Consecutive Experience with Left Bundle Branch Area Pacing in a High-Volume Australian Centre.

INTRODUCTION: Left-bundle branch area pacing (LBBAP) is a relatively new technique for conduction system pacing. Australian safety and efficacy data is currently lacking. We aim to evaluate the learning curve, medium-term safety, and lead performance in a high-volume Australian setting. METHODS: We performed a retrospective cohort study of 200 consecutive LBBAP procedures performed by a single operator at two centres between January 2019 and May 2020. Left bundle branch area pacing was performed predominantly via left subclavian access using a 69 cm Medtronic SelectSecure 3830 pacing lead and a preformed non-steerable C315-His sheath. Procedural success was defined as evidence of left septal or left bundle branch area capture as evidenced by a right bundle branch block-like paced morphology. Procedural characteristics, and follow-up (including lead performance) data were collected. Procedural efficiency over time, as well as safety data, were collected. RESULTS: Median age was 78.26 years (interquartile range [IQR] 71-85), 37% were female. Atrial fibrillation was present in 22%. The left ventricular ejection fraction <50% in 24%, atrioventricular (AV) block was present in 43.5%, left bundle branch block in 22.5% and right bundle branch block in 24.5%. Acute procedural success was 91.5%. Implant threshold was 0.6V @ 0.5 ms, and 0.75V @ 0.5 ms at 11.9 months of follow-up. The QRS was significant reduced (baseline 134 ms vs implant 114 ms, p<0.001) There was a reduction in procedural time and X-ray dose over the course of the study. There were no complications specific to LBBAP. CONCLUSION: LBBAP appears to be a safe and effective pacing strategy. The QRS duration was significantly reduced compared to baseline. There appears to be an early learning curve with LBBAP.

Conduction characteristics at the crista terminalis during onset of pulmonary vein atrial fibrillation.

INTRODUCTION: Focal atrial fibrillation (AF) may initiate with an irregular rapid burst of atrial ectopic (AE) activity from a pulmonary vein (PV) focus, but how AF is maintained it is not known. The crista terminalis (CT) is an important line of block in atrial flutter (AFL), but its role in AF has not been determined. The aim of this study was to examine the conduction properties of the CT during onset of AF. METHODS AND RESULTS: In 10 patients (mean age 38 +/- 8 years), we analyzed conduction across the CT during onset of focal AF from an arrhythmogenic PV and during pacing from the same PV at cycle lengths of 700 and 300 ms. A 20-pole catheter was positioned on the CT using intracardiac echocardiography. In 10 control patients with no history of AF, we analyzed conduction across the CT during pacing from the distal coronary sinus at 700 and 300 ms. In all 10 AF patients, AF was initiated with 1 to 9 AE beats (median 5) from a PV. During sinus rhythm, there were no split components (SC) recorded on the CT. During PV AE activity, discrete SC were recorded on the CT in all patients over 6.3 +/- 0.9 bipoles (3.7 +/- 0.3 cm). Maximal splitting of SC was 66 +/- 31 ms (37-139). There was an inverse relationship between AE coupling intervals and the degree of splitting between SC in all patients. Degeneration to AF was preceded by progressive decrement across the CT. SC were recorded during PV pacing at 700 and 300 ms (maximal distance between SC of 24 +/- 3 ms and 43 +/- 5 ms, respectively, P < 0.001). Maximum SC at CT in controls was 13 +/- 8 ms at 700 ms (P = 0.06 vs AF patients) and 16 +/- 9 ms at 300 ms (P < 0.01 vs AF patients). CONCLUSION: (1) These observations provide evidence of anisotropic, decremental conduction across the CT during onset of focal AF and during pacing from the same PV. A line of functional conduction block develops along this anatomic structure (CT). Whether this line of block acts as an initiator of AF or simply contributes passively to nonuniform fibrillatory conduction is unknown. (2) In some patients with focal AF, development of conduction block along the CT may provide a substrate for typical AFL.

Pulmonary vein paced activation sequence mapping: comparison with activation sequences during onset of focal atrial fibrillation.

INTRODUCTION: Atrial fibrillation (AF) may originate from a single focus, with the vast majority observed within the pulmonary veins. To facilitate mapping, we hypothesized that there would be a characteristic right atrial endocardial activation sequence pattern associated with pacing and spontaneous focal activity from each of the four pulmonary veins. METHODS AND RESULTS: In 10 patients with focal AF, a standardized set of catheters was positioned in the right atrium. These included a 20-pole catheter along the crista terminalis, a decapolar catheter in the coronary sinus (CS), and a His-bundle electrode. Pacing (700 and 300 msec) was performed with a mapping catheter from each of the four pulmonary veins. Activation sequence maps were created by measurement of activation times to each of the recording bipoles with the proximal CS bipole as the arbitrary reference point. Similar maps were constructed for the activation sequence of the pulmonary vein ectopic that initiated AF. There was a characteristic right atrial activation map created by pacing each pulmonary vein that corresponded closely with the map from the same pulmonary vein during initiation of focal AF. The pulmonary vein of origin could be distinguished on the basis of this characteristic pattern and some stereotypic observations. CS activation occurred proximal to distal for right pulmonary veins and distal to proximal for left pulmonary veins. Significant differences in activation timing between the CS and crista terminalis differentiated upper from lower pulmonary veins. CONCLUSION: There is a characteristic right atrial activation map for activity arising from each of the four pulmonary veins that corresponded closely with the map from the same pulmonary vein during initiation of focal AF. These findings may facilitate mapping and ablation of focal AF.