Table 1 Abbreviations

Outcome measures

The efficacy outcomes included successful implantation rate, adequate pacing performance, 6-minute walk test (6MWT), cardiac function, length of hospital stay, health-related quality of life and device durability. Safety outcomes included cardiac perforation, cardiac tamponade, pericardial effusion, pulmonary oedema, AF, device failure (dislodgement, migration, embolisation, malfunction, battery issues), repeat surgery (for device retrieval and revisions), venous thromboembolism, vascular complications, bleeding, infections, mortality, pacemaker syndrome, cardiomyopathy, pericarditis, activity restrictions, overall complication rates and other device- or procedure-related adverse events. Some of the measures used which are not self-explanatory are detailed in the following paragraphs.

Adequate pacing performance

Adequate pacing performance is evaluated based on several key parameters. The pacing threshold, or capture threshold, should ideally be less than or equal to 1.5 V at 0.4 ms pulse width for ventricular pacing (VP) and less than or equal to 1.0 V at 0.4 ms pulse width for atrial pacing, with lower values preferred to reduce battery consumption and ensure effective capture. Sensing amplitude, which reflects intrinsic signal detection, should be 5 mV or more for ventricular sensing (R-wave amplitude) and 1.5 mV or more for atrial sensing (P-wave amplitude) to ensure proper sensing and minimise the risk of under-sensing events. Pacing impedance, which helps assess lead integrity and connection, should be between 300 to 1,500 ohms. Values outside this range may indicate lead failure, insulation damage, or poor connection. The percentage of VP should ideally be less than 40% in non-dependent people to minimise unnecessary pacing but should be 100% in pacemaker-dependent individuals. AV synchrony of more than or equal to 90% is considered optimal for dual-chamber pacemakers, ensuring physiological pacing and reducing the risk of AF.

Global Longitudinal Strain (GLS)

GLS is an advanced echocardiographic parameter that measures myocardial deformation, reflecting left ventricular (LV) systolic function more sensitively than ejection fraction (EF). It quantifies the percentage of myocardial shortening during contraction, with more negative values indicating better function. The normal range for GLS is typically between -18% to -22%, with values closer to zero suggesting impaired LV function. A GLS less negative than -16% is often considered abnormal and may indicate early myocardial dysfunction.

Right Ventricular Free Wall Strain (RVFWS)

Right Ventricular Free Wall Strain (RVFWS) is an echocardiographic measure of the deformation of the RV free wall during contraction. The normal range for RV free wall strain is typically more negative than -20%, with values less negative than -17% suggesting impaired RV function.

Tricuspid Annular Plane Systolic Excursion (TAPSE)

TAPSE is a measure of right ventricular (RV) function that evaluates RV longitudinal systolic performance. TAPSE is measured using TTE and the systolic displacement of the annulus is recorded in millimetres. A lower TAPSE value, typically less than 17 mm, suggests impaired RV function and is often seen in conditions such as pulmonary hypertension (HTN) and heart failure.

Mitral Annular Plane Systolic Excursion (MAPSE)

MAPSE assesses the longitudinal contraction of the LV myocardium, to evaluate LV function. Like TAPSE, MAPSE is measured using TTE, recording the displacement of the mitral annulus during systole. Normal values usually exceed 10 mm. A reduced MAPSE value indicates impaired LV function, which is commonly seen in people with heart failure or cardiomyopathy.

N-terminal pro B-type Natriuretic Peptide (NT-pro-BNP)

NT-pro-BNP is a biomarker that reflects cardiac stress and heart failure. It is released by the heart in response to increased ventricular wall tension due to volume overload or myocardial dysfunction. Elevated NT-pro-BNP levels are associated with worsening heart failure, with values above 125 pg/mL in non-acute settings or 300 pg/mL in acute settings indicating a significant risk of heart dysfunction.

Health-related Quality of Life
The SF-36 is a widely used questionnaire that measures health-related quality of life (HRQoL) across eight domains, including physical and mental health. Each domain is scored from 0 to 100, with higher scores indicating better health. Scores are summarised into physical and mental component scores, standardised to a mean of 50 (SD 10). Normal values in the general population typically range from 70 to 95, and a change of 5–10 points is considered clinically meaningful. It is commonly used to assess the impact of illness or treatment on peoples' overall well-being.

The 6-Minute Walk Test (6MWT)

6MWT is a functional exercise test used to evaluate a person's cardiovascular endurance and overall functional capacity. During the test, the person is instructed to walk as far as possible within 6 minutes on a flat, measured surface. The total distance covered in metres is recorded and compared over time to assess disease progression or response to treatment. A normal 6MWT distance varies by age, sex, and comorbidities, but in healthy adults, it typically ranges from 400 to 700 metres. Distances below 300 metres often indicate significant impairment in cardiovascular or pulmonary function.