Q. Why are palpitations occurring even after pacemaker implantation?

Hello doctor,

My 71-year-old father was admitted to the hospital for palpitation occurrence and fast heart beating at 143 beats per minute. He was feeling dizziness in the morning. He was given injections to reduce the heart rate and has taken Holter monitoring for one day. He had previously undergone two stent placements for blocks. According to his Holter reading, the doctor said his heart pauses for two seconds sometime in 24 hours. He has both bradycardia and tachycardia. They suggested him a biventricular pacemaker implantation that is a St. Jude medical pacemaker. He is allergic to Penicillin. During his discharge, he was prescribed the following medicines: Prolomet XL 25 mg two times a day, Xarelto once a day, Glycomet-GP 1 one and a half tablets a day, Ecosprin AV 150/10 capsules one a day, and Pantocid one a day. He takes his medicines regularly but once in 10 days, the palpitation occurs for about 10 to 15 minutes ranging 20 and sometimes 105 and then it stops. Palpitation does not come every day. The doctor says there is no need to worry. My concern is why does the palpitation occur even after the pacemaker implantation. Is there any way to stop the palpitation? Is it a serious issue. Please help me.