The electrophysiological characteristics and meanings in left bundle branch pacing based on unipolar and bipolar pacing.

Left bundle branch pacing (LBBP) is considered as an innovative physiologic pacing form because of lower thresholds compared with His bundle pacing and can partially resolve distal bundle disease (1). Our group had reported a novel LBBP lead implantation procedure guided by electrocardiogram (ECG) and electrogram (EGM) morphology under beat-to-beat monitoring, and found the isoelectric interval was a safe and precise endpoint for implantation, and was feasible in 87.8% (2). Few studies described the ECG and EGM characteristics of bipolar pacing due to the inaccuracy of selective left bundle branch pacing (SLBBP). This is the first case to report the electrophysiological characteristics of four unipolar or bipolar pacing modes and try to analyze the potential mechanism of different ECG and EGM morphology.

[Study on Impedance of Implantable Cardiac Pacemaker in Unipolar/Bipolar Pacing Mode by in Vitro Experiment].

The unipolar/bipolar pacing mode of pacemaker is related to its circuit impedance, which affects the battery life. In this study, the in vitro experiment scheme of pacemaker circuit impedance test was constructed. The human blood environment was simulated by NaCl solution, and the experimental environment temperature was controlled by water bath. The results of in vitro experiments showed that under the experimental conditions similar to clinical human parameters, the difference between the circuit impedance of bipolar mode and unipolar mode is 120~200 Ω. The results of the in vitro experiment confirmed that the circuit impedance of bipolar circuit was larger than that of unipolar mode, which was found in clinical practice. The results of this study have reference value to the optimization of pacing mode and the reduction of pacemaker power consumption.

Variation in activation time during bipolar vs extended bipolar left ventricular pacing.

BACKGROUND: Cardiac resynchronization therapy (CRT) is typically delivered via quadripolar leads that allow stimulation using either true bipolar pacing, where stimulation occurs between two electrodes (BP) on the quadripolar lead, or extended bipole (EBP) left ventricular (LV) pacing, with the quadripolar electrodes and right ventricular coil acting as the cathode and anode, respectively. True bipolar pacing is associated with reductions in mortality and it has been postulated that these differences are the result of enhanced electrical activation. MATERIALS AND METHODS: Patients undergoing a CRT underwent an electrocardiographic imaging study where electrical activation data were recorded while different LV pacing vectors were temporarily programmed. RESULTS: There were no differences in the total electrical activation times or dispersion of electrical activation between biventricular pacing with bipolar or corresponding EBP LV vector configurations (left ventricular total activation time [LVtat] BP 74.70 ± 18.07 vs EBP 72.4 ± 22.64; P = 0.45). When dichotomized according to etiology, no difference was observed in the activation time with either BP or EBP pacing (LVtat BP ischemic cardiomyopathy 72.2 ± 17.4 vs BP dilated cardiomyopathy 79.9 ± 18.9; P = 0.38). CONCLUSIONS: Bipolar pacing alters the mechanical activation sequence of the LV and is associated with reductions in all-cause mortality. It has been postulated these benefits derive from improvements in electromechanical activation of the LV. Our study would suggest that true bipolar pacing does not necessarily result in more favorable activation of the LV or improved electrical resynchronization and other mechanisms should be explored.

Diagnostic accuracy of pace spikes in the electrocardiogram to diagnose paced rhythm.

OBJECTIVE: To determine how often cardiac resynchronization therapy (CRT) pacing systems generate visible pace spikes in the electrocardiogram (ECG). METHODS: In 46 patients treated with CRT pacing systems, we recorded ECGs during intrinsic rhythm, atrial pacing and ventricular pacing. ECGs were analysed for atrial and ventricular pace spikes by two experienced ECG readers blinded to the pacing therapy and to the study purpose. RESULTS: Atrial pacing generated visible pace spikes in less than 70% of the ECGs, whereas ventricular pacing generated visible pace spikes in about 90% of ECGs. The sensitivity of manual ECG interpretation for pace spikes was low for atrial pacing (Reader 1: 0.62 [95% confidence interval (CI) 0.50-0.74]; Reader 2: 0.65 [95% CI 0.53-0.77]) and moderate for ventricular pacing (Reader 1: 0.88 [95% CI 0.81-0.93]; Reader 2: 0.93 [95% CI 0.87-0.97]). CONCLUSIONS: In patients with CRT pacing systems, the absence of visible pace spikes in the ECG does not rule out paced rhythm.

Six transition patterns and seven capture types in different left bundle branch bipolar pacing configurations.

Aims: This study aims to explore the different transition patterns and capture types during two bipolar pacing tests based on the selective left bundle branch (LBB) capture determined by the continuous pacing and recording technique. Methods: In total, 67 patients completed two unipolar and two bipolar pacing tests based on selective LBB capture during screwing-in for left bundle branch pacing (LBBP) using the continuous pacing and recording technique. The electrophysiological characteristics and potential mechanisms of different pacing configurations were further evaluated in this study. Results: We found six transition patterns and derived seven capture types in two bipolar pacing tests according to the analysis of continuous electrocardiogram and electrogram changes. Compared with the conventional configuration of "Tip-Ring+" bipolar pacing, "Ring-Tip+" testing had a lower threshold for simultaneous capture of the LBB and the left and right ventricular septum myocardium (1.57 vs. 2.84 V at 0.5 ms) and was the only configuration to yield the peculiar "LBBP + right ventricular septum pacing (RVSP)" capture type. Conclusions: In this study, we observed for the first time that "Ring-Tip+" bipolar pacing allows for a lower clinically applicable pacing threshold for simultaneous capture of the LBB and left and right ventricular septum myocardium, and the peculiar "LBBP + RVSP" capture type. This may be a more advantageous physiological pacing configuration, warranting further investigation and application in the future. Lay summary: Based on the specific selective LBB capture, we first found six transition patterns and derived seven capture types in two bipolar pacing tests due to the different thresholds of the LBB, left ventricular septal myocardial, and right ventricular septal myocardial. Compared with the conventional configuration of "Tip-Ring+" bipolar pacing, "Ring-Tip+" testing had a lower threshold for simultaneous capture of the LBB and the left and right ventricular septum myocardium (1.57 vs. 2.84 V at 0.5 ms) and was the only configuration to yield the peculiar "LBBP + RVSP" capture type. More pacing strategies should be released and investigated to achieve the best physiological pacing according to the individualized electrophysiological characteristics of patients.

Electrophysiological characteristics and possible mechanism of bipolar pacing in left bundle branch pacing.

BACKGROUND: Left bundle branch pacing is a physiological pacing modality with a low and stable threshold. The electrophysiological characteristics and mechanisms of bipolar pacing remain unclear. OBJECTIVES: This study aimed to assess the electrophysiological characteristics of bipolar pacing of left bundle branch pacing and to infer the mechanisms underlying each electrocardiogram and electrogram waveform morphology. METHODS: A total of 65 patients who strictly met the criteria for left bundle branch capture were enrolled. The changes in the morphology of the electrocardiogram and electrogram during the threshold testing with different outputs on unipolar and bipolar pacing were recorded. The electrophysiological characteristics were then analyzed. RESULTS: Four distinct morphologies and 3 different types of transitions during bipolar pacing threshold testing were identified; we labeled the 4 types of morphologies as nonselective (NS)-bipolar-left bundle (LB), NS-cathodal-LB, selective (S)-cathodal-LB, and left ventricular septal-cathodal. Except left ventricular septal-cathodal, the other 3 types (NS-bipolar-LB, NS-cathodal-LB, and S-cathodal-L) had a short and constant V6 R-wave peak time (RWPT) (64.8 ± 7.7 ms vs 65.7 ± 7.8 ms vs 65.7 ± 7.3 ms). The paced QRS (P-QRS) complex was the narrowest in NS-bipolar-LB rather than in NS-cathodal-LB (118.2 ± 14.2 ms vs 133.8 ± 15.8 ms; P < .001). NS-bipolar-LB had a higher threshold than did NS-cathodal-LB (2.5 ± 1.2 V vs 0.8 ± 0.4 V; P < .001). CONCLUSION: With a higher output on bipolar pacing, NS-bipolar-LB capture had the shortest V6 RWPT, V1 RWPT, and P-QRS. S-cathodal-LB capture had the longest V1 RWPT and P-QRS complex.

Study on Impedance of Implantable Cardiac Pacemaker in Unipolar/Bipolar Pacing Mode by in Vitro Experiment / 中国医疗器械杂志

The unipolar/bipolar pacing mode of pacemaker is related to its circuit impedance, which affects the battery life. In this study, the in vitro experiment scheme of pacemaker circuit impedance test was constructed. The human blood environment was simulated by NaCl solution, and the experimental environment temperature was controlled by water bath. The results of in vitro experiments showed that under the experimental conditions similar to clinical human parameters, the difference between the circuit impedance of bipolar mode and unipolar mode is 120~200 Ω. The results of the in vitro experiment confirmed that the circuit impedance of bipolar circuit was larger than that of unipolar mode, which was found in clinical practice. The results of this study have reference value to the optimization of pacing mode and the reduction of pacemaker power consumption.