Many, many (many) time I went to the e.r. with symptoms you describe, only to be told 'it sn't a heart attack, given a g.i. coctail, & sent home asymptomatic.
You surely know my now, from your own research that pericarditis is inflamation of the paricardium. As for the imaging showing 'shards of blood clots' they may have been seondary to your presenting symptoms, & may have pre-existed before your arrival @ the e.r.