High blood pressure is amazingly prevalent, affecting nearly half of all Americans. It’s a major risk factor for heart attack, stroke, kidney failure, eye damage, and more. Unfortunately, this condition remains highly prevalent despite the numerous medications designed to treat it. For many patients, adhering to medications can be difficult, and for others, some medicines are not effective in reducing blood pressure levels. But what if there were a way to lower blood pressure at the source, the heart?

First, let’s examine how the heart relates to blood pressure. It might seem obvious, but it’s actually quite complex. The heart draws blood in and pushes it out with each beat. The amount of blood pumped is called the stroke volume. A good stroke volume helps to ensure the heart has enough blood pressure to deliver oxygen throughout the body. A healthy heart will pump out around 50-70% of the total volume of blood. This means there remains some unpumped fluid in the heart chambers after pumping is complete. When the next heartbeat comes, the heart muscle has to stretch enough to accommodate this unpumped blood. This extra blood increases our blood pressure because of the Frank-Starling law of the heart.

The Frank-Starling law of the heart is over 100 years old and states that the amount our heart muscles stretch before pumping scales with the force they deliver when pumping. Think of a rubber band. If you stretch it a little, it’ll flop back in place. If you stretch a rubber band a lot, almost to its breaking point, it’ll snap back so hard as to leave a welt on your skin. The heart is similar; extra blood in the heart before pumping increases the pressure of each beat and maintains our blood pressure. If there were a way to lower the amount of blood in the chamber after beating, it follows that blood pressure may be lowered. Note that just the pressure would be lowered. The stroke volume would (ideally) remain the same. But how could we do this?

For most people, we don’t have any way of convincing the heart to empty more effectively. For a select few, however, the hardware may already be in place. Pacemakers are amazing technology that has helped countless people whose hearts aren’t working properly. Over a million pacemakers are implanted every year worldwide and help people with arrhythmias. Arrhythmias are conditions that involve irregular heartbeat. Pacemakers are surgically implanted devices that send small amounts of electricity where they are needed in the heart. Heart muscles are triggered by this little zap and beat in response to it. Pacemaker rhythms can be customized for several types of conditions, and can even be programmed after being implanted to adapt to changing patient conditions. This is where a pacemaker’s ability to help with high blood pressure is theorized.

By customizing how a pacemaker fires, it is possible to cause the heart to release more of its contents and lower the amount of blood remaining in the heart before pumping. According to the Frank-Starling law of the heart, this should result in lower blood pressure (indeed, early clinical trials show this to be the case).

Finally, we have to make sure changes to our blood pressure bypass the sympathetic nervous system. This pathway, also called the “fight or flight” pathway, helps ensure the body is awake, alert, and alive. Integral to this system are receptors that sense our blood pressure. If the sympathetic nervous system senses a prolonged drop in blood pressure, it kicks in to correct this. This is a critical system that keeps us from constantly fainting but can be problematic when trying to lower blood pressure. A clever workaround being investigated is to have a pacemaker lower the blood pressure intermittently. It runs the chamber-emptying algorithm for short periods of time. This may help bypass our sympathetic nervous responses. If clinical trials bear out, pacemakers may be able to change not just the pace of the heart, but the pressure too!

Staff Writer / Editor Benton Lowey-Ball, BS, BFA

References:

Centers for Disease Control and Prevention. (2023). Facts about hypertension. U.S. Department of Health & Human Services. https://www.cdc.gov/bloodpressure/facts.htm

Mond, H. G., & Proclemer, A. (2011). The 11th world survey of cardiac pacing and implantable cardioverter-defibrillators: calendar year 2009–a World Society of Arrhythmia’s project. Pacing and clinical electrophysiology : PACE, 34(8), 1013–1027. https://doi.org/10.1111/j.1540-8159.2011.03150.x

Kalarus, Z., Merkely, B., Neužil, P., Grabowski, M., Mitkowski, P., Marinskis, G., … & Kuck, K. H. (2021). Pacemaker‐Based Cardiac Neuromodulation Therapy in Patients With Hypertension: A Pilot Study. Journal of the American Heart Association, 10(16), e020492. https://www.ahajournals.org/doi/full/10.1161/JAHA.120.020492

Mitchell, L.B. (2023). Cardiac pacemakers. Merck Manual, Professional Version. https://www.merckmanuals.com/professional/cardiovascular-disorders/overview-of-arrhythmias-and-conduction-disorders/cardiac-pacemakers 

Neuzil, P., Merkely, B., Erglis, A., Marinskis, G., de Groot, J. R., Schmidinger, H., … & Kuck, K. H. (2017). Pacemaker‐mediated programmable hypertension control therapy. Journal of the American Heart Association, 6(12), e006974. https://www.ahajournals.org/doi/full/10.1161/JAHA.117.006974

Sequeira, V., & van der Velden, J. (2015). Historical perspective on heart function: the Frank–Starling Law. Biophysical reviews, 7, 421-447. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5418489