My Husband Has Had A Pacemaker For Almost 5 Years

my husband has had a pacemaker for almost 5 years now and he has lately been having a lot of muscle spasms in his chest where the pacemaker is located it says it feels like a grabbing sensation but he has his pacemaker and heart monitored he reads his heart rates through a machine which in turns sends the reading to his hospital. The last time we went for his checkup the reading did not show any problems with his heart so I am wondering what this could be?