Risk for Permanent Pacemaker After TAVI
Risk for Permanent Pacemaker After TAVI
This comprehensive analysis of the currently available literature reveals that approximately every 7th patient undergoing TAVI will require a permanent PM after the procedure. Compiling data from more than 5,000 patients published to date, it is obvious that patients with severe aortic stenosis receiving a CVP have a more than 3-fold higher risk for the need of a permanent PM than individuals fitted with an ESP. Finally, preexisting RBBB appears to be an important predictor for development of complete AV block and subsequent PM need.
Injury of the ventricular septum with an increased risk for PM requirement has also been noted after transcoronary alcohol septal ablation (TASH) in patients with hypertrophic obstructive cardiomyopathy. The incidence of PM requirement after TASH is similar to that of TAVI. Some groups identified preexisting LBBB as a risk factor for PM need after TASH, due to procedure-related new onset of RBBB with subsequent complete AV-block. The proposed mechanism for the development of high degree AV block after TASH in patients with preexisting LBBB, is alcohol-induced necrosis of the interventricular septum with subsequent destruction of the right bundle branch of the specific conduction system. Compared to TASH procedures, mechanical stress to the left bundle branch and/or AV-node is an important factor for emergence of potential PM requirement after TAVI. Apparently, this mechanism is particularly relevant in individuals with preexisting RBBB in whom additional traumatic destruction of the left bundle branch may result in complete heart block.
With respect to TAVI procedures, it has been reported that CVP can exert significantly more mechanical stress to the left bundle branch than the ESP due to its self-expanding and stabilizing nitinol-frame positioned in the LVOT. The ESP has a smaller frame so that direct contact to the interventricular septum can be avoided. In agreement with these pathophysiological considerations, our analysis demonstrates a 6-fold higher risk ratio for development of LBBB and a more than 3-fold higher risk ratio for PM-requiring high-degree AV block after CVP compared to ESP implantation.
There is a lack of prospectively designed clinical studies determining clinical predictors for the development of high-degree AV block after TAVI. Only 7 of the 32 studies selected, comprising a total of 550 patients, aimed to identify ECG-derived predictors. The only significant predictor consisted of the presence of a RBBB before the TAVI procedure. In contrast, a preexisting LBBB was not associated with a higher risk of the need of a permanent PM. The importance of a new LBBB after TAVI is still unclear due to the lack of systematic data concerning this subject. On the basis of the results of this analysis, therefore, prophylactic PM implantation before TAVI should be considered on a patient-by-patient basis in subjects with preexisting RBBB before TAVI. Use of an ESP should be specifically considered in those patients.
Other potential factors associated with the development of AV block include the depth of prosthesis implantation in the left ventricular outflow. Because of the design of CVP, it extends usually more into the left ventricular outflow tract than ESP. Therefore it is recommended to try to implant the valves, especially the CVP, not too deep in the left ventricular outflow tract. Because of the anatomical variability of insertion of the left bundle branch and/or course of the AV node, injury of these structures and the associated risk for PM requirement cannot be completely excluded. Aortic calcification, particularly in the area of the noncoronary cusp, as well as of the adjacent left ventricular outflow tract, has been reported to be a predictor for postprocedural incidence of PM implantation in 1 study.
Despite the fact that the majority of included trials in our analysis have not explicitly reported second- or third-degree AV-block as indication for PM implantation after TAVI, analysis of 8 trials, which had defined AV block II or III as the sole indication for PM implantation showed an even higher incidence of post-TAVI PM implantation (P = 0.019). Hence, inappropriate indication leading to excess of PM implantation in the 14 studies not reporting predefined indications for postprocedural implantation is highly unlikely.
There are some potential limitations of our study. Despite all efforts to exclude duplicity of study results (i.e., results of single center studies also being included in multicenter reports); complete study selection bias cannot be completely excluded. Another potential bias could be related to the learning curve of operators. To minimize such an influence of a learning curve we included only studies in our analysis which comprised at least 30 patients without prior implanted permanent PM. Lack of systematic information about concomitant medical therapy in patients developing AV block is also a potential limitation. Finally, another important limitation is the heterogeneity of criteria applied for PM indication in the various studies.
Discussion
Main Findings
This comprehensive analysis of the currently available literature reveals that approximately every 7th patient undergoing TAVI will require a permanent PM after the procedure. Compiling data from more than 5,000 patients published to date, it is obvious that patients with severe aortic stenosis receiving a CVP have a more than 3-fold higher risk for the need of a permanent PM than individuals fitted with an ESP. Finally, preexisting RBBB appears to be an important predictor for development of complete AV block and subsequent PM need.
Incidence and Mechanism for Development of High Degree AV Block After TAVI
Injury of the ventricular septum with an increased risk for PM requirement has also been noted after transcoronary alcohol septal ablation (TASH) in patients with hypertrophic obstructive cardiomyopathy. The incidence of PM requirement after TASH is similar to that of TAVI. Some groups identified preexisting LBBB as a risk factor for PM need after TASH, due to procedure-related new onset of RBBB with subsequent complete AV-block. The proposed mechanism for the development of high degree AV block after TASH in patients with preexisting LBBB, is alcohol-induced necrosis of the interventricular septum with subsequent destruction of the right bundle branch of the specific conduction system. Compared to TASH procedures, mechanical stress to the left bundle branch and/or AV-node is an important factor for emergence of potential PM requirement after TAVI. Apparently, this mechanism is particularly relevant in individuals with preexisting RBBB in whom additional traumatic destruction of the left bundle branch may result in complete heart block.
With respect to TAVI procedures, it has been reported that CVP can exert significantly more mechanical stress to the left bundle branch than the ESP due to its self-expanding and stabilizing nitinol-frame positioned in the LVOT. The ESP has a smaller frame so that direct contact to the interventricular septum can be avoided. In agreement with these pathophysiological considerations, our analysis demonstrates a 6-fold higher risk ratio for development of LBBB and a more than 3-fold higher risk ratio for PM-requiring high-degree AV block after CVP compared to ESP implantation.
Predictors of Total AV Block After TAVI
There is a lack of prospectively designed clinical studies determining clinical predictors for the development of high-degree AV block after TAVI. Only 7 of the 32 studies selected, comprising a total of 550 patients, aimed to identify ECG-derived predictors. The only significant predictor consisted of the presence of a RBBB before the TAVI procedure. In contrast, a preexisting LBBB was not associated with a higher risk of the need of a permanent PM. The importance of a new LBBB after TAVI is still unclear due to the lack of systematic data concerning this subject. On the basis of the results of this analysis, therefore, prophylactic PM implantation before TAVI should be considered on a patient-by-patient basis in subjects with preexisting RBBB before TAVI. Use of an ESP should be specifically considered in those patients.
Other potential factors associated with the development of AV block include the depth of prosthesis implantation in the left ventricular outflow. Because of the design of CVP, it extends usually more into the left ventricular outflow tract than ESP. Therefore it is recommended to try to implant the valves, especially the CVP, not too deep in the left ventricular outflow tract. Because of the anatomical variability of insertion of the left bundle branch and/or course of the AV node, injury of these structures and the associated risk for PM requirement cannot be completely excluded. Aortic calcification, particularly in the area of the noncoronary cusp, as well as of the adjacent left ventricular outflow tract, has been reported to be a predictor for postprocedural incidence of PM implantation in 1 study.
Despite the fact that the majority of included trials in our analysis have not explicitly reported second- or third-degree AV-block as indication for PM implantation after TAVI, analysis of 8 trials, which had defined AV block II or III as the sole indication for PM implantation showed an even higher incidence of post-TAVI PM implantation (P = 0.019). Hence, inappropriate indication leading to excess of PM implantation in the 14 studies not reporting predefined indications for postprocedural implantation is highly unlikely.
Study Limitations
There are some potential limitations of our study. Despite all efforts to exclude duplicity of study results (i.e., results of single center studies also being included in multicenter reports); complete study selection bias cannot be completely excluded. Another potential bias could be related to the learning curve of operators. To minimize such an influence of a learning curve we included only studies in our analysis which comprised at least 30 patients without prior implanted permanent PM. Lack of systematic information about concomitant medical therapy in patients developing AV block is also a potential limitation. Finally, another important limitation is the heterogeneity of criteria applied for PM indication in the various studies.