Experts call them re-entry arrhythmias. They are completely uncontrollable phenomena. And unpredictable. When they affect the left ventricle, the part of the heart that has to push the heart needed by the whole organism, they can create potentially lethal fibrillations. And in any case, even without causing a crazy rhythm that essentially leads to cardiac arrest because the ventricle contracts unnecessarily, they can be very serious.
Control them? It’s difficult. Even and especially if they develop on the scar of a previous heart attack, where drugs cannot act. But now, thanks to research conducted by expert cardiologists at the Texas Heart Institute coordinated by Mehdi Razavi and biomedical engineers at the University of Texas at Austin led by Elizabeth Cosgriff-Hernandezthere is hope to limit the risks.
Thanks to a special hydrogel which, injected into the vessels, reaches the cardiac area where the abnormal rhythms arise and is capable of acting as an “on-site” electrode, we can hope to find a simple and effective local control system in the future (perhaps connected to a pacemaker) to reduce risks. The original strategy, currently tested only on experimental models, is described in a research published on Nature Communications.
by Federico Mereta
The hydrogel works in impossible-to-reach areas
The challenge is linked to the difficulty in treating some cases of ventricular arrhythmia, which are essentially linked to the difficulty in reaching the scarred cardiac tissues after a heart attack with electrical stimuli. The available drugs, precisely because the cardiac cells are not substantially destroyed by ischemia, are unable to reach the area. The hydrogel developed by overseas researchers, however, has characteristics that allow it to reach inaccessible cells, directly stimulating areas of the heart that cannot be reached in any other way.
In practice they behave like real electrodes that can be easily applied inside the vessels and go up to the heart through them. Studies are currently focused on experimental animals. It has been shown that thanks to a very small probe it is possible to create a real “highway” for signals.
As reported in a note from the Texan institute, Cosgriff-Hernandez “when injected into the target vessels, the conductive hydrogel conforms to the morphology of the patient’s vessels. The addition of a traditional pacemaker to this gel allows stimulation that resembles native conduction of the heart – effectively mimicking the heart’s native electrical rhythm – and extinguishes the cause of the arrhythmia, providing painless defibrillation.”
by Federico Mereta
What are short circuits in re-entry arrhythmias
Threatening ventricular arrhythmias (tachycardia or fibrillation) very often arise from scarring of the left ventricular wall of the heart; the most typical and frequent are post-infarction scars. “Within these scars, multiple and complex reentry circuits form, with very variable shape, length and conductive capacity, which can involve from tiny to large areas of myocardial tissue – he explains Giulio Molon, Director of the complex Cardiology Operational Unit at the Irccs Sacro Cuore Don Calabria in Negrar (Verona). When the condition of the electrical stimulus inside this ventricular scar finds circuits with slowing of the conduction speed and others with unidirectional conduction block, short circuits are created so that the stimulus runs quickly inside the scar itself, giving rise to tachycardia or ventricular fibrillation”.
From this mechanism, we understand the name: we speak of re-entry tachycardia precisely because the stimulus travels along the circuit using one of its branches and then returns through another branch, creating a real short circuit. These are therefore very dangerous and potentially fatal situations: for this reason arrhythmias of this type must be prevented or promptly resolved .
“Currently the therapies that can be used are antiarrhythmic drugs,transcatheter ablation or the implantation of a defibrillator – says Molon. All these therapies show variable effectiveness (drugs and ablation) and also sometimes significant management problems. The defibrillator shows more positive results, however it can sometimes create acceptance problems, especially after the shock has been delivered which is generally very annoying and sometimes even painful.”
by Federico Mereta