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Sunday, March 28, 2021

Some Pacemaker program features do not work well with His Bundle Pacing

 Some pacemaker programming features do not work well with His Bundle pacing and may cause some  problems raising the question of why have pacemaker manufacturers  not developed programs and algorithms specific to His Pacing . 

In particular the automatic  capture threshold determination(ACM for automatic capture management) program may give falsely high thresholds leading to  setting the capture voltage safety factor too high leading to premature battery depletion as illustrated in a case report referenced later in this article.

If the His lead is placed in the ventricular port (pulse generators used with CRT have three ports) the ACM  which is based on the evoked potential will indicate the RV capture threshold , i.e. not the His threshold. If the RV threshold is higher than the His threshold then the ACM determination will be falsely high. If ,by chance the right ventricular evoked potential is approximately the same as the His potential then ACM works just fine , except you don't know if it working right or not. 

If the His lead is in the LV port, since it is based on the LVP-RVS conduction times the threshold will be that with lowest value either RV myocardial or His. 

The ventricular capture program is activated nightly at 1:am and if unsuccessful another attempt is made every half hour.

Articles by Vijayaraman and Burri has explicated the problems with automatic capture algorithms and HBP and the basic recommendation is that those features be turned off or at most turned to monitor. 

Quoting Vijayaraman, 2018 JACC ;" Utility of automatic threshold testing feature is limited in HBP. In patients with selective HBP  due to lack of evoked potential,this feature may fail to detect the true  His capture threshold. On the contrary in patients with nonselective HBP this feature will detect myocardial capture threshold rather than His bundle capture. " 

Quoting Starr and Burri (Heart Rhythm 2019)

"The RV capture management algorithm of Medtronic devices considers an RVS event that occurs in the 110 ms window following pacing to be V capture ( i.e. it does not specifically detect the evoked  potential)." The authors  then explain that in cases of RBBB selective His Pacing  may have the erroneous diagnosis of non capture  could if the pace capture interval falls outside of the 110 ms window.

Quoting Burri,(2019) ;

"RV capture management algorithms are based on detection of the evoked potential which is absent in case of selective his bundle capture.Even in the case of non-selective capture, the algorithm seldom yields accurate results and the feature should either be inactivated to switched to  "monitor"

The following case report illustrates one undesirable clinical outcome when the ACM is set to "program" but fortunately the problem was quickly corrected.

Wu et al ( 1) report a case in Clinical Case reports in 2020 in which the Medtronic capture management algorithm caused a large and inappropriate increase in the voltage setting.The patient was a 72 year old man with a second degree heart block who was implanted with a His Lead resulting in selective His pacing with an initial Voltage of < 1.5 volts at 0.4 ms.However the next day the EKG now showed nonselective His pacing pattern and the Voltage was set at 5.00V at 1 ms.

 The authors believe that the automatic capture management system which was set on  the factory default setting of adaptive repeatedly noted "pacing capture loss" and reputedly increased the RV voltage. The treating physicians recognized the problem and changed the ACM setting to monitor before significant battery depletion had occurred.

It is not possible from the case report to know  when this event occurred .There were two articles published in 2019 that called attention to problems with the adaptive setting for automatic capture management systems such that the adaptive setting should not be considered the default position. 

As of this writing there seems to be no IPG (PM) specifically designed for His pacing nor is there an automatic capture threshold program designed for HBP. I wonder how often various pacing settings are just left to the factory settings when a PM is implanted with His pacing  even though there is information available in the literature indicating  that  a device features that worked well for right apical ventricular pacing  will not work in His-bundle pacing. 

1) Wu, Jung-Pin et al Automatic capture management may cause   unnecessary battery depletion in selective His Bundle Pacing Clinical Case Reports 2020. DOI 10.1002/ccr3.3168

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