Safer, targeted approaches to treat atrial fibrillation
Atrial fibrillation, shortened to A-Fib in the U.S. and AF in the U.K., affects millions and is seen as a serious contributor to heart failure and stroke. Treatment can vary, but a relatively new process called Pulsed Field Ablation is beginning to gain interest from doctors, patients and OEMs.
With atrial fibrillation the heartbeat becomes irregular and often abnormally fast, sometimes doubling its rate. It’s caused by changes to the heart tissue and can lead to strokes or heart failure if untreated. According to the Centers for Disease Control and Prevention (CDC), about 2% of the world’s younger people and 9% of those over 65 have AF, and the British Heart Foundation cites a 50% rise in diagnosis of the condition over the past decade.
Ablation is one medical procedure used to treat atrial fibrillation. It involves inserting a thin catheter with small electrodes on its tip through a vein until it reaches the heart. The electrodes measure the heart’s activity, determining the exact location of the problem.
Energy is then sent along the catheter to that site. This may be a radio frequency (RF) signal that heats and cauterizes the tissue. Alternatively, cryoablation may be used. Here, gas is pumped into the offending tissue via a thin needle to freeze it.
The relatively new technique of pulsed field ablation (PFA) selectively ablates (destroys) the cardiac tissue that causes the abnormal electrical signals that lead to arrhythmia. It does so without damaging the surrounding tissues by applying a series of microsecond-long, high-intensity electrical pulses to create pores in the cell membranes. The process is called electroporation. It disrupts the homeostasis of the affected cells, killing them.
Looking closer at pulsed field ablation
Unlike traditional thermal ablation techniques such as RF ablation or cryoablation, PFA applies electrical fields at the cellular level, causing minimal thermal damage to surrounding tissues. Its first use in the U.K. was announced in June 2022.
Pulmonary vein isolation (PVI) is the key measure of the success of cardiac ablation procedures. A recent National Library of Medicine report cited a review of seven trials involving 2023 patients that first-pass PVI was 80% to 90% for RF ablation, 97.6% on average for cryoablation, and 100% for PFA. Patient follow up also indicated lower complication rates for PFA and recurrence rates of only 1.78%, over an order of magnitude lower than that for thermal techniques. PFA also proved to be a faster procedure and had the additional benefit that it resulted in faster recovery time for patients.
Treating atrial fibrillation
High-voltage pulse generators are the core of PFA systems, delivering short, high-voltage pulses from a storage capacitor. The systems generate pulses with precise control of the voltages, duration and frequency. The applied voltage can be up to several kV. Self-healing polypropylene capacitors with metal foil electrodes that have a low dissipation factor are suited to this high level of pulse duty.
The pulses can induce electromagnetic interference (EMI) in the monitoring and recording circuits of the PFA system. Electronic design therefore needs to take account of both unwanted common mode and differential mode currents. Countermeasures may include diodes for over-voltage protection and capacitor-inductor combinations for limiting undesirable induced currents.
EMI considerations can be of critical importance in medical equipment. One PFA system manufacturer, Farapulse Inc., which was acquired by Boston Scientific in 2021, developed and applied for patents for circuits whose sole purpose was the “reduction or removal of noise originating from a therapeutic or surgical apparatus.”
Designing power systems in pulsed field ablation
The power system within a PFA delivery unit will include an AC-DC power supply, lower voltage DC-DC isolation converters, and high-voltage DC-DC modules for charging the capacitors that deliver the energy pulses for the process. There may sometimes be an additional AC-DC power supply to power the system’s display screen.
The AC-DC units must be rated for the appropriate level of grid isolation, power factor correction, EMI protection and leakage current.
Pulsed field ablation power supply block diagram
The high-voltage units, which are usually rated between 60 watts and 250 watts, typically have a 24 VDC to 380 VDC input and come with output voltages up to 6,000 VDC, or even higher for some other medical procedures. Fast rise times and controlled voltage overshoot are important parameters.
The power supplies within a PFA unit need to meet the appropriate medical standards for the application and their function within the system. They also require high-performance filtering to address the EMI concerns cited earlier. The most frequently cited standards for medical power supplies are the International Electrotechnical Commission‘s IEC 60601-1-1 and 60601-1-2.
Safety features ensure the electrical pulses are delivered within safe limits to prevent unintended damage, and this includes real-time monitoring of the electrical output and feedback mechanisms to adjust the pulses as needed. Advanced algorithms are used to control the timing and sequence of the pulses as well as to process the data collected during the procedure.
PFA systems may be used in tandem with cardiac imaging technologies such as ultrasound or MRI to provide a detailed view of the heart’s anatomy and to monitor the ablation process.
Conclusion
PFA is a significant advancement in the treatment of cardiac arrhythmias, offering a safer and more targeted approach compared to conventional ablation techniques. The electronic technologies embedded in PFA systems are complex and sophisticated, reflecting the need for precision, safety and user control in such a critical medical procedure.
As technology progresses, we can expect further advancements that will enhance the capabilities and safety profile of PFA, potentially making it the standard of care for treating cardiac arrhythmia in the future.
