count the number of patients who were diagnosed with status-post ptca within the same month after late effect cv dis nos since 4 years ago.
select count( distinct t1.subject_id ) from ( select admissions.subject_id, diagnoses_icd.charttime from diagnoses_icd join admissions on diagnoses_icd.hadm_id = admissions.hadm_id where diagnoses_icd.icd9_code = ( select d_icd_diagnoses.icd9_code from d_icd_diagnoses where d_icd_diagnoses.short_title = 'status-post ptca' ) and datetime(diagnoses_icd.charttime) >= datetime(current_time,'-4 year') ) as t1 join ( select admissions.subject_id, diagnoses_icd.charttime from diagnoses_icd join admissions on diagnoses_icd.hadm_id = admissions.hadm_id where diagnoses_icd.icd9_code = ( select d_icd_diagnoses.icd9_code from d_icd_diagnoses where d_icd_diagnoses.short_title = 'late effect cv dis nos' ) and datetime(diagnoses_icd.charttime) >= datetime(current_time,'-4 year') ) as t2 on t1.subject_id = t2.subject_id where t1.charttime < t2.charttime and datetime(t1.charttime,'start of month') = datetime(t2.charttime,'start of month')