How to prevent internal bleeding from blood thinners

I'm a 78 yro male with chronic heart disease. I have had atrial fibrillation and that has caused cardiac blood clots built up. In order to cure my atrial fibrillation, my doctor needs to do a electrical shock to my heart to reset the rhythm. In order to do this electrical shock, my doctor needs to clear up the blood clot to a satisfactory level to reduce the risk of having a stroke during the electrical shock. He prescribed me a strong blood thinner named pradaxa for 4 weeks but unfortunately I had severe bleeding from duodenum days ago due to the common side effect from blood thinners.  So I needed to stop taking any blood thinners at the moment. I was prescribed with Nexium from the GI doctor to cure my duodenum ulcer/bleeding first.

My problem is I have to be back on pradaxa ASAP. What drugs can help preventing gastro bleeding while taking pradaxa? Any suggestion is appreciated.