What could cause a pulsation after having a pacemaker implanted?

Symptoms such as you describe could be caused by a number of problems, including lead perforation or pacemaker syndrome. Here is more information on those problems:

Lead perforation. The wires (also called leads, pronounced leeds) that deliver tiny pulses of electricity to the heart usually stay where a doctor places them. Sometimes, though, a lead can move out of position and poke through the heart muscle and into the sac around the heart (the pericardium), the chest wall, or the diaphragm. Perforation can cause symptoms ranging from shortness of breath or chest pain to cough, constant hiccups, or abdominal pain.

Pacemaker syndrome. This uncommon condition occurs when a pacemaker throws off the careful coordination between the beating of the upper and lower chambers of the heart. It can create a wide variety of symptoms, such as dizziness, shortness of breath, fatigue, feeling a pulsation in the neck or abdomen, headache, or extra chest colds.

Someone with symptoms like yours should consult a cardiologist or an electrophysiologist (a doctor who specializes in heart rhythm problems). Diagnosing the problem usually requires an x-ray and an electrocardiogram, as well as tests of the pacemaker to determine how it is working.