Programmed deep septal stimulation: A novel maneuver for the diagnosis of left bundle branch capture during permanent pacing

Abstract

Introduction: Permanent deep septal stimulation with capture of the left bundle branch (LBB) enables maintenance/restoration of the physiological activation of the left ventricle. However, it is almost always accompanied by the simultaneous engagement of the local septal myocardium, resulting in a fused (nonselective) QRS complex, therefore, confirmation of LBB capture remains difficult. Methods: We hypothesized that programmed extrastimulus technique can differentiate nonselective LBB capture from myocardial-only capture as the effective refractory period (ERP) of the myocardium is different from the ERP of the LBB. Consecutive patients undergoing pacemaker implantation underwent programmed stimulation delivered from the lead implanted in a deep septal position. Responses to programmed stimulation were categorized on the basis of sudden change in the QRS morphology of the extrastimuli, observed when ERP of LBB or myocardium was encroached upon, as: "myocardial," "selective LBB," or nondiagnostic (unequivocal change of QRS morphology). Results: Programmed deep septal stimulation was performed 269 times in 143 patients; in every patient with the use of a basic drive train of 600 milliseconds and in 126 patients also during intrinsic rhythm. The average septal-myocardial refractory period was shorter than the LBB refractory period: 263.0 ± 34.4 vs 318.0 ± 37.4 milliseconds. Responses diagnostic for LBB capture ("myocardial" or "selective LBB") were observed in 114 (79.7%) of patients.Conclusions: A novel maneuver for the confirmation of LBB capture during deep septal stimulation was developed and found to enable definitive diagnosis by visualization of both components of the paced QRS complex: selective paced LBB QRS and myocardial-only paced QRS. K E Y W O R D S effective refractory period, electrocardiogram, left bundle branch pacing, nonselective capture, refractoriness

Permanent left bundle branch pacing: What is the mechanism of divergent responses during programmed stimulation?

“…Consequently, myocardial paced QRS and selective LBB paced QRS was observed over a wide range of coupling intervals. This contrasted with the recent report where the difference in LBB ERP and local myocardial ERP was only 55 ms (263 vs 318 ms) when assessed with a 600 ms basic drive train—resulting in approximately 20% of cases where a diagnostic response during programmed stimulation could not be evoked 2 …”

“…During permanent pacing of the conduction system, it is important to confirm that direct capture of the His bundle or the left bundle branch (LBB) was achieved. Using programmed stimulation, differences in refractoriness between the conduction system and the myocardium can be exploited to provide the diagnosis of conduction system capture 2,3 . The diagnosis is based on the visualization of one or both components of the fused nonselective paced QRS, which is selective myocardial capture QRS and/or selective conduction system capture QRS.…”

“…The diagnosis is based on the visualization of one or both components of the fused nonselective paced QRS, which is selective myocardial capture QRS and/or selective conduction system capture QRS. However, while this method works very well during His bundle pacing, its performance during LBB pacing was suboptimal, probably due to a smaller difference between effective refractory period (ERP) of the local septal myocardium and LBB when using standard pacing protocols 2,3 . Denker et al 4 devised specific programmed stimulation protocols to show that abrupt changes in cycle length impact refractoriness of the myocardium and conduction system divergently.…”

“…At the final lead position, during threshold assessment (pacing output reduction), no change in the QRS morphology was observed, with just the loss of capture when the low output of 0.5 V@0.5 ms was reached—pointing either to myocardial capture only or to equal capture thresholds of LBB and myocardium. To confirm LBB capture, programmed stimulation was performed 2 …”

ECG patterns of successful permanent left bundle branch area pacing in bradycardia patients with typical bundle branch block

“…A recent study has provided the evidence for fused pacing of LBB and septal myocardium during selective and nonselective LBB pacing by programmed extra-stimulus technique. 19 In addition, bipolar pacing could sometimes provide additional capture of RV endocardium. Therefore, RV backup pacing is not routinely needed.…”