ConTempoRary Cardiac Stimulation in Clinical practicE: lEft, BivEntriculAr, Right, and conDuction System Pacing

Cardiac pacing with implantable electronic cardiac devices and transvenous leads has been introduced since 1960 and is considered a safe, effective and low-risk therapy. The most common indications for permanent cardiac pacing are sinus node dysfunction and atrioventricular blocks. In Europe, pacemaker implants exceed 1000 per million inhabitants. The aim of this therapy is not only to improve patients survival but also their quality of life, which is an essential aspect in assessing patients clinical status and prognosis.

Nowadays, five types of cardiac pacing are recognised in clinical practice:

• Endocardial right chambers pacing: the device is implanted in the subcutaneous subclavian area and it is connected to transvenous leads implanted in the right cardiac chambers, which detect intrinsic electrical activity and stimulate when needed;
• Epicardial pacing: this procedure is often performed in conjunction with cardiac surgery;
• Cardiac resynchronisation therapy (CRT): it delivers biventricular or left ventricular pacing in order to correct interventricular electromechanical dyssynchrony and to improve cardiac output;
• Conduction system pacing: it stimulates the His bundle or the left bundle branch area downstream of the conduction block, in order to restore a physiological electromechanical activation.
• Leadless pacing: via a percutaneous approach through a large-calibre vein, leadless device is placed inside the right ventricle.

These pacing modalities have different possibilities to restore a normal cardiac electromechanical activation, resulting in different degrees of mechanical efficiency in terms of systolic output and diastolic pressures, with consequent effects on improvement/onset of heart failure and cardiopulmonary performance of our patients.

Right ventricular pacing induces a dyssynchronous cardiac activation pattern that can lead to left systolic dysfunction and a consequent increased risk of death related to the development of heart failure.

These observations led to the study of alternative cardiac pacing modalities since the 1990s, in order to improve the clinical outcome of patients with symptomatic bradyarrhythmias. The study of pathological ventricular activation due to left bundle-branch block represents the pathophysiological premise of cardiac resynchronisation in patients with systolic dysfunctional heart failure, and constitutes the developmental model for physiological pacing.

CRT improves mortality and quality of life in patients with heart failure and reduced left ventricular ejection fraction. Typically left ventricular pacing is achieved by placing a catheter in the posterolateral area through a venous branch of the coronary sinus. Unfortunately, despite several years of experience in this field, clinical non-response to this therapy is observed in between 20% and 40% of patients, mostly due to the inability to reach the appropriate pacing site because of anatomical difficulties/absence of veins in the target area.

Recently, conduction system pacing (CSP) has rapidly emerged as an alternative pacing modality to both right ventricular pacing (RVP) and CRT, in order to achieve a more physiological pacing. His bundle pacing (HBP) is considered the physiological pacing "par excellence", but the results in literature show rather frequent technical difficulties due to high pacing thresholds, inadequate ventricular signal amplitude for the detection of intrinsic cardiac activity, low success rate and risk of progression of conduction system pathology in patients with infranodal conduction defects.

Left bundle area pacing has more recently emerged as a viable alternative to achieve physiological pacing with haemodynamic parameters similar to those of HBP, but with lower and stable pacing thresholds, ventricular signal amplitude adequate for the detection of intrinsic cardiac activity and high success rate.

Several experiences with different pacing systems have been published, mainly single-centre studies with small sample sizes and different definitions of conduction system pacing success.

In non-randomised comparative studies, and thus with methodological limitations, clinical superiority over conventional right ventricular pacing, and a substantial efficacy equivalent to CRT in patients with left bundle-branch block, has been shown, creating the preconditions for widespread use of the CSP.

Considering, therefore, the widespread use of the latter technique and the high rate of implants that can potentially benefit from physiological pacing, evaluating safety, feasibility, timing and benefits becomes more crucial than ever.

Therefore, the goal of this observational study is to evaluate the clinical characteristics of patients undergoing permanent cardiac pacing and to compare procedural efficacy and safety of different implantation approaches in the clinical practice of the participating centres.

The contribution of non-fluoroscopic anatomical and electrophysiological reconstruction systems to device implantation procedures will also be evaluated.

The investigators will collect clinical and procedural data from patients with an indication for permanent cardiac pacing who have consecutively undergone an implantable electronic device implant procedure at the Electrophysiology Laboratories of the participating centres over a period of 120 months from the time of approval with a follow-up of an equal 120 months.

Patients will be classified according to the type of stimulation:

1. Right chambers endocardial pacing;
2. Cardiac resynchronisation therapy;
3. Conduction system pacing:
4. His bundle pacing
5. Left bundle branch area pacing. In addition, the efficacy and safety at 30 days, and the efficacy and safety at 6 and 12 months of the various pacing modalities, will be evaluated.

The investigators defined efficacy at 30 days the presence of stable electrical parameters - or, if unstable, not requiring early re-intervention, the absence of cardiovascular hospitalizations and the absence of cardiovascular death.

The investigators defined safety at 30 days the absence of procedural complications, such as haematoma requiring re-intervention or with haemoglobin loss >2gr/dl, pneumothorax, pericardial effusion requiring drainage, lead dislocation, cardiac implantable electronic device (CIED) infection or a re-intervention for any cause.

Equally, the investigators defined efficacy at 6-12 months the presence of stable electrical parameters - or, if unstable, not requiring re-intervention, the absence of cardiovascular hospitalizations, the absence of cardiovascular death, the occurrence of heart failure, the occurrence or worsening of atrial or ventricular tachyarrhythmias.

Therefore, the investigators defined safety at 6-12 months the proper functioning of the device, the absence of infection and the absence of re-intervention for any cause.