Relazione tra differenti morfologie del QRS pre-impianto e sensing dell'onda R del pacemaker.

BACKGROUND: Appropriate R-wave sensing is essential for proper pacemaker function. Undersensing occurs when the pacemaker fails to detect spontaneous myocardial depolarization, leading to asynchronous pacing. The primary causes of undersensing include pacemaker programming issues (incorrect sensing threshold), inadequate myocardial voltage signals, lead or pacemaker failure (fibrosis, fracture, etc.), and electrolyte abnormalities. Additionally, conduction system disorders, such as right bundle branch block, may be underdiagnosed and often overlooked cause. AIM OF THE STUDY: The influence of different pre-implant QRS morphologies, as right bundle branch block, on pacemaker R-wave sensing values has not been systematically explored previously. This study aimed to identify potential differences in R-wave sensing values due to different pre-implant QRS morphologies, explore a potential role of lead position and fixation in determining changes in R-wave sensing at baseline, evaluate R-wave sensing modifications during long-term follow-up. METHODS: We prospectively enrolled 197 consecutive patients who underwent clinically indicated PM implantation at our tertiary center. Clinical and electrocardiographic parameters were collected before implantation. QRS morphologies were divided into narrow QRS, right bundle branch (RBBB) and left bundle branch block (LBBB). The implantation procedure followed routine practice and operators’ preferences. Monopolar and bipolar R-wave sensing values, bipolar pacing thresholds, and bipolar lead impedances were collected immediately after implantation and at 6, 12, 24 and 36 months follow-up. RESULTS: The study population was composed of 197 patients (mean age 79.6 years-old, 57.9% male), divided into three categories based on surface EKG: narrow QRS (116, 58,9%), LBBB (31, 15,7%) and RBBB (50, 25,4%). The baseline analysis showed significantly lower values in both monopolar (p 0,042) and bipolar (p < 0.001) R-wave sensing values in the RBBB group compared to the LBBB and narrow QRS groups. Univariate linear regression analysis was executed to identify determinants of bipolar R-wave sensing. The only parameters that showed statistical significance were age (p 0.024), QRS morphology (Narrow QRS – RBBB p 0.001; LBBB – RBBB p 0.001), impedance (p 0.006) and Unipolar R-wave sensing. These variables were then analyzed in the linear multivariate regression to identify independent determinants of bipolar R-wave sensing, evidencing that the RBBB morphology is an independent determinant with statistical significance both compared to Narrow QRS (p 0.009) and LBBB (p 0.004). Interestingly, unipolar sensing still remains a significant determinant of bipolar R-wave sensing (p < 0.001). No significant differences between the groups were found depending on the lead position (p 0,245). During follow-up, bipolar R-wave sensing showed statistically significant yet clinically irrelevant reduction of the values, due to a lowering in the narrow QRS and right bundle branch block groups; left bundle branch block group showed stable values over follow-up time. Monopolar R-wave sensing at implantation resulted to be the only independent predictor of significant bipolar R-wave sensing modifications during follow-up. CONCLUSIONS: We found that pre-implant RBBB was an independent determinant of lower PM bipolar R-wave sensing values at implantation; lead position did not influence bipolar R-wave sensing values. A clinically irrelevant trend in lowering bipolar sensing values was observed in the right bundle branch block and narrow QRS groups at the 36 follow-up.