Here is the link to the world's smallest transcathether pacemaker system. 99.2% implant success rate and 0% chance of infection in 725 patients that underwent global trial. Used for paroxysmal AV block, bradyarrythmias and sinus bradycardia (CVS lecture).The pacemaker is size of a vitamin pill. Once inserted it is difficult to remove after encapsulation because of the development of fibrotic tissue.

http://www.medtronic.com/us-en/healthcare-professionals/products/cardiac-rhythm/pacemakers/micra-pacing-system.html