of RRC. uATT = Uncontrolled Abrupt Torque Transfer Events where Helix rotation > input rotation. Open table in a new tab