mosseri et al.1 ) reported that conduction disturbances were more frequent in patients with compromised blood flow of the septal branches after coronary artery bypass grafting ( cabg ) operation . they analyzed the association of conduction disturbance and the location of cad in 43 patients , who had permanent pacemaker implantation and coronary angiography ( cag ) , by classifying coronary pathology into 4 categories ( table 1 ) , and reported that compromised blood flow to septal branch and right coronary artery ( rca , type iv anatomy ) was significantly associated with severe conduction disturbances.2 ) henceforward , several studies reported the predominance of type ii and type iv anatomy in patients with severe conduction disturbance.3)4 ) although there are several studies supporting the causal relationship of conduction disturbances and underlying coronary anatomy , this association is not clear , particularly from the view of avb reversibility . in a study by omeroglu et al.5 ) 8 patients with cad and complete avb were treated with cabg operation , but none of these patients recovered from complete avb after revascularization . yesil et al.6 ) investigated 53 patients who had third - degree avb and significant cad , and the result showed only a small percentage of patients recovered from a third - degree avb ( 19% in medical and 27% in interventional treatment ) without statistically significant difference . these studies may indicate that revascularization is not helpful in the recovery of conduction disturbances . in this regards , we evaluated the association of avb and cad , to elucidate whether avb is reversible in patients with cad . this study was approved by the institutional review board of seoul national university hospital ( irb no . h-1109 - 011 - 376 ) . from january 2005 to june 2011 , 280 consecutive patients with clinically - significant new - onset avb admitted to seoul national university hospital via outpatient clinic or emergency department were enrolled . clinically - significant avb requiring pacemaker was defined as follows ; complete avb and advanced avb including 2 : 1 avb . ninety - two patients , who underwent pacemaker revision and implantable loop recorder insertion , were excluded and total 188 patients were analyzed in this study ( fig . baseline demographic variables of gender , age , height , weight , body mass index ( kg / m ) , smoking status and amount of smoking in pack - year , history of diabetes mellitus , hypertension , hypercholesterolemia , renal insufficiency , cerebrovascular accident , atrial fibrillation , cad , prior revascularization therapy ( including percutaneous coronary intervention and cabg ) , other prior open heart surgeries , cardiomyopathies , congenital heart disease , valvular heart disease , a family history of sudden cardiac death , and a family history of premature cad in first - degree relatives ( < 55 years in males and < 65 years in females ) were identified based on the electronic medical records . coronary artery disease was determined on the result of cag , coronary ct angiography , and myocardial single photon emission computerized tomography ( spect ) . significant cad was defined as > 50% stenosis of epicardial coronary artery by cag and coronary ct angiography , or perfusion decrease of myocardial spect . coronary pathologies were classified into 4 types according to classification of mosseri et al.2 ) ; type i , lesions not related to septal branches or the atrioventricular ( av ) node ; type ii , lesions compromising blood supply to septal branches emerging from the left anterior descending artery ( lad ) ; type iii , lesions compromising blood supply to the av node ; and type iv , lesions compromising blood supply both to septal branches emerging from the lad and to the av node ( table 1 ) . when determining coronary pathologies , results of myocardial spect were not counted , as it could not designate the specific location . the  test or the fisher exact test was used for categorical variables . to evaluate the association of cad and conduction disturbance which require implantation of permanent pacemaker , univariate and multivariate all statistical analyses were performed with software , statistical package for the social sciences ( spss ) 18.0 ( spss inc . , chicago , il , usa ) and a p<0.05 was considered statistically significant . this study was approved by the institutional review board of seoul national university hospital ( irb no . h-1109 - 011 - 376 ) . from january 2005 to june 2011 , 280 consecutive patients with clinically - significant new - onset avb admitted to seoul national university hospital via outpatient clinic or emergency department were enrolled . clinically - significant avb requiring pacemaker was defined as follows ; complete avb and advanced avb including 2 : 1 avb . ninety - two patients , who underwent pacemaker revision and implantable loop recorder insertion , were excluded and total 188 patients were analyzed in this study ( fig . baseline demographic variables of gender , age , height , weight , body mass index ( kg / m ) , smoking status and amount of smoking in pack - year , history of diabetes mellitus , hypertension , hypercholesterolemia , renal insufficiency , cerebrovascular accident , atrial fibrillation , cad , prior revascularization therapy ( including percutaneous coronary intervention and cabg ) , other prior open heart surgeries , cardiomyopathies , congenital heart disease , valvular heart disease , a family history of sudden cardiac death , and a family history of premature cad in first - degree relatives ( < 55 years in males and < 65 years in females ) were identified based on the electronic medical records . coronary artery disease was determined on the result of cag , coronary ct angiography , and myocardial single photon emission computerized tomography ( spect ) . significant cad was defined as > 50% stenosis of epicardial coronary artery by cag and coronary ct angiography , or perfusion decrease of myocardial spect . coronary pathologies were classified into 4 types according to classification of mosseri et al.2 ) ; type i , lesions not related to septal branches or the atrioventricular ( av ) node ; type ii , lesions compromising blood supply to septal branches emerging from the left anterior descending artery ( lad ) ; type iii , lesions compromising blood supply to the av node ; and type iv , lesions compromising blood supply both to septal branches emerging from the lad and to the av node ( table 1 ) . when determining coronary pathologies , results of myocardial spect were not counted , as it could not designate the specific location . the  test or the fisher exact test was used for categorical variables . to evaluate the association of cad and conduction disturbance which require implantation of permanent pacemaker , univariate and multivariate logistic regression analysis all statistical analyses were performed with software , statistical package for the social sciences ( spss ) 18.0 ( spss inc . , chicago , il , usa ) and a p<0.05 was considered statistically significant . irreversible avb was observed in 173 patients ( ib group ) who had undergone implantation of a permanent pacemaker . there were significant differences in gender , smoking status , and serum level of high density lipoprotein - cholesterol ( hdl - c ) and c - reactive protein ( crp ) between the 2 groups . in the ib group , 75 ( 43.4% ) were male and 11 ( 6.4% ) were current smokers , while rb group had 11 ( 73.3% ) males and 4 ( 26.7% ) current smokers ( p=0.031 for gender , p=0.021 for smoking status ) . serum level of hdl - c was higher in ib group ( 46.5610.95 mg / dl vs. 40.0010.07 mg / dl , p=0.030 ) , whereas crp was higher in rb group ( 0.531.24 mg / dl vs. 1.991.80 mg / dl , p=0.014 ) . there was no difference in other characteristics between the two groups . in the ib group , 129 ( 74.6% ) had no cad on admission , 40 ( 23.1% ) had stable angina , 2 ( 1.2% ) presented with unstable angina , and 2 ( 1.2% ) presented with acute myocardial infarction ( ami ) . in contrast , the rb group had 13 ( 86.7% ) with ami , one ( 6.7% ) with stable angina , and one ( 6.7% ) without cad on admission ( p<0.001 ) . on the aspect of cad type and reversibility of avb , 13/15 ( 86.7% ) patients had ami , 0/2 ( 0% ) had unstable angina , and 1/41 ( 2.4% ) with stable angina had reversible avb ( fig . the proportion of reversible avb in patients with ami was significantly higher than other groups ; patients without cad , with stable angina , and with unstable angina . the reversibility of avb was analyzed according to the distribution of coronary pathology ( table 3 ) . 43 ( 24.9% ) of 173 patients in the non - ami group and 15 ( 100.0% ) of 15 patients in the ami group had cad . avb was rarely reversible in the non - ami group as only one of 43 patients ( 2.3% ) showed reversible avb . in contrast , 13 of 15 patients with ami ( 86.7% ) had reversible avb and there were significant difference between non - ami group and ami group ( p<0.001 ) . among 15 patients with ami , 11 patients had inferior wall st - segment elevation myocardial infarction ( stemi ) and 1 patient had anterior wall stemi . there were 2 patients with ami in ib group , showing inferior and anterior wall stemi for each . rca lesions were found in 25 ( 15.0% ) in the non - ami group and 14 ( 93.3% ) in the ami group ( p<0.001 ) by cag . the proportion of reversible avb among patients with rca lesion was also significantly higher in ami group ( p<0.001 ) . according to mosseri et al's2 ) classification , the number of patients with cad in the non - ami group were : 4 ( 9.3% ) type i anatomy , 9 ( 20.9% ) type ii anatomy , 7 ( 16.3% ) type iii anatomy , and 23 ( 53.5% ) type iv anatomy . one patient whose avb was reversible had type iii anatomy . in the ami group , according to this same classification system , no patients had type i anatomy , 1 ( 6.7% ) patient had type ii , 5 ( 33.3% ) patients had type iii , and 9 ( 60.0% ) patients had type iv . the proportions of reversible avb in type iii and type iv were higher in the ami group ( p=0.072 for type iii and p<0.001 for type iv ) . the composite of type ii and iv , in which septal blood flow of lad is compromised in common , was found in 32 ( 74.4% ) patients from the non - ami group and avb was irreversible in all patients , while the composite was found in 10 ( 66.6% ) patients of ami group and 9 ( 90.0% ) patients had reversible avb ( p<0.001 ) . among demographic variables and the status of cad on admission , we identified factors that showed significant association with reversibility of avb by univariate and multivariate logistic regression analysis ( table 4 ) . univariate analysis revealed several significant factors ; male gender { odds ratio ( or ) 3.593 , 95% confidence interval ( ci ) 1.101 - 11.732 , p=0.034 } , current smoker ( or 5.355 , 95% ci 1.464 - 19.594 , p=0.011 ) , cad ( or 41.045 , 95% ci 5.245 - 321.208 , p<0.001 ) , and ami on admission ( or 555.750 , 95% ci 72.302 - 4271.773 , p<0.001 ) . multivariate analysis was used to clarify these uncertainties and showed an obvious result ; ami on admission was the only associated factor ( or 350.409 , 95% ci 21.406 - 5736.146 , p<0.001 ) . irreversible avb was observed in 173 patients ( ib group ) who had undergone implantation of a permanent pacemaker . there were significant differences in gender , smoking status , and serum level of high density lipoprotein - cholesterol ( hdl - c ) and c - reactive protein ( crp ) between the 2 groups . in the ib group , 75 ( 43.4% ) were male and 11 ( 6.4% ) were current smokers , while rb group had 11 ( 73.3% ) males and 4 ( 26.7% ) current smokers ( p=0.031 for gender , p=0.021 for smoking status ) . serum level of hdl - c was higher in ib group ( 46.5610.95 mg / dl vs. 40.0010.07 mg / dl , p=0.030 ) , whereas crp was higher in rb group ( 0.531.24 mg / dl vs. 1.991.80 mg / dl , p=0.014 ) . in the ib group , 129 ( 74.6% ) had no cad on admission , 40 ( 23.1% ) had stable angina , 2 ( 1.2% ) presented with unstable angina , and 2 ( 1.2% ) presented with acute myocardial infarction ( ami ) . in contrast , the rb group had 13 ( 86.7% ) with ami , one ( 6.7% ) with stable angina , and one ( 6.7% ) without cad on admission ( p<0.001 ) . on the aspect of cad type and reversibility of avb , 13/15 ( 86.7% ) patients had ami , 0/2 ( 0% ) had unstable angina , and 1/41 ( 2.4% ) with stable angina had reversible avb ( fig . the proportion of reversible avb in patients with ami was significantly higher than other groups ; patients without cad , with stable angina , and with unstable angina . the reversibility of avb was analyzed according to the distribution of coronary pathology ( table 3 ) . 43 ( 24.9% ) of 173 patients in the non - ami group and 15 ( 100.0% ) of 15 patients in the ami group had cad . avb was rarely reversible in the non - ami group as only one of 43 patients ( 2.3% ) showed reversible avb . in contrast , 13 of 15 patients with ami ( 86.7% ) had reversible avb and there were significant difference between non - ami group and ami group ( p<0.001 ) . among 15 patients with ami , 11 patients had inferior wall st - segment elevation myocardial infarction ( stemi ) and 1 patient had anterior wall stemi . there were 2 patients with ami in ib group , showing inferior and anterior wall stemi for each . rca lesions were found in 25 ( 15.0% ) in the non - ami group and 14 ( 93.3% ) in the ami group ( p<0.001 ) by cag . the proportion of reversible avb among patients with rca lesion was also significantly higher in ami group ( p<0.001 ) . according to mosseri et al's2 ) classification , the number of patients with cad in the non - ami group were : 4 ( 9.3% ) type i anatomy , 9 ( 20.9% ) type ii anatomy , 7 ( 16.3% ) type iii anatomy , and 23 ( 53.5% ) type iv anatomy . one patient whose avb was reversible had type iii anatomy . in the ami group , according to this same classification system , no patients had type i anatomy , 1 ( 6.7% ) patient had type ii , 5 ( 33.3% ) patients had type iii , and 9 ( 60.0% ) patients had type iv . the proportions of reversible avb in type iii and type iv were higher in the ami group ( p=0.072 for type iii and p<0.001 for type iv ) . the composite of type ii and iv , in which septal blood flow of lad is compromised in common , was found in 32 ( 74.4% ) patients from the non - ami group and avb was irreversible in all patients , while the composite was found in 10 ( 66.6% ) patients of ami group and 9 ( 90.0% ) patients had reversible avb ( p<0.001 ) . among demographic variables and the status of cad on admission , we identified factors that showed significant association with reversibility of avb by univariate and multivariate logistic regression analysis ( table 4 ) . univariate analysis revealed several significant factors ; male gender { odds ratio ( or ) 3.593 , 95% confidence interval ( ci ) 1.101 - 11.732 , p=0.034 } , current smoker ( or 5.355 , 95% ci 1.464 - 19.594 , p=0.011 ) , cad ( or 41.045 , 95% ci 5.245 - 321.208 , p<0.001 ) , and ami on admission ( or 555.750 , 95% ci 72.302 - 4271.773 , p<0.001 ) . multivariate analysis was used to clarify these uncertainties and showed an obvious result ; ami on admission was the only associated factor ( or 350.409 , 95% ci 21.406 - 5736.146 , p<0.001 ) . the main finding of this study is that avb in patients with ami is usually reversible , while avb in patients with cad other than ami is usually irreversible . this result indicates that permanent pacemaker implantation should be delayed in cases of ami . to our knowledge , the present study is the first to describe the reversibility of avb in each type of cad . although we could not provide the optimal timing to confirm the reversibility of avb in each type of cad , the results of this study deserve special consideration . the causal relationship between avb and inferior wall ami avb complicates inferior wall ami in 10% to 15% of cases,7 - 9 ) and most of these patients can be recovered from avb by revascularization.10 - 12 ) however , the association of cad other than ami and reversibility of avb is still unclear and is rarely studied . in this context , we tried to evaluate the association of avb and cad , in order to elucidate whether avb is reversible in patients with cad . the blood supply of the av node is from the posterior interventricular artery , which is a branch of rca in right - dominant individuals . in the remainder of individuals , the av node is still supplied by the posterior interventricular artery , but that artery is a branch of the left circumflex artery ; the coronary circulation of these individuals is considered left - dominant . intraventricular conduction system is supplied by septal branches from lad , especially the first septal perforator branch from proximal lad.13 ) this physiologic background has been supported by several studies . mosseri et al.2 ) reported that a compromised blood flow of the septal branch and the rca were associated with conduction disturbances . tandoan et al.,3 ) yesil et al.,14 ) and wei et al.4 ) reported similar results ; stenoses of septal branch from lad or rca are associated with avb . however , revascularization of the stenosed coronary artery could not reverse conduction disturbances.5)6 ) in the present study , status of cad on admission showed significant difference between the ib group and the rb group . the majority of the ib group had no evidence of cad , while the rb group was mainly consisted of ami patients . patients with ami recovered from avb after revascularization therapy in most of cases , which is concordant with previous reports.10 - 12 ) in contrast , almost all patients without ami eventually underwent implantation of a pacemaker , as they did not recover to sinus rhythm . with this result , we can postulate that patients with avb and ami have a higher chance to return to sinus rhythm by coronary revascularization , and it is not applied to the patients without ami . patients with new - onset avb might present with ami , unstable angina , or stable angina . when planning implantation of pacemaker in these patients , it should be noted that dual - antiplatelet therapy is usually required after pci in the era of drug - eluting stent.15 ) on the other hand , dual - antiplatelet therapy at the time of pacemaker implantation might increase the risk of bleeding complication and extend procedure time.16 - 18 ) considering this clinical aspect and our study results , we recommend application of different therapeutic strategies for each entity ( fig . if a patient of new - onset avb presents with ami , revascularization therapy is definitely required for treatment of ami . but for the treatment of avb which is a resultant feature of ami , pacemaker implantation should be delayed as this type of avb has very high probability to return to sinus rhythm after appropriate revascularization . if a patient with avb presents with unstable angina , we recommend that the patient undergo pacemaker implantation first , and then revascularization therapy . in the present study , considering the necessity of dual - antiplatelet therapy after coronary interventions,15 ) it would be rational to undergo pacemaker implantation prior to revascularization . if patients of new - onset avb have no evidence of ami or unstable angina , then pacemaker implantation would be the most important treatment , because the reversibility of avb in these patients is hardly expected . the result of multivariate analysis in table 4 confirmed the strong causal relationship between ami and new - onset avb . male gender , smoking status , and existence of cad were significantly associated factors on univariate analyses , but not on multivariate analysis . as male gender and smoking status are distinct risk factors of cad , it seems that gender and smoking status are not major components in the reversibility of avb . the most important aspect of this result is the strong association of ami and reversibility of avb , but not cad itself . this result also poses a question of whether cag as a routine procedure prior to implantation of permanent pacemaker is mandatory . the location of pathologic coronary artery among patients with irreversible avb showed similar distribution , compare to the results of previous several studies ( table 5).2 - 6)14 ) in the present study , type iv was the most common type of coronary pathology and type ii was the second most common type in ib group ; type i anatomy observed in 9.1% of patients with cad , type ii in 22.7% , type iii in 15.9% , and type iv in 52.3% . in the study by yesil et al.14 ) the distribution of coronary pathology was 9.6% type i , 38.7% type ii , 16.0% type iii , and 35.0% type iv . tandoan et al.3 ) studied 78 patients who had pacemaker implantation and angiographically proven cad , and the distribution was 19% type i , 24% type ii , 11% type iii , and 45% type iv . in the study by mosseri et al.2 ) type i and iv were the most frequently observed types ( 44.4% for each type ) among 36 matched patients with permanent pacemaker . generously , type ii and type iv were much more frequently observed in patients with irreversible avb which required implantation of permanent pacemaker . thus , our study result supports the association of avb and underlying cad , which compromise the blood flow to septal branch or the rca . the similarity shared by our result and previous studies not only supports the validity of our study , but also increases the potential for generalization . by screening all patients with new - onset avb who visited our hospital , majority of patients had no evidence of cad , while only 2 patients presented with unstable angina . second , this was an observational retrospective study , based on the electronic medical records . no standardized protocol was used to indicate tests in advance , although attending physicians referred to guidelines for managing avb . third , a further prospective study is required to investigate the effect of revascularization on the reversibility of avb . our results show that avb in patients with ami is usually reversible after revascularization treatment , while patients with avb ( without ami ) usually required implantation of a permanent pacemaker , irrespective of the presence of cad . avb in patients with cad other than ami is usually irreversible , therefore implantation of a pacemaker should be considered on a preferential basis . majority of patients had no evidence of cad , while only 2 patients presented with unstable angina . second , this was an observational retrospective study , based on the electronic medical records . no standardized protocol was used to indicate tests in advance , although attending physicians referred to guidelines for managing avb . third , a further prospective study is required to investigate the effect of revascularization on the reversibility of avb . our results show that avb in patients with ami is usually reversible after revascularization treatment , while patients with avb ( without ami ) usually required implantation of a permanent pacemaker , irrespective of the presence of cad . avb in patients with cad other than ami is usually irreversible , therefore implantation of a pacemaker should be considered on a preferential basis .