Conventional pacemakers involve placing a lead through a valve into the bottom right chamber of the heart. Research has shown that this approach is associated with an increased risk of valve dysfunction, mortality, and impairment of cardiac function.

Newer pacemakers, such as leadless pacemakers and pacemakers that engage directly with the heart's native conduction system (known as left bundle branch pacemakers), are increasingly being adopted. However, the impact of these newer pacing technologies on cardiac function and the tricuspid valve, as well as how they compare with each other, remains unclear.

The investigators aim to study the impact of leadless pacemakers and left bundle branch pacemakers on cardiac function and the tricuspid valve by conducting an acute study in addition to the routine pacemaker implantation procedure for which participants have been referred. Both procedures will be performed during a single session under general anaesthesia. Outcomes from this study will improve understanding of how these pacing technologies affect cardiac and valvular function and how they compare with each other. These findings will help guide decision-making regarding the optimal type of pacemaker to adopt, particularly for patients at greatest risk of developing tricuspid valve dysfunction or impaired cardiac function.

Transvalvular right ventricular pacing (TVP) is a guideline-directed first-line treatment for high-degree AV block and sick sinus syndrome. However, TVP is associated with an increased risk of pacing-induced cardiomyopathy (PIM), tricuspid regurgitation (TR), and right ventricular dysfunction (RVD). Leadless right ventricular pacing (LP) and left bundle branch area pacing (LBBAP) are emerging as attractive alternatives to conventional TVP. While preliminary studies have investigated the impact of LP and LBBAP on left ventricular function, there is limited information on how these modalities compare with each other and their effects on right ventricular and tricuspid valve function. The investigators aim to perform an acute mechanistic study involving a head-to-head comparison of LBBAP and LP to evaluate their acute effects on biventricular and tricuspid valve function.

EXPERIMENTAL DETAILS AND DESIGN

Study design: Twenty patients will be prospectively recruited and undergo an acute mechanistic study during the same session prior to undergoing their allocated permanent pacemaker implantation, which will be performed according to standard clinical practice.

Study population

Inclusion criteria: Patients aged ≥18 years referred for permanent pacemaker implantation at a single centre (Guy's and St Thomas' NHS Foundation Trust, UK) with high-degree AV block, including Mobitz II and complete heart block, or scheduled for AV node ablation, and with LVEF ≥50%.

Exclusion criteria: LVEF <50%, severe TR, severe RV dysfunction, clinically unstable AV block requiring temporary pacing or isoprenaline infusion, left bundle branch block, previous tricuspid valve annuloplasty or replacement, aortic valve replacement, life expectancy <1 year, end-stage renal failure, contraindication to cardiac MRI, CT, or TOE, pregnancy, contraindication to anticoagulation, peripheral vascular disease precluding insertion of femoral catheters, or insufficient capacity to provide informed consent.

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Meta-analysis: Studies comparing PIM rates between TVP and LP have yielded mixed results. As part of this fellowship, the investigator will also perform a systematic review and meta-analysis comparing the rates of PIM between LP and TVP to provide a more definitive assessment of whether LP is superior to TVP in reducing the incidence of PIM.

OUTCOME MEASURES AND STATISTICAL ANALYSIS

Hypothesis 1: There is a significant difference in the risk of acute PIM between LP and LBBAP.

Acute PIM will be assessed using TOE. A χ² test will be used to compare the proportion of acute PIM between the LBBAP and LP pacing configurations.

Hypothesis 2: LP is associated with a lower risk of acute TR progression compared with LBBAP.

Acute TR progression will be assessed using TOE by evaluating the degree of TR at baseline and during temporary pacing. A χ² test will be used to compare the proportion of TR progression between the LBBAP and LP pacing configurations.

Hypothesis 3: There is no significant difference in the risk of acute RVD between LP and LBBAP.

Acute RVD will be assessed using TOE by measuring TAPSE, RVEF, and RV GLS at baseline and during temporary pacing. Analysis of variance (ANOVA) will be used to compare the mean changes in TAPSE, RVEF, and RV GLS between the LBBAP and LP pacing configurations.

Mechanistic hypotheses

Hypothesis 4: LBBAP is associated with less electrical dyssynchrony compared with LP.

Electrical dyssynchrony will be assessed using ECGi by measuring VEU and LVDI at baseline and during the LBBAP and LP pacing configurations. ANOVA or the Kruskal-Wallis test will be used, depending on data distribution, to compare VEU and LVDI between the LBBAP and LP pacing configurations.

Hypothesis 5: LBBAP is associated with a higher rate of positive acute haemodynamic response than LP.

Acute haemodynamic response will be assessed using intracardiac pressure wires to measure LV dP/dt and RV dP/dt at baseline and during the LBBAP and LP pacing configurations. ANOVA will be used to compare LV dP/dt and RV dP/dt between the LBBAP and LP pacing configurations.

Hypothesis 6: There is no significant difference in activation times and electrical dyssynchrony measurements produced by in silico modelling and in vivo ECGi studies.

Activation times and electrical dyssynchrony will be compared between the in silico modelling and in vivo ECGi studies. Specifically, LVAT, BVAT, VEU, and LVDI will be compared between the two groups using the Student's t-test or Mann-Whitney U test, depending on data distribution.

Inclusion Criteria:

• All patients aged ≥18 referred for a permanent pacemaker at a single centre (Guys and St. Thomas' NHS Foundation Trust, UK) with high degree AV block, including Mobitz II and complete heart block, or scheduled AV node ablation, and LVEF ≥50%.

Exclusion Criteria:

• LVEF <50%, severe TR, severe RV dysfunction, clinically unstable AV block requiring temporary pacing or isoprenaline infusion, left bundle branch block, previous TV annuloplasty or replacement, aortic valve replacement, life expectancy <1 year, end-stage renal failure, contraindication to cardiac MRI, CT or TOE, pregnancy, contraindication to anticoagulation, peripheral vascular disease precluding insertion of femoral catheters and insufficient capacity to consent to the study.

All patients referred for permanent pacemaker implantation with preserved LVEF at baseline.