Development and validation of a risk score for predicting the difficulty in leadless pacemaker implantation

MICRA™, a leadless pacemaker system, is an established modality for cardiac pacing. However, implantation can be technically challenging in certain anatomical contexts. Purpose: To identify anatomical predictors of procedural difficulty during MICRA™ implantation using preoperative CT imaging, and to develop a scoring system for risk stratification. Methods: We retrospectively analyzed MICRA™ implantations performed at our institution. Procedural difficulty was defined as a delivery system in/out time ≥30 minutes and/or ≥3 deployment attempts. Logistic regression identified independent anatomical predictors, which were incorporated into a scoring system. The first 122 patients formed the development cohort; the remaining 37 patients comprised the validation cohort. Model discrimination was assessed. Results: Procedural difficulty occurred in 31% of both cohorts. Four anatomical features were independently associated with difficulty: right atrial enlargement >45 mm, right ventricular septal angle >55° or <45°, IVC–to–tricuspid valve angle <128°, and posterior offset from the IVC ostium to the tricuspid valve <35 mm. Each predictor was assigned 1 point to create a Difficulty Score (range: 0–4). In the development cohort, difficulty incidence rose sharply with higher scores, reaching 75% at a score of 3 and 100% at a score of 4. The model showed excellent discrimination (AUC = 0.87). In the validation cohort, a similar trend was observed, with moderate discriminative performance (AUC = 0.69). Conclusions: Specific anatomical features on preoperative CT are associated with difficulty in implanting MICRA™. The proposed Difficulty Score may assist in procedural planning and patient selection.