What Causes Sudden Outbreak Of Hives In A Person With Heart Disease?

i have congestive heart failure, with internal defib recently had ablation surgery and have had hives ever since. They have been unbearable for the past two weeks my entire body burns from scratching I know I m not supposed to scratch but sometimes its impossible not to. My dr. hasnt found a reason for the hives wondering if it could have anything to do with my illness? Thank you