In USA a single chamber pacemaker is generally indicated for patients with chronic atrial fibrillation with concomitant symptomatic bradycardia such as seen with AV block de novo or after creation of complete heart block for definitive rate control measure. A single chamber pacemaker in the Right atrium among patients with sick sinus syndrome with intact AV nodal function in my opinion is a legit indication, although rarely practiced in US.

As for technical aspect of implantation, it is a relatively simple procedure as you have to implant a single lead. Pacemaker generator is smaller. Procedure time is shorter. Complication rates are lower as you only need a single needle stick to get venous access.

With a single chamber permanent pacemaker implantation in RV apex, their is increased risk of atrial fibrillation, thrombo-embolism and poorer survival. If we need to implant a single chamber PPM in RV the preferable site is RV outflow tract. Data from DAVID trial suggest that at least in patients with poor LV systolic function the outcomes are worse for RV pacing.

More recent article suggest that on long term follow up RV pacing in apex as compared to RVOT is associated with poorer outcome.

Abdul Wase MD FACC FACP FHRS

Dayton, OH

USA

The difference between single and dual chamber pacemakers is essentially in the fact that a single chamber pacemaker has only one lead implanted (typically in the right ventricle) and a dual chamber has two, one in the atrium and one in the RV.

From an EP point of view, the only true indication for a ventricular based single chamber device is chronic atrial fibrillation with pauses or bradycardia.

Single chamber atrial based pacing can be used in sinus node diseased without concommitant AV node disease. This can be tested at implant by pacing AAI at 130-140bpm and ensuring there is one to one AV conduction. In saying that most physicians will implant a dual chamber device as about 3-5% of people with sinus node disease will develop AV node disease per year.

Whether physiological pacing (AAI or DDD) gives a clinical benefit over VVI pacing has been the subject of a number of randomised multicentre trials. In summary most benefir is seen in patients with Sinus node disease with reduction in AF, embolic events, and heart failure hospitalisations. The DANISH study in the second report demonstrated a mortality benefot for AAI vs VVI. In AV block patients the evidence is less strong particularly in patients >75yrs (UKPACE trial). The evidence in AV block patients may be muddied by the deleterious effects of unwanted RV apical pacing.

Without doubt the follow-up of a dual chamber device is more complicated and needs more expertise in terms of optimising the device to the patient and requires more understanding of device timing cycles, particulalrly with respect to the upper rate beaviour of the pacemker