Cardiac Surgical ProceduresPerioperative CareIntraoperative ComplicationsDipyridamolePostoperative ComplicationsSurgical Procedures, OperativePreoperative CareHeart DiseasesPerioperative PeriodVascular Surgical ProceduresSurgical Procedures, ElectiveAnesthesiaRisk AssessmentHeart ArrestTreatment OutcomeThallium RadioisotopesRetrospective StudiesRisk Factors