how many times patient 84042 had received a lt heart angiocardiogram procedure since 6 years ago.
select count(*) from procedures_icd where procedures_icd.icd9_code = ( select d_icd_procedures.icd9_code from d_icd_procedures where d_icd_procedures.short_title = 'lt heart angiocardiogram' ) and procedures_icd.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 84042 ) and datetime(procedures_icd.charttime) >= datetime(current_time,'-6 year')