Cardiac pacing is the only effective treatment for symptomatic bradycardia. The right ventricular apex (RVA) has become the most frequently used ventricular pacing site. However, RVA pacing has been shown to cause left ventricular (LV) dyssynchrony wich can lead to LV dysfunction and development of heart failure. Recent studies in animals have demonstrated that pacing at the LV septum induces significantly less ventricular dyssynchrony than RVA pacing and is able to improve LV function to a similar degree as biventricular (BiV) pacing. In addition it was shown that a LV septum lead can be placed permanently by driving a lead with extended helix from the RV side through the inter-ventricular septum into the LV endocardial layer. This was shown to be a feasible and safe procedure and lead stability was shown during four months of follow-up in otherwise healthy and active canines. LV septum pacing may therefore be a good treatment alternative in patients with symptomatic bradycardia, as well as patients with an indication for cardiac resynchronization therapy (CRT). The purpose of this study is to translate the findings from preclinical studies to the clinical situation by investigating the feasibility, long-term lead stability and safety of LV septum pacing by transvenous approach through the inter-ventricular septum in patients.

Cardiac pacing is the only effective treatment for symptomatic bradycardia. After the introduction of the implantable pacemaker (PM), the right ventricular apex (RVA) has become the most frequently used ventricular pacing site. However, clinical studies have shown that RVA pacing leads to left ventricular (LV) dyssynchrony, and on the long run to adverse structural changes (remodeling), a higher risk of developing atrial fibrillation and heart failure, and higher mortality.

Recognition of the adverse effects of RVA pacing has generated interest in alternative ventricular pacing sites. Recent studies in animals have shown that pacing at the LV septum induces significantly less ventricular dyssynchrony than RVA pacing. In addition it was shown that a LV septum lead can be placed permanently by introducing a custom lead with extended helix transvenously and, after positioning it against the RV septum, driving it through the inter-ventricular septum into the LV endocardial layer. This was shown to be a feasible and safe procedure and lead stability was shown during four months of follow-up in otherwise healthy and active canines.

Animal studies have also shown that LV septum pacing is able to improve LV function to a similar degree as simultaneous biventricular (BiV) pacing used in cardiac resynchronization therapy (CRT). CRT was introduced to restore the abnormal ventricular activation and contraction in patients with heart failure and intra-ventricular conduction delay. Large clinical trials have shown that CRT improves LV systolic pump function, reverses structural remodelling, improves quality of life and exercise tolerance, and decreases mortality. Unfortunately, problems encountered during positioning and fixation of the LV pacing lead in the coronary vein result in suboptimal or loss of CRT in at least a quarter of CRT candidates and require re-operation in 7% during follow up.

The adverse effects of RVA pacing, the limitations of BiV pacing and the promising effects of LV septum pacing in preclinical studies have led to the idea that LV septum pacing may be a good treatment alternative in patients with symptomatic bradycardia, as well as patients with an indication for CRT. In the latter category, CRT could then be performed using a single ventricular pacing lead, thus limiting the number of lead implantations, and thereby reducing complication rate and implantation costs as well as avoiding the difficult access route through the coronary vein.

It is the aim of this study to translate the findings from preclinical studies to the clinical situation by investigating the feasibility, long-term lead stability and safety of LV septum pacing by transvenous approach through the inter-ventricular septum in patients with a PM or CRT indication. The results may have a large impact on future pacing therapy. The LV septum may become the universal pacing site, being preferred for anti-bradycardia therapy, and being an equal alternative for BiV pacing, but easier to apply, less invasive and more cost-effective.

Inclusion Criteria:

1. Cardiac pacing indication for sinus node dysfunction (dual chamber pacemaker) or indication for CRT (BiV pacemaker).

   • Patient with sinus node dysfunction:
   • Normal left ventricular ejection fraction (LVEF > 50%)
   • Left ventricular end-diastolic diameter (LVEDD) < 55mm
   • QRS duration < 100ms
   • Patient with CRT indication:
   • Non-ischemic cardiomyopathy
   • LVEF is < 35%
   • Typical left bundle-branch block on surface ECG
   • QRS duration >150ms
   • NYHA functional class I-III

2. Greater than 18 years of age

3. Stable sinus rhythm at the time of inclusion

4. Willing and capable of giving informed consent

Exclusion Criteria:

1. Ventricular pacing dependent
2. High degree AV block
3. Previous septal myocardial infarction
4. Previously implanted pacing device
5. Abnormal venous anatomy
6. Left ventricular septum wall thickness >10mm determined by echocardiography
7. Presence of severe valvular disease
8. Presence of an ongoing progressive terminal disease associated with a reduced likelihood of survival for the duration of the study

Study subjects are recruited from patients referred to the out-patient pacemaker/ICD clinic of our hospital.