What medical problems can occurr after implantation of pacemakers?

There are many. Early: bleeding into the pacemaker pocket / infection, lead dislodgment, perforation, arrhythmias. Late: infection, arrhythmias, pacemaker malfunction anytime: pacemaker syndrome (also known as av dyssynchrony syndrome) symptoms may not improve if the indication for pacemaker insertion were soft or not really present. This is not uncommon.