The QRS Interval After Pacemaker Implant: An Independent Mortality Risk Factor

We have been pacing the right ventricular apex, creating an artificial left bundle branch block (LBBB) for more than 4 decades. We learned that some patients would develop dys-synchronization and hence heart failure due to QRS widening. If the lead is implanted in the left bundle area and a narrow QRS is achieved, those patients with LBBB will improve after implant, but those with non-LBBB morphologies might not benefit from QRS narrowing. However, there is not enough information regarding patients with narrow or wide QRS with different types of atrioventricular block that could also benefit from QRS narrowing.

Demonstrate that a narrow-paced QRS is a significant determinant of mortality in patients receiving a permanent pacemaker despite the previous QRS morphology.

We analyzed 204 patients from our pacemaker database. We attempted to implant the lead in the septal area. In our lab, we utilized standard lead electrodes. The criteria for appropriate implant were an electrogram with injury potential, an acceptable lead positioning in the right anterior oblique and left anterior oblique, and a ventricular bipolar threshold less or equal to 1.0 V @ 0.5 ms. QRS duration was assessed according to the global QRS method (from the earliest onset of the QRS in any of the 12 simultaneously recorded standard leads). A QRS interval of 135 ms was determined as a cutoff point using a receiver operator curve (mortality).

The first implants were performed in March 2008 and ended in March 2024. A narrow QRS (<135 ms) was observed in 140 subjects (140/204, 68%). The primary endpoint (death from cardiovascular cause) was met in 10 (4.9%) patients. LBBB was present before implant in 29 patients and a QRS <135 ms was measured in 12/29 (41%). We did not observe more complications compared with the conventional technique. The survival curve using Kaplan-Meier analysis comparing the 2 groups was significantly different with a significant mortality reduction in the narrow QRS group.

A narrow-paced QRS is an independent variable associated with increased survival rates.