A moment of great agitation. A race. A few lines of fever, or more simply, a few too many coffees or a cigarette. There are many elements that make the heart beat faster, sometimes to the point of making us feel the beat in our throat. But be careful. There are cases where the tachycardia, generically defined as a heart rate above 100 beats per minute, is maintained over time. Maybe without us realizing it. And over time, unfortunately, the heartbeat becomes less and less “efficient” and the heart itself, given that less blood arrives, can suffer from the situation. Now, thanks to research, we know what happens in these cases. The study was based on cardiac cells created in the laboratory starting from human stem cells, to the point of “building” a heart model which made it possible to reveal how tachycardia induces a change in the heart’s ability to nourish itself, facilitating the appearance of pathologies. like decompensation. The investigation, published on Nature Biomedical Engineeringwas conducted by a team coordinated by Joseph Wudirector of the Stanford Cardiovascular Institute, in collaboration with Chengyi Tu.
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What happens if there is tachycardia
The experts examined over 400 samples of cardiac tissue, created from stem cells, to see how cardiac cells function under stress from excessive beats. These steps are extremely complex and time consuming. As Tu explains in a note from Stanford University, “producing engineered heart tissue is very different from growing cells in a dish. The timeline is very long.” In fact, it is not enough to induce them mature cardiac units starting from stem cells. It is also necessary to structure these cells on a tailor-made scaffold and let them mature for the necessary time. Once they obtained this cellular “skeleton”, the experts evaluated what happens in case of tachycardia by electrically stimulating the cells in the laboratory. Result: the units progressively lose their ability to contract, which can even halve after a few days. But once the rhythm returns to normal, the cellular capacity recovers. From the experimentation, it also emerges how we can act on cellular energy in the future, modifying it positively. As? Experimentation shows that in case of tachycardia, the integration of tissues with NAD (Nicotinamide Adenine Dinucleotide), a sort of natural “fuel” that increases cellular energy, can accelerate the recovery of cardiac muscle cells. And therefore promote their well-being.
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Hopes for the failing heart
This observation could prove to be of great interest for the prevention and treatment of pathologies, such as heart failure, linked to the chronic persistence of tachycardia. In fact, when the accelerated rate is maintained over time, the atria and ventricles may not fill completely, with repercussions on cardiac physiology (and not only). Above all, in these circumstances the normal mechanism of energy production can be modified. In fact, instead of using fats to beat as normally happens (this reaction requires oxygen in quantity), if the heart beats for a long time with an insufficient hemodynamic reaction it begins to use sugars as an energy source. This, together with the relative lack of oxygen, leads to a modification in the normal mechanism that induces energy production, i.e. the ratio of NAD (i.e. the oxidized form of Nicotinamide Adenine Dinucleotide) and NADH (i.e. the reduced version). Why is this relationship important? Thanks to the balance of these two components, a basic protein for the well-being of the heart, called SERCA, works best. In practice – as the authors of the study explain – SERCA protein levels act like the accelerator and brake pedal for a car. So if the availability of NAD increases, the heart’s accelerator is pushed and the SERCA protein strengthens the heartbeat of the engineered cells. Otherwise, with the action of the “brake”, the engineered heart tissues hit the brakes, making them beat more weakly. From this observation, demonstrated experimentally, it is hoped that we will be able to better deal with prolonged tachycardia in the future.
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How the heartbeat changes
Every sixty seconds the cardiac cycle completes approximately seventy times. But there are very significant variations from person to person. In athletes, where the heart is very trained and the contraction capacity of the ventricles increases because their muscle fibers are more developed and also the “chamber” within which the blood is found is larger, it can even go down to up to 40 -50 beats per minute. In any case, the heartbeat can accelerate and slow down, within 24 hours, even in the same individual. A run, an intense emotion or even a few lines of fever are enough for the heart rate to increase. The mechanism through which this sudden change occurs is extremely complex and elaborate, and is completely involuntary. In practice, an alteration occurs in the sending of impulses by the sinus node, which is richly innervated and receives hormonal signals. When we have a fever, for example, the body’s metabolism must increase because the temperature rises. And therefore there is a need for more energy, supported by an increase in the capacity of the circulatory stream in which the blood is pushed by the heart. If we go for a run, however, all the muscles need a greater quantity of oxygen, and the ways to obtain it are “out of breath” (i.e. an increase in the frequency of breathing) and an increase in the number of heartbeats.
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