Hello! thanks for your query, I understand your query, His shivering(chills) may or may not be due to his pacemaker placement. Shivering(chills) is a sign of an ongoing infection especially when accompanied by fever. Although rare, he may be experiencing an endocarditis following his pacemaker placement. Endocarditis is when the inner lining(endocardium) of your heart is inflamed. With implanted cardiac pacemakers, bacteria may have entered the blood stream. I suggest you to take Him to His cardiologist for further laboratory work up such as complete blood count, blood culture and echocardiography. If an endocarditis is confirmed he may be asked to take antibiotics accompanied by immediate surgical removal of the entire pacing system. Hope this helps, a feedback is greatly appreciated. Thank You.