Left Bundle Branch Versus Minimized Ventricular Pacing in Patients With Sick Sinus Syndrome and Prolonged AV Interval

Eligible subjects who provide written informed consent will be randomly assigned in a 1:1 ratio to either the LBBAP group or the MVP group. Randomization will be available 24 hours a day using an Interactive Web Response System (IWRS). Randomization will be stratified by the presence of a history of AF. For patients who meet the inclusion and exclusion criteria before the procedure, randomization will be performed beforehand. For patients with SSS requiring PPM implantation, whose AV conduction status cannot be evaluated before the procedure due to conditions such as junctional rhythm, marked bradycardia (<50 bpm), or isorhythmic dissociation, randomization can be performed after the demonstration of PR with atrial pacing at a targeted atrial rate of 60 bpm during the procedure.

LBBAP group

• All pacemaker implantation should be performed in a standard manner.
• A lead should be placed in the right atrial appendage or septum where acceptable sensing (P wave >1mV) and pacing threshold (<1V at 0.4ms width) are achieved.
• V lead should be placed in the right ventricular septum where conduction system pacing can be achieved with acceptable sensing and pacing threshold. The pacing morphology should be compatible with His bundle pacing, right ventricular pacing, selective and non-selective left bundle branch pacing, or left fascicular pacing.

LBB pacing -Lead position deep in the interventricular septum, ~1-2cm from the distal His bundle potential, LBB potential to QRS interval in the range of 15-34 ms, normal QRS axis, fulfilled criteria for conduction system capture.

Left fascicular pacing

-Capture of the LBB fascicles or its distal arborization, short potential to QRS interval (<25ms), abnormal paced QRS axis with presence of criteria for conduction system capture. Pacing is more distant from the His bundle (2-4cm), defined as left anterior, mid-septal, and posterior fascicle.

Left ventricular septal pacing)

• Capture of the left side of the interventricular septum without direct activation of the left conduction system.
• Terminal R-wave in V1, deep septal position of the pacing lead in the basal to mid-septal area, absence of criteria for conduction system capture.

The primary objective for the LBBAP group is the achievement of conduction system capture with LBBAP. However, based on the physician's discretion or the situations in the operating room, His bundle pacing can be accepted as alternatives to LBBAP.

MVP group

• All pacemaker implantation should be performed in a standard manner.
• A lead should be placed in the right atrial appendage or septum where acceptable sensing (P wave >1mV) and pacing threshold (<1V at 0.4ms width).
• V lead should be placed in the right ventricular apex or septum where acceptable sensing (R wave >5mV) and pacing threshold (<1V at 0.4ms width).
• The RythmiQ™ mode should be turned on.
• Sensing and pacing AV intervals recommended to be >300ms (default value or more), and should not be <200ms to minimize the ventricular pacing.

Inclusion criteria

• >18 years old
• Sinus node dysfunction with symptoms
• Atrioventricular conduction delay (PR interval > 200ms)

Exclusion criteria

• Subject was unable to provide written informed consent or participate in long-term follow-up.
• Permanent atrial fibrillation
• Pre-existing cardiac implantable electronic device
• Persistent advanced atrioventricular conduction disturbance (2:1 block, Mobitz type II, or 3rd degree)
• Mechanical tricuspid valve
• Ventricular septal defect or scar
• Left ventricular ejection fraction < 35% who indicated cardiac resynchronization therapy
• Previous heart transplantation
• Pregnant and/or lactating women
• Life expectancy <2 year
• Patients who are actively participating in another drug or device investigational study, which have not completed the primary endpoint follow-up period