During any given day, an average healthy heart beats at many different rates based on physical and mental activities. Rates are slowed when sleeping or sedentary, and higher during physical activity, or when doing something mentally stressful or something that takes focus.
Rate response pacing is how devices like pacemakers and ICDs adapt their heart rate pacing based on your physical (and sometimes physiological) demands. Without this, hearts that rely on a device would only beat at one rate, day in and day out, and would not properly support daily activities. But there are different technologies on the market and you should know that you have options when deciding what rate response pacing will best suit your needs.
Pacing Based on Motion: Accelerometers
Simple pacemakers use a single sensor, called an Accelerometer to sense motion and to know when to increase the heartbeat. For example, during walking, jogging or jump-roping, an Accelerometer would sense the increased motion and increase your heart rate in response. While your doctor may be able to tune your device based on your activity level, there can be times when your heart rate won’t match your needs. Accelerometers can’t sense gentle motions such as doing yoga, bicycling, kayaking or skiing, and tend to pace the same for both going up and down stairs. Even more importantly, Accelerometers have no way to detect changes in metabolic need due to mental activity, stress or emotional factors, like focusing on a puzzle, riding a roller coaster or getting into a heated argument.
Pacing Based on Breathing: Minute Ventilation and The Blended Sensor
Another rate response technology is Minute Ventilation, which paces based on a sensor that detects respiratory rates, essentially increasing the heart rate when breathing is heavier. These are almost always used in combination with an Accelerometer, which is commonly referred to as a Blended Sensor. A Blended Sensor relies on the Accelerometer to pick up on motion and then the Minute Ventilation kicks in to provide more accurate pacing. This method can greatly improve the response of a device for gentle motions and is considered a major improvement over the Accelerometer alone. Blended sensing has been used effectively for many patients who were not satisfied with pacing from an Accelerometer.
However, even with a Blended Sensor, there can still be a lag in increased heart rate. In a normal heart, your heart rate increases before your breathing does, so if you start up a hill on your bicycle, your heart starts pumping faster and then you begin breathing heavier. With a Blended Sensor, your heart rate will increase as you go up the hill, but you it may still feel like you have hit a wall in the time between when you start working harder and when your device picks up on the increase in your oxygen intake. Also worth noting is that Minute Ventilation is only available on pacemakers and it does require a significant amount of tuning to make it custom-fitted and effective for each individual.
Pacing Based on Algorithm: Closed Loop Stimulation
The newest rate response pacing method is called Closed Loop Stimulation or CLS for short. Devices with CLS respond to physiological needs and acute mental stress through a complex algorithm. CLS detects minute changes of the contractions in the heart and translates this into increased or decreased heart rate. This means that regardless of activity level, CLS will detect changes in the need for oxygen and respond with appropriate heartbeats. This is valuable in that your heart will respond to gentle motions, like the bicycling example, as well as emotional experiences, like watching a scary movie or a sharing a passionate kiss with your significant other. Unlike Minute Ventilation, CLS is available on not only pacemakers, but also defibrillators and heart failure devices, and it requires little to no customization because it leverages machine-learning, essentially learning from your heart.