Background: His-bundle pacing has grown in popularity in recent years. This form of conduction system pacing provides a more physiological pattern of ventricular activation (Lewis et al., 2019). Since then, studies about His-bundle pacing have come to light. What does it mean for us? And ‘us’ I mean physiologists. it means learning a new way of following up a device patient.
As physiologists, keeping our knowledge up to date in cardiac pacing is crucial to our role, and presently we can easily get our hands on the nearest Ellenbogen book to feed our knowledge. However, with conduction system pacing, it is different, His-bundle pacing learning material is scarce. There are no detailed books to go to, no EGMs we can peruse at our leisure, no teaching sessions run by the pacing companies. The first studies are now being produced and brand-new data is being gathered.
Implant procedure – equipment: We have been spoilt by the enormous variety of equipment that we have available to us for RV apical pacing. This diminishes completely with His-bundle pacing. Currently on the market there is one His lead available – made by Medtronic – the Selectsecure 3830-69cm. The other accessories needed to compliment a His implant mimics that of an LV implant.
PSA: On the Medtronic PSA-standard settings need to be adjusted. The His signal is much smaller than your typical R wave, so the atrial sensitivity needs to be at the lowest number. The gain needs to be set to 0.05 mv/mm and the intracardiac signal to AEGM. As His thresholds are higher, your pulse width needs to be at 1.0 ms. And for those who would like to get into EP – it gets exciting, as you get to increase your sweep speed to 50 mm/sec or 100 mm/sec, this separates the Atrial, His and Ventricular EGMs.
His measurements: New measurements are needed for His pacing. A HV time should be measured – this will indicate whether or not the patient will require a back-up RV lead. You still perform sensing but it will be a smaller signal. You still perform a threshold but it will be higher. When you are performing a threshold – it will be at 1.0 ms and should be performed in both unipolar and bipolar. We are looking at V1 and the complex to change.
Choosing a pacemaker: Unlike RV apical pacing where it’s predominantly either AAI/VVI or DDD box – there’s more to think about with His-bundle pacing. There are in fact at least seven different combinations you could have. The factors you have to take into consideration are – the devices will differ greatly between a CRT or a DDD PPM (permanent pacemaker) and whether or not you need a backup RV lead.
Programming: Depending which port your His lead is in, will then dictate controversial changes like safety pacing OFF, ventricular blanking after AP to its maximum value, decreasing your atrial sensitivity, fixed His lead output to 5 v @ 1.0 ms. Then the mode – would DVI mode work better than a DDD mode, you may not need to use RV reducing algorithms as His pacing does not have deleterious effects.
Follow up: During a follow up, we use 12-lead ECG’s. Your follow up intervals will need to be 6-monthly, this is due to a study by Abderrahman et al. (2018) showed that HIS-bundle leads tend to be initially less stable than RV leads. Examining the 12-lead is crucial to see how well the His-lead is being captured. Narrow/positive/biphasic is best.
Conclusion: We have reached an exciting time in cardiac pacing. In the not so distant future – there should be the development of new leads, new tools, new pacemakers and new battery technology to aid the demand of His-bundle pacing.